Changes

==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. The PRRS virus is only moderately resistant to environmental degradation and is easily inactivated by phenol, formaldehyde, and most common disinfectants.

==Transmission and Epidemiology==

==Transmission and Epidemiology==

The virus is spread by contact with infected pigs, and infection also be transmitted venereally via infected semen. Blood, saliva, urine, milk and semen from infected animals have all been shown to contain PRRS virus. Fomites, such as contaminated needles, boots, overalls and transport vehicles can also transmit PRRS, as can certain species of insects including [[Musca spp.|house flies]]. Aerosol transmission is thought to occur, particularly under conditions of high humidity, low temperatures, and low wind speeds, but this has been difficult to reproduce in the field and experimentally. Once infected, adult animals shed PRRS virus for up to 86 days, and younger, weaned pigs for 157 days. Virus excretion in semen can persist for up to 93 days after infection. This lengthy persistence of infection is an important factor in the maintenance of infection within a herd.

The virus is spread by contact with infected pigs, and infection also be transmitted venereally via infected semen. Blood, saliva, urine, milk and semen from infected animals have all been shown to contain PRRS virus. Fomites, such as contaminated needles, boots, overalls and transport vehicles can also transmit PRRS, as can certain species of insects including [[Musca spp.|house flies]]. Aerosol transmission is thought to occur, particularly under conditions of high humidity, low temperatures, and low wind speeds, but this has been difficult to reproduce in the field and experimentally. Once infected, adult animals shed PRRS virus for up to 86 days, and younger, weaned pigs for 157 days. Virus excretion in semen can persist for up to 93 days after infection and can transmit disease in female pigs during breeding. This lengthy persistence of infection is an important factor in the maintenance of infection within a herd. Infection of sows occurs through natural breeding or artificial insemination. The advent of artificial insemination and boar studs has created a need for strict biosecurity and monitoring of PRRS virus in these facilities.

==Pathogenesis==

==Pathogenesis==