As the world swine population continues to grow both domestically and internationally, it can open doors to producers and veterinarians to visit production locations away from home. In some cases, this may involve going to a location which is known to have diseases that are not present in the United States. Knowing this, it is good to review biosecurity measures that can be taken to minimize risk of pathogen transmission and keep our borders safe. On this topic, we all stand on common ground; to protect our USA national swine herd from 4 viruses we are free of: ASFV, HC, PRV and FMD.
Although there are a number of foreign animal diseases (all noted above) circulating in other nations and swine populations, the one that is at the forefront of today’s news headlines is African Swine Fever, or ASF. In China, the first case of ASF was diagnosed in the beginning of August, and since then, over 50 cases have been confirmed by the government with over 500,000 pigs having been euthanized thus far. Only by understanding the risks and transmission of this pathogen can we keep this virus outside of our borders. Specifically, the risks from highest to lowest of harboring and transmitting ASF are blood, meat, direct pig contact, and mechanical vectors such as shoes and clothing. Proof of concept investigations also indicates that feed and feed ingredients need to be considered as risks and may be added to the above list. More on this later in this article.
European Studies have shown that ASF has the ability to survive and remain viable in blood for over 4 months, and depending on the storage temperature of processed meats, up to 300 days. With this in mind, it is incredibly important that any meat products imported from an ASF positive nation are screened or entrance prohibited to minimize the risk of transmission to the United States. Prohibiting international farm workers from consuming pork on site from a source other than the on-site farm will decrease the associated risk of transmission. All other food items entering farms should be sourced from grocery stores and not wet markets that hold the potential of containing multiple species present from multiple sources, sometimes which are processed together.
On the perspective of blood, a single drop of blood from a pig infected with ASF can contain over 6 logs of a virus- more than enough be the nidus of infection for a population of naive pigs. Therefore, using a disinfectant known to inactivate the ASF virus such as Virkon or 2% sodium hydroxide on contaminated surfaces will prove helpful in reducing the risk of mechanical transmission through blood. When performing necropsies, one must take extra precautions to decrease bodily contamination and spread of this virus by using proper cleanup and disposal methods of any carcass.
Regarding fomites and international travel, there are many ways to decrease risk, with the first being establishing clothing and shoes that are only used for (international) travel. Any clothing items that are taken overseas when returning to the US should be washed immediately in hot water and dried with hot air to kill any pathogens that may be present. After cleaning, they should be separated from the rest of a wardrobe as an additional layer of biosecurity. In addition, upon arrival back home, all objects that have been taken to China including a computer, phone, chargers, and anything else, are all wiped down with disinfectant wipes immediately after arriving home. After items have dried one time, all items are wiped down a second time and left to dry fully. The National Pork Board recommends a minimum of 48 hours of downtime after international travel before returning to a farm in the United State; https://library.pork.org/media/?mediaId=371C9B8F-E590-4850-B4C74439D76F6999
Many groups, including Pipestone, would include a safety factor of additional nights using a minimum of five nights as the protocol for returning from a trip overseas after visiting any swine farm.
Finally, one topic that has not been mentioned up until this point would be the idea of responsible importation. Based on research that Dee et al. have completed in 2018 on the survival of feed ingredients in shipping models across the Atlantic and Pacific Oceans, there is an understanding that a number of viruses, including ASF, are hearty enough to survive a trans-oceanic journey. With this information, an equation can be generated for imported feed ingredients to estimate the need of an additional storage period based on The necessity of the proposed import, the estimated contamination level at the source, the complete transport time from source to mill, and if effective mitigants are available. The research also provides details on half-lives of various viruses in these different feed ingredients. With the knowledge that an ingredient sourced internationally could potentially be contaminated with virus, one of the main mechanisms for reducing the risk of entry into a US herd would be to enact a voluntary downtime period to allow for the virus concentrations to decrease below the levels that would permit oral disease transmission, please see: https://library.pork.org/?mediaId=7EC4E922-752C-4151-82A6CE7CCEB6B37A Only by everyone in the industry understanding the risks and repercussions of a foreign animal disease in the US and doing their part to prevent it can we continue to keep our national swine herd free of ASF and other FADs.
In closing, for all producers, now would be a good time to confirm that you have the correct phone number and contact information of your respective state and local veterinarian, so in the event of any alarming clinical signs, an investigation can be conducted as soon as possible to confirm a diagnosis.
Joseph Yaros, DVM