U.S. hog producers endured some brutal setbacks last year amid the havoc wreaked on supply chains as the Covid-19 pandemic set in. Unfortunately, some producers throughout the Midwest are also dealing with a new and more deadly strain of a common foe, porcine reproductive and respiratory syndrome (PRRS). This emerging strain, PRRS 1-4-4, began showing up last fall and so far appears to be concentrated in southern Minnesota and northern Iowa, at least for now. From what veterinarians are reporting, the strain is extremely aggressive and has broken through onto farms that have successfully prevented PRRS outbreaks for years. What’s more, it seems impervious to immunity against other PRRS strains, including both previous exposure and vaccination.
The Swine Health Information Center (SHIC) and American Association of Swine Veterinarians (AASV) recently held a webinar to share what they have learned about strain 1-4-4, which is available HERE. Among the presenters is Dr. Paul Yeske of Swine Vet Center, who warns that the virus moves through herds quickly once clinical signs emerge as the new strain produces a lot of virus. Clinical signs include hogs going off feed, increased sow and piglet mortality, increased abortions, and increased post-weaning mortality. According to Yeske, sow farms affected have seen as much as seven weeks of production aborted. Sow deaths are pegged at between 10% to 20% while weaned pig losses are estimated to be as high as 80%. Surviving hogs also appear to witness sharply slower growth during finishing.
PRRS 1-4-4 follows a similar outbreak path as other strains of the virus, with high disease pressure accompanied by high losses for roughly two to four weeks, followed by a sow recovery period. However, the Advisory Committee did note that it appears to require a prolonged time to stabilize sow units with an outbreak of PRRS 1-4-4. First litters feature fewer live births and increased mummies of piglets.
Producers also need to be aware that vaccinated herds and herds previously exposed to PRRS virus have witnessed outbreaks of the 1-4-4 strain. As with all PRRS virus, the best defense is a strong biosecurity system and Yeske urges hog producers to review those and shore up any weaknesses sooner rather than later. That includes a review of all the different ways the virus could possibly enter a herd and how often those activities are being performed. Current colder weather favors PRRSV survival and spread, potentially increasing the infection pressure.
PRRS in pigs can be transmitted from infected to susceptible pigs through different routes. The main route is direct transmission when infected pigs are in contact with others on the same farm, or in the same barn or pen. Besides this direct horizontal transmission, vertical transmission can also occur when the PRRS virus crosses the placental barrier during the last trimester of gestation and it can replicate in the endometrial and placental tissues. Indirect transmission is also possible. Different vectors and contaminated fomites can spread the PRRS virus on the farm and to other farms as well. In addition, airborne transmission is possible between different pens or barns, or through slurry. It should be borne in mind that the PRRS virus can survive for days in favorable conditions such as organic material, high humidity and low temperatures.
The total cost of productivity losses due to PRRSV in the U.S. national breeding and growing-pig herd is estimated at around $664 million annually, though many argue that figure fails to capture the full scope of the disease’s economic impact. PRRS has been and is currently the swine disease with the greatest economic impact on the worldwide swine industry. Only a few countries with a representative population remain PRRS-free. To learn more about biosecurity, check out the USDA’s Animal and Plant Health Inspection Service resources HERE. (Sources: SHIC, SMEC.IAState, HIPRA)