The Epizootiology of African swine fever in Africa

Abstract

The incidence of African swine fever virus in different body tissues in two populations of East African warthogs and the distribution of the virus in the tick population of Kenya, Tanzania and Uganda were studied. There was no evidence of transplacental infection or of excretion of the virus in the milk. In view of experimental evidence, infection by ingestion was improbable. Infected ticks were found in 40% of burrows in Kenya and Tanzania, but in none in Uganda. The highest rate of infection was in adult ticks, while no first-stage nymphs were infected. The virus recovered from ticks appeared to be similar to the typical field strain. Virus proliferation occurred in the ticks. Persistent infection with some strains of virus was acquired by laboratory ticks when fed on reacting pigs or infected blood in capillary tubes. The disease was transmitted by feeding for 18-34 weeks after the original infective feed. Trans-stadial transmission occurred regularly with the Uganda strain of virus but infrequently with the Tengani strain. Virus was excreted from the tick in the coxal fluid and probably also in the saliva. Relatively small doses of virus by the nasal and parenteral routes infected pigs regularly, while large doses by mouth failed to do so. Natural transfer of virus from wild to domestic pigs might take place when infected ticks are carried into piggeries. Although a large DNA virus, the African swine fever virus satisfied all the basic requirements for an arbovirus. -BMW.