Abstract:
We investigated the possibility that sylvatic circulation of African swine fever virus (ASFV)
in warthogs and Ornithodoros ticks had extended beyond the historically affected northern part of
South Africa that was declared a controlled area in 1935 to prevent the spread of infection to the rest of
the country. We recently reported finding antibody to the virus in extralimital warthogs in the south
of the country, and now describe the detection of infected ticks outside the controlled area. A total of
5078 ticks was collected at 45 locations in 7/9 provinces during 2019–2021 and assayed as 711 pools
for virus content by qPCR, while 221 pools were also analysed for tick phylogenetics. Viral nucleic
acid was detected in 50 tick pools representing all four members of the Ornithodoros (Ornithodoros)
moubata complex known to occur in South Africa: O. (O.) waterbergensis and O. (O.) phacochoerus
species yielded ASFV genotypes XX, XXI, XXII at 4 locations and O. (O.) moubata yielded ASFV
genotype I at two locations inside the controlled area. Outside the controlled area, O. (O.) moubata and
O. (O.) compactus ticks yielded ASFV genotype I at 7 locations, while genotype III ASFV was identified
in O. (O.) compactus ticks at a single location. Two of the three species of the O. (O.) savignyi complex
ticks known to be present in the country, O. (O.) kalahariensis and O. (O.) noorsveldensis, were collected
at single locations and found negative for virus. The only member of the Pavlovskyella subgenus of
Ornithodoros ticks known to occur in South Africa, O. (P.) zumpti, was collected from warthog burrows
for the first time, in Addo National Park in the Eastern Cape Province where ASFV had never been
recorded, and it tested negative for the viral nucleic acid. While it is confirmed that there is sylvatic
circulation of ASFV outside the controlled area in South Africa, there is a need for more extensive
surveillance and for vector competence studies with various species of Ornithodoros ticks.
