Changes

===Clinical Signs===

===Clinical Signs===

Concurrent infections

There appears to be two distinct clinical phases to PRRS: reproductive failure and post-weaning respiratory diseases. When sows are infected period of acute disease is seen, which is characterised by lethargy, inappetance and pyrexia. Severe infections may also be associated with vestibular signs, and death of up to 10% of the sow stock can occur. Reproductive failure is characterised by increased numbers of stillborn piglets, mummified foetuses, abortions, premature farrowings, and weak piglets. Lactating sows often display anorexia and agalactia, which leads to a rise in preweaning mortality. Signs are also seen in the piglets themselves, including a "thumping" respiratory pattern which on post-mortem examination is revealed to be associated with ls a severe, necrotising, interstitial pneumonia.  

with other pathogens are also common.

RRS appears to have 2 distinct clinical phases: reproductive failure and postweaning respiratory diseases. The reproductive phase of the disease includes increases in the number of stillborn piglets, mummified fetuses, premature farrowings, and weak-born pigs. Stillbirths and mummies may increase up to 25-35%, and abortions can be >10%. Anorexia and agalactia are evident in lactating sows and result in increased (30-50%) preweaning mortality. Suckling piglets develop a characteristic thumping respiratory pattern, and histopathologic examination of lung tissue reveals a severe, necrotizing, interstitial pneumonia. PRRS is capable of crossing the placenta in the third and possibly second trimester of gestation. Piglets may also be born viremic and transmit the virus for 112 days after infection. Performance after weaning is also affected. Infection with PRRS virus results in destruction of mature alveolar macrophages, which has led to the hypothesis that infection results in the suppression of the immune system; however, controlled studies indicate that the virus may actually enhance specific parameters of the immune response.

Performance after weaning is also affected. Infection with PRRS virus results in destruction of mature alveolar macrophages, which has led to the hypothesis that infection results in the suppression of the immune system; however, controlled studies indicate that the virus may actually enhance specific parameters of the immune response.

Outbreaks of the reproductive form of PRRS have been reported to last 1-4 mo, depending on the facilities and initial health status of the pigs. In contrast, the postweaning pneumonic phase can become chronic, reducing daily gain by 85% and increasing mortality to 10-25%. Numerous other pathogens are commonly isolated along with PRRS virus from affected nursery or finishing pigs. Other bacteria such as Streptococcus suis , Escherichia coli , Salmonella choleraesuis , Haemophilus parasuis , and Mycoplasma hyopneumoniae have been reported, as well as viruses such as porcine respiratory coronavirus and swine influenza virus. Finally, differences in the clinical response to PRRS virus may also be due to strain variation. Studies have demonstrated the ability of different isolates to induce varying degrees of interstitial pneumonia in CD/CD (cesarean-derived/colostrum-deprived) piglets after intranasal inoculation.

Outbreaks of the reproductive form of PRRS have been reported to last 1-4 mo, depending on the facilities and initial health status of the pigs. In contrast, the postweaning pneumonic phase can become chronic, reducing daily gain by 85% and increasing mortality to 10-25%. Numerous other pathogens are commonly isolated along with PRRS virus from affected nursery or finishing pigs. Other bacteria such as Streptococcus suis , Escherichia coli , Salmonella choleraesuis , Haemophilus parasuis , and Mycoplasma hyopneumoniae have been reported, as well as viruses such as porcine respiratory coronavirus and swine influenza virus. Finally, differences in the clinical response to PRRS virus may also be due to strain variation. Studies have demonstrated the ability of different isolates to induce varying degrees of interstitial pneumonia in CD/CD (cesarean-derived/colostrum-deprived) piglets after intranasal inoculation.