Porcine reproductive and respiratory syndrome (PRRS) often kills baby pigs and causes economic hardship for pig farmers. Affected mothers lose up to 10 percent of their pregnancies. Their babies are spontaneously aborted or are stillborn. As many as 20 percent to 30 percent of survivors may suffer and die from respiratory disease, such as pneumonia. The PRRS virus is said to primarily attack a pig's immune system, leaving the body open to a host of other infections, particularly in the lungs. Some pigs develop a chronic infection and become carriers but show no symptoms. The virus is transmitted via semen, saliva and blood. Those pigs herded closely together and transported at close quarters by trucks may be more susceptible to infection.
This complex disease has been attributed to both arterivirus and calicivirus infections, but is not well understood. It has some AIDS-like symptoms, with secondary infections arising from viral damage to macrophage and lymphocyte cells of the immune system, involvement of the lymph nodes and is transmissible by shared needle use. However, the differences between PRRS and AIDS are claimed to be obvious to researchers and no trace of the disease has been found in people or pig meat.
About 75 percent of US pig herds are infected with PRRS. Vaccines have only partially been effective. The disease also has been creating hugh economic problems for animal husbandry in many other nations since at least the mid-1980s and appears to be growing in frequency.