Is there any possibility of incursion and spreading of PRRSV through pork? Should farmworkers avoid touching or bringing pork to the farm for PRRS prevention?
The risk of spreading PRRSV through pork cannot be 100% excluded; however, the likelihood is very low.
First, a comparatively high amount of virus would be needed to infect a pig with PRRSV through the oral route (1 x 105.3 TCID50) compared to parenteral exposure (≤20 particles can result in infection). Also, the probability of acute infection with high amounts of replicating virus being present is rather low in slaughter age pigs compared to younger piglets. Nevertheless, some pigs might bring PRRSV to the slaughterhouses.
Target cells for PRRSV replication are cells of the monocytic lineage, mainly fully differentiated macrophages, while muscle cells are not susceptible to the virus. Therefore, resident virus that might be present in pork mainly results from residual infected blood not from infected myocytes.
Therefore, rather low levels of virus can be expected in pork. The probability of survival of the virus will highly depend on pH value (while the virus is stable at pH 6.5 – 7.5, it will rapidly loose infectivity outside this range) and temperature (PRRSV is stable for several days to weeks at 4°C or minus 20°C).
Several studies, most performed in the early years of PRRSV research in the mid 90s, investigated the survival of PRRSV in pig meat/muscle tissues; in conclusion, they found that PRRSV could occasionally be isolated from a low number of meat samples from experimentally infected pigs early after infection (less than 14 days post infection).
Most experiments investigating the potential transmission of PRRSV to pigs through pork failed to show infection. However, one study did proof that PRRSV could be infectious through the oral route via feeding of meat obtained from recently infected pigs to pigs that have been starved for two days.
In conclusion, research has shown that theoretically and under experimental conditions it might be possible to infect pigs with PRRSV through pork; however, considering also the likelihood of acute infection and virus titres being present in slaughter pigs, the likelihood of PRRSV introduction into pig herds through pork is extremely low.
University of Veterinary Medicine, Vienna