Changes

===Clinical Signs===

===Clinical Signs===

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.  

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 results in 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. Oedema may be seen around the eyes, and there is considerable variation in the size of piglets within litters.

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.

Post-weaning performance is also affected, with daily live weight gain reduced by up 85% and increases in mortality by up to 25%. Lethargy and a loss of appetites is seen as in adult pigs, and weanling fail to thrive. Breathing is laboured and there may be obvious respiratory distress. The skin can appear red and blotchy, with a rough hair coat.

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 reportedly last between one and four months, depending on the initial health status on the pigs and the management of the outbreak. However, the post-weaning respiratory phase can become chronic, creating major production problems.

 

Secondary infections commonly occur. Bacteria previously reported to be associated with PRRS include ''Streptococcus suis'', ''Escherichia coli'', '''Salmonella choleraesuis'', ''Haemophilus parasuis'' and ''Mycoplasma hyopneumoniae''. Viral infections such as porcine respiratory coronavirus and swine influenza virus are also possible.

===Laboratory Tests===

===Laboratory Tests===