Porcine circovirosis (Porcine circovirosis type 2 (PCV2), PMWS,(PDNS)

Description

Porcine circovirus is caused by porcine circovirus type 2 (PCV2). Clinically it is presented as a disease which deteriorates animals from the weaning to the finishing period producing a high mortality rate. The virus is ubiquitous globally. It is very small and very resistant to the environment. There are two serotypes: Type 1, which does not cause any known disease, and Type 2, which causes disease in pigs. Although the PCV2 has been present in pigs for several years without any clinical manifestation, a mutation or an introduction of a new strain caused a deterioration syndrome with high mortality. There are several different strains (PCV2a, PCV2b, PCV2c, etc.), although vaccines that have the first known strains seem to give adequate protection against all the strains.

A special sign of PCV2 is the dermatitis and nephropathy porcine syndrome. This syndrome appears mainly in growing and finishing pigs, and rarely affects other groups. As its name indicates, its clinical presentation is through skin lesions and affects the kidneys. Possibly the clinical signs appear eventually in a small number of animals. Mortality of affected pigs is almost 100%.

 

Symptoms

Sows and lactating piglets

• Abortions.
• General reproductive failure.

 

Weaners and growers

• It is a slow and progressive disease with a high level of mortality in affected pigs.
• Normally starts around 6 to 8 weeks of age. Weaned pigs lose weight and gradually present emaciation. Present rough coat and pale or yellowish skin.
• Sudden death.
• Increase of peripheral lymph nodes size, especially between rear limbs.
• Some cases may present diarrhea.
• May show respiratory difficulty caused by interstitial pneumonia
• Incoordination.
• Mortality index after weaning can be 6 to 10%, although sometimes it is much higher (29%). In older pigs, mortality can be up to 10%.
• Extended greasy brown or red-purple spots of different sizes and shapes in chest, abdomen, thighs and front limbs. Most of the pigs that develop these extended spots die.
• Depression.
• May have fever.
• Normally do not move.
• Weight loss.

Causes / contributing factors

• Infected feces.
• Mechanical dissemination through clothes, equipment, trucks, etc.
• Continuous production.
• High population density.
• Injections seem to disseminate the virus in the herd in a more rapid way.
• Co-infections specially PRRS or parvovirus.

 

Diagnosis

• Due to the fact that most farms have antibodies for porcine circovirus, tests to detect antibodies in blood do not help with the diagnosis.
• Clinical signs are not specific, so in order to have a diagnosis, it is often necessary to perform post-mortem examinations in several pigs.
• The diagnosis is based in three factors:
  • Lymph depletion.
  • High amount of PCV2 present in tissue (immunohistochemical tests)
  • The clinical picture corresponds to a PCV2 infections.
• Macroscopical lesions in the post-mortem examination are variable. The carcass is emaciated and can have a yellowish aspect (icteric).
• Kidneys might be swollen and have white granules in the surface.
• In pigs whose rear limbs are affected, lymph nodes have a bigger size, like big grapes.
• Many conditions such as starvation, malnourishment, lack of water, gastric ulcers, enzootic pneumonia, ileitis, PRRS and other diseases can have similar symptoms. All these diseases have to be discarded if a specific diagnosis is to be done.
• Two diseases that deserve a special mention are dermatitis and nephropathy porcine syndrome, which relates to PCV2 and indicate a vascular systemic infection, which usually results in death.
• Skin lesions led to suspect of an immune complex associated to an abnormal stimulation f the immune system. This implies antigen-antibody reactions.
• The most important lesions are found in kidneys, which are swollen, pale and have little dots related to small hemorrhages in its surface.

Control / prevention

• In affected countries: vaccination is nearly implemented in all farms due to its great efficacy.
• Control of other diseases such as enzootic pneumonia and PRRS.

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