A persistent reproductive form exhibits decreases in the farrowing rate and irregular returns to estrus. The enzootically infected breeding herd may appear normal on clinical evaluation. Chronic PRRS problems are typical in seropositive herds which add seronegative, susceptible animals without proper isolation and acclimatization. Growing Pigs Piglets can be infected in utero and be born weak. This is often associated with premature farrowing.
Infected litters are weak, unthrifty, or splay-legged.
Increasing incidence of bruising and hemorrhaging during processing has been reported. Preweaning mortality has been reported as high as 80 percent. Most consistent clinical signs observed are associated with respiratory disease or ill-thrift. Actinobacillus pleuropneumoniae , swine influenza virus, porcine respiratory coronavirus, and pseudorabies virus. Direct contact is the most prominent route of exposure.