Ports of entry, feed ingredients key in fight against deadly swine virus

African swine fever is tough, and infection with one strain offers little cross-protection
Published on September 25, 2019
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Imported animal feed can carry African swine fever virus and other pathogens devastating to swine herds.

Dr. Gilbert Patterson said those trying to keep pathogens out of U.S. herds can focus their efforts best by knowing which ingredients are most likely to contain viable virus and where they are most likely to arrive at a U.S. port.

Aerial view of the Port of Long Beach container yard
Federal agriculture authorities have warned that African swine fever could arrive through cargo or passengers.

"It's well documented: African swine fever does live in feed; it can be transferred to pigs by eating contaminated feed," he said. "An ASF outbreak is going crazy right now in China. It's got the U.S. industry on edge, very worried that it's going to come here, and we're trying to make decisions as to how to best mobilize our protection."

Dr. Patterson is a faculty member at Lincoln Memorial University College of Veterinary Medicine and the program manager and principal researcher for the college's Center for Animal and Human Health in Appalachia. In a session at AVMA Convention 2019 this August in Washington, D.C., he noted that feed ingredients and their containers have been implicated in the U.S. arrival of porcine epidemic diarrhea virus in 2013, and that virus killed an estimated 10 million U.S. pigs in the first year after arrival.

African swine fever can wipe out entire herds, killing some pigs without causing clinical signs. In addition to fever, ill pigs can develop vomiting, diarrhea, lesions, blotches, and breathing difficulties. The virus spreads through bodily fluids, ticks, and meat, and Dr. Patterson noted that previous research indicates it can remain viable during overseas shipments in feed.

Federal agriculture authorities have warned the virus could arrive through cargo or passengers.

Officials with the Department of Agriculture and Customs and Border Protection have increased searches of people and goods entering the U.S., and they have added Beagle teams that can find smuggled food at airports and seaports. USDA officials also have warned that people arriving from countries with ASF outbreaks should wait at least five days between arriving in the U.S. and visiting any sites with pigs.

Legislation introduced in July also would let CBP hire hundreds of agriculture specialists to meet a 700-person need, as well as provide money for more dog teams. At the same time, USDA officials have filled vacancies among veterinarians at ports of entry by having other veterinarians with the agency take on work in ports.

In a separate presentation at the convention, Dr. Chris Oura, who is a professor of veterinary virology at the University of the West Indies and a former ASF expert for the World Organisation for Animal Health (OIE), described the difficulty in protecting pigs once the virus reaches a country. He said the ASF virus has hundreds of proteins, and it is able to evade porcine immune systems.

"So, it's extremely large, extremely complicated, and extremely tough," he said.

The virus has been neglected by researchers, Dr. Oura said. At least 24 genotypes of the ASF virus circulate in Africa, and he said the pigs that survive infection with the strain circulating in China, for example, will have limited to no cross-protection against others.

"If we stand a chance, we might get a vaccine against that in the next 10 years or five years," Dr. Oura said. "But, then, you have to remember that there's all these waiting in Africa to come out, and that vaccine won't protect against those."

Dr. Oura described the virus's spread since reaching Spain and Portugal in the late 1950s, after which it was carried in contaminated pork products, reused syringes, and water sources to herds elsewhere in Europe and the Caribbean before it continued its human-aided spread to Russia and China.

The virus has become endemic in wild boars of Eastern Europe and Russia, and he thinks it will be endemic in wild pigs of Asia. But he said that ASF outbreaks that are identified early can be controlled.

On Aug. 22, officials from the Food and Agriculture Organization of the United Nations reported that about 1.7 million pigs had been culled in China to control ASF since August 2018, and more than 4 million pigs were culled in Vietnam since February. Dr. Oura cited reports out of China in saying the official death toll may be a substantial underestimate, and he said China had about 400 million pigs before ASF reached the country.

FAO officials also reported in May that Balkan countries were forming plans to combat ASF in wild boar and backyard pig populations. Those pig populations and the lack of a vaccine have hampered efforts to control spread of the disease.

Dr. Patterson said he analyzed the potential hazards in swine feed ingredients from other countries, using trade data from the U.S. International Trade Commission. He found more than 400 product codes that likely are connected with swine farming.

The volumes and sources of feed ingredients show the risk of disease introduction, he said.

Some of the viruses deadly to swine, including the ASF and PED viruses, survive well in soy products, Dr. Patterson said. The U.S. imported about 55 million kilograms of soy products in 2018. About 60% of that volume entered the U.S. at San Francisco, and another 25% came in through three ports: Seattle, Baltimore, and Los Angeles.

Kansas State University researchers recently found the ASF virus can survive a simulated 30-day transoceanic voyage in contaminated plant-based feed and ingredients, according to a university press release. The research team, led by Dr. Megan Niederwerder, assistant professor of diagnostic medicine and pathobiology at KSU's College of Veterinary Medicine, found that the half-life of the virus in feed ranges from about 10-14 days with exposure to the temperatures and humidity levels of a transoceanic shipment.

This means it would take approximately two weeks for the total viable virus concentration to decay by half its original count under shipping conditions. The study is available online in the journal Emerging Infectious Diseases.

Previous research identified which ingredients present higher risk of introducing ASF, he said, and his data show where those ingredients are most likely to arrive. Customs and Border Protection is responsible for 300 ports and about 415 ingredients that could be fed to swine, and this information could help agency officials decide where to send equipment or people, he said.

While Dr. Patterson focused his work on swine, he sees potential to use the same resources and tools to help reduce risks of pathogens affecting other species.

"I think it's got huge implications for public health, food safety, as well as food defense in terms of just knowing where things are coming in," he said.

Related JAVMA content:

Customs, APHIS inspectors needed at ports to meet growing demand (Sept. 15, 2019)

U.S. braces for African swine fever (May 15, 2019)