Humoral response to an equine encephalitis vaccine in healthy alpacas

Principal investigators:

Bedenice D, Bright A, Pedersen DD, Dibb J Department of Clinical Sciences,
Cummings School of Veterinary Medicine
Tufts University
North Grafton, MA 01536
J Am Vet Med Assoc. 2009 Feb 15;234(4):530-4.

OBJECTIVE: To determine humoral responses to an equine encephalitis vaccine in healthy alpacas.

DESIGN: Clinical trial.

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 less than or equal 2-years-old that were seropositive (16/17) was significantly higher than percentage of animals greater than 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 less than or equal 2-years-old that were seropositive (24/24) was significantly higher than percentage of animals greater than 6-years-old that were seropositive (27/33). For both farms, geometric mean titer on day 70 was significantly higher in animals less than 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.