Streptococcus equi zooepidemicus Infection in Pigs

Streptococcus equi zooepidemicus (S zooepidemicus) is classified in Lancefield group C and causes respiratory disease in a variety of mammals. This pathogen has been reported as causing an important outbreak as well as sporadic cases in China. It is likely a very important but underreported cause of disease in Southeast Asian countries because diagnostic laboratories lack the capacity to properly identify this bacterium. In 2019, S zooepidemicus sequence type (ST) 194 emerged in North America (Canada and US) and was associated with high-mortality outbreaks affecting sows; however, pigs of any age after weaning appear to be susceptible to infection.

Clinical and postmortem findings are similar to those of bacterial septicemia. Patients present with fever (> 40°C) within 8 hours of infection, lethargy, huddling, reluctance to rise, and going off feed. Sows at any gestational stage may abort or suffer resorption, strongly affecting reproductive performance. Mortality rates range from 50%–90%, depending on herd health status, leading to important economic losses.

Autogenous vaccines do not seem to prevent infection and disease nor lead to passive immunity transfer. Outbreak control relies solely on prolonged treatment with antimicrobials. Because resistance emerges rapidly during outbreaks, depopulation has sometimes been required to eliminate S zooepidemicus from affected herds.