Sexual Transmission of African Swine Fever Virus in the Tick, Ornithodoros monbata porcinas, Walton

Abstract

Adult male ticks of the species Ornithodoros moubata porcinus were injected with 2 strains of African swine fever (ASF) virus by feeding on capillaries of injected pig blood. Virtually all of them became persistently infected and were placed in separate tubes with single clean fenmales. No transfer of virus to the female was detectable at 8 days following copulation, as evidenced by the presence of an exospermatophore at the genital orifice; after the 48th day, however, 120 of 137 females (87.6%) were infected. Virus ivas probably transjeired in the seminal fluid secreted by the accessory glands. Virus infection in sexually-infected lemales was systemic, as proved by the excretion of virus in the coxal fluid and by the ability to transmit ASF virus to pigs during ‘natural’ feeding. The titre of virus in these ticks corresponded closely with that following an infective blood meal. Transovarial infection was not demonstrable in 11 batches of their eggs or unfed, first-stage nyniphal offspring. Transjer of virus from infected female to clean male ticks occurred in only one 0f 35 instances where copulation had definitely occurred. It was concluded that male-to-female transmission of ASF virus occurs frequently in O. moubata and is probably an important factor in maintenance ot the virus iu tick populations. The phenomenon may well account for the 6-fold increase in tick infection rates, which was recorded between the late nyniphal and adult stages in ‘wild’ ticks collected from wart hog burrows in N. Tanzania. The behaviour of ASF virus in O. moubata is closely analogous to that reported Jor Rickettsia rickettsi in Dcrmaccntor andcrsoni and, less frequently, Jor Borrelia duttoni in O. moubata.