Genetic Clue for Fighting Swine Virus
Perry October 18, 2007
Agricultural Research Service (ARS) scientists are part of a team that has
found a vital clue for battling a disease called porcine reproductive and
respiratory syndrome virus (PRRSV), which costs U.S. swine producers about $560
PRRSV-infected pigs are susceptible to pneumonia and reproductive
losses, and infected sows give birth to weak piglets. It can take weeks or even
months for them to recover from the virus, which evolves and adapts quickly to
environmental challenges like vaccines and medications.
Kuhar conduct research at the ARS
Parasitic Diseases Laboratory in Beltsville, Md. Working with animal
scientist Rodger Johnson and graduate student Derek Petry at the
University of Nebraska-Lincoln, they
evaluated two lines of swine for genetic resistance to PRRSV. The Nebraska
Index line (I) was chosen because of its improved reproductive traits, and the
Hampshire by Duroc cross (HD) was selected for its high growth rates.
All pigs in both groups became infected after exposure to PRRSV.
However, I pigs generally recovered more quickly, maintained higher levels of
weight gain during their illness and had lower body temperatures. In addition,
samples of blood, lung and bronchial lymph node tissue showed that virus levels
cleared more quickly in PRRSV- resistant I and HD pigs.
The scientists then looked at the tissue expression of 11 genes and
one "housekeeping" gene involved in the immune response to PRRSV. Both I and HD
swine showed significant activity in 11 of the 12 genes, but the type of
activity differed between the two groups.
High pre-infection blood levels of one protein,
interleukin-8IL8was found to be significantly associated with
PRRSV-resistant pigs. Low levels of another protein,
interferon-gammaIFNGin blood and in RNA samples was also correlated
with PRRSV resistance.
These findings support existing research that indicates animal breeds
with high growth rates devote less energy to immune and disease traits. This
information will facilitate work into developing genetic tools for increasing
swine resistance to PRRSV.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.