Evaluation of protective immunity in gilts inoculated with the NADC-8 isolate of porcine reproductive and respiratory syndrome virus (PRRSV) and challenge-exposed with an antigenically distinct PRRSV isolate.
OBJECTIVE
To determine whether intrauterine inoculation of porcine reproductive and respiratory syndrome virus (PRRSV) interferes with conception and whether exposure to one strain of PRRSV provides protection against challenge-exposure (CE) with homologous or heterologous strains of PRRSV.


METHODS
40 gilts.


METHODS
Gilts were inoculated by intrauterine administration of a PRRSV isolate (NADC-8) at breeding. Inoculated and noninoculated gilts were exposed oronasally to homologous (NADC-8) or heterologous (European isolate) PRRSV during late gestation. Specimens from gilts and fetuses were tested against CE virus. Lack of virus in gilts indicated protective immunity for the dam, in fetuses indicated protection of gilt from reproductive losses, and in both groups indicated complete protection.


RESULTS
In the homologous CE group, interval from inoculation to CE ranged from 90 to 205 days, and protection was complete. In the heterologous CE group, interval from inoculation to CE ranged from 90 to 170 days, and protection was incomplete. The CE virus was detected in gilts necropsied 134 to 170 days after CE and in a litter necropsied 170 days after CE.


CONCLUSIONS
Homologous protection can be induced in gilts by exposure to live PRRSV. Heterologous protection from reproductive losses can be induced in gilts by exposure to live PRRSV; however, this protection is incomplete and may have a shorter duration than homologous protection.


CONCLUSIONS
Exposure of swine to enzootic PRRSV will provide protection against homologous PRRSV-induced reproductive losses. Extent and duration of protection against heterologous PRRSV may be variable and dependent on antigenic relatedness of the virus strains used for inoculation and CE.
Lager
K M
KM
Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service, Ames, IA 50010, USA.
Mengeling
W L
WL
Brockmeier
S L
SL
D000818:Animals; D000917:Antibody Formation / Q000276:immunology; D000956:Antigens, Viral / Q000276:immunology; D001947:Breeding; D001992:Bronchoalveolar Lavage Fluid / Q000821:virology; D003588:Cytopathogenic Effect, Viral; D005260:Female; D005312:Fetal Blood / Q000821:virology; D007114:Immunization / Q000379:methods / Q000662:veterinary*; D008297:Male; D019318:Porcine Reproductive and Respiratory Syndrome / Q000276:immunology* / Q000517:prevention & control*; D019316:Porcine respiratory and reproductive syndrome virus / Q000276:immunology*; D011247:Pregnancy; D013552:Swine
D000956:Antigens, Viral