Key Messages

• Clinical presentation of PRRSV depends on the trimester of gestation of infected females and on the age of infected pigs.
• It induces fever, pneumonia, lethargy, failure to thrive, and mortality. Also, red-blue colouring of skin and oedema.
• In sows, it can cause abortions, premature farrowings, stillborn foetuses, agalactia and post-weaning return to oestrus and increased sow mortality.
• Most of the clinical signs have been reproduced experimentally but the typical field usually complicate the clinical presentation.
• In finishing pigs as well as in unbred gilts and boars, frequent subclinical infections can also be found.

Article Brief

The clinical presentation and signs of PRRSv infection differs significantly between herds. And it has two different types of clinical signs: reproductive and respiratory.

In sows and gilts, the clinical presentation of PRRSV depends on the trimester of gestation (if gestating) of the infected female.

It induces abortions in gestating sows that may be sporadic to storm outbreaks and can persist for short periods 10 to 12 weeks and up to four to six months. Also, late term abortions or premature farrowing are seen in late infections, with stillborn foetuses, partially autolysed or mummified.

Other clinical signs in sows and gilts can be, in different degrees of intensity: fever, lethargy, anorexia, pneumonia, red-blue colouring of ears and vulva, subcutaneous edema, agalactia and post-weaning return to oestrus and increased sow mortality.

Pigs infected in utero or shortly after birth show severe dyspnoea, tachypnea, anorexia, fever and conjunctivitis. Other signs like periocular oedema, blue discoloration of ears, eritema, diarrhoea, shaking, and rough hair are also commonly seen. Moreover, mortality rates can go up to 100 per cent.

Weaned piglets and finishing pigs

PRRSV infection in pigs depend also on the age of the pig infected and are characterised by fever, pneumonia, lethargy, failure to thrive and mortality.

Most of the clinical signs described for PRRS infections on the field have also been reproduced by experimental PRRS infections; but the typical field co-infections may confuse and complicate the clinical presentation. These concurrent infections often increase mortality in a synergistic manner up to 15 per cent.

In finishing pigs as well as in unbred gilts and boars, frequent subclinical infections can also be found.

Gross lesions caused by PRRSV infection also differ broadly and depend on the virus strain, genotype of the pigs and stress factors (environment and health status of the pig herd).

Lung lesions differ from none to diffuse consolidation and are commonly complicated by lesions resulting from concurrent bacterial infections, which can be separate or intermixed.

Reference

Rossow, K.D. 1998. Porcine reproductive and respiratory síndrome. (A review). Vet. Pathol. 35:1-20.

October 2015