Know the feed risk factors for African swine fever

As African swine fever (ASF) continues its insidious spread through China and surrounding countries, the need to keep it out of US herds becomes more imperative.

So far China has lost more pigs than are produced in the US, and analysts predict the death loss is likely much higher.

Although the ASF virus doesn’t affect humans, it’s deadly to pigs. Megan Niederwerder, DVM, PhD, a veterinarian and virologist at Kansas State University, has been researching foreign animal disease (FAD) risks associated with feed ingredients.

And she’s in the right spot to do it: Not only does Kansas State University have valuable resources, but the Biosecurity Research Institute in Manhattan, Kansas, allows researchers to work directly with FADs, including the currently circulating strain of ASF — Georgia 2007 — in a safe and secure laboratory.

Niederwerder says that previous research and epidemiological investigations linking feed to the transmission and spread of porcine epidemic diarrhea virus laid the groundwork for follow-up work on ASF. Her latest study focused on understanding the minimum infectious dose required for infection through feed as well as through contaminated liquid.

“We found that the [ASF] virus could be easily transmitted through the oral route, with higher doses required for infection in feed,” Niederwerder said in a presentation at the American Association of Swine Veterinarians conference.

“Another aspect of the study was the use of statistical modeling to predict the likelihood of infection if the pig had repeated exposures.  We believe repeated exposures over time are more realistic of what would happen in the field if, let’s say, a contaminated batch of feed was delivered to the farm. We found that with each feed exposure, the likelihood of infection increased.”

Preventive measures

With imported feed as a known risk factor for transmitting ASF, the next steps include preventive measures to help reduce that risk, Niederwerder said.

In collaboration with Scott Dee, DVM, PhD, with Pipestone Applied Research, and Diego Diel, DVM, PhD, with South Dakota State University, Niederwerder has utilized a transboundary model that helps researchers and producers understand which feed ingredients actually support virus survival.

Based on that model and through additional work, Niederwerder said researchers are developing data with regard to half-life of viruses and how they degrade over time. Viruses can survive for longer periods in cold temperatures, she explained. She and other researchers hope to provide additional recommendations on storage time based on holding temperature.

Hold times can greatly reduce the level of virus, but there’s still a measure of risk.

“There are several mitigation strategies that we can implement to reduce the risk of virus transmission in feed,” she said. “The more knowledge we gain about ASF virus stability and transmission in feed, and the more procedures we put in place based on this knowledge, the more we can continue to reduce the risk with feed-related biosecurity protocols.”

Management measures to protect your herd

One of the first measures producers can take is to know where their feed ingredients are coming from, Niederwerder said. Feed ingredients have global distribution, so understanding this factor and knowing which FADs are circulating in the countries of origin are important to reducing risk. She said it’s also vital to understand and incorporate best-management practices related to the personnel who manufacture, process and handle the feed, to reduce the risk of feed serving as a transmission vector for diseases into a farm.

“We need to consider the processing procedures for each ingredient and what ingredients are more likely to be contaminated versus others, since some agricultural practices [such as drying and threshing grains] will increase the likelihood of contamination for certain ingredients,” Niederwerder said.

“In the US, we should consider mitigation tools such as chemical mitigants, storage time and heat treatments,” she added. “We’re still learning about how the virus survives in feed, but utilizing tools and solutions once the ingredients arrive into our country will help reduce this risk in feed.”

The next steps are to understand the effect of chemical mitigants on the ASF virus in feed and feed ingredients, Niederwerder said, but it’s not all about ASF.

“We’re also doing research on other foreign animal diseases of concern to the swine industry, including classical swine fever virus and the Chinese variant strain of pseudorabies, to understand how these viruses survive in feed and feed ingredients using the transboundary model,” she added.

Other risk factors to watch

Feed contamination is a major concern because feed is present on farms, but the illegal importation of contaminated pork products also is a major risk. The federal government and the US Customs and Border Patrol are aware of the devastation that would occur should ASF enter this country. They’ve become more vigilant with stepped-up efforts to identify and confiscate illegal products.

Niederwerder said she isn’t aware of research thus far on items like coveralls or boots that may be imported from China and used on farms, but she has demonstrated that the ASF virus can survive in pet foods subjected to transboundary environmental conditions.

The bottom line is to become hyper-vigilant on all aspects of biosecurity as the industry works to keep ASF out of the country.

“Producers should be thinking about how diseases may be introduced into the herd, not only through feed but through all known introduction routes,” Niederwerder said, adding that the industry must be vigilant in understanding the critical science of FADs.

If producers can recognize and investigate health abnormalities as quickly as possible, their veterinarians will be able to diagnose FADs before they have a chance to spread.