• View in gallery

    Distribution of major RVVs among mesocarnivores in the United States, including Puerto Rico, for 2015 through 2019. Darker shading indicates counties with confirmed animal rabies cases in the past 5 years; lighter shading represents counties bordering enzootic counties without animal rabies cases that did not satisfy criteria for adequate surveillance. Small nonenzootic areas with no rabies cases reported in the past 15 years are shaded if they are in the vicinity of known-enzootic counties and do not satisfy criteria for adequate surveillance. ARC FX = Arctic fox RVV. AZ FX = Arizona fox RVV. CA SK = California skunk RVV. MG = Dog-mongoose RVV. NC SK = North central skunk RVV. RC = Eastern raccoon RVV. SC SK = South central skunk RVV.

  • View in gallery

    Cases of rabies among wildlife in the United States, by year and species, 1967 through 2019.

  • View in gallery

    Reported cases of rabies involving raccoons, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

  • View in gallery

    Reported cases of rabies involving skunks, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

  • View in gallery

    Reported cases of rabies involving foxes, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

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Rabies surveillance in the United States during 2019

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  • 1 Poxvirus and Rabies Branch, Division of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, CDC, Atlanta, GA 30333.
  • | 2 Wildlife Services, APHIS, USDA, Concord, NH 03301.
  • | 3 Centre of Expertise for Rabies, Ottawa Animal Health Laboratory, Canadian Food Inspection Agency, Ottawa, ON K2H 8P9, Canada.
  • | 4 Centro Nacional de Programas Preventivos y Control de Enfermedades, Secretaria de Salud de Mexico, 11800 Miguel Hidalgo, CDMX, Mexico.

Abstract

OBJECTIVE

To provide epidemiological information on animal and human cases of rabies occurring in the United States during 2019 and summaries of 2019 rabies surveillance for Canada and Mexico.

ANIMALS

All animals submitted for laboratory diagnosis of rabies in the United States during 2019.

PROCEDURES

State and territorial public health departments and USDA Wildlife Services provided data on animals submitted for rabies testing in the United States during 2019. Data were analyzed temporally and geographically to assess trends in domestic and wildlife rabies cases.

RESULTS

During 2019, 53 jurisdictions submitted 97,523 animal samples for rabies testing, of which 94,770 (97.2%) had a conclusive (positive or negative) test result. Of these, 4,690 tested positive for rabies, representing a 5.3% decrease from the 4,951 cases reported in 2018. Texas (n = 565 [12.0%]), New York (391 [8.3%]), Virginia (385 [8.2%]), North Carolina (315 [6.7%]), California (276 [5.9%]), and Maryland (269 [5.7%]) together accounted for almost half of all animal rabies cases reported in 2019. Of the total reported rabid animals, 4,305 (91.8%) were wildlife, with raccoons (n = 1,545 [32.9%]), bats (1,387 [29.6%]), skunks (915 [19.5%]), and foxes (361 [7.7%]) as the primary species confirmed with rabies. Rabid cats (n = 245 [5.2%]) and dogs (66 [1.4%]) accounted for > 80% of rabies cases involving domestic animals in 2019. No human rabies cases were reported in 2019.

CONCLUSIONS AND CLINICAL RELEVANCE

The overall number of animal rabies cases decreased from 2018 to 2019. Laboratory diagnosis of rabies in animals is critical to ensure that human rabies postexposure prophylaxis is administered judiciously.

Introduction

The annual rabies surveillance report presents the official statistics for animal rabies in the United States. The present report summarizes laboratory and epidemiological data collected during 2019 from 53 jurisdictions in the United States and provides an overview for Canada and Mexico. This report also summarizes national advances in terrestrial wildlife rabies control and laboratory diagnostic testing and reviews animal exposures for human rabies cases in the United States from 2000 through 2020.

The epidemiology of rabies in North America differs from that in Africa and Asia, where > 99% of reported human rabies deaths are mediated by dogs.1 With the elimination of the dog RVV from the United States, terrestrial mesocarnivores and bats are now the only reservoirs of Rabies lyssavirus in this country.2,3 Terrestrial reservoir species include raccoons (Procyon lotor), skunks (family Mephitidae), foxes (Vulpes spp and Urocyon cinereoargenteus), and the small Indian mongoose (Herpestes auropunctatus) in Puerto Rico. Distinct RVVs are associated with each terrestrial reservoir species and can be readily distinguished by antigenic and molecular methods. These RVVs occur in geographically distinct regions, and transmission is primarily between members of the same species. Terrestrial RVVs include the eastern raccoon RVV; south central, north central, and California skunk RVVs; Arizona gray fox RVV; arctic fox RVV; and dog-mongoose RVV (Figure 1). At least 20 known phylogenetic lineages of rabies virus associated with bats have been identified among the 51 bat species indigenous to North America.4,5,6 Because bats are relatively unconstrained by geographic barriers, rabies is present in bats throughout the North American continent.

Figure 1
Figure 1

Distribution of major RVVs among mesocarnivores in the United States, including Puerto Rico, for 2015 through 2019. Darker shading indicates counties with confirmed animal rabies cases in the past 5 years; lighter shading represents counties bordering enzootic counties without animal rabies cases that did not satisfy criteria for adequate surveillance. Small nonenzootic areas with no rabies cases reported in the past 15 years are shaded if they are in the vicinity of known-enzootic counties and do not satisfy criteria for adequate surveillance. ARC FX = Arctic fox RVV. AZ FX = Arizona fox RVV. CA SK = California skunk RVV. MG = Dog-mongoose RVV. NC SK = North central skunk RVV. RC = Eastern raccoon RVV. SC SK = South central skunk RVV.

Citation: Journal of the American Veterinary Medical Association 258, 11; 10.2460/javma.258.11.1205

Rabies surveillance is crucial to facilitate prevention and control of human and animal rabies.7,8 Large-scale rabies control of wildlife has been successful in eliminating the dog-coyote and gray fox RVVs from Texas and preventing westward expansion of the eastern raccoon RVV from the eastern United States.9,10 Human rabies exposures remain relatively common as a result of interactions with wildlife and unvaccinated domestic animals; an estimated 55,000 people receive rabies postexposure prophylaxis annually in the United States.11 Continued surveillance is therefore necessary to detect trends in rabies, notably geographic expansion, translocation of rabies from enzootic to nonenzootic areas, introduction of new RVVs through international travel, and host shift events. Any of these trends can dramatically impact public health as well as animal welfare and production.12,13,14,15

Reporting and Analysis

Human and animal rabies have been nationally notifiable conditions in the United States since 1944.16,17 In collaboration with the Council of State and Territorial Epidemiologists, the CDC published case definitions for use in public health surveillance in 1990 and republished the definitions in 1997 and 2009.18,19 Laboratory-confirmed cases of rabies in humans and animals are reportable to state public health officials and notifiable to the CDC National Rabies Surveillance System. The Council of State and Territorial Epidemiologists recommends that 9 key variables be included in each report of a rabid animal, notably animal species, animal capture location, RVV, and information related to exposure of humans or animals.19 Reporting timeliness is outlined by the Council of State and Territorial Epidemiologists. Confirmed rabid animals with a history of international travel in the past 60 days and any diagnosis of rabies in humans should be reported to the CDC within 24 hours. All other confirmed cases of animal rabies should also be reported to the CDC within standard timelines.20

The National Rabies Surveillance System is a laboratory-based surveillance system that consists of 125 state public health, agriculture, and university laboratories performing the direct fluorescent antibody test.21,22 Both active and passive rabies surveillance are conducted in the United States. Animals tested through the passive surveillance system are typically implicated in a human or domestic animal exposure, although specific testing criteria vary by state and local jurisdiction. Passive surveillance accounts for 95% of reported rabid animals. The USDA Wildlife Services conducts active surveillance in selected areas for the purpose of monitoring rabies spread and evaluating rabies management in wildlife populations. Animal rabies confirmatory testing and rabies virus genetic typing are performed at the National Rabies Reference Laboratory in Atlanta23,24 and at regional reference laboratories throughout the United States.

For the present report, animal rabies cases and variant typing results reported to the National Rabies Surveillance System in 2019 were summarized and compared with historical temporal and geospatial trends. Percentages of rabid animals were calculated by including only conclusive test results (ie, a positive or negative result) in the denominator; animals in an unsatisfactory testing condition or with indeterminate test results were excluded from analysis. Numbers of rabies cases in major animal reservoirs (bats, raccoons, skunks, and foxes) for 1967 through 2019 were analyzed to identify temporal trends of rabies in these animals (Figure 2). Numbers of rabid animals and percentages of samples that tested positive for rabies in 2019 were compared with mean values for the previous 5 years (2014 through 2018) and were considered significantly different from the mean value when outside the 95% confidence interval. Because rabies epidemiology in the United States is well described and follows discrete species and geographic patterns, rabid terrestrial animals without RVV information were assumed to be infected with the local enzootic terrestrial RVV.25 Rabid skunks infected with the eastern raccoon RVV or the skunk RVV were depicted separately. Rabid bats without variant typing information were assumed to be infected with a bat RVV, but the RVV was not further differentiated owing to limited information on the diversity and distribution of bat RVVs. To prioritize RVV typing for rabies-positive animals that could impact rabies control and prevention in the United States, all confirmed cases of animal rabies were classified according to their epidemiological importance on the basis of species, geographic features, and travel history. Trends in RVV testing and RVV typing results for samples of epidemiological importance were analyzed by animal species.26,27

Figure 2
Figure 2

Cases of rabies among wildlife in the United States, by year and species, 1967 through 2019.

Citation: Journal of the American Veterinary Medical Association 258, 11; 10.2460/javma.258.11.1205

Terrestrial rabies-free designations can impact recommendations for postexposure prophylaxis in humans and for quarantining and testing of domestic animals exposed to potentially rabid wildlife.7,28 Criteria for freedom from terrestrial RVVs are developed for public health purposes and applied to the county level. Counties with records of rabid terrestrial animals in the past 15 years are considered enzootic for rabies virus unless variant typing was performed and showed that all rabid animals in the county were infected with a bat RVV, laboratory and epidemiological investigations found that all rabid animals in the county had been translocated with no evidence of onward transmission, or results of laboratory testing of ≥ 15 terrestrial reservoir animals or ≥ 30 domestic nonreservoir animals (dogs, cats, or cattle) were negative during the past 5 years and no bordering counties had reported any rabid animals in the past 5 years.

Summaries of 2019 rabies surveillance for Canada and Mexico were provided by the Canadian Food Inspection Agency Centre of Expertise for Rabies29 and the Centro Nacional de Programas Preventivos y Control de Enfermedades of the Secretaria de Salud (Ministry of Health), respectively.

Samples Tested for Rabies

During 2019, a total of 97,523 animal samples were submitted for rabies testing in the United States and its territories (29.7 animals submitted/100,000 US human population), of which 95,053 (97.5%) were considered suitable for testing (including samples with positive, negative, and inconclusive test results). This represented a 2.7% decrease in the number of animals tested, compared with the number tested during 2018 (97,735). Of 94,770 animals with a positive or negative test result, 4,690 (4.9%) tested positive for rabies, a 5.3% decrease from the number that tested positive in 2018 (4,951). During 2019, the USDA Wildlife Services detected 213 rabid animals among a total of 6,612 animals tested with the direct rapid immunohistochemical test,30 accounting for 7.0% of all animals tested in 2019 and 4.5% of all animal rabies cases reported in 2019.

Rabies in Wildlife

Wildlife accounted for 91.8% (4,305/4,690) of animal rabies cases reported in 2019, representing a 6.2% decrease from the 4,589 rabid wildlife reported in 2018 (Table 1). In 2019, raccoons were the most frequently reported rabid animals in the United States, representing 32.9% (1,545) of all animal rabies cases, followed by bats (29.6% [1,387]), skunks (19.5% [915]), and foxes (7.7% [361]). Six states (Hawaii, Idaho, Mississippi, Nevada, Oregon, and Washington) were classified as not enzootic for terrestrial reservoirs (Figure 1).

Table 1

Cases of animal and human rabies in the United States, including Puerto Rico, during 2019.

Domestic animalsWildlife
LocationPrimary reservoirTotal animal casesDomestic animalsWildlifeCatsCattleDogsHorses and donkeysSheep and goatsOther domestic*BatsRaccoonsSkunksFoxesOther wildlifeRodents and lagomorphsHumans% Pos 20192018 casesChange (%)
AKArctic fox1248004000000800027.3%933.3%
ALRaccoon50248002000927462d002.7%57–12.3%
ARSkunk26422110200701500003.3%31–16.1%
AZSkunk138313530000055062144e0015.4%163–15.3%
CASkunk276227420000023004130005.5%22622.1%
COSkunk1635158112001a52210310009.6%328–50.3%
CTRaccoon41338111000522721f1u03.7%402.5%
DCRaccoon90900000036000004.1%22–59.1%
DERaccoon92720000006100006.1%21–57.1%
FLRaccoon12913116120100023712155g005.2%11017.3%
GARaccoon22213209803110911446354h1v012.2%261–14.9%
HINone00000000000000000.0%00.0%
IASkunk80800000080000000.6%10–20.0%
IDBat15114100000140000004.0%1225.0%
ILBat54054000000540000001.6%85–36.5%
INBat10010000000100000000.7%13–23.1%
KSSkunk5513427221101003200005.5%3083.3%
KYSkunk13112001000110100001.5%18–27.8%
LASkunk808000000205001w01.6%11–27.3%
MARaccoon131512641000034552461i6x05.0%10031.0%
MDRaccoon269192501510021b19184113303y07.7%2680.4%
MERaccoon1091108000001c953252001z010.5%1090.0%
MISkunk591581000004601200001.6%79–25.3%
MNSkunk36234100010270610001.8%3212.5%
MOSkunk24024000000220200001.2%2020.0%
MSBat30300000030000000.9%5–40.0%
MTSkunk18018000000170100003.8%175.9%
NCRaccoon31535280221200102612675494j007.7%332–5.1%
NDSkunk52301010010200001.1%12–58.3%
NESkunk21021000000180300001.4%22–4.5%
NHRaccoon34232200000913721k004.8%333.0%
NJRaccoon2492222721001003213930152l9aa09.0%20123.9%
NMSkunk27225100010511270004.5%1580.0%
NVBat20020000000200000005.2%1442.9%
NYRaccoon3913435724415009917342354m4ab06.4%32022.2%
NYCRaccoon24123100000121100003.3%1471.4%
OHBat42042000000384000001.0%54–22.2%
OKSkunk24717133000401111n002.9%30–20.0%
ORBat90900000090000002.6%15–40.0%
PARaccoon2494720237145001714215213o4ac05.7%356–30.1%
PRMongoose4526192023100000019p0049.5%3145.2%
RIRaccoon300300000007156101ad04.5%2142.9%
SCRaccoon14817131130301087829142q009.5%10048.0%
SDSkunk16115001000130200002.8%156.7%
TNSkunk2322110100094800001.3%29–20.7%
TXSkunk56530535164640028943173291r004.5%695–18.7%
UTBat12012000000120000003.6%14–14.3%
VARaccoon3854633930781002219281361s7ae010.1%3820.8%
VTRaccoon1601600000025422t1af01.4%24–33.3%
WABat90900000090000002.8%40–77.5%
WISkunk38038000000380000001.9%2552.0%
WVRaccoon82176515000208484401ag05.7%40105.0%
WYSkunk240240000001211010004.0%40–40.0%
Total4,6903854,3052453966221031,3871,545915361574005.0%4,951–5.3%
% 2019100.08.2%91.8%5.2%0.8%1.4%0.5%0.2%0.1%29.6%32.9%19.5%7.7%1.2%0.9%
% Pos 20194.9%0.8%8.9%1.2%4.0%0.3%2.8%1.6%1.5%5.5%11.7%24.1%19.5%2.4%2.1%
Total 20184,9513624,5892413363131021,6351,4991,0043576727
Change (%)–5.3%6.4%–6.2%1.7%18.2%4.8%69.2%0.0%50.0%–15.2%3.1%–8.9%1.1%–14.9%48.1%

Other domestic includes a1 llama, b1 ferret, and c1 ferret.

Other wildlife includes d1 bobcat and 1 coyote; e2 bobcats, 1 coyote, and 1 javelina; f1 bobcat; g1 bobcat, 1 coyote, and 3 otters; h4 bobcats; i1 coyote; j3 bobcats and 1 deer; k1 bobcat; l2 coyotes; m1 bobcat, 2 deer, and 1 fisher; n1 coyote; o2 bobcats and 1 weasel; p19 mongooses; q2 coyotes; r1 coyote; s1 otter; and t2 coyotes.

Rodents and lagomorphs include u1 groundhog, v1 groundhog, w1 squirrel, x6 groundhogs, y3 groundhogs, z1 groundhog, aa9 groundhogs, ab4 groundhogs, ac4 groundhogs, ad1 groundhog, ae1 beaver and 6 groundhogs, af1 groundhog, and ag1 groundhog.

— = Not applicable. NYC = New York City. Pos = Positive.

Primary reservoir refers to the most common RVV in the locality.

Bats

During 2019, 25,327 bats were tested for rabies and had a conclusive test result, of which 1,387 (5.5%) were confirmed positive for rabies. This represented a 15.2% decrease from the number of rabid bats reported in 2018 (1,635; Table 1). The percentage of rabid bats among the total tested (5.5%) was significantly lower than the mean percentage during the previous 5 years (6.3%; 95% CI, 5.8% to 6.8%; Table 2). Forty-nine jurisdictions reported rabid bats during 2019. No rabid bats were reported in Alaska, Delaware, Hawaii, or Puerto Rico. Bats were the only rabid animals detected in 9 states (Iowa, Illinois, Indiana, Mississippi, Nevada, Oregon, Utah, Washington, and Wisconsin) in 2019. Over 60% of the rabid bats were reported from 9 states: Texas (n = 289 [20.8%]), California (230 [16.6%]), New York (99 [7.1%]), Arizona (55 [4.0%]), Illinois (54 [3.9%]), Colorado (52 [3.7%]), Michigan (46 [3.3%]), Ohio (38 [2.7%]), and Wisconsin (38 [2.7%]).

Table 2

Number of animals reported to be rabid in the United States, including Puerto Rico, and percentages of samples tested for rabies that yielded positive results for 2014 through 2019.

20192014–2018
AnimalsNo. of rabid animalsNo. of animals tested with positive or negative resultPercentage of samples with positive resultNo. of rabid animalsPercentage of samples with positive result
Mean95% CIMean95% CI
Domestic animals
 Cats24521,1691.2258238–2781.21.0–1.3
 Cattle399854.06030–915.03.0–7.0
 Dogs6622,4720.36257–660.30.3–0.3
 Horses and donkeys227772.81810–252.41.4–3.3
 Sheep and goats106241.6108–131.71.2–2.2
Wildlife
 Bats1,387*25,3275.5*1,6351,482–1,7876.35.8–6.8
 Raccoons1,54513,17111.71,5241,264–1,78312.29.9–14.5
 Skunks9153,79624.11,185839–1,53226.321.9–30.7
 Foxes361*1,85419.5324300–34818.816.9–20.6
All domestic animals38546,2300.8410371–4490.90.8–0.9
All wildlife4,30548,5408.94,7614,028–5,4949.78.5–10.8
All animals4,69094,7704.95,1714,414–5,9285.34.8–5.8

Significantly different from mean value for 2014 through 2018.

Eight states reported a ≥ 50% increase in the number of rabid bats detected, compared with the number detected in 2018: Kansas (233% increase), Missouri (57% increase), New Hampshire (125% increase), Oklahoma (300% increase), South Dakota (117% increase), Tennessee (50% increase), Wisconsin (52% increase), and West Virginia (300% increase). Five states reported a decrease in the number of bat rabies cases detected, compared with the number detected in 2018: Connecticut (64% decrease), Georgia (50% decrease), Pennsylvania (65% decrease), Vermont (60% decrease), and Washington (78% decrease).

Variant typing results were reported for 390 (28.1%) of the rabid bats (Table 3). Among the bats tested for rabies, 9,939 (39.2%) were described beyond the taxonomic level of order; big brown bats (Eptesicus fuscus; n = 6,767) were the most commonly tested, followed by Mexican free-tailed bats (Tadarida brasiliensis; 1,334) and evening bats (Nycticeius humeralis; 347; Table 4).

Table 3

Rabies virus variants identified in domestic and wild animals in the United States, including Puerto Rico, during 2019.

Domestic animalsWildlife
VariantCatsCattleDogsHorses and donkeySheep and goatsOther domesticRaccoonsBatsSkunksFoxesOther wildlifeRodents and lagomorphsTotalSEInon-SEI
Raccoon78192253140302001191511876339537
South central skunk21586014402353111353112241
North central skunk3131100026200372413
California skunk100000002010022220
Arctic fox000000000000000
Arizona gray fox10000000101440291910
Cosmopolitan dog001000000000110
Mongoose (Puerto Rico)001000000000110
Bat20000013901600400299100
Variant reported1062535124244839049217320121,719797921
No variant reported139143110611,09799742318837282,9719012,066
Total infected2453966221031,5451,38791536157404,6901,6982,987
Variant typed (%)43.3%64.1%53.0%54.5%40.0%66.7%29.0%28.1%53.8%47.9%35.1%30.0%36.7%46.9%30.8%
Variant typed (%), 2014–2018
 Mean (%)28.649.454.950.427.783.321.330.945.338.327.321.732.341.025.0
 95% CI23.4–33.843.3–55.646.7–63.123.3–77.47.1–48.254.1–112.616.8–25.821.2–40.742.4–48.321.0–55.610.1–44.410.5–32.927.2–37.439.7–42.224.3–25.8

SEI = Samples of epidemiological importance.

Table 4

Species of bats submitted for rabies testing in the United States during 2019.

Species (common name)No. testedNo. positivePercentage positive
Order Chiroptera (unspecified)15,3887044.6%
Eptesicus fuscus (big brown bat)6,7672623.9%
Tadarida brasiliensis (Mexican free-tailed bat)1,33426519.9%
Nycticeius humeralis (evening bat)347113.2%
Myotis lucifugus (little brown bat)293175.8%
Lasiurus borealis (Eastern red bat)242177.0%
Lasionycteris noctivagans (silver-haired bat)17084.7%
Myotis californicus (California myotis)16342.5%
Myotis velifer (cave myotis)10033.0%
Lasiurus cinereus (hoary bat)662537.9%
Parastrellus hesperus (canyon bat)582441.4%
Myotis spp (not further differentiated)45715.6%
Lasiurus intermedius (northern yellow bat)421126.2%
Perimyotis subflavus (tricolored bat)3825.3%
Lasiurus seminolus (Seminole bat)3525.7%
Myotis evotis (long-eared myotis)3525.7%
Antrozous pallidus (desert pallid bat)3326.1%
Myotis ciliolabrum (western small-footed myotis)2400.0%
Myotis yumanensis (Yuma myotis)21314.3%
Myotis volans (long-legged myotis)20210.0%
Myotis austroriparius (southeastern myotis)1915.3%
Myotis thysanodes (fringed myotis)1700.0%
Leptonycteris yerbabuenae (lesser long-nosed bat)1200.0%
Lasiurus ega (southern yellow bat)900.0%
Desmodus rotundus (common vampire bat)*88100.0%
Lasiurus xanthinus (western yellow bat)6466.7%
Nyctinomops femorosaccus (pocketed free-tailed bat)5120.0%
Myotis keenii (Keen myotis)500.0%
Rousettus aegyptiacus (Egyptian rousette)500.0%
Plecotus townsendii (Townsend big-eared bat)500.0%
Myotis leibii (eastern small-footed myotis)300.0%
Macrotus californicus (California leaf-nosed bat)22100.0%
Myotis septentrionalis (northern long-eared bat)200.0%
Lasiurus blossevillii (western red bat)200.0%
Family Molossidae100.0%
Plecotus rafinesquii (Rafinesque big-eared bat)100.0%
Artibeus jamaicensis (Jamaican fruit-eating bat)100.0%
Choeronycteris mexicana (Mexican long-tongued bat)100.0%
Myotis occultus (Arizona myotis)100.0%
Pteropus spp (fying foxes; not further differentiated)100.0%
Total25,3271,3875.5%

Nonnative bat species submitted from a wildlife research center in Wisconsin.

Raccoons

A total of 13,171 raccoons tested for rabies in 2019 had a conclusive test result, of which 1,545 (11.7%) were confirmed positive (Figure 3). This represented a 3.1% increase from the 1,499 rabid raccoons reported in 2018 (Table 1). The percentage of rabid raccoons among the total tested (11.7%) was similar to the mean percentage during the previous 5 years (12.2%; 95% CI, 9.9% to 14.5%; Table 2). The number of raccoon rabies cases peaked in 1993, at 5,912.31

Figure 3
Figure 3

Reported cases of rabies involving raccoons, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

Citation: Journal of the American Veterinary Medical Association 258, 11; 10.2460/javma.258.11.1205

Twenty states, the District of Colombia, and New York City remained enzootic for the eastern raccoon RVV. These states accounted for 97.0% of all rabid raccoons reported in 2019. Variant typing was conducted on 403 of the 1,498 (26.9%) rabid raccoons from eastern raccoon RVV enzootic states, all of which were confirmed to be infected with the eastern raccoon RVV. The remaining 47 (3.0%) rabid raccoons were reported from states where the eastern raccoon RVV is not enzootic: Colorado (n = 2), New Mexico (1), Texas (43), and Wyoming (1). Variant typing results were reported for 45 of the 47 (96%) rabid raccoons from states where the eastern raccoon RVV was not enzootic. Forty-four were infected with the south central skunk RVV (Texas, New Mexico, and Wyoming), and 1 was infected with a bat RVV (Texas).

Four jurisdictions reported a ≥ 50% increase in the number of raccoon rabies cases detected, compared with the number detected in 2018: New York City (110% increase), Rhode Island (67% increase), South Carolina (86% increase), and West Virginia (92% increase). Four jurisdictions reported a ≥ 50% decrease in the number of raccoon rabies cases detected, compared with the number detected in 2018: Arizona (100% decrease), California (100% decrease), District of Columbia (71% decrease), and Vermont (55% decrease). Of the 3,303 rabies cases involving terrestrial mammals that were detected in 2019, 77.7% were reported from states where the eastern raccoon RVV was enzootic.

Skunks

A total of 3,796 skunks tested for rabies in 2019 had a conclusive test result, of which 915 (24.1%) were positive (Figure 4). This represented an 8.9% decrease from the number of rabid skunks reported during 2018 (1,004; Table 1). The percentage of rabid skunks among the total tested (24.1%) during 2019 was similar to the mean percentage during the previous 5 years (26.3%; 95% CI, 21.9% to 30.7%; Table 2).

Figure 4
Figure 4

Reported cases of rabies involving skunks, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

Citation: Journal of the American Veterinary Medical Association 258, 11; 10.2460/javma.258.11.1205

Eight of the 21 states where skunk RVVs were considered enzootic reported a ≥ 50% decrease in the number of rabid skunks during 2019, compared with the number detected in 2018: Colorado (56% decrease), Kentucky (75% decrease), Missouri (50% decrease), North Dakota (50% decrease), Oklahoma (56% decrease), South Dakota (75% decrease), Tennessee (58% decrease), and Wyoming (56% decrease). Six of the 21 states where skunk RVVs were considered enzootic reported a ≥ 50% increase in the number of rabid skunks: Arizona (72% increase), Louisiana (400% increase), Michigan (500% increase), Minnesota (100% increase), Nebraska (50% increase), and New Mexico (71% increase).

Variant typing results were reported for 492 of the 915 (53.8%) rabid skunks. Two hundred thirty-five were infected with the south central skunk RVV, 200 were infected with the eastern raccoon RVV, 26 were infected with the north central skunk RVV, 20 were infected with the California skunk RVV, 10 were infected with Arizona gray fox RVV, and 1 was infected with a bat RVV (Table 3).

Foxes

A total of 1,854 foxes tested for rabies in 2019 had a conclusive test result, of which 361 (19.5%) were confirmed rabid (Figure 5). This represented a 1.1% increase from the 357 reported in 2018 (Table 1). The percentage of rabid foxes among the total submitted for testing (19.5%) was similar to the mean percentage during the previous 5 years (18.8%; 95% CI, 16.9% to 20.6%; Table 2). No animals were reported infected with the Texas gray fox RVV in 2019; the last animal reported with this RVV was a cow from Texas in 2013.32

Figure 5
Figure 5

Reported cases of rabies involving foxes, by RVVs, in the United States, including Puerto Rico, during 2019. See Figure 1 for key.

Citation: Journal of the American Veterinary Medical Association 258, 11; 10.2460/javma.258.11.1205

Other wild animals

During 2019, Puerto Rico reported testing 20 mongooses, of which 19 were rabid, a 35.7% increase from the 14 rabid mongooses reported in 2018. Other reported rabid wildlife included 16 bobcats (Lynx rufus), 12 coyotes (Canis latrans), 3 deer (Cervidae family), 1 fisher (Martes pennanit), 1 javelina (Tayassu tajacu), 4 otters (Lontra canadensis), and 1 weasel (Mustella sp; Table 1). Rabid rodents and lagomorphs reported in 2019 included 1 beaver (Castor canadensis), 38 groundhogs (Marmota monax), and 1 squirrel (Sciuridae family). Variant typing was performed on 20 (35.1%) of the 57 other wild animals and on 12 of the 40 (30.0%) rodents and lagomorphs reported to be rabid (Table 3).

Rabies in Domestic Animals

During 2019, domestic animals accounted for 47.4% of all animals submitted for rabies testing and 8.2% (385/4,690) of all animal rabies cases reported. The 385 rabid domestic animals reported in 2019 represented a 6.4% increase, compared with the 362 reported in 2018 (Table 1). More than half of the 385 rabid domestic animals detected in 2019 were reported from 6 jurisdictions: Pennsylvania (n = 47), Virginia (46), Texas (30), North Carolina (35), New York (34), and Puerto Rico (26).

Dogs

In 2019, 22,737 dogs were submitted for rabies testing. Of the 22,472 dogs with a conclusive test result, 66 (0.3%) were confirmed rabid. This represented a 4.8% increase from the 63 rabid dogs reported in 2018. Greater than 80% of the rabid dogs were reported from 8 jurisdictions: Puerto Rico (n = 23 [34.8%]), Virginia (8 [12.1%]), Texas (6 [9.0%]), Pennsylvania (4 [6.0%]), Alaska (4 [6.0%]), Georgia (3 [4.5%]), Oklahoma (3 [4.5%]), and South Carolina (3 [4.5%]). The percentage of dogs that tested positive for rabies among the total tested was unchanged from the mean percentage for 2014 through 2018 (0.3%). Among the 8 (12.1%) rabid dogs for which vaccination status was reported, 1 had been vaccinated 1 week before it tested positive for rabies, 1 had a history of rabies vaccination without date information, and the others were not vaccinated. The RVV was provided for 35 (53.0%) of the reported rabies-positive dogs, among which 22 were infected with the eastern raccoon RVV, 8 were infected with the south central skunk RVV, 3 were infected with the north central skunk RVV, 1 with a travel history to Puerto Rico was infected with the mongoose RVV, and 1 with a travel history from Egypt was infected with a cosmopolitan dog RVV (Table 3).

Cats

A total of 21,357 cats were submitted for rabies testing in 2019. Of the 21,169 cats with a conclusive test result, 245 (1.2%) were confirmed rabid. This represented a 1.7% increase from the 241 rabid cats reported in 2018 (Table 1). The percentage of cats that tested positive for rabies among the total tested (1.2%) was unchanged from the mean percentage during the previous 5 years (1.2%; 95% CI, 1.0% to 1.3%; Table 2). Rabies vaccination status was reported for 13 (5.3%) rabid cats. Three of the rabid cats had a history of expired rabies vaccination, and the others were not vaccinated. Greater than 80% of the rabid cats were reported from states where the eastern raccoon RVV was considered enzootic: Pennsylvania (n = 37 [15.1%]), Virginia (30 [12.2%]), New York (24 [9.8%]), North Carolina (22 [9.0%]), New Jersey (21 [8.6%]), Maryland (15 [6.1%]), West Virginia (15 [6.1%]), South Carolina (13 [5.3%]), Florida (12 [4.9%]), and Georgia (8 [3.3%]). The RVV was provided for 106 (43.3%) of the reported rabid cats (Table 3). Most (78 [73.6%]) were infected with the eastern raccoon RVV, and the rest were infected with the south central skunk RVV (21 [19.8%]), north central skunk RVV (3 [2.8%]), California skunk RVV (1 [0.9%]), Arizona gray fox RVV (1 [0.9%]), or a bat RVV (2 [1.9%]).

Other domestic animals

A total of 985 cattle tested for rabies in 2019 had a conclusive test result, of which 39 (4.0%) were confirmed rabid. This represented an 18.2% increase in the number of rabid cattle, compared with the number reported in 2018 (33; Table 1). The percentage of cattle that tested positive for rabies among the total tested (4.0%) was similar to the mean percentage for the previous 5 years (5.0%; 95% CI, 3.0% to 7.0%; Table 2). North Carolina reported the highest number of rabid cattle (12 [30.8%]), followed by Virginia (7 [17.9%]), Texas (4 [10.3%]), New York (4 [10.3%]), and Oklahoma (3 [7.7%]). Twenty-two rabid horses were reported in 2019, a 69.2% increase compared with the 13 reported in 2018. The percentage of horses that tested positive for rabies among the total tested (2.8%) was similar to the mean percentage for the previous 5 years (2.4%; 95% CI, 1.4% to 3.3%). Other reported rabid domestic animals included 10 goats and sheep, 2 ferrets, and 1 llama.

Rabies in Humans

No human rabies cases were reported in the United States during 2019. From 2000 through 2020, a total of 52 human rabies cases were reported in the United States and its territories, representing a mean of 2.5 cases/y. The mean age was 40 years, and 40 (77%) of the affected individuals were male (Table 5). Thirty-eight cases were indigenously acquired (ie, the reported animal exposure occurred in the United States or its territories, the RVV that was identified matched an indigenous source, or no international travel was reported), and 14 cases were imported (ie, the reported animal exposure occurred internationally or the RVV that was identified matched a foreign source). The countries of origin for the imported cases were the Philippines (3 cases), Haiti (2 cases), India (2 cases), Mexico (2 cases), and Afghanistan, Brazil, El Salvador, Ghana, and Guatemala (1 case each). Indigenous cases were reported from 23 states and territories, including California (5 cases), Texas (5 cases), Wisconsin (3 cases), Florida (2 cases), Indiana (2 cases), Minnesota (2 cases), Missouri (2 cases), Puerto Rico (2 cases), and Arkansas, Delaware, Georgia, Iowa, Massachusetts, Maryland, Michigan, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Utah, Virginia, and Wyoming (1 case each). Exposure to bats or to RVVs associated with bats was responsible for 31 (82%) of the 38 indigenous cases, with involved RVVs associated with T brasiliensis (14 cases), Lasionycteris noctivagans (5 cases), L noctivagans or Perimyotis subflavus (4 cases), P subflavus (3 cases), and Myotis sp (1 case). The remaining indigenously acquired cases were a result of infection with the eastern raccoon RVV from the eastern United States (4 cases), the dog-mongoose RVV from the Caribbean (2 cases), or an unknown RVV (1 case).

Table 5

Cases of rabies in humans in the United States, including Puerto Rico, by circumstances of exposure and RVV, January 2000 through December 2020.

Date of onsetDate of deathReporting stateAge (y)SexExposure*RVV
13 Sep 0020 Sep 00CA49MContactBat, Tb
26 Sep 009 Oct 00NY54MBite, GhanaDog, African
3 Oct 0010 Oct 00GA26MContactBat, Tb
8 Oct 0025 Oct 00MN47MContactBat, Ln-Ps
12 Oct 001 Nov 00WI69MContactBat, Ln-Ps
19 Jan 014 Feb 01CA72MUnknownDog, Philippines
18 Mar 0231 Mar 02CA28MUnknownBat, Tb
21 Aug 0231 Aug 02TN13MContactBat, Ln-Ps
14 Sep 0228 Sep 02IA20MUnknownBat, Ln-Ps
10 Feb 0310 Mar 03VA25MUnknownRaccoon, eastern United States
28 May 035 Jun 03PR64MBite, Puerto RicoDog-mongoose, Caribbean
23 Aug 0314 Sep 03CA66MBiteBat, Ln
9 Feb 0415 Feb 04FL41MBite, HaitiDog, Haiti
27 Apr 043 May 04AR20MBite (organ donor)Bat, Tb
25 May 0431 May 04OK53MLiver transplantBat, Tb
27 May 0421 Jun 04TX18MKidney transplantBat, Tb
29 May 049 Jun 04TX50FKidney transplantBat, Tb
2 Jun 0410 Jun 04TX55FArterial transplantBat, Tb
12 Oct 04SurvivedWI15FBiteBat, unknown
19 Oct 0426 Oct 04CA22MUnknown, El SalvadorDog, El Salvador
27 Sep 0527 Sep 05MS10MContactBat, unknown
4 May 0612 May 06TX16MContactBat, Tb
30 Sep 062 Nov 06IN10FBiteBat, Ln
15 Nov 0614 Dec 06CA11MBite, PhilippinesDog, Philippines
19 Sep 0720 Oct 07MN46MBiteBat, unknown
16 Mar 0818 Mar 08CA16MBite, MexicoFox, Tb related
19 Nov 0830 Nov 08MO55MBiteBat, Ln
25 Feb 09SurvivedTX17FContactBat, unknown
5 Oct 0920 Oct 09IN43MUnknownBat, Ps
20 Oct 0911 Nov 09MI55MContactBat, Ln
23 Oct 0920 Nov 09VA42MContact, IndiaDog, India
2 Aug 1021 Aug 10LA19MBite, MexicoBat, Dr
24 Dec 1010 Jan 11WI70MUnknownBat, Ps
30 Apr 11SurvivedCA8FUnknownUnknown
30 Jun 1120 Jul 11NJ73FBite, HaitiDog, Haiti
14 Aug 1131 Aug 11NY25MContact, AfghanistanDog, Afghanistan
21 Aug 111 Sep 11NC20MBite (organ donor)Raccoon, eastern United States
1 Sep 1114 Oct 11MA40MContact, BrazilDog, Brazil
3 Dec 1119 Dec 11SC46FUnknownBat, Tb
22 Dec 1123 Jan 12MA63MContactBat, My sp
6 Jul 1231 Jul 12CA34MBiteBat, Tb
31 Jan 1327 Feb 13MD49MKidney transplantRaccoon, eastern United States
16 May 1311 Jun 13TX28MUnknown, GuatemalaDog, Guatemala
12 Sep 1426 Sep 14MO52MUnknownBat, Ps
30 Jul 1524 Aug 15MA65MBite, PhilippinesDog, Philippines
17 Sep 153 Oct 15WY77FContactBat, Ln
25 Nov 151 Dec 15PR54MBiteDog-mongoose, Puerto Rico
5 May 1721 May 17VA65FBiteDog, India
6 Oct 1721 Oct 17FL56FBiteBat, Tb
28 Dec 1714 Jan 18FL6MBiteBat, Tb
15 Jul 1823 Aug 18DE69FUnknownRaccoon, eastern United States
16 Oct 184 Nov 18UT55MContactBat, Tb

Data for exposure history are reported when plausible information was reported directly by the patient (if lucid or credible) or when a reliable account of an incident consistent with rabies virus exposure (eg, dog bite) was reported by an independent witness (usually a family member). Exposure histories are categorized as bite, contact but no known bite was acknowledged (eg, waking to find bat on exposed skin), or unknown (eg, no known contact with an animal was elicited during case investigation).

Rabies virus variants associated with terrestrial animals in the United States, including Puerto Rico, are identified with the names of the reservoir animal (eg, dog or raccoon), followed by the name of the most definitive geographic entity (usually the country) from which the variant has been identified. Rabies virus variants associated with bats are identified with the names of the species of bats in which they have been found to be circulating. Because information regarding the location of the exposure and the identity of the exposing animal is almost always retrospective and much information is frequently unavailable, the location of the exposure and the identity of the animal responsible for the infection are often limited to deduction.

Infection was not identified until 2013, when an organ recipient developed rabies.

Dr = Desmodus rotundus. Ln = Lasionycteris noctivagans. My sp = Myotis species. Ps = Perimyotis subflavus. Tb = Tadarida brasiliensis.

An animal bite or animal contact was reported in 35 (67%) of the 52 cases, and organ and tissue transplantation from 2 separate donors resulted in 5 cases (10%); the rabies virus exposure was unknown in 12 (23%) cases. The mean time from symptom onset to death was 17 days. Only 3 survivors were reported, 2 of whom received advanced supportive care including a drug-induced coma and ventilator support and 1 of whom had presumptive abortive human rabies and received supportive care but never required intensive treatment.33,34,35 One survivor received a single dose of rabies vaccine and human rabies immune globulin after the onset of symptoms, but rabies postexposure prophylaxis was not administered in any other cases.

National Rabies Control Efforts

Primary rabies prevention and control efforts in the United States are led by municipal, county, and state health departments. Jurisdictions focus on preventative measures such as encouraging vaccination of pets (to prevent secondary rabies exposure from wildlife reservoirs); providing animal control services and shelters to respond to sick, nuisance, and unwanted animals; providing risk assessments and laboratory diagnosis of animals suspected to have been exposed to rabies virus; and assisting with access to rabies postexposure prophylaxis for persons confirmed or suspected to have been exposed to rabies virus. Management of rabies in wildlife populations to prevent the spread of and eventually eliminate specific RVVs in mesocarnivores is a collaborative effort led by the USDA Wildlife Services, the Texas Department of State Health Services, other state agencies, and the CDC. The focus of these large-scale programs involves using oral rabies vaccination as the primary rabies control strategy for targeting wild carnivore populations. Oral rabies vaccination is used to reduce the impacts of wildlife rabies on human and animal health, prevent specific RVVs from gaining a larger geographic footprint, and decrease the substantial costs associated with rabies prevention and control.

During 2019, the national rabies management program maintained an oral rabies vaccination zone to prevent the spread of the eastern raccoon RVV in 14 eastern states. The zone was located along the US-Canada border in parts of Maine and extending to New York and from Lake Erie at the New York-Ohio-Pennsylvania border south through the Appalachia region to the Alabama-Georgia-North Carolina-Tennessee border. Additionally, state and county collaborators conducted oral rabies vaccination programs in local jurisdictional areas of Florida, Maryland, and New Jersey. In these areas, a total of 10,060,230 baits (vaccinia-rabies glycoprotein recombinant vaccine baits,36 69.1%; and adenovirus-rabies glycoprotein recombinant vaccine baits,37 30.9%) were distributed across more than 127,000 km2. In addition, a total of 1,066,700 baits (vaccinia-rabies glycoprotein recombinant vaccine baits, 97.0%; and adenovirus-rabies glycoprotein recombinant vaccine baits, 3.0%) were distributed across more than 43,000 km2 along the US-Mexico border in Texas to prevent the reintroduction of the canine-coyote RVV.

Rabies in Canada and Mexico

Canada

In 2019, the Canadian Food Inspection Agency tested 3,360 animal samples for rabies, of which 115 (3.4%) were positive (8.9 animals tested/100,000 Canada human population).29 This represented an 18.2% increase in the number of samples tested, compared with the number tested in 2018 (2,842). However, the number of positive samples in 2019 represented a 37.2% decrease, compared with the 183 rabid animals identified in 2018. The increase in samples tested was due to a rise in bat submissions in the 3 months following detection of a human rabies case caused by a bat exposure in mid-July. The increased number of negative samples also contributed to a decrease in the percentage of positive samples, as did a substantial decrease in the number of raccoon rabies cases detected through the wildlife rabies surveillance program in the province of Ontario in 2019.

As in 2018, bats represented the highest percentage of rabies cases in Canada in 2019 (n = 66 [57.4%]), followed by striped skunks (Mephitis mephitis; 22 [19.1%]), dogs (10 [8.7%]), and raccoons (9 [7.8%]). Although 89.6% (103/115) of animal rabies cases in 2019 involved wildlife species, domestic animals accounted for 41.0% (1,376/3,360) of the samples submitted for testing. Most of the samples tested during 2019 (2,379 [70.8%]) came from animals that had potentially exposed a person to rabies virus; of these, 472 had also potentially exposed a domestic animal. Other samples came from animals that had only contacted a domestic animal (22.5%) or did not have any documented contact with humans or domestic animals (6.7%). Most of the samples without any documented contact with humans or domestic animals (172/224 [76.8%]) were obtained as a result of wildlife surveys. Thirty-three of the wildlife survey samples submitted to the Canadian Food Inspection Agency for confirmatory testing following initial analysis in provincial laboratories with the direct rapid immunohistochemical test or by means of conventional immunohistochemical staining on formalin-fixed, paraffin-embedded tissues had positive direct fluorescent antibody test results. None of the animals from which these samples had been obtained had any reported exposure to humans or domestic animals. An additional 5 big brown bats from Saskatchewan (n = 4) and British Columbia (1) and 2 skunks from Saskatchewan had positive results for immunohistochemical staining performed by an external laboratory and reported to the Canadian Food Inspection Agency. However, samples from these animals were not submitted for confirmatory testing.

As in 2018, Ontario submitted the highest number of animal samples for testing (n = 1,819) and had the highest number of animal rabies cases (65). The number of rabies cases attributed to the eastern raccoon RVV decreased by 66.2%, compared with the number reported in 2018 (n = 65), with only 22 cases reported in 2019. Of these, 9 cases involved raccoons and 12 involved skunks. There was a single case of eastern raccoon RVV spillover into a domestic dog. In addition to cases caused by the eastern raccoon RVV, Ontario recorded 41 cases in bats, but no cases caused by the fox RVV. This represented the first year with no cases attributable to this variant since the detection of a fox RVV outbreak in southwestern Ontario in 2015. Two additional cases of rabies detected in a skunk and a mink (Neovison vison) were attributed to an RVV associated with big brown bats. One case due to eastern raccoon RVV was detected in a skunk in the province of New Brunswick, a disappointing finding after 23 months without a detection of this RVV, despite similar levels of surveillance during this time. Three rabid bats were also detected in New Brunswick in 2019.

Similar to previous years, only rabies cases due to bat RVVs were detected in British Columbia (7 bats) and Alberta (6 bats). Saskatchewan recorded cases involving skunks (n = 5), dogs (2), bats (8), and a bovid (1), and Manitoba recorded cases in 1 cat, 1 dog, and 2 skunks. Quebec recorded cases in 3 dogs and 1 wolf, all infected with the arctic fox RVV, along with 1 case in a big brown bat and 1 case in a skunk caused by an RVV associated with big brown bats. One of the dog cases was detected in southern Quebec following its relocation from the north of the province for adoption. The wolf case was detected in a community just south of the 55th parallel; both this case and the one involving the translocated dog were considered to be of epidemiological importance with respect to the potential for reintroduction of the artic fox RVV into the south of the province.38

The territory of Nunavut recorded cases due to the arctic fox RVV in 4 arctic foxes and 3 dogs. Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island, and Yukon recorded no rabies cases in 2019, although the numbers of samples from each of these jurisdictions that were tested were low (range, 1 to 14, except 53 samples were submitted from Newfoundland and Labrador).

Nine human suspect cases from 5 provinces were investigated in 2019, with the direct fluorescent antibody assay, a reverse transcriptase PCR assay, or both performed on various specimens. Of these, 1 involving a 21-year-old male from British Columbia was positive.39 In this case, the nuchal skin biopsy sample yielded negative results for both the direct fluorescent antibody assay and reverse transcriptase PCR assay, and serum and CSF were negative for rabies virus neutralizing antibody. However, 2 serial saliva samples yielded positive results with the reverse transcriptase PCR assay. Nucleoprotein gene sequencing and phylogenetic analysis revealed infection with an RVV associated with silver-haired bats (L noctavagans). The patient died 5 days after initial hospitalization.39 Prior to this case, the last case of human rabies diagnosed in Canada involved a patient who was infected on the island of Hispaniola in 2012.

Mexico

During 2019, a total of 22,924 samples were submitted to the Public Health State Laboratory and the Instituto de Diagnóstico y Referencia Epidemiológicos Rabies Diagnostic Laboratory for rabies testing, of which 20,994 (91.6%) were dog samples, 1,365 (6.0%) were cat and other domestic animal samples, and 565 (2.5%) were bat and other wildlife samples. Among the total tested animals (n = 22,024; 17.3 animals tested/100,000 Mexico human population), 74 (0.3%) were reported positive for rabies. This represented a 36.8% decrease from the 117 rabies cases reported in 2018.

Of the 74 rabies cases, 61 (82.4%) involved domestic animals, including 59 cattle, 1 goat, and 1 cat. The 59 rabid cattle were reported from Guerrero (n = 28), Jalisco (6), Michoacán (2), Nuevo León (3), Puebla (6), and San Luis Potosí (14). The rabid goat was reported from Guerrero. An unvaccinated domestic cat housed in an animal shelter was reported positive for rabies by the state of Yucatán, with antigenic characterization indicating the virus was associated with a lineage of wildlife RVVs. The remaining 13 rabies cases involved wildlife, including 1 bobcat reported from Baja California Sur; 4 skunks reported from Baja California Sur, Jalisco, Sonora, and Yucatán; and 8 bats reported from Jalisco (n = 1), Nuevo León (6), and San Luis Potosí (1). Results of antigenic characterization were available for 18 (24%) of the 74 rabies-positive animals, with V9 (a T brasiliensis RVV), V11 (a Desmodus rotundus RVV) identified in bats, V3 (also a D rotundus RVV), V8 (a skunk variant known in the United States as the south central skunk RVV), and V11 identified in cattle. The rest of the positive samples were still in the process of being characterized.

During 2019, there were no cases of human rabies transmitted by dogs or associated with wildlife in Mexico, and no cases infected with the canine RVV were reported. The elimination of dog-mediated human rabies was achieved mainly through the use of 2 strategies: intensive campaigns in the past 10 years to vaccinate dogs and cats during the national weeks of rabies vaccination (18 million doses distributed annually at no cost to the owners), and prompt administration of rabies postexposure prophylaxis for individuals attacked by animals susceptible to rabies. In October 2019, Mexico received official validation from the World Health Organization as a country free from dog-mediated human rabies.40

Discussion

Approximately 100,000 domestic and wild animals are tested annually for rabies virus in the United States, with most of these animals tested following exposure of humans or domestic animals. The number of animals submitted for rabies virus testing in the United States peaked in 2008, followed by a declining trend from 2009 through 2019 that largely corresponded with the raccoon rabies virus epizootic and reflected a postepizootic, enzootic state. The number of animals submitted for rabies testing in 2019 (n = 97,523) was comparable to the mean number of animals submitted over the past 5 years (99,186; 95% CI, 94,645 to 103,727). Although the number of rabies-positive animal cases reported in 2019 decreased by 5.3%, compared with the number reported in 2018, positivity rates remained similar to mean positivity rates of the past 5 years, with the exception of the positivity rate for bats. Bats were the second most frequently identified rabid animals in the United States in 2019 after raccoons. This followed 4 consecutive years of bats being the most frequently reported rabid animals.41 The reasons for the decreases in the number of rabies-positive bats and the bat rabies positivity rate, compared with values for 2014 through 2018, were unclear, and understanding the relative effects of possible surveillance artifacts, bat population dynamics, and enzootic transmission will require further research. The increasing number of rabies-positive foxes since 2016 in the southwest warrants further surveillance and research to better characterize the threat of an expanding geographic distribution and the effect on enzootic rabies transmission in other terrestrial reservoirs.42,43

No human rabies cases were reported in any US states or territories during 2019 or 2020, and the last confirmed case of human rabies occurred in Utah in October 2018.44 Bat rabies is the leading cause of human rabies in the United States since the near elimination of canine rabies in the 1950s and freedom from canine RVVs in 2007.2,3 With no vaccination-based options for rabies control in bats, maintaining public awareness of the risks posed by bat exposure is indispensable to preventing bat-associated rabies in humans.

Testing animals for rabies in the United States serves multiple purposes, including directing recommendations for postexposure prophylaxis in humans and quarantining or testing recommendations for domestic animals, identifying spatial and temporal trends that can impact these recommendations, and evaluating oral rabies vaccination efforts in target species (eg, raccoons). Collecting information on animal species, the location of capture or sampling, and RVV is critical to ensure that sufficient information is available to meet the latter 2 objectives. Categorizing samples as being of epidemiological importance allows state and federal laboratories to prioritize variant typing and encourages timely reporting to the CDC.26,27 Several cases in 2019 illustrated the necessity of performing timely RVV typing of samples of epidemiological importance. For example, a lamb in New Mexico was found to be infected with the eastern raccoon RVV, which is enzootic > 1,600 km to the east (Figure 1). An investigation determined that the animal was legally purchased in New York before developing clinical signs in New Mexico. In this case, the sample met conditions for categorization as a sample of epidemiological importance because it was obtained from livestock with a history of travel across an enzootic RVV territory. The potential establishment of the eastern raccoon RVV through onward transmission in a naive raccoon population was averted thanks to swift investigation and variant typing. In Louisiana, a squirrel located 50 km from the nearest terrestrial RVV territory (south central skunk) tested positive for rabies. This sample was categorized as being of epidemiological importance and promptly typed, and the south central skunk RVV was confirmed, indicating the likely presence of undetected circulation of the south central skunk RVV in the area (although natural or human translocation of the squirrel prior to the development of clinical signs could not be ruled out). Testing samples of epidemiological importance is also key to detecting the introduction of foreign RVVs. In Kansas, a rabies-positive dog was confirmed with the cosmopolitan dog RVV following fraudulent importation from Egypt.14 For this reason, all rabies-positive dogs in the United States should undergo RVV typing. Another notable sample of epidemiological importance underscored the importance of surveillance in nonindigenous bat species. Wisconsin reported 8 vampire bats (D rotundus) in a captive bat population in a research facility that were positive for the vampire bat RVV. Neither vampire bats nor the vampire bat RVV is indigenous to the United States. In this situation, the bats were wild-caught and legally imported from Mexico into the United States for a rabies vaccine efficacy study,45 although the importation of vampire bat RVV was accidental. Given the potential risk of expansion of the vampire bat range in the Americas,46 increased rabies surveillance in bats in the southern border states is recommended.26 These cases highlight the value of using samples of epidemiological importance to strengthen surveillance to better understand epidemiological cycles and enable local, state, and federal collaborators to allocate limited public resources to the most impactful events.

Although the National Rabies Surveillance System is a highly robust and efficient system, surveillance completeness is inconsistent across reporting entities, especially with regard to RVV typing. Only 36.7% of rabies-positive animals had results of RVV typing submitted to the National Rabies Surveillance System in 2019. Although this was lower than desired, it represented an increase, compared with the previous 5-year mean, and continued a 7-year trend in increasing RVV reporting. Equally encouraging was the significantly higher RVV reporting rate for samples of epidemiological importance (46.9%), compared with samples that were not considered to be of epidemiological importance (30.8%), which followed an increasing trend in the mean RVV reporting rate for samples of epidemiological importance from 2014 through 2018 (41.0%). In 2019, 28% of rabid bats had a reported RVV typing result. Although it is unlikely that emerging RVVs in North America will differ in pathogenicity or susceptibility to modern cell culture vaccines, understanding the diversity of RVVs and transmission dynamics can enhance our understanding of rabies diversity in the United States and enable better forecasting of emerging RVVs. Because variant typing is unrealistic for all rabies-positive bats in the United States, nonindigenous bats species, bats in southern border states, and bat species that are not commonly found to be infected with the rabies virus should be prioritized for testing.26

Rabies has been detected in most of the 51 bat species found in the United States.4,5,6 In 2019, rabies was identified in 23 bat species. However, > 50% of rabid bats were not identified to the species level. Of the bats submitted for rabies testing during 2019, only 39% were identified to the genus or species level (9,939 bats), whereas 15,388 had no identification beyond the order Chiroptera. Bat identification is typically based on morphological features, and dichotomous keys can help with bat species identification.4 However, the use of keys requires operator experience, and some bat species and subspecies are difficult to distinguish on the basis of morphological features alone.47,48,49,50,51 In other instances, specimens submitted for rabies testing may be unsatisfactory for morphological characterization owing to their condition. Sequencing is an alternative approach for host identification that does not rely on the preservation of morphological features.47,52 Sequencing of the host genome from any tissue (including brain) can be a quick, accurate method of bat species identification. Improving species identification for rabid bats could inform which bat species are acting as rabies reservoirs in various states or regions, leading to improvements in the understanding of rabies ecology.

In addition to the dozens of bat species that act as potential rabies vectors, there are at least 20 known phylogenetic lineages of rabies virus associated with bats in the United States.43,53 Rabies transmission is thought to occur between conspecifics in most cases; however, there are many documented cases of transmission between bat species as well as from bats to other mammals.43,53,54 Thus, defining RVVs solely on the basis of the species of a rabid bat is not always accurate, and additional characterization is required. Antigenic methods that include panels of monoclonal antibodies have been developed for bat RVV typing54,55,56,57; however, resolution depends heavily on how many monoclonal antibodies are used. There is currently no commercial set of monoclonal antibodies that can be used to distinguish all the major RVVs in bats in the United States. Molecular methods such as reverse transcriptase PCR assays and LN34 short amplicon sequencing58 can also be used for low-resolution typing of RVVs. Full genome and partial genome approaches have been published53,55,57; however, sequencing of larger genomic regions is required to distinguish all known bat RVVs with high confidence. New low-cost, high-throughput genotyping methods59 are being implemented in the United States for sequencing rabies virus nucleoprotein and glycoprotein genes for high-resolution genetic typing. Such sequencing approaches can be further enhanced by adding host genes for identification of the host species. Improving both bat species identification and bat RVV identification would go a long way toward understanding the distribution of bat rabies across the United States. This information could be used to generate detailed maps of the distributions of distinct bat RVVs that could be used in public health investigations and in the identification of novel RVVs, translocations, and host-shift events.

Acknowledgments

The authors declare that there were no conflicts of interest.

Use of trade names and commercial sources is for identification only and does not imply endorsement by the US Department of Health and Human Services. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the CDC.

The authors thank the state and territorial public health and agriculture departments and laboratories for their contributions of rabies surveillance data and human case investigations. The authors also thank Jinxin Gao, Rene Edgar Condori, Yu Li, Pamela Yager, Subbian Satheshkumar Panayampalli, and other staff of the CDC Poxvirus and Rabies Branch for their help and support.

Abbreviations

RVV

Rabies virus variant

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Contributor Notes

Address correspondence to Ms. Ma (HJV4@cdc.gov).

This article has not undergone external peer review.