Serological Response of Alpacas to Rabies Vaccination

Principal investigators:

Julie E Dechant(1) DVM, MS, DACVS and W David Wilson(2) BVMS, MRCVS
(1) Department of Surgical and Radiological Sciences, and
(2) Department of Medicine and Epidemiology, School of Veterinary Medicine
University of California-Davis, Davis, CA, USA

Objective: To compare the serological (antibody) response produced following rabies vaccination using 2 protocols in alpacas that have not previously been vaccinated against rabies.

Procedure: Twenty client-owned alpacas not previously vaccinated for rabies were recruited. Alpacas had to be healthy, at least 3 months of age, and not pregnant for inclusion in the study. Alpacas were grouped by age (crias (less than 6 months) vs. adults (>1 year)) and animals were randomly assigned to one of two vaccination protocols (one-dose vs. two-dose). The one-dose protocol followed manufacturer's recommendations; whereas the two-dose protocol included a booster vaccination at 4 weeks. Alpacas were monitored for signs of local or systemic reactions. Blood samples were collected immediately prior to vaccination, and again during weeks 2, 4, 6, 10, 16, 24, 32, 40, and 52.

Results: No obvious adverse reactions were noted. Median vaccination titers peaked at week 6, and median vaccination titers were maintained above the 0.5 IU//m1 titer indicative of a protective response throughout 52 weeks. The two-dose protocol induced a greater antibody titer than the one-dose protocol, but this was only significant at weeks 6 and 10. When analyzed by age, crias produced higher antibody responses than adults, which was significant at weeks 16 and 24.

Conclusions: The study findings suggest that the one-dose protocol appears adequate, because the increased titers associated with the two-dose protocol were short-lived. There appears to be an age-effect on the response to rabies vaccination, in that crias produced a more pronounced and durable response than adults.