Objective—To evaluate herd-level risk factors for
seropositive status of cattle to 1 or more bluetongue
Animals—110 herds of cattle in Nebraska, North
Dakota, and South Dakota.
Procedure—Blood samples were collected before
and after the vector season. Samples were tested
for antibodies against bluetongue virus by use of a
commercially available competitive ELISA. Factors
evaluated included descriptors of geographic location
and management practices. Trapping of insect
vectors was conducted to evaluate vector status on
a subset of 57 operations. A multivariable logistic
regression model was constructed to evaluate associations.
Results—For the full data set, altitude and latitude
were associated with risk of having seropositive cattle
(an increase in altitude was associated with an
increase in risk, and a more northerly location was
associated with a decrease in risk of a premise having
seropositive cattle). Import of cattle from selected
states was associated with an increase in risk of having
seropositive cattle. From the subset of herds with
data on vector trapping, altitude and latitude were
associated with risk of having seropositive cattle, similar
to that for the full model. However, commingling
with cattle from other herds was associated with a
decrease in risk of seropositivity.
Conclusions and Clinical Relevance—Findings
reported here may be useful in generating additional
hypotheses regarding the ecologic characteristics of
bluetongue viruses and other vector-borne diseases
of livestock. Sentinel surveillance programs are useful
for documenting regionalization zones for diseases,
which can be beneficial when securing international
markets for animals and animal products. (Am J Vet
Objective—To compare neutralizing antibody response
between horses vaccinated against West Nile virus
(WNV) and horses that survived naturally occurring
Design—Cross-sectional observational study.
Animals—187 horses vaccinated with a killed WNV vaccine
and 37 horses with confirmed clinical WNV infection.
Procedure—Serum was collected from vaccinated
horses prior to and 4 to 6 weeks after completion of
an initial vaccination series (2 doses) and 5 to 7
months later. Serum was collected from affected
horses 4 to 6 weeks after laboratory diagnosis of
infection and 5 to 7 months after the first sample was
obtained. The IgM capture ELISA, plaque reduction
neutralization test (PRNT), and microtiter virus neutralization
test were used.
Results—All affected horses had PRNT titers ≥ 1:100 at
4 to 6 weeks after onset of disease, and 90% (18/20)
maintained this titer for 5 to 7 months. After the second
vaccination, 67% of vaccinated horses had PRNT titers
≥ 1:100 and 14% had titers < 1:10. Five to 7 months
later, 33% (28/84) of vaccinated horses had PRNT titers
≥ 1:100, whereas 29% (24/84) had titers < 1:10.
Vaccinated and clinically affected horses' end point
titers had decreased by 5 to 7 months after vaccination.
Conclusions and Clinical Relevance—A portion of
horses vaccinated against WNV may respond poorly.
Vaccination every 6 months may be indicated in certain
horses and in areas of high vector activity. Other
preventative methods such as mosquito control are
warranted to prevent WNV infection in horses. (J Am
Vet Med Assoc 2005;226:240–245)