Clearance of African swine fever virus from infected tick (Acari) colonies.

Three laboratory colonies of the argasid tick Onithodoros moubata porcinus van der Merwe were started from collections made in 1983 at three different sites in Zimbabwe. All of the colonies contained ticks infected with African swine fever (ASF) virus that was readily transmitted by bite to domestic pigs. Although they were maintained on virus-free pig blood, ASF virus infections persisted in the colonies for at least 1 yr. Despite the fact that ASF virus passes transstadially, sexually, and transovarially in this tick species sometime during the following year, the virus disappeared from the colonies. Studies comparing fecundity in infected and uninfected lots of O. moubata porcinus showed that mortality rates were considerably higher among the infected ticks. A similar study with Ornithodoros erraticus Lucas, a tick that harbors and transmits ASF virus on the Iberian Peninsula, gave essentially the same results. This is probably a factor involved in the clearance of ASF virus from tick populations that are not subjected to reinfection. How this information may be applied in the eradication of African swine fever in Portugal and Spain is discussed.