Protecting U.S. herds from the African Swine Fever requires diligence
September 20, 2018
BROOKINGS, S.D. – The recent incursion and expansion of African Swine Fever (ASF) into China has raised concerns among U.S. producers and regulatory officials, said Russ Daly, Professor, SDSU Extension Veterinarian.
"It's easy to consider a pig disease on the other side of the world to be a very distant problem. However, as illustrated by the 2013 entry of Porcine Epidemic Diarrhea Virus into the U.S., global trade and movement of equipment, animal products and feed ingredients means that stable viruses can move around the world more efficiently than ever," he said.
Does African Swine Fever pose a threat to the U.S.?
African Swine Fever is not currently in the U.S., and Daly said animal health and producer groups across the industry are monitoring the ASF situation and putting preemptive measures in place should a case develop in the U.S.
However, maintaining disease-free herds also depends upon the diligence of American hog producers, Daly explained.
"It is not here yet. And, if it would enter the U.S., rapidly identifying the disease is the critical first step in preventing a single case from starting a nationwide outbreak," Daly said.
Recommended Stories For You
What should producers be on the lookout for?
In a large operation, Daly said a first clue would be illness in all age groups of pigs.
"The signs of illness will depend upon what strain of ASF gets to our shores. Depending on the ASF strain, the signs might resemble a nasty case of PRRS (porcine reproductive and respiratory syndrome)," he explained. "The highly virulent strains represent the worst case scenario: sudden death losses, approaching 100 percent."
ASF Signs: Pigs develop fever, reddened skin in their extremities (ears, tail, lower chest and belly) and begin to huddle and pile to regulate their body temperature.
Pigs would be listless, go off feed, and begin to "thump" or breathe with difficulty. There may be some vomiting and diarrhea.
These signs could also be seen with systemic infections like salmonellosis or erysipelas.
"If the ASF strain that comes in is of lesser virulence, then the signs won't be as intense," Daly said.
He explained that pigs would develop fever, become listless, and go off their feed.
"Mortality is lower but still might hit 30-70 percent. The survivors will develop chronic infections, with weight loss, swollen joints, breathing problems and spots of skin infection – which could mimic erysipelas or forms of circovirus infection."
Since ASF could look like other, more routine diseases, Daly said diagnosis is critical. To correctly diagnose, swine producers should call their veterinarian when any unusual illnesses or death losses become apparent. If veterinarian suspects ASF, they will contact the South Dakota State Veterinarian's Office, to determine if testing is necessary.
"Any potential foreign animal disease such as this is investigated by state and federal regulatory vets, who send the appropriate samples to national labs for diagnosis," Daly explained.
How is ASF transferred?
ASF is not transferable to humans. However, among pigs the highly-contagious ASF virus mostly moves between pigs through the nose and mouth. It infects the tonsils in the back of the throat and spreads from there through the bloodstream to the whole body (explaining why signs are more general than specific to an organ system).
Since live pigs aren't imported into the U.S. from countries with infected ASF herds, if the virus were to enter the U.S., Daly said it would most likely enter a farm through contaminated feed ingredients and spread easily between hogs through direct contact.
He explained that in those countries where herds are infected with ASF, the disease spreads through contact with waste scraps of pork products fed to pigs, contact with wild pigs infected with the disease and bites from ticks.
"Modern confinement pork production and the lack of the tick vector in this part of the country minimizes the risk of these forms of spread in the U.S.," Daly said.
Challenges of ASF
ASF's ability to survive long periods outside the pig is perhaps the most challenging aspect of the disease, Daly explained. "It easily survives 30 days in pig environments, and can survive three to six months in uncooked or undercooked pork," he said. "It's especially resistant to freezing, and is not affected by many of the usual disinfectants used in pork production."
Should an outbreak occur, Daly said much attention will need to be paid to decontaminating the pig's housing and surroundings afterward.
Currently, there is no vaccine or treatment for ASF and pigs on infected farms must be destroyed, and strict movement and quarantine actions will be taken.
"Clearly, preventing the incursion of ASF is of utmost importance to U.S. pork producers," Daly said. "Should the worst case happen, though, a quick response – beginning with a call to a veterinarian – when "something doesn't look right" will be the best way to limit the potential damage.'"