Epidemiology of African horsesickness: antibodies in free-living elephants (Loxodonta africans) and their response to experimental infection.

The presence of low levels of group- and type-specific antibodies against African horsesickness virus in the serum of some free-living elephants was reconfirmed. Experimental infection resulted in conflicting results. No detectable viraemia nor virus could be demonstrated in the organs of the six elephant calves and none of them mounted significant levels of neutralizing antibodies against the virus. On the other hand, all calves showed a slight rise in ELISA titres. This rise, however, was modest when compared with the rise in experimentally infected zebra. The presence of low levels of group- and type-specific antibodies in the serum of some free-living elephants is judged to be the result of natural hyper-immunization due to frequent exposure to infected biting insects. Elephants should therefore, despite the presence of low levels of antibodies, be regarded as poorly susceptible and unlikely to be a source of African horsesickness virus.