Porcine Reproductive and Respiratory Syndrome (PRRS)

Cause
Diagnosis
Treatment and Control
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Introduction

This disease was first recognized in 1987 in the US although it appeared in Europe at about the same time. The disease was characterized by abortion, premature farrowing, stillborn and mummified pigs, respiratory disease with death loss and chronic poor performance of nursing and weaned pigs.

Cause

PRRS is caused by an RNA virus that is a member of the genus artervirus. PRRS virus is easily inactivated by heat; drying and common disinfectants but will persist for long periods of time at freezing temperatures. The PRRS viruses are genetically diverse and mutate rapidly. The virus is shed in nasal-oral secretions, urine, feces and semen. Contact with an animal shedding the virus is thought to be the common route of infection.

Diagnosis

PRRS virus can be isolated from blood only during the early stages of acutely ill animals. Mature animals quickly mount an immune response. Detection of antibodies to PRRS is a commonly used diagnostic aid but will not be useful if the animals have been vaccinated because current tests do not differentiate between antibodies to native strain or commercial vaccine strains.
Symptoms:

Breeding females	Fever, depression, decreases appetite, sudden onset of reproductive abnormalities lasting 2-6 months: Abortions (>70 days), 2-4X the number of stillborn piglets, increase in weak piglets born
Boars	Fever, depression, decreases appetite- often no clinical symptoms
Nursery pigs	respiratory disease, secondary bacterial and viral infections
Finishing pigs	Fever, depression, decreases appetite, coughing, secondary bacterial and viral infections

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Treatment and Control

There is no treatment for the viral infection. Secondary bacteria infections should be treated with the appropriate drugs. Prevention and control of PRRS employs strategies similar to other diseases and will depend on the size and type of operation. Vaccinations do not prevent the animals from infection but will minimize the symptoms following infection. Vaccination programs must be individually designed.