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==Introduction==

==Introduction==

Porcine reproductive and respiratory syndrome (PRRS) first appeared in the USA in 1987, although subsequent serologic evidence indicated that it had been circulating for some time prior to being recognised. The disease was seen in Europe in 1990 and reported in Humberside in the UK in 1991. PRRS is caused by an arterivirus, and leads to abortions, mortality and reduced growth, significantly impacting pig welfare and production economics worldwide. This disease has emerged as one of the most important diseases of the pig industry across the globe in recent times. Besides Europe and North America, it was identified in China in 1995 and is present in Japan, Vietnam, the Philippines, Malaysia, and Korea among other countries in Asia. Australia, New Zealand, several European countries are currently free of the disease.

Porcine reproductive and respiratory syndrome (PRRS) first appeared in the USA in 1987, although subsequent serologic evidence indicated that it had been circulating for some time prior to being recognised. The disease was seen in Europe in 1990 and reported in Humberside in the UK in 1991. PRRS is caused by an arterivirus, and leads to abortions, mortality and reduced growth, significantly impacting pig welfare and production economics worldwide. This disease is now found in most areas of the world where pigs are raised. Besides Europe and North America, it was identified in China in 1995 and is present in Japan, Vietnam, the Philippines, Malaysia, and Korea among other countries in Asia. Australia, New Zealand, several European countries are currently free of the disease.

==Aetiology==

==Aetiology==

PRRS is an immunosuppressive disease. The virus that causes the disease, PRSS virus, is an arterivirus, within the [[:Category:Arteriviridae|Arteriviridae]] family. The arteriviruses are the only genus contained within the Arterivirdae family, and other members include the agent responsible for [[Equine Viral Arteritis|equine viral arteritis]] and lactate dehydrogenase-elevating virus of mice. The viruses are host-specific and antigenically distinct, and establish persistent infections after invasion.

The virus that causes PRRS is an arterivirus, within the [[:Category:Arteriviridae|Arteriviridae]] family. The arteriviruses are the only genus contained within the Arterivirdae family, and other members include the agent responsible for [[Equine Viral Arteritis|equine viral arteritis]] and lactate dehydrogenase-elevating virus of mice. The viruses are host-specific and antigenically distinct, and establish persistent infections after invasion.

==Transmission and Epidemiology==

==Transmission and Epidemiology==

==Treatment and Control==

==Treatment and Control==

There is currently no known effective treatment for PRRS. Non-steoidal anti-inflammatory drugs have been used in an attempt to reduce fever, and appetite stimulants to counteract inappetance and poor weight gain. However, these appear to have minimal benefit. Antibiotics may be used to counteract secondary bacterial infections.

There is currently no known effective treatment for PRRS. Non-steoidal anti-inflammatory drugs have been used in an attempt to reduce fever, and appetite stimulants to counteract inappetance and poor weight gain. However, these appear to have minimal benefit. Antibiotics may be used to counteract secondary bacterial infections. As treatment for PRRS is ineffective, prevention is very important. Successful control of the disease is difficult, because of virus variation, large swine populations, and unresolved issues of transmission. In some smaller herds, immunity may be sufficient so that infection is not causing significant economic losses, in which case no intervention is necessary. Often, there are sufficient losses to consider some or all of the following points for control. A control program should be tailored to fit the individual farm situation. In herds where PRRS is not present, bought-in stock and semen should be PRRS-free, and any animals joining the herd should be quarantined on-site before being introduced to the cohort. Pigs should be tested on arrival to the unit, and again 45-60 days later before they join the main herd. In herds where PRRS is endemic, breeding gilts may be exposed to adult sows before they become pregnant in order to induce immunity. Existing infection can also be eliminated by multisite production and segregated early weaning, but the long-term risk of reinfection is high. Complete depopulation, disinfection and repopulation can also be successful, as can test-and-removal strategies.

 

As treatment for PRRS is ineffective, prevention is very important. In herds where PRRS is not present, bought-in stock and semen should be PRRS-free, and any animals joining the herd should be quarantined on-site before being introduced to the cohort. Pigs should be tested on arrival to the unit, and again 45-60 days later before they join the main herd. In herds where PRRS is endemic, breeding gilts may be exposed to adult sows before they become pregnant in order to induce immunity. Existing infection can also be eliminated by multisite production and segregated early weaning, but the long-term risk of reinfection is high. Complete depopulation, disinfection and repopulation can also be successful, as can test-and-removal strategies.  

Both modified live and killed vaccines are available. These are effective in controlling outbreaks and preventing economic losses.

Both modified live and killed vaccines are available. These are effective in controlling outbreaks and preventing economic losses.