Laboratory investigation of PRRS virus infection in three swine herds


Article by:
D. Zeman, R. Neiger, M. Yaeger, E. Nelson, D. Benfield, P. Leslie-Steen, J. Thomson, D. Miskimins, R. Daly, M. Minehart. 1993. J Vet Diagn Invest 5:522-528

This report describes the clinical and pathologic effects of PRRS virus infection in 3 herds.
Clinical signs on all farms began in 1991 and continued into 1992.

Herd 1. A 120-sow farrow-to-finish swine herd started with a respiratory outbreak in growing and finishing pigs with moderate morbidity (35%) and low mortality (1%). In a few months, a reproductive failure syndrome with high-incidence affected pregnant sows and continued for 2 months. The clinical picture in sows was:
• 2-3 days of anorexia
• one-week premature farrowings
• increase of stillborn pigs
• higher mummies
• weak or “thumping” piglets
• Higher piglet mortality
At that time there was no virus was isolation but all 30 sow-samples had PRRS antibodies. Later, PRRSv was isolated retrospectively from 2 piglets.

Herd 2. A 2,800-sow farrow-to-finish swine herd started with smaller litter size, mummified piglets, and small weak born piglets. Initially, abortions were not part of the syndrome. After this initial outbreak a high-morbidity low-mortality respiratory outbreak affected 2,000 pigs in the grower/finisher phase. 2 months later, another respiratory disease occurred in the grow-finishing pigs (around 2000) but on this case it affected close to 100% of the pigs and the mortality was 5%.
The pathogens detected were salmonellosis, Actinobacillus pleuropneumoniae, and Pasteurella multocida. The respiratory disease also moved into the nursery and neonatal pigs where 8% of piglets were “thumping”. 12 week-old pigs had severe pneumonia with pleurisy and again Salmonella sp. Actinobacillus pleuropneumoniae was found and later Actinomyces pyogenes was isolated from a hog with mild purulent exudate. Although initial virus isolation was negative, later attempts resulted positive.

Herd 3. This 120-sow farrow-to-finish swine farm had and increased incidence of respiratory problems in nursery pigs. Later, this outbreak affected grower, finishing pigs and also farrowing rooms. 3 months later, a syndrome appeared in piglets and sows that showed vomiting and diarrhoea, and 15% of the sows had abortions and stillbirths.
Different submission of tissues were done and the main pathogens found were: Mycoplasma hyopneumoniae, Haemophilus parasuis, Streptococcus suis and Actinomyces pyogenes from the lungs of different affected animals, also Actinobacillus lignieresi was isolated from a pig with pneumonia and pleurisy. The lungs were positive for PRRS virus by both FA testing and virus isolation.
The clinical picture indicates that PRRSv infection increases the incidence of other common diseases in all three cases.