Clinical effects of porcine reproductive and respiratory syndrome virus on pigs during the early postnatal interval.
OBJECTIVE
To determine the effect of congenital and early postnatal infection of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) on postnatal survival and growth.


METHODS
20 pregnant gilts and their pigs and fetuses.


METHODS
16 pregnant gilts (principals) comprising 4 groups (4 gilts/group) were exposed oronasally to 4 strains of PRRSV (a vaccine strain, and 3 field strains) at or about day 90 of gestation. Four pregnant gilts (controls) were kept under similar conditions, except for exposure to PRRSV. Samples collected from pigs before ingestion of colostrum and samples and specimens collected from pigs at selected times thereafter were tested for PRRSV and homologous antibody. Pigs were observed for clinical signs and were weighed at birth and at weekly intervals until they were euthanatized and necropsied at about 3 weeks of age.


RESULTS
At least some members of all litters of principal gilts were infected congenitally. Most noninfected, liveborn littermates became infected within the first week of life. Infection of pigs with field strains did, and infection of pigs with the vaccine strain did not, adversely affect postnatal survival and growth rate. All infected pigs had generalized lymph node enlargement.


CONCLUSIONS
Exposure of pregnant gilts to either attenuated (vaccine) or virulent (field) strains of PRRSV can result in congenital infection. Vaccine as well as field strains can be transmitted postnatally from infected to noninfected littermates. Pigs infected with field strains have a poorer rate of survival and growth than do noninfected pigs.


CONCLUSIONS
Because attenuated (vaccine) PRRSV can cause congenital infection and be transmitted postnatally from congenitally infected to immune-naive pigs, the use of attenuated virus during gestation is, at best, questionable.
Mengeling
W L
WL
Virology Swine Research Unit, National Animal Disease Center, USDA-Agricultural Research Service, Ames, IA 50010, USA.
Lager
K M
KM
Vorwald
A C
AC
D000818:Animals; D000831:Animals, Newborn; D000914:Antibodies, Viral / Q000097:blood; D003126:Colostrum / Q000821:virology*; D005260:Female; D018445:Infectious Disease Transmission, Vertical / Q000662:veterinary*; D008198:Lymph Nodes / Q000473:pathology; D016676:Macrophages, Alveolar / Q000821:virology*; D019318:Porcine Reproductive and Respiratory Syndrome / Q000473:pathology / Q000503:physiopathology / Q000635:transmission*; D019316:Porcine respiratory and reproductive syndrome virus / Q000302:isolation & purification*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000662:veterinary*; D013552:Swine
D000914:Antibodies, Viral