Abstract:
African swine fever virus (ASFV) infection in adult Ornithodoros porcinus
(Murry 1877, sensu Walton 1979) ticks collected from warthog burrows in southern
and East Africa was assessed using a duplex genomic amplification approach that
is informative with respect to the invertebrate host species and infecting sylvatic cycle virus. DNA extracted from individual ticks was used as template for the
simultaneous amplification of a C-terminal 478-bp ASFV p72 gene region and a
∼313-bp fragment of the tick mitochondrial 16S rRNA gene, under optimized reaction
conditions. Within-warthog burrow infection rates ranged from 0% to 43% using this
approach, and phylogenetic analysis of 16S gene sequences revealed the presence
of three geographically discrete O. porcinus lineages, but no support for subspecies
recognition. False negatives are precluded by the inclusion of host species-informative
primers that ensure the DNA integrity of cytoplasmically located genome extracts.
In addition, infection rate estimates are further improved as false positives arising
from carry-over contamination when performing a two-step nested polymerase chain
reaction are negated by the one-step approach. Phylogenetic comparison of fulllength virus gene sequences with the partial C-terminal p72 gene target confirmed the
epidemiological utility of the latter in a sylvatic setting. The method is therefore of
particular value in studies assessing the prevalence and diversity of ASFV in relation
to the African sylvatic tick vector and holds potential for investigating the role of
alternative tick species in virus maintenance and transmission.
