Objective—To document shedding of porcine reproductive
and respiratory syndrome (PRRS) virus in
mammary gland secretions of experimentally inoculated
sows, to evaluate effects of vaccination during
gestation on virus shedding during the subsequent
lactation, and to evaluate shedding of PRRS virus in
milk of sows in commercial herds.
Animals—6 sows seronegative for PRRS virus were
used for experiment 1, and 2 sows were retained for
experiment 2. For experiment 3, 202 sows in commercial
herds were used.
Procedure—In experiment 1, 2 sows were inoculated
with PRRS virus, 2 sows were vaccinated with modified-
live PRRS virus vaccine, and 2 sows served as
control pigs. Mammary gland secretions were
assayed for PRRS virus. In experiment 2, pregnant
vaccinated sows from experiment 1 were vaccinated
with another modified-live PRRS virus vaccine.
Mammary gland secretions were assayed in the
same manner as for experiment 1. For experiment 3,
milk collected from 202 sows in commercial herds
was assayed for PRRS virus.
Results—In experiment 1, PRRS virus was detected in
mammary gland secretions of both vaccinated and 1 of
2 virus-inoculated sows. In experiment 2, virus was not
detected in samples from either vaccinated sow. In
experiment 3, all samples yielded negative results.
Conclusions and Clinical Relevance—Naïve sows
inoculated late in gestation shed PRRS virus in mammary
secretions. Previous vaccination appeared to
prevent shedding during the subsequent lactation.
Results for samples obtained from sows in commercial
herds suggested that virus shedding in mammary
gland secretions of such sows is uncommon. (Am J
Vet Res 2001;62:1876–1880)
In 1989, a syndrome characterized by reproductive disorders in sows and respiratory disease in growing pigs was first reported in the southeastern United States, which was rapidly followed by reports of the disease throughout North America.1,2 A number of pathogens were initially implicated as the cause of this disease. The major breakthrough came in 1991 when a virus, initially referred to as Lelystad virus, was identified in the Netherlands.3,4 Subsequently, Koch's postulates were fulfilled when experimental aerosol exposure of sows with cell-cultured Lelystad virus resulted in clinical manifestations of the disease.3,5 In the United
Objective—To estimate the annual cost of infections
attributable to porcine reproductive and respiratory syndrome
(PRRS) virus to US swine producers.
Sample Population—Data on the health and productivity
of PRRS-affected and PRRS-unaffected breeding
herds and growing-pig populations were collected
from a convenience sample of swine farms in the
midwestern United States.
Procedure—Health and productivity variables of
PRRS-affected and PRRS-unaffected swine farms
were analyzed to estimate the impact of PRRS on
specific farms. National estimates of PRRS incidence
were then used to determine the annual economic
impact of PRRS on US swine producers.
Results—PRRS affected breeding herds and growing-pig
populations as measured by a decrease in reproductive
health, an increase in deaths, and reductions
in the rate and efficiency of growth. Total annual economic
impact of these effects on US swine producers
was estimated at $66.75 million in breeding herds and
$493.57 million in growing-pig populations.
Conclusions and Clinical Relevance—PRRS imposes
a substantial financial burden on US swine producers
and causes approximately $560.32 million in
losses each year. By comparison, prior to eradication,
annual losses attributable to classical swine fever
(hog cholera) and pseudorabies were estimated at
$364.09 million and $36.27 million, respectively
(adjusted on the basis of year 2004 dollars). Current
PRRS control strategies are not predictably successful;
thus, PRRS-associated losses will continue into
the future. Research to improve our understanding of
ecologic and epidemiologic characteristics of the
PRRS virus and technologic advances (vaccines and
diagnostic tests) to prevent clinical effects are warranted.
(J Am Vet Med Assoc 2005;227:385–392)