From late December 2004 until early February 2005, a Wyoming goat herd with approximately 135 bred does and 3 bucks, consisting primarily of a variety of crossbred meat-type goats, experienced an abortion storm in which 44 does aborted, resulting in 75 aborted fetuses and 1 neonatal death. Several does died during parturition. The resulting kidding rate was approximately 67% (91/135). The herd was initially assembled in the summer of 2003 with goats from local producers, and 55 pregnant and nonpregnant does were added from an out-of-state source in December 2003. Upon arrival of the new additions, the herd experienced abortions associated with Coxiella burnetii, as confirmed by the Wyoming State Veterinary Laboratory. Abortions continued throughout the winter, resulting in the loss of approximately 55 kids and 6 does. During treatment with tetracycline, the does and kids were separated from the adult bucks in mid May 2004, with no common fences between the 2 groups. No additional goats were introduced into this population from an outside source from January 2004 through December 2004, when the abortions began.
The does and juvenile goats were brought in from pasture on December 1, 2004, and penned with the bucks for breeding. In the latter part of December 2004, the first abortions occurred. It was not the intention of the producer to have begun kidding at this time; however, 2 juvenile bucks left with the does and remaining kids had apparently bred does in late summer. Because the herd previously experienced infection with C burnetii, the owner presumed the abortions represented another such outbreak. The first live kid was born on February 9, 2005. On the basis of an estimated 150day gestation period for goats, the breeding date was approximately September 13, 2004. Although it was impossible to determine the length of time prior to the extrapolated breeding date when other breedings occurred, the gestational age of the aborted fetuses was likely approximately 100 days. Five aborted fetuses were sent to the Wyoming State Veterinary Laboratory for testing. The fetuses, 3 male and 2 female, ranged in weight from 0.22 to 1.39 kg (0.48 to 3.06 lb; median, 0.8 kg [1.8 lb]) and ranged in crown rump length from 17 to 33 cm (median, 25 cm). The fetal tissues were processed routinely, sectioned at 5.0 Mm, and stained with H&E. Lesions in 4 of the 5 fetuses consisted of discrete, variably sized, randomly located foci of necrosis scattered in the lung; liver; and, when available, spleen. In all tissues, but most notably in the liver, viable cells surrounding foci of necrosis contained intranuclear inclusion bodies. The inclusions varied from those filling the entire nucleus to smaller bodies associated with distinctive margination of the nuclear chromatin. Virus isolation was attempted on pooled tissues from individual fetuses in ovine embryonic kidney cells. A herpesvirus that reacted with a fluorescein-conjugated BHV-1 antibody was isolated from 1 fetus (CpHV-1 is antigenically related to BHV-1, the etiologic agent of infectious bovine rhinotracheitis1); all other virus isolation attempts yielded negative results. No bacterial pathogens were cultured from the 5 fetuses. Herpesvirus abortion was diagnosed in all fetuses except 1, which had no lesions and no isolated virus.
Results of serologic testing of 241 goats for anti–CpHV-1 antibodies after an abortion storm from 2004 to 2005. Data indicate number of goats in each category.
The herpesvirus isolate was identified as CpHV-1 by use of DNA sequencing; DNA was extracted from infected cells with a commercial reagent.a Two hundred nanograms of DNA was added to a nested PCR reaction with 1X buffer,b 1.5mM MgCl2, 15 pmol of each primer, 7.5% DMSO, 0.2μM dNTPs, and 1.25 units of Taq DNA polymerase.b Conditions of the PCR assay were 1 cycle at 94°C for 4 minutes; 35 cycles at 94°C for 15 seconds, 55°C for 30 seconds, and 72°C for 1 minute; and 1 cycle at 72°C for 10 minutes. The second reaction was performed the same as the first, except for modifying the DMSO to 5% and use of 5 μL of the first reaction product. Primers targeted a region coding for glycoprotein C of CpHV-1.2 The PCR product was sequenced and compared with sequences in Genbank. On the basis of clinical and laboratory findings, a diagnosis of CpHV-1 abortion was made.
Nineteen of the 44 (43%) does that had aborted were bred back and gave birth to at least 1 live kid in summer 2005. Thus, the owner chose to keep all of the female kids born alive in February as well as all of the yearling and older does, regardless of whether they had aborted. Adult bucks present before and during the initial outbreak were kept with a young buck that was purchased in December 2005 (1 year following the abortion storm).
Specific aims of the investigation reported here were to identify the likelihood of adult-to-neonate transmission of CpHV-1 during and following the abortion storm, identify the percentage of goats potentially latently infected with CpHV-1, and determine the fertility of does previously infected with or that had aborted because of CpHV-1. Blood samples were obtained from the entire flock in mid December 2005, approximately 1 year from the initial outbreak. Young goats in the flock born during the outbreak were then approximately 10 months old, well past the period at which maternal antibody titers are detectable.3 Two hundred forty-one sera were tested for antibodies against CpHV-1 by use of a standard serum neutralization test in bovine turbinate cells (30 to 300 TCID50 of virus in 2-fold serially diluted serum, beginning at 1:4). Sera that yielded positive results for anti–CpHV-1 antibodies typically had low titers (1:4 to 1:32) that ranged from 1:4 to 1:128 (Table 1).
Only adult goats present during the outbreak yielded positive results. Neither the does or bucks born after the abortion storm, the young goats born in June and July of 2005 from does that had aborted and were bred back, nor the young buck introduced into the herd in December 2005 had detectable antibodies against CpHV-1. Therefore, adult-to-neonate transmission was not observed. This suggested that exposure to potentially contaminated aborted material or does that had recently aborted did not resulted in transmission of the disease.
Numbers of goats testing positive or negative for antibodies against CpHV-1 after an abortion storm, grouped according to sex and pregnant verses nonpregnant does.
No evidence of CpHV-1 abortion was observed during the 2006 kidding season (Table 2). The higher kidding rate in does with positive results for antibodies (97/110 [88%]), compared with does with negative results (82/106 [77%]), was not attributed to antibody status. Rather, a large portion (24/37) of the latter was born in 2005, and their lower kidding rate was attributed to young age. Furthermore, the 2006 kidding rates for does present during the abortion storm of 2005 that did and did not have anti–CpHV-1 antibodies were nearly identical to (97/110 [88%] vs 14/16 [87.5%], respectively) and were greater than the kidding rate (91/135 [67%]) associated with the abortion storm the previous year. Therefore, CpHV-1 exposure had no apparent effect on the reproductive success of does after the initial CpHV-1 outbreak.
Discussion
Caprine herpesvirus-1 has been linked to sporadic abortion storms, vulvovaginitis, balanoposthitis, and respiratory disease in adult goats, as well as to generalized disease and enteritis in neonatal kids.4,5,6,7,8,9,10 Although CpHV-1 abortion storms have been reported throughout North America,4,5,11,12 there have been few followup reports on flock management following such outbreaks. Veterinarians and goat producers are therefore left with little information to base culling and other disease management decisions following CpHV-1 abortion storms. Like all alphaherpesviruses, CpHV-1 has the potential of latently infecting its host. Although it is not known what percentage of goats become latently infected with the virus following an acute infection, it can be presumed that all animals having neutralizing antibody titers to CpHV-1 have the potential of being latently infected.
Fetal death has been detected at days 92 and 125 of gestation.13 Additionally, infection of a doe on day 125 of gestation resulted in fetal death 10 days later.13 These data are consistent with the extrapolated dates of breeding, abortion, and kidding in the outbreak reported here. If the pregnant does were in the proximity of day 100 of gestation, it is possible they were infected with CpHV-1 upon, or shortly after, introduction of the bucks on December 1, 2004. Approximately 3 weeks passed before abortions were observed. This was an adequate amount of time for 1 or more latently infected does or bucks to begin shedding virus through nasal or vaginal secretions or lesions on the genitals. Because 3 bucks and many does had positive antibody titers, any of these goats could have been the source of infection. Experimental reactivation of CpHV-1 has historically been difficult to induce and often requires administration of large doses of dexamethasone.14,15,16 Natural reactivation, however, seems to be linked with estrus in does and could be a major contributor in maintaining the virus in goat populations by enabling spread of the virus during the mating season.17 Depending on the site where virus is shed upon reactivation, this could occur via the respiratory route or sexually.
All of the bucks and does (both those that had aborted and those that had live kids) were penned together. Therefore, if either aborted material or does that had recently aborted were significant factors in disease transmission, one would expect many of the younger goats to have seroconverted. The data from this outbreak suggest that kids born alive in the wake of a CpHV-1 abortion storm may remain unaffected by the virus and are thus at low risk of being latently infected with CpHV-1. A report3 of a CpHV-1 abortion storm in Quebec, Canada, indicated that nearly all kids born to seropositive does were themselves seropositive. However, it was not stated at what age blood was drawn from the kids, and it is possible that the antibodies detected were derived from maternal transfer and not from CpHV-1 infection. In the Wyoming outbreak, approximately 48% (116/241) of the total goats tested positive for CpHV-1 antibodies. Of the adult goats present at the time of the outbreak, 81% (116/143) tested positive for CpHV-1 antibodies and were potentially latently infected with CpHV-1.
To identify herpesvirus abortion in goats, a combination of virus isolation, fluorescein-conjugated antibody staining, and histologic examination of fetuses may be used. Because ruminant alpha-herpesviruses have antigenic cross-reactivity,1 confirmatory identification of CpHV-1 should be based on sequence analysis of a virus isolate or tissue sample. Serologic data are of limited use because positive results are only indicative of exposure, which may not be recent. Once CpHV-1 infection has been identified in a goat herd, it is possible to identify potentially latently infected goats by testing for antibodies against CpHV-1. Additionally, serologic testing of kids should not be performed until maternal antibodies have dissipated, to avoid false-positive results. Although the kids in this report were approximately 10 months old at the time of testing, it has been reported that maternally transferred anti–CpHV-1 antibodies are undetectable after approximately 4 months of age.7
Although no diseases caused by CpHV-1 were observed the year following the outbreak, it should be noted that in latently infected goats, reactivation and shedding of CpHV-1 can occur. Additionally, because it was unknown whether any of the latently infected goats began shedding virus during kidding in 2006, it was not known whether previous exposure to the virus provided any protection against virus challenge. However, high serum neutralizing antibody titers against equine herpesvirus-1 do not necessarily confer protection from abortion induced by this virus in horses.18 The data reported here suggest that rather than culling an entire flock after a CpHV-1 abortion storm, serologic testing could be used to identify potentially latently infected goats for culling. In the herd reported here, 81% of the adult goats present during the outbreak were potentially latently infected. Because none of the kids born alive during the 2004 outbreak had positive results for antiCpHV-1 antibodies, blood lines of superior goats could be maintained by retaining those kids as replacements for seropositive adult goats.
An inactivated CpHV-1 vaccine is protective against disease.19 Also, does vaccinated with a vaccine-cream suspension applied directly to the vaginal mucosa by use of an inactivated CpHV-1 vaccine have reduced severity of genital lesions after challenge, compared with unvaccinated controls.20 However, no commercial CpHV-1 vaccine is presently available in the United States, and it is unlikely that such a vaccine will be developed because of the small market size. Antibodies directed against BHV-1 will react with CpHV-1, but antibodies developed against CpHV-1 have little, if any, reactivity against BHV-1.1 Thus, it has been suggested that BHV-1 vaccines could be used in goats to protect against CpHV-1 infection. However, a challenge study found that vaccinating goats with an attenuated glycoprotein E–deleted BHV-1 vaccine induced only partial protection against CpHV-1 infection.21 No studies have determined whether vaccination would protect against CpHV-1 abortion. In the United States, neither the prevalence of seropositive goats nor the prevalence of disease associated with them is known.
ABBREVIATIONS
| BHV-1 | Bovine herpesvirus-1 |
| CpHV-1 | Caprine herpesvirus-1 |
DNAzol reagent, Invitrogen Corp, Carlsbad, Calif.
GoTaq Flexi DNA polymerase, Promega Corp, Madison, Wis.
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