by Sally Colby
Veterinarians and producers have kept a close eye on African swine fever (AFS) for the past several years, but it’s getting closer to the U.S.
A collaborative effort by Cornell University’s Extension work team, New York Pork Producers and New York State Ag & Markets produced an update on AFS. Dr. Eireann Collins, DVM, with NYS Department of Agriculture & Markets/Animal Industry, presented the history and current status of the disease.
“Our main mission is to detect, control and eradicate infectious disease in food and fiber producing animals,” said Collins. “African swine fever is one of the biggest global threats to both the swine industry and pigs currently.”
Collins described the AFS virus as a large DNA envelope virus, and as is the case with other viruses, including influenza and COVID, there can be many genotypes, or different strains, with variety of virulence (how contagious it is).
When AFS was discovered in Kenya in 1921, it was primarily a disease of wild pigs but it also affected domestic pigs. “In 1921, these pigs were primarily reservoir hosts,” said Collins. “At the time, the virus was maintained because there was a tick-to-pig-to-tick transmission. Pigs were adapted to African swine fever, as were the ticks. Unfortunately, for our domestic pigs, it is highly infectious and highly fatal. Currently there is no vaccine to protect pigs, and currently no treatment available.”
After its start in Africa, the virus began to spread to other parts of the world in the mid to late 1900s. Collins said spread at the time was due primarily to pork products being fed to pigs, garbage feeding at ports or through the transport of infected wild boar for hunting preserves.
Collins said AFS was diagnosed in the Republic of Georgia in 2007, and from there it spread to the Caucasus and into Russia. The disease was identified in Eastern Europe in 2015, then in China in 2018.
“China produces over 50% of the world’s total pork supply,” said Collins, adding that 406 million pigs are on feed in China. “In 2018, 98% of Chinese pork production came from small-scale producers with less than 100 pigs.”
AFS spread throughout Southeast Asia, eventually affecting more than 50 countries, primarily on small scale pig farms. By 2019, it was estimated that AFS had killed 25% of the world’s pig population. China alone depopulated 100 million pigs, making it the most significant animal disease in modern history.
Collins said AFS is an incredibly devastating disease that will impact producers as well as consumers. But how did AFS go from brewing in a certain part of the world to 25% of the world swine herd being depopulated?
“The virus itself is extremely hardy, so it can survive for several days in feces and contaminated pens,” said Collins. “It can service in processed pork (such as dried hams), for almost half a year, and in frozen carcasses or frozen meat for years.” Feeding contaminated pork to pigs through waste (garbage) or through carcasses is one of the most efficient ways to spread the disease. Collins added that people have illegally brought pig products to the U.S. from countries where AFS is present, including pork from Vietnam that was intercepted at a Boston port.
Once AFS is present in a country, transmission can occur in several ways, including direct contact with infected pigs. “All secretions can spread the virus, but it can also be spread through infected clothing, vehicles (feed truck, rendering truck) and other equipment and water runoff with blood, diarrhea or other feces.” Other known vectors include the soft tick and other biting ticks.
Collins described the disease progression: after a domestic pig is exposed to the virus, there’s an incubation period of about five to 21 days. In domestic pigs, AFS results in rapid morbidity and mortality – animals become ill quickly and succumb to disease quickly. Feral pigs sometimes show fewer clinical signs and may not become as ill as domestic pigs, so there’s a risk of them becoming a reservoir species. Collins noted that this is a serious concern in areas where feral pigs are present.
Clinical signs of infection include fever, lack of appetite, lethargy, weakness and hemorrhage. “We see bleeding spots with the skin turning blue,” said Collins. “Other signs include bloody diarrhea, abortion and respiratory disease.”
In 2019-2020, China announced it was going to start restocking its pig population to reach 90% of pre-AFS levels. However, China has not eliminated the disease. In May 2021, Meat and Livestock Australia announced they had identified a new strain that had already killed eight million pigs in that country.
Of serious concern to U.S. pork producers is that this past summer, AFS was identified in the Dominican Republic, then in Haiti. “The Dominican Republic is very close to Puerto Rico,” said Collins, adding that a daily ferry moves between the Dominican Republic and Puerto Rico. “Puerto Rico is a U.S. territory, so by OIE (World Organization for Animal Health) standards, if Puerto Rico becomes infected, the U.S. would be considered infected, which would have devastating consequences for international trade. The USDA is working with the OIE to set up Puerto Rico as a surveillance zone, so if an infection is diagnosed in Puerto Rico, we could protect mainland trade. However, that still puts us at great risk for this disease transferring from the Caribbean onto the continental U.S., and New York is a gateway for that.”
Unfortunately, it isn’t unusual for people selling pork products to attempt to bypass U.S. embargoes. Collins noted that the Beagle brigade identified and stopped 50 shipping containers of infected, illegal pork from entering the U.S.
Since garbage feeding is considered a high-risk activity, the U.S. has regulations requiring garbage feeders to be licensed, including cooking garbage for a certain time at a certain temperature. Collins said 27 states, including Florida, allow garbage feeding, and that Florida is geographically close to countries with active AFS.
“There’s no vaccine and no treatment for African swine fever,” said Collins. “The only way to prevent infection is through biosecurity. At the national level, we have port embargoes and surveillance programs in place. But at the farm level, it’s up to producers to protect their stock, and the best way to do that is to plan – now.”