How long boars shed the virus in semen when infected with PRRSV? What is the clinical manifestation of the sows inseminated with semen from PRRS infected boars? Can we suspect PRRSV involvement when PCV2 vaccinated farms showed 20% early abortion around 25 days after artificial insemination (AI)?
Here is a detailed explanation to all the questions raised above regarding PRRSV transmission through semen and abortion rates:
Possible causes of 20% early abortions rate in sows
Abortion in sows could be classified as follows:
- 1. Insemination (fertilization) to implantation stage (~14days).
- 2. During implantation stage (14 – around 35days).
- 3. Fetal growth stage (35days~).
Causes of abortion in sows are diverse including seasonal and environmental factors (such as high heat), toxin (mycotoxins), nutritional factors (vitamins) and infectious agents.
Single or multiple factors can be involved in the abortion. We have to remember that environmental factors are common cause of early abortion in healthy sows.
Bacterial diseases such as Brucellosis, Letospirosis and viral agents as porcine parvovirus (PPV), Japanese encephalitis virus, porcine circovirus 2/3, encephalomyocarditis virus (EMCV), pseudorabies and porcine reproductive and respiratory virus (PRRSV) are known to cause abortion in pregnant sows.
Contamination of the semen extender (E. coli, Klebsiella, Streptococci, Pseudomonas, etc.) and infectious disease with febrile reaction such as swine influenza virus are recommended to be tested.
Laboratory test is required to find the cause of the abortion for the diagnosis and control.
Importance of semen in PRRSV transmission
PRRS virus is a most economically important pathogen in pig industry worldwide and very difficult to control in endemic regions.
Among various sources of the PRRSV transmission boar semen also plays a very important role.
PRRSV infected boars shed the virus in semen from 14 days to several months and a small amount of the virus cause seroconversion in inseminated PRRS-naïve sows.
But PRRS virus can cross the placenta around 90 days after gestation in normal physiological condition therefore early abortion is not a common in pregnant sows due to the PRRSV.
Early abortion around 25days post service is most likely not associated with PRRSV.
Infectious agent involvement and/or immune status of the sows to common pathogens such as PPV, Aujeszky’s virus, Japanese encephalitis virus, swine influenza virus need to be tested for the definitive diagnosis.
For more information regarding the importance of the semen in PRRSV transmission, visit chapter 2 “Epidemiology > Transmission within herds” of this site.
University of Konkuk, South Korea