This research project assessed the African swine fever virus’s (ASFV) nucleic acid and antibody detection in tonsil scrapings, cheek swabs, oral fluids, blood, and some tissues across three commercial antibody ELISA assays, two nucleic acid extraction platforms and two commercial real-time PCR kits. The study used a mildly virulent strain of ASF that was weakened from a very virulent strain (Mozambique 78), this allowed for survival of the pigs for >90 days post-inoculation (dpi). We also evaluated the impact of a mock co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) through use of a modified live vaccine. The positivity rate for viral nucleic acid varied widely across sample types with blood and oral fluid being the most reliable. Detection of ASFV nucleic acid in blood peaked at days 8 to 21 post ASF inoculation and in oral fluid 1-7 days post inoculation. Buccal swabs and tonsillar scrapings had significantly different rates of detection compared to blood and oral fluids. Serum had the positivity rate for antibody detection and was significantly different from oral fluids. Antibodies were consistently detectable after 12 dpi. Overall, there was an insignificant by consistent trend that the ASFV inoculated group had a higher rate of ASFV nucleic acid and antibody detection across kits compared to the ASFV and PRRSV inoculated group. Group sample sizes may have limited the ability to statistically detect a difference, but further study is needed. Overall, there were some statistical differences between PCR kit detection, no difference in extraction kits, and no difference in serum in the ELISA antibody kits. One kit was unable to detect antibodies in oral fluids, nor did that kit’s protocol call for oral fluid use, but two other kits were consistent in their detection. Tests should be used to evaluate herd status and repeat testing will be important for reliable surveillance. Antibody detection is the most reliable means to detect the status of herds. Contact Dr. Karyn Havas with any questions (karyn.havas@pipestone.com).

Key Findings:

  • Real-time polymerase chain reaction results
  • Oral fluid and blood samples were the most reliable sample types for nucleic acid detection.
  • The percent of samples that were positive varied considerably over the 93 days with day 1 to 21 being the most reliable detection period.
  • There were some minor statistical differences between PCR kits and extraction kits used.
  • Enzyme-linked immunosorbent assay results
  • Blood had a greater reliability of antibody detection than oral fluids.
  • Detection was most reliable after 12 days post-infection.
  • There was no difference significant difference in the ability to detect antibodies against ASF in serum, and the Innoceleris and IDScreen indirect oral fluids ELISA showed no statistical difference in detection using oral fluids.
  • Co-infection (proxy was vaccination with a PRRS MLV) showed a consistent trend of decreased ability to detect viral nucleic acid in all sample types and antibodies in serum across all test kits.
  • Antibody detection is a key tool to be used when looking for infections that could have occurred up to two weeks prior, particularly in situations with attenuated viruses, where detection of the virus is not reliable.