Immunologic responses and reproductive outcomes following exposure to wild-type or attenuated porcine reproductive and respiratory syndrome virus in swine under field conditions.
OBJECTIVE
To compare immunologic responses and reproductive outcomes in sows housed under field conditions following controlled exposure to a wild-type strain of porcine reproductive and respiratory syndrome virus (PRRSV strain WTV) or vaccination with a modified-live virus (MLV) vaccine.


METHODS
Randomized controlled trial.


METHODS
30 PRRSV-naïve 10-week-old female pigs.


METHODS
Humoral and cell-mediated immune responses were monitored while pigs were held in isolation for 84 days after inoculation with the WTV strain (n = 10), inoculation with the WTV strain and 42 days later vaccination with a killed-virus vaccine (10), or vaccination with an MLV vaccine (10). Reproductive outcomes were measured after pigs were released into the farm herd.


RESULTS
Inoculation with the WTV strain, regardless of whether a killed-virus vaccine was subsequently administered, elicited faster and more substantial production of strain-specific neutralizing antibodies, as well as a more rapid generation of interferon-gamma secreting cells, than did vaccination with the MLV vaccine. Despite the enhanced immune responses in pigs inoculated with the WTV strain, animals vaccinated with the MLV vaccine produced a mean of 2.45 more pigs than did sows exposed to the WTV strain, mainly because of a lower rate for failure to conceive.


CONCLUSIONS
Results suggest that current assays of immunity to PRRSV correlate only imperfectly with degree of clinical protection and that the practice of controlled exposure of sows to a circulating PRRSV strain should be reconsidered in light of negative clinical outcomes.
Department of Veterinary Pathobiology, School of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA.
James F
JF
Lowe
Federico A
FA
Zuckermann
Lawrence D
LD
Firkins
William M
WM
Schnitzlein
Tony L
TL
Goldberg
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D005260:Female; D008098:Litter Size; D019318:Porcine Reproductive and Respiratory Syndrome / Q000276:immunology* / Q000517:prevention & control / Q000821:virology; D019316:Porcine respiratory and reproductive syndrome virus / Q000276:immunology* / Q000472:pathogenicity; D011247:Pregnancy; D018873:Pregnancy Rate; D012098:Reproduction; D013552:Swine; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated; D014765:Viral Vaccines / Q000008:administration & dosage / Q000276:immunology*
D000914:Antibodies, Viral; D014613:Vaccines, Attenuated; D015164:Vaccines, Inactivated; D014765:Viral Vaccines