PRRS: the most costly disease of pig production

Porcine reproductive respiratory syndrome virus (PRRSV) is the most economically impactful disease in pig production in the UK. The first ‘R’ is due to the reproductive signs you see when PRRSV infects ‘non-immune’ sows; you may see increased regular or irregular returns to service, and late abortions/early farrowing with litters containing mummies, stillborn, weak and/or apparently healthy piglets. The sows may also appear sick, have a fever, and may get purple/blue extremities (hence the traditional name of ‘blue ear’). During acute PRRSV outbreaks you may also see sick pigs with fevers in the feeding herd. You should always consider the notifiable diseases, particularly Classical/African Swine Fever, as a differential when you see pigs with high temperatures (≥40°C). In herds with endemic PRRSV, flare ups of reproductive signs may occur, but the biggest economic impact is via its affect on respiratory health, hence the second ‘R’ of PRRS. PRRSV particularly targets pulmonary alveolar macrophages, so it is the immune defences of the lung that are seriously compromised. This amplifies other diseases such as Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis, Haemophilus parasuis (Glässers) and influenza, resulting in increased coughing and mortality.