Rabies vaccination of captive mammals in zoologic collections continues to be controversial because no parenteral vaccines are licensed for use in nondomestic mammals by the USDA and few rabies vaccination trials have been reported in nondomestic large mammal species.1–6 Despite these concerns, the use of killed-rabies virus vaccines has been recommended for many mammals in zoologic collections.1,6,7 These vaccination recommendations are based on the assumption that a killed virus vaccine has no risk of inducing an infection and may provide protection against rabies.1,5 Most captive mammals in zoos are considered to be at low risk for infection with rabies virus because they are typically managed with a strict quarantine program, are generally isolated from indigenous wildlife, and are observed daily for abnormal behavior. However, exposures in zoologic collections occasionally occur.8
Rabies has been occasionally observed in elephants, and 6 cases from Asia have been reported in Asian elephants (Elephas maximus).9–15 In those elephants, the paralytic form of rabies predominated; however, aggressive behavior has been observed in some cases.10,12–14 Most published accounts indicate that rabid domestic dogs were the source of infection and that the dogs had bitten the limbs or trunk of the elephants. In North America, captive elephants can potentially be bitten by rabid wild carnivores (eg, raccoons, skunks, and foxes) while unattended, especially during the night when husbandry practices of leaving food with elephants overnight may attract a potential rabies virus–reservoir species to the elephant-holding facilities. Insectivorous bats could also transmit rabies virus to elephants in North America. In Latin America, vampire bats (Desmodus rotundus) have been associated with cattle rabies, and these bats could potentially feed on captive elephants. Therefore, a rabies virus vaccination program for elephants maintained in captivity may prevent infection and provide protection for humans that come in contact with elephants through their vocation or recreational means.
The purpose of the study reported here was to evaluate the humoral immune response of Asian elephants after IM vaccination with either 1 or 2 doses of a commercially available inactivated rabies virus vaccine and evaluate the anamnestic response to a single-dose booster vaccination given on day 344.
Rapid fluorescent focus inhibition test
Rabies virus–neutralizing antibody
Geometric mean titer
Imrab Bovine Plus, Merial Inc, Athens, Ga.
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