Objective—To estimate when foot-and-mouth disease virus (FMDV) would first be detected in bulk tank milk of dairies after exposure to FMDV.
Sample Population—Hypothetical dairy herds milking 100, 500, or 1,000 cows.
Procedures—For each day after herd exposure to FMDV, infection, milk yield, and virolactia were simulated for individual cows with low and high rates of intraherd transmission to estimate when a PCR assay would detect virus in bulk tank milk. Detection limits were based on assumptions for the number of virus genomes per milliliter of milk and for analytical sensitivity of a PCR assay.
Results—A mean of 10% of the cows was predicted to have FMD lesions from 7 to 8 days and from 13.5 to 15 days after herd exposure for herds with high and low intraherd transmission rates, respectively. Herd bulk milk volume decreased by 10% by 8.5 to 9.5 days and by 15 to 16.5 days after herd exposure for herds with high and low transmission rates, respectively. Mean times by which FMDV would be first detected in bulk milk were 2.5 days and 6.5 to 8 days after herd exposure, which were extended for 10 to 11 days and 17 to 18 days for herds with high and low transmission rates, respectively.
Conclusions and Clinical Relevance—PCR screening of bulk milk for FMDV would likely detect FMDV in dairy herds several days sooner than might be expected for owner reporting of clinical signs and thus should be worthy of consideration for regional, national, or global FMD surveillance.
Objective—To estimate the extent to which infection
with Mycobacterium avium subsp paratuberculosis
(MAP) of cows in a large dairy was attributable to the
infection status of their dams.
Design—Retrospective longitudinal study.
Animals—625 dam-daughter pairs of Holstein cows.
Procedure—Serologic test results were compared
between cows and their dams. Logistic regression
was used to assess whether a cow's serologic status
was associated with its dam's serologic status.
Infection with MAP attributable to being born to a
seropositive dam was estimated for individual cows
and for the herd.
Results—Cows with seropositive dams were 6.6
times as likely to be seropositive, compared with
cows of seronegative dams. For seropositive cows
born to seropositive dams, 84.6% of seropositivity
was attributable to being born to a seropositive dam
and 15.4% to other exposures, including exposure as
calves to flush water that contained feces of adult cattle.
For the herd as a whole, the seropositive status in
34% of seropositive cows was attributable to being
born to a seropositive dam.
Conclusions and Clinical Relevance—For dairy
herds that breed seropositive cows, subsequent
transmission of MAP to their daughters, either congenitally
or via exposure to feces and colostrum of
the dam shortly after birth, can contribute substantially
to maintaining prevalence of MAP in a herd.
Removal of seropositive, clinically unaffected cows
and their daughters would be necessary to reduce
infection with MAP attributable to congenital or periparturient
transmission from dam to daughter. (J Am
Vet Med Assoc 2005;227:450–454)
Objective—To develop a spatial epidemic model to
simulate intraherd and interherd transmission of footand-
mouth disease (FMD) virus.
Sample Population—2,238 herds, representing
beef, dairy, swine, goats, and sheep, and 5 sale yards
located in Fresno, Kings, and Tulare counties of
Procedure—Using Monte-Carlo simulations, a spatial
stochastic epidemic simulation model was developed
to identify new herds that would acquire FMD following
random selection of an index herd and to assess
progression of an epidemic after implementation of
mandatory control strategies.
Results—The model included species-specific transition
periods for FMD infection, locations of herds,
rates of direct and indirect contacts among herds, and
probability distributions derived from expert opinions
on probabilities of transmission by direct and indirect
contact, as well as reduction in contact following
implementation of restrictions on movements in designated
infected areas and surveillance zones.
Models of supplemental control programs included
slaughter of all animals within a specified distance of
infected herds, slaughter of only high-risk animals
identified by use of a model simulation, and vaccination
of all animals within a 5- to 50-km radius of infected
Conclusions and Clinical Relevance—The FMD
model represents a tool for use in planning biosecurity
and emergency-response programs and in comparing
potential benefits of various strategies for control
and eradication of FMD appropriate for specific populations.
(Am J Vet Res 2003;64:195–204)
Objective—To assess estimated effectiveness of
control and eradication procedures for foot-andmouth
disease (FMD) in a region of California.
Sample Population—2,238 herds and 5 sale yards in
Fresno, Kings, and Tulare counties of California.
Procedure—A spatial stochastic model was used to
simulate hypothetical epidemics of FMD for specified
control scenarios that included a baseline eradication
strategy mandated by USDA and supplemental control
strategies of slaughter or vaccination of all animals within
a specified distance of infected herds, slaughter of
only high-risk animals identified by use of a model simulation,
and expansion of infected and surveillance zones.
Results—Median number of herds affected varied
from 1 to 385 (17% of all herds), depending on type
of index herd and delay in diagnosis of FMD.
Percentage of herds infected decreased from that of
the baseline eradication strategy by expanding the
designated infected area from 10 to 20 km (48%),
vaccinating within a 50-km radius of an infected herd
(41%), slaughtering the 10 highest-risk herds for each
infected herd (39%), and slaughtering all animals
within 5 km of an infected herd (24%).
Conclusions and Clinical Relevance—Results for the
model provided a means of assessing the relative merits
of potential strategies for control and eradication of
FMD should it enter the US livestock population. For the
study region, preemptive slaughter of highest-risk herds
and vaccination of all animals within a specified distance
of an infected herd consistently decreased size and
duration of an epidemic, compared with the baseline
eradication strategy. (Am J Vet Res 2003;64:205–210)
Objective—To assess relative costs and benefits of
vaccination and preemptive herd slaughter to control
transmission of foot-and-mouth disease (FMD) virus
Sample Population—2,238 herds and 5 sale yards
located in Fresno, Kings, and Tulare counties of
Procedure—Direct costs associated with indemnity,
slaughter, cleaning and disinfecting livestock premises,
and vaccination were compared for various eradication
strategies. Additional cost, total program cost,
net benefit, and benefit-cost value (B/C) for each supplemental
strategy were estimated, based in part on
results of published model simulations for FMD.
Sensitivity analyses were conducted.
Results—Mean herd indemnity payments were estimated
to be $2.6 million and $110,359 for dairy and
nondairy herds, respectively. Cost to clean and disinfect
livestock premises ranged from $18,062 to
$60,205. Mean vaccination cost was $2,960/herd.
Total eradication cost ranged from $61 million to $551
million. All supplemental strategies involving use of
vaccination were economically efficient (B/C range,
5.0 to 10.1) and feasible, whereas supplemental
strategies involving use of slaughter programs were
not economically efficient (B-C, 0.05 to 0.8) or feasible.
Conclusions and Clinical Relevance—Vaccination
with a highly efficacious vaccine may be a cost-effective
strategy for control of FMD if vaccinated animals
are not subsequently slaughtered and there is no
future adverse economic impact, such as trade
restrictions. Although less preferable than the baseline
eradication program, selective slaughter of highest-risk herds was preferable to other preemptive
slaughter strategies. However, indirect costs can be
expected to contribute substantially more than direct
costs to the total cost of eradication programs. (Am J Vet Res 2003;64:805–812)
Objective—To estimate direct and indirect contact
rates on livestock facilities and distance traveled
between herd contacts.
Sample Population—320 beef, dairy, goat, sheep,
and swine herds, 7 artificial insemination technicians,
6 hoof trimmers, 15 veterinarians, 4 sales yard owners,
and 7 managers of livestock-related companies
within a 3-county region of California.
Procedure—A questionnaire was mailed to livestock
producers, and personal and telephone interviews
were conducted with individuals.
Results—Mean monthly direct contact rates were
2.6, 1.6, and 2.0 for dairies with < 1,000, 1,000 to
1,999, and ≥ 2,000 cattle, respectively. Mean indirect
contact rates on dairies ranged from 234 to 743 contacts/
mo and increased by 1 contact/mo as herd size
increased by 4.3. Mean direct monthly contact rate
for beef herds was 0.4. Distance traveled by personnel
and vehicles during a 3-day period ranged from
58.4 to 210.4 km. Of livestock arriving at sales yards,
7% (500/7,072) came from ≥ 60 km away, and of
those sold, 32% (1,180/3,721) were destined for a
location ≥ 60 km away. Fifty-five percent (16/29) of
owners of large beef herds observed deer or elk within
150 m of livestock at least once per month.
Conclusions and Clinical Relevance—Direct and
indirect contacts occur on livestock facilities located
over a wide geographic area and at a higher frequency
on larger facilities. Knowledge of contact rates may
be useful for planning biosecurity programs at the
herd, state, and national levels and for modeling
transmission potential for foot-and-mouth disease
virus. (Am J Vet Res 2001;62:1121–1129)
Objective—To characterize husbandry practices that could affect the risks of foreign animal disease in miniature swine.
Study Population—106 owners of miniature swine.
Procedures—An online survey of owners of miniature swine was conducted to obtain information about miniature pig and owner demographics; pig husbandry; movements of pigs; and pig contacts with humans, other miniature swine, and livestock.
Results—12 states, 106 premises, and 317 miniature swine were represented in the survey. More than a third (35%) of miniature swine owners also owned other livestock species. Regular contact with livestock species at other premises was reported by 13% of owners. More than a third of owners visited shows or fairs (39%) and club or association events (37%) where miniature swine were present. More than 40% of owners fed food waste to miniature swine. Approximately half (48%) of the veterinarians providing health care for miniature swine were in mixed-animal practice.
Conclusions and Clinical Relevance—Results of this study indicated that miniature swine kept as pets can be exposed, directly and indirectly, to feed and other livestock, potentially introducing, establishing, or spreading a foreign animal disease such as foot-and-mouth disease. In addition, the veterinary services and carcass disposal methods used by miniature swine owners may reduce the likelihood of sick or dead pigs undergoing ante- or postmortem examination by a veterinarian.
Objective—To estimate transmission of bovine viral
diarrhea virus (BVDV) and crude morbidity and mortality
ratios in BVDV-vaccinated and unvaccinated dairy
heifer calves managed under typical dairy drylot conditions.
Design—Randomized clinical trial.
Animals—106 female Holstein calves.
Procedure—Seroconversion rates for BVDV types I
and II and proportional morbidity and mortality ratios
were compared between calves given a killed BVDV
type-I vaccine at 15 days of age and a modified-live
BVDV type-I vaccine at 40 to 45 days of age (n = 53)
and calves given no BVDV vaccines (53). Sera were
collected at 45-day intervals as calves moved from
individual hutches to corrals holding increasingly larger
numbers of calves. Seroconversion was used as
evidence of exposure to BVDV.
Results—Crude proportional morbidity (0.16) and
mortality (0.17) ratios for control calves did not differ
significantly from those of vaccinated calves (0.28
and 0.12, respectively). The proportion of control
calves that seroconverted to BVDV type I through 9
months of age (0.629) was significantly higher than
that of vaccinated calves that seroconverted, unrelated
to vaccination, during the same period (0.536).
Estimated overall protective effect of vaccination
against BVDV type I through 4 to 9 months of age
was 48%. The proportion of control calves that seroconverted
to BVDV type II (0.356) was not different
from that of vaccinated calves (0.470).
Conclusions and Clinical Relevance—Findings suggest
that calfhood vaccination may be an appropriate
strategy to help reduce short-term transmission of
some but not necessarily all strains of BVDV. (J Am
Vet Med Assoc 2001;219:968–975)
Objective—To estimate risk and identify risk factors
for congenital infection with bovine viral diarrhea virus
(BVDV) not resulting in persistent infection and examine
effect of congenital infection on health of dairy
Procedures—Calves from 2 intensively managed drylot
dairies with different vaccination programs and
endemic BVDV infection were sampled before ingesting
colostrum and tested with their dams for BVDV
and BVDV serum-neutralizing antibodies. Records of
treatments and death up to 10 months of age were
obtained from calf ranch or dairy personnel. Risk factors
for congenital infection, including dam parity and
BVDV titer, were examined by use of logistic regression
analysis. Effect of congenital infection on morbidity
and mortality rates was examined by use of survival
Results—Fetal infection was identified in 10.1% of
calves, of which 0.5% had persistent infection and
9.6% had congenital infection. Although dependent
on herd, congenital infection was associated with
high BVDV type 2 titers in dams at calving and with
multiparous dams. Calves with congenital infection
had 2-fold higher risk of a severe illness, compared
with calves without congenital infection.
Conclusions and Clinical Relevance—The unexpectedly
high proportion of apparently healthy calves found
to be congenitally infected provided an estimate of the
amount of fetal infection via exposure of dams and
thus virus transmission in the herds. Findings indicate
that congenital infection with BVDV may have a negative
impact on calf health, with subsequent impact on
herd health. (Am J Vet Res 2003;64:358–365)
Objective—To develop models that could be used to
predict, for dairy calves, the age at which colostrumderived
bovine viral diarrhea virus (BVDV) antibodies
would no longer offer protection against infection or
interfere with vaccination.
Design—Prospective observational field study.
Animals—466 calves in 2 California dairy herds.
Procedure—Serum BVDV neutralizing antibody titers
were measured from birth through 300 days of age.
The age by which colostrum-derived BVDV antibodies
had decayed sufficiently that calves were considered
susceptible to BVDV infection (ie, titer ≤ 1:16) or
calves became seronegative was modeled with survival
analysis methods. Mixed-effects regression
analysis was used to model colostrum-derived BVDV
antibody titer for any given age.
Results—Half the calves in both herds became
seronegative for BVDV type I by 141 days of age and for
BVDV type II by 114 days of age. Rate of antibody decay
was significantly associated with antibody titer at 1 to 3
days of age and with whether calves were congenitally
infected with BVDV. Three-month-old calves were predicted
to have a mean BVDV type-I antibody titer of 1:32
and a mean BVDV type-II antibody titer of 1:16.
Conclusions and Clinical Relevance—Results provide
an improved understanding of the decay of
BVDV-specific colostrum-derived antibodies in dairy
calves raised under typical field conditions.
Knowledge of the age when the calf herd becomes
susceptible can be useful when designing vaccination
programs aimed at minimizing negative effects of
colostrum-derived antibodies on vaccine efficacy
while maximizing overall calf herd immunity. (J Am
Vet Med Assoc 2002;221:678–685)