North American swine producers and the related industry have been taking great pains over the past few years to keep African swine fever out of the United States. Although African swine fever is one of three foreign animal the U.S. livestock industry wants to keep out of the country, the other two — classical swine fever (CSF) and foot and mouth disease (FMD) have infected U.S. hogs and were eradicated long ago. CSF, also known as hog cholera, was stamped out in 1978, and FMD, which affects all split-hooved animals, was eradicated in 1929.
ASF has not yet infected U.S. swine herds. It has, however, made appearances in the western hemisphere. Cuba, the Dominican Republic and Haiti battled and eradicated ASF in their swine populations in the 1970s.
What is African swine fever?
African swine fever is one of the most severe diseases of pigs, having a drastic impact on the pig industry. ASF first appeared in domestic pigs in East Africa in the 1900s. It subsequently spread to Europe; appearing first in Portugal, then Spain and further countries. Eradication was achieved in Europe apart from Sardinia in the mid- 1990s.
In 2007, ASF then appeared in Georgia — spreading then to Russia and the Caucasus region, and other eastern European countries. In 2018, it continued to spread westward, affecting domestic pig and wild boar populations.
In 2018, ASF virus also reached the world’s largest pig producer: China. Mongolia reported its first outbreak in 2019. In the years since its outbreak in China, ASF has been identified in Southeast Asian counties and European countries, including Germany and Poland in wild boar populations in September of 2020.
ASF is a highly-contagious hemorrhagic disease caused by a virus of the family Asfarviridae. It is often fatal in domestic pigs and wild boars. The primary control strategy for ASF in domestic swine is stamping-out. Currently, there is no vaccine available. Given the financial implications and limitations in trade, eradication is the ultimate goal.
ASF is a notifiable disease listed by the World Organization for Animal Health (OIE) and must be reported. ASF virus is considered a Foreign Animal Disease by the United States Department of Agriculture and therefore swine byproduct imports from ASF-positive countries are forbidden. Any suspicion of ASF must be notified to the Minnesota Board of Animal Health and the USDA.
How ASF is spread
Due to the absence of an effective vaccine, introduction and spread of ASF onto domestic pig farms can only be prevented by strict compliance with biosecurity measures.
ASF virus is highly stable and temperature resistant and can persist in the environment for a long time. The main mechanisms of spread include direct pig-to-pig contact, including with wild pigs; movement of infected live animals; and improper disposal of manure and dead animals Contact with contaminated pork and byproducts will spread the virus, as well as consumption of contaminated feed (swill feeding). Ticks — specifically soft ticks found in the western/southwestern U.S. — can transmit ASF. The virus can be transferred by a manure slurry; introduction of genetic materials and replacement animals; contaminated vehicles and other fomites, clothing, footwear or equipment; and, of course, workers and visitors.
Planning in place
Swine producers and allied industry have put together strategies to monitor and prevent ASF from infecting North American pig populations, and Minnesota leads the charge. The University of Minnesota College of Veterinary Medicine swine team, along with Minnesota Pork Producers, the Minnesota Board of Animal Health, the Minnesota Department of Agriculture and U of M Extension have worked together as the Emergency Disease Management Committee for Swine to implement a plan.
The plan developed strategies for action in the event that ASF would infect Minnesota, the Upper Midwest or the North American swine herd. In September 2019 fourteen swine-producing states worked together for four days through a functional exercise to determine what steps would be taken by all affiliated partners if ASF struck.
Now in the Western Hemisphere
On July 28, 2021, the USDA announced that it had identified ASF in samples from the Dominican Republic. USDA receives quarterly samples from a lab in the Dominican Republic, and originally identified eight samples positive for ASF. Further testing provided information that the ASF infection had spread further than the original results indicated.
The Dominican Republic swine herd is produced in both larger, more commercial-type farms established on the eastern end of the island, and in small backyard settings (with 20 pigs or fewer) found throughout most of the regionals of the Dominican Republic. The positive samples were discovered in the smaller herds, many of which are loosely housed, or allowed to run free.
The source of the ASF virus is suspected to be from garbage fed to the pigs — perhaps from ship or airplane food garbage. Isolation of the virus has revealed it has the same genetic makeup of the ASF virus of the Georgian outbreak in 2007.
The United States currently does not exchange pork products or live pigs with the Dominican Republic because they have Classical Swine Fever in their country. Because they are a FAD positive locale, these animals and products are not allowed to move into the United States. This is considered a positive factor in keeping the ASF virus from moving into other countries in this hemisphere.
USDA is currently sending lab equipment and technical assistance to the Dominican Republic as they request it. Scientists from the University of Minnesota’s veterinary swine group will be traveling to the Dominican Republic within this month to assist with eradication of the outbreak. The Dominican Republic has set up strategies to assist their producers with stamping out the virus and to provide compensation for those producers affected.
Biosecurity — Keeping Minnesota swine safe
The plan to keep ASF out of our U.S. and Minnesotan swine population comes back to meticulous biosecurity. Biosecurity is the action of keeping disease out of the herd, and also stopping the spread of any disease within the herd.
There are a number of important elements in a successful biosecurity plan. Separate new pigs before bringing them into your herd and monitor them for signs of disease. If pigs become sick, separate them and contact your veterinarian.
Don’t visit other swine farms. If you must visit another farm, take a shower and wash your clothing before and after your visit. Vehicles and tools can carry disease. Don’t share equipment with other farms and clean tools after use.
Limit visitors to your farm and reduce on-farm traffic as much as possible. Ask all visitors about recent travel outside the country. Do not let anyone who has been in an ASF-affected country onto your farm for at least five days after they enter the United States.
Garbage feeding laws
The Minnesota Board of Animal Health issues permits to people who feed food waste to livestock. In order to prevent the introduction and spread of diseases like ASF, the Board conducts routine inspections of farms which are permitted to feed garbage. All livestock on permitted farms must appear healthy.
Food waste containing meat or has come into contact with meat, must be cooked to at least 212 F (100 C) for at least 30 minutes. Cooked and uncooked food waste must be separated and stored appropriately. Rodents and pests must be kept away from uncooked food waste.
Feeding areas and trucks must be cleaned and sanitized as needed, and trucks used for hauling food waste over public roads must be leak-proof. Unconsumed food waste and dead livestock must be disposed of properly.
Feral swine are pigs which live in the wild. Feral swine pose a significant threat because they can carry dangerous diseases which the swine industry has worked hard to eradicate from domestic pigs.
Minnesota prohibits importation of feral swine, swine who were feral at any point in their lifetime and feral swine carcasses. There are exceptions for some processed products. You can contact the Board of Animal Health to learn more about import restrictions.
Know the signs
Producers can familiarize themselves with the symptoms of ASF. If pig caretakers see unusual health issues or unexplained deaths, they should contact the herd veterinarian immediately.
Some signs of an ASF infected pig include: fever; discoloring of the skin; loss of appetite; vomiting or diarrhea; difficulty breathing; weakness; or sudden death.
We’re currently in the swine exhibition season with pigs moving across the landscape to shows and fairs. Any pigs returning home to be with other pigs must be isolated for 14 to 30 days to ensure their good health. Unusual symptoms should be reported to the pigs’ veterinarian.
Dr. Cesar Corzo recently answered ASF questions from U of M Extension swine educators Sarah Schieck Boelke and Diane DeWitte and that can be heard at z.umn.edu/PodcastEpisode25.
Information for this article was sourced from University of Minnesota Extension, the U of M Center for Animal Health and Food Safety, and the Minnesota Board of Animal Health.
Diane DeWitte is an Extension Educator specializing in swine for the University of Minnesota Extension. Her e-mail address is firstname.lastname@example.org