Evaluation of the Efficacy of West Nile Virus Vaccination in the Greater One-Horned Rhinoceros (Rhinoceros unicornis)
Given the broad range of species that have seroconverted or been affected by the disease caused by West Nile virus (WNV), rhinoceros are presumed to be susceptible to the virus.1,2 A 2004 North American zoo-wide census conducted for the annual greater one-horned rhinoceros (Rhinoceros unicornis) SSP Veterinary Advisor report revealed that 10 out of 21 institutions vaccinate their greater one-horned rhinoceros collection for WNV using the equine protocol for the killed vaccine (Innovator®, Fort Dodge Animal Health, Fort Dodge, IA, USA). Pre- and post-vaccine antibody titers were not measured in any of these animals. The objective of this study was to assess the serologic response of the greater one-horned rhinoceros to the killed equine WNV vaccine. Five immunologically naïve greater one-horned rhinoceros at three institutions in the United States were vaccinated using the commercial equine killed vaccine according to manufacturer’s recommendations. All animals were evaluated for an immune response based on comparisons of their pre- and post-vaccination antibody titers, serum protein electrophoresis, complete blood cell count, and serum biochemistry profile. Seroconversion did not occur in any of these animals following WNV vaccination, nor were there consistent changes in other hematologic parameters to support a detectable immune response. Possible factors in the lack of immune response may include ineffectiveness of the killed product, inadequate dosage and/or frequency of administration. Further investigation is warranted to evaluate whether changes in product type or administration might incite a humoral response in these animals.
The authors thank the animal care staff of the Cincinnati Zoo and the San Francisco Zoo for participating in this project, and the Toronto Zoo for the inclusion of two of their animals in this project. Special thanks to the animal management staff of The Wilds for assistance with animal handling in this project.
1. Calle, P.P., G.V. Ludwig, J.F. Smith, B.L. Raphael, T.L. Clippinger, E.M. Rush, T. McNamara, R. Manduca, M. Linn, M.J. Turell, R.J. Schoepp, T. Larson, J. Mangiafico, K.E. Steele, and R.A. Cook. 2000. Clinical aspects of West Nile virus infection in a zoological collection. Proc. Am. Assoc. Zoo Vet. and Int. Assoc. Aqu. Anim. Med. Joint Conf. Pp. 92–96.
2. Ludwig, G.V., P.P. Calle, J.A. Mangiafico, B.L. Raphael, D.K. Danner, J.A. Hile, T.L. Clippinger, J.F. Smith, R.A. Cook, and T. McNamara. 2002. An outbreak of West Nile virus in a New York city captive wildlife population. Am. J. Trop. Med. Hyg. 67(1):67–75.