Porcine Reproductive and Respiratory Syndrome

Also known as: PRRS, blue eared pig disease

Description

Porcine reproductive and respiratory syndrome was first recognised in the USA in 1987 and spreadto Europe in 1990 and the UK in 1991. Infection in the UK was initially seen in the Humberside area, but despite restrictions being placed on the movement of breeding stock outwith the infected zone, the disease spread to many parts of the country. PRRS is caused by a virus, of which different strains occur in the USA and Europe. The european strains are much milder in terms of their pathogenic potential than the US strains. The acute phase of disease lasts approximately 4-16 weeks. The most consistent featurs are reproductive lossed in pregnant stoock, increased pre-weaning mortality and inluenza-like illness affecting all ages of pigs. American strains of virus are much more virulent than European strains, causing sow martality in addidion to pneumonia and reporductive failure.

• The syndrome is caused by a small enveloped RNA virus which belongs to the new Arteriviridae group
• Replicates in and destroys macrophages and endothelial cells causing vasculitis -> viraemia -> virus shedding (nasal secretions, faeces)
• Clinical signs: respiratory and reproductive failure, weaned pigs, tachypnoea, eyelid oedema, conjunctivitis
• Moderate to severe interstitial pneumonia in the cranial lobe
• Superimposed bacterial infections are common
• Infectious disease in swine that emerged 10 years ago
• Today, PRRS is endemic in many if not all the pig-producing countries

PRRS Porcine reproductive and respiratory syndrome virus (Lelystad virus). There is abortion late in gestation with respiratory tract illness in live piglets (interstitial pneumonia).

Virus

Antigenicity

• Isolates vary in virulence
• Some are subclinical

Hosts

• Pigs: aka Blue Ear or Lelystad virus

Transmission and Epidemiology

• Discovered in Holland in 1990
• Highly contagious
• Survives well on fomites
• Transfer may also be aerosol or via semen
• Exacerbated by immunosuppression (eg by porcine circovirus 2)

Pathogenesis

• Infects alveolar macrophages, followed by interstitial pneumonitis
• Persistent infection of Monocytes followed by leukopenia and thrombocytopenia
• Mostly affects piglets
• In adults, cyanotic appearance due to vascular lesions
• Transplacental spread leads to abortion, mummification, or resorption

Diagnosis

Clinical Signs

Clinical signs include non-specific illness (anorexia and dullness) in sows, with reproductive losses occuring 1-2 weels later. In piglets, PRRS is characterised by inthriftiness, respiratory illness and mortality. Signs are similar in all ages of growing stock. Effects on neonatal piglets can be severe. Respiratory distress is seen, in addition to scour, unthriftiness and high mortality. Infection of boars may lead to impaired semen quality. Blue ears, snout and vulva can be seen in 1-5% of sows. Reproductive problems include infertility (normal oestrus delated, retuns to service increased), premature farrowing, stillbriths and weakly piglets.

Laboratory Tests

• ELISA for virus antibody
• Rising antibody titres as a retrospective diagnosis (4X increase)

Control

• Certified Specific Pathogen Free units exclude by quarantine
• Management: all in/all out, screening AI semen
• Vaccine available