ASF Virus Persists in Recovered Pigs, By Marty Misener from South West Ontario Veterinary Services

African swine fever (ASF) continues to be high on the list of transboundary diseases that can result in devastating damage to pork production. This devastating nature of ASF has sparked an unprecedented level of international collaboration. One example of this collaboration is the research partnership between the USA and Viet Nam. This collaboration benefits Viet Nam because it provides access to additional technical expertise and other resource in battling ASF. The USA benefits by gaining real world access to the disease control efforts in Viet Nam. Having “boots on the ground” allows for an accelerated learning curve involving diagnostics, vaccines and other control measures. Unfortunately ASF is persisting in Viet Nam. The number of pigs that recover from ASF infection depends on the strain of ASF that is involved. Although the percentage of infected pigs that recover is small it is not zero. These researchers wanted to evaluate the viral antigen distribution and lesions in recovered pigs post ASFV infection. Ten pigs that recovered from ASF at 6 weeks of age were monitored and assessed for anti-ASFV antibodies and viremia until slaughter. The five major organs (lung, liver, spleen, kidney, and lymph nodes) of these pigs were evaluated for microscopic lesions and viral antigen distribution.

The researchers found the following:

  • Anti-ASFV antibody was consistently observed to be high (S/P% ≥ 80) until slaughter
  • ASFV viremia levels were very high (7 log10 copies/mL) at 6 weeks of age and gradually decreased to undetectable levels at 12 weeks of age (6th week post-infection).
  • ASFV-associated lesions in the organs of these pigs at slaughter were mild and nonspecific.
  • ASF virus was detected in surveyed organ tissues in 70 % of recovered pigs but was not present in serum. (Details of infectivity assays were not provided)

Take Home Message:

  • ASF-recovered pigs have the potential to be carriers of the ASFV and therefore could participate in the spread of the virus.
  • ASF-recovered pigs are more likely to occur in feral pig populations as well as in domestic outbreaks that are under the radar of health authorities.
  • ASF-recovered pigs may enhance the risk of the disease becoming endemic in infected countries.

Ref: Danh Cong Lai , Taehwan Oh , Hien The Nguyen , Duy Tien Do  The study of antigen carrying and lesions observed in pigs that survived post African swine fever virus infection  Trop Anim Health Prod . 2022 Aug 12;54(5):264. doi: 10.1007/s11250-022-03229-0.