PRRS Virus Infection and Disease

• The severity of PRRS virus infection can vary widely and range from a near complete lack of clinical signs to devastating outbreaks of reproductive and respiratory disease. • PRRS virus infection occurs mainly in a cell of the immune system called a macrophage. Macrophages are found throughout many tissues in the body. • Clinical signs in the breeding herd may include anorexia (off-feed), fever, lethargy, nervous signs, purplish discoloration of the ears and vulva, and abortion. Litters born to recently infected dams may have increased rates of mummification, still births, and weak-born piglets. Piglets in these litters may carry the virus for an extended period. • Boars infected with PRRS virus can show similar signs as sows. Infection does not usually impact the fertility of the semen but virus can be found in the ejaculate of boars for several months after being infected. • Newborn piglets infected with the virus can demonstrate severe respiratory disease. Nervous signs as well as anorexia and lethargy have also been reported. Other common diseases of young pigs may become more prevalent and severe during a PRRS outbreak. • In an experimental setting, piglets infected with PRRS virus often show minimal clinical signs. However, in a field setting, PRRS virus infection frequently has a more pronounced effect due to its interaction with the pig’s environment, immune status, and concurrent diseases.