Contact between soft tick vectors of African swine fever virus and invasive wild pigs in the southeastern USA.

Background: African swine fever virus is a transboundary pathogen of high economic impact to the global pork industry. Florida has multiple factors that contribute to the high risk of introduction of African swine fever virus (ASFV) including high levels of commerce and human migration between Florida and Caribbean nations with ASFV, established backyard swine production, abundant populations of invasive wild pigs (Sus scrofa), and the presence of a soft tick species (Ornithodoros turicata americanus) that has been found to be a competent vector of ASFV in laboratory experiments. To better assess the hazard of ASFV vector-borne transmission in Florida, we documented contact between invasive wild pigs and O. t. americanus throughout Florida.

Methods: We surveyed gopher tortoise (Gopherus polyphemus) burrows throughout Florida and collected O. t. americanus from infested burrows. To identify definitive contact between invasive wild pigs and soft ticks, we used established real time polymerase chain reaction primers and a probe to detect the deoxyribonucleic acid (DNA) of invasive wild pigs in the bloodmeals of O. t. americanus.. To detect potential wild pig-soft tick contact, we surveyed for evidence of pig activity within 5 m of an infested burrow entrance.

Results: Across 61 sites, we found that 203 of 591 burrows (34%) were infested with the soft tick, O. t. americanus. Ten burrows across 57 sites (18%) had soft ticks with wild pig DNA in their abdomens. In total, 6 of 591 burrows (1%) had evidence of invasive wild pigs near the entrance. Three infested burrows had evidence of wild pigs near the entrance, one of these burrows also had soft ticks that were positive for wild pig DNA. Including both definitive and potential wild pig-soft tick contact, 12 of 61 sites (20%) had evidence of wild pig-soft tick association.

Conclusions: In Florida, contact between invasive wild pigs, a potential reservoir for ASFV, and O. t. americanus, a competent vector, was measurable and occurred throughout the distribution of the vector. Florida is at risk not only for ASFV emergence but establishment of this pathogen in a sylvatic cycle. In addition to managing invasive wild pigs, future ASFV response planning needs to include plans for surveying and managing vector populations should an outbreak occur.