Objective—To determine humoral responses to an equine encephalitis vaccine in healthy alpacas.
Animals—39 healthy alpacas on 1 farm and 86 healthy alpacas on a second farm.
Procedures—All alpacas were given 3 doses IM of a bivalent, killed-virus equine encephalitis vaccine, with 4 weeks between doses. Eastern equine encephalitis (EEE) virus neutralizing antibody responses were determined with a plaque reduction neutralization assay every 14 days in alpacas on the first farm and 70 days after the first dose of vaccine on the second farm.
Results—For alpacas on the first farm, geometric mean virus neutralizing antibody titer peaked 2 weeks after the third vaccine dose was given (ie, day 70). At this time, 29 of 38 (76%) animals were seropositive for antibodies against EEE virus, and percentage of animals ≤ 2 years old that were seropositive (16/17) was significantly higher than percentage of animals > 6 years old that were seropositive (1/5). For alpacas on the second farm, 76 (88%) were seropositive on day 70, and percentage of animals ≤ 2 years old that were seropositive (24/24) was significantly higher than percentage of animals > 6 years old that were seropositive (27/33). For both farms, geometric mean titer on day 70 was significantly higher in animals < 2 years old than in animals > 6 years old.
Conclusions and Clinical Relevance—Results suggested that inoculation of alpacas with 3 doses of a bivalent, killed-virus equine encephalitis vaccine induced a humoral antibody response against EEE virus.
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)