Eastern equine encephalitis virus (EEEV) is a mosquito-borne viral disease reported in numerous species.2 Of all U.S. states, Florida has the greatest number of cases of EEEV reported in horses and humans.2 Vaccination is recommended in horses in endemic areas1,5 and has also been used in other species. There are no clinical reports of EEEV in elephants, although elephants have shown seropositivity to other mosquito-borne diseases such as Japanese encephalitis virus and West Nile virus.4 Vaccination of elephants at Disney’s Animal Kingdom against EEEV was elected since EEEV is endemic in Florida2 and cases of EEEV have been documented in other species at the park.
In this study, 10 African elephants at Disney’s Animal Kingdom were vaccinated annually with Encevac-T with Havlogen (Intervet Inc., Millsboro, DE) for EEEV. Blood was drawn annually or biannually to evaluate EEEV titers via hemagglutination inhibition assay at Cornell University. Few studies have been done to evaluate EEEV titers to the vaccine3,6 and a protective titer has not been determined. Five elephants remained seronegative for EEEV despite yearly vaccination, while the other five elephants displayed low, inconsistent titers. Possibilities for these results include poor antigenic stimulation, short-lived antibody response, low antigenic mass compared to muscle mass, stimulation of primarily cell-mediated immunity, or vaccine failure. In the future, it may be prudent to vaccinate more frequently during vector season to maintain titers for longer periods of time or use techniques to evaluate cell-mediated immunity against EEEV.
The authors wish to thank the elephant staff, veterinarians, veterinary technicians, and medical records staff of Disney’s Animal Kingdom for their participation and support in this study.
1. American Association of Equine Practitioners Vaccination protocols. http://www.aaep.org/core_vaccinations.htm. (VIN editor: link was not accessible as of 1/6/21.)
2. Center for Disease Control. Eastern equine encephalitis (EEE) virus. http://www.cdc.gov/ncidod/dvbid/arbor/eeefact.htm. (VIN editor: link was not accessible as of 1/6/21.)
3. Howe MA, Townsend HG, Kohler AK, Hussey S, Breathnach C, Barnett C, et al. Immune responses to commercial equine vaccines against equine herpesvirus-1, equine influenza virus, eastern equine encephalomyelitis, and tetanus. Vet Immunol Immunopathol. 2006;111:67–80.
4. Mikota SK, Fowler ME. Biology, Medicine, and Surgery of Elephants. Ames, IA: Blackwell Publishing; 2006.
5. Morris C. Eastern Equine Encephalitis. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences; 2006.
6. Olsen GH, Turell MJ, Pagac BB. Efficacy of eastern equine encephalitis immunization in whooping cranes. J Wildl Dis. 1997;33:312–315.