A study of African swine fever virus infected ticks (Ornithodoros moubata) collected from three villages in the ASF enzootic area of Malawi following an outbreak of the disease in domestic pigs

Abstract

SUMMARYA detailed study was made in 1983-5 in three villages in Mchinji district in the African swine fever (ASE) enzootic area of Malawi, following an outbreak of ASF which affected all three villages.Ticks of the Ornithodoros moubata complex were collected from both pig sties and houses shortly after the outbreak. and approximately 240/ contained ASF virus. The proportion of ticks infected did not differ significantly in the three villages, or more surprisingly in different types of premises, and was equivalent in all stages of ticks. The proportion infected decreased with the passage of titne but infected ticks were still present in all three villages 8 months after the outbreak, some with high titres of virus.The proportion of seropositive pigs in the three villages approached t 00( following the outbreak, with many apparently healthy pigs beiing seropositive. It is suggested that Malawian isolates of ASF virus mav be less virutlent in African than European breeds of (lomestic pig. 1981(Haresnape, 1984 Haresnape, Lungu & Mamu, 1985;Haresnape, Lungu & Mamu, 1987). One of these was in Bongera locality in 1983 where at least 130 pigs died, but estimates of the numbers of pigs affected have always been difficult to obtain. Since many more outbreaks probably go unreported, it is likely that several thousand village pigs have died as a result of ASF in the enzootic area of Malawi over the last few years, and many more in epizootics outside the enzootic area which are characterized by a mortality approaching 100% (Haresnape, Lungu & Mamu, 1985). INTRODIU(TIONA serological survey undertaken between 1981 and 1984 included 10 localities in Mchinji district, and seropositive pigs were identified in all of them. Between 21 and 74 % of the pigs were seropositive and highest proportion was in the southwest part of the district. Mortality was estimated from serological data to be between 47 and 83 % for one locality in the district and between 77 and 92 % for another (Haresnape, Lungu & Mamu, 1985).It has been suggested that most outbreaks of ASF outside the enzootic area probably start following introduction of infected meat from an affected area, but that some outbreaks within the enzootic area may represent new incursions of virus from a natural reservoir (Haresnape, Lungu & Mamu, 1985). The soft tick, Ornithodoros moubata, which is known to be a reservoir of ASF virus and vector of the disease (Plowright, Parker & Pierce, 1969; Thomson et al. 1983), is common both in houses and pig pens (kholas) in the enzootic area, particularly in Mchinji district (Haresnape & Mamu, 1986). Collections of these ticks were started in 1982, and examined for the presence of ASF virus. Up to November 1983, 1262 ticks collected from pig kholas in eight villages in Mchinji district were tested, and only three were infected. None of the 977 ticks collected from houses in the same villages were infected. The three infected ticks were from kholas in three different villages in the west part of Mchinji district and there had been suspected ca...

Scientific review on African Swine Fever

“…In Malawi, infection rates of 1-3% were commonly reported in Ornithodoros ticks infesting pigpens (Haresnape, 1988), which was similar to rates reported for wild ticks inhabiting warthog burrows (Plowright, 1981); however, infection rates could reach 11-24% after an ASF outbreak occurring a few months ago (Haresnape, 1989).…”

“…ASFV infected ticks were found in pigpens and houses from Mchinji district which is in the centre of the ASF enzootic area and no ticks were found infected outside this zone; in all villages where infected ticks were collected, deaths of pigs from ASF had been reported shortly beforehand (Haresnape, 1988). The overall infection rate was approximately 3% but was much higher (24%) just after an ASF outbreak; the proportion of infected ticks decreased with the passage of time but infected ticks were still present in all villages several months after outbreaks, which greatly suggest the role of domestic ticks as vectors and reservoirs (Haresnape, 1989). Finally, concerning wild areas, the unique warthog habitat in which ticks were found during the study was in Lilonde National Park in the Southern region of Malawi, which is well outside the ASF enzootic area; none of the ticks collected there were infected, although further south in Lengwe National Park, five of six warthog sera were seropositive for ASFV (Haresnape, 1988).…”

African swine fever: how can global spread be prevented?

“…In endemic areas, spread at local level is often associated with free-ranging pig production, local pig (Haresnape & Wilkinson 1989). …”

“…other information In affected regions, high levels of seropositivity have been observed in apparently healthy animals (Haresnape & Wilkinson 1989). …”

3.3 Afrikanische Schweinepest

“…Die Tiere versterben oftmals akut (Montgomery, 1921). Über die Familie der echten Schweine hinaus kann das Virus in Lederzecken der Gattung Ornithodoros replizieren , Plowright et al, 1970, Haresnape and Wilkinson, 1989. Diese dienen dem ASPV als kompetente Vektoren und als Reservoir (Pini and Hurter, 1975, Wilkinson, 1986, Boinas et al, 2014.…”