Effect of High Temperature Exposure and Laboratory Processing Techniques on the Diagnostic Performance of Dry Swabs for the Detection of African Swine Fever Virus.

One of the key surveillance strategies for the early detection of an African swine fever (ASF) incursion into a country is the sampling of wild or feral pig populations. In Australia, the remote northern regions are considered a risk pathway for ASF incursion due to the combination of high numbers of feral pigs and their close proximity to countries where ASF is present. These regions primarily consist of isolated arid rangelands with high average environmental temperatures. A specific objective of this study was to assess whether the exposure of swabs to the high temperatures that may be encountered in outback Australia, over an extended period, would reduce the diagnostic sensitivity (DSe) of real-time PCR (qPCR) to detect ASF virus (ASFV). We found that the extended heat exposure (up to 45 °C) of FLOQSwabs or GenoTube swabs, either prior to blood sampling or post sampling, showed no reduction in the DSe of the ASFV qPCR compared to swabs stored at room temperature (~21 °C). We also assessed an improved DNA extraction method for samples collected using GenoTube swabs to obtain DSe results comparable to FLOQSwabs. Taken together, these experiments demonstrate that dry swabs can provide the basis for an effective low-cost surveillance system for ASF in situations where extended exposure to high environmental temperatures is unavoidable.