Rabies and rabies-related viruses in Zimbabwe: Historical, virological and ecological aspects

Abstract

Rabies spread rapidly through Zimbabwe after its re-introduction in 1950. Within six years, widespread vaccination of dogs had brought the disease under control. Thereafter, until 1986, there was considerable fluctuation in the occurrence as the epizootics spread into wildlife and cattle. A massive epizootic followed breakdown in rabies control during the civil war in the country. Diagnostic methods in use in the country were shown to have a high degree of accuracy, comparable to that elsewhere. During the period of study, human rabies occurred most commonly as a result of dog bites and conformed to human disease seen elsewhere. Rabies in dogs, jackals and cattle was epizootic in nature and comprised 90 percent of all confirmed cases. The distribution was related to land-use type. Vaccination in dogs showed a negative correlation to the incidence of dog rabies in most provinces; it was estimated that 700 000 dogs should be vaccinated annually by 1990 to control rabies. Jackals were shown to be very susceptible to rabies as well as being efficient vectors, especially to cattle. Rabies vaccine for dogs proved effective in protecting cattle. Surveys revealed no evidence for enzootic rabies in mongooses or jackals, though epizootics in mongooses were prolonged. Examination of rabies virus strains by monoclonal antibodies showed minor differences which were species-specific in mongooses. Rabies vaccines were effective against all the strains tested. The rabies-related Mokola virus was isolated from six cats and a dog which had showed nervous disease. Lagos bat virus was found in one cat. Experimentally, the LD50 for Mokola virus in cats was between 5,0 and 5,7 (logs) mouse intracerebral LD50s. Cats given lower doses showed seroconversion. Virus was present in salivary glands of some cats which died. During surveys, Duvenhage virus was isolated from an insectivorous bat and antibodies to Mokola virus were found in 17,5 percent of gerbils, suggesting that they may act as a reservoir host. These rodents were also shown to be very susceptible to experimental infection.