PRRS in Pigs: Welfare and Disease Control
PRRS Overview
Porcine Reproductive and Respiratory Syndrome (PRRS) is caused by a positive-sense RNA arterivirus. It exists as two genotypes: North American (Type 2, PRRS-2) and European (Type 1, PRRS-1). It is a globally widespread disease causing significant reproductive failure in sows (late-term abortions, mummified foetuses, stillbirths, weak piglets) and respiratory disease in growing pigs. Novel highly pathogenic strains (HP-PRRS) cause severe acute disease.
Welfare Consequences
Infected piglets develop laboured breathing, fever, reduced growth, and high mortality. Post-weaning respiratory disease complex (PRDC), often involving co-infections with Mycoplasma, Pasteurella, and porcine circovirus, is exacerbated by PRRS. Reproductive failure causes large numbers of stillbirths and weak piglets, all of whom suffer before dying. Chronically infected pigs have suppressed immune function and increased susceptibility to secondary infections.
Diagnosis and Surveillance
Serology (ELISA) detects antibodies; PCR detects viral RNA. Monitoring of sow reproductive records, piglet mortality, and respiratory health provides early warning. Gilt management (entry testing, acclimation) is critical to maintaining herd stability. Differentiating PRRS genotype and strain informs control strategy.
Control and Vaccination
PRRS control is challenging due to the virus's high mutation rate and multiple strains. Modified live vaccines (MLV) are widely used and reduce disease severity. Herd stabilisation programmes using controlled exposure or whole-herd vaccination followed by a closed-herd period can achieve PRRS stability. Strict biosecurity (air filtration, controlled entry, lorry washing) reduces new virus introduction. Elimination (test-and-removal or depopulation-repopulation) is possible but costly.
Farm-Level Welfare Management
Early identification and treatment of severely affected pigs (prompt euthanasia if treatment unlikely to be successful) limits suffering. Good colostrum management, split-suckling of large litters, and heat provision for weak piglets improve survival. Reducing concurrent stressors (good ventilation, low stocking density, minimising mixing) reduces the welfare impact of PRRS infection. Herd health plans should explicitly address PRRS control as a welfare priority.