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May 01, 2020

Guarding against an outbreak, expecting its arrival

Swine veterinarians describe strategies in expected fight against African swine fever
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Swine veterinarians have watched for more than a year as the viral outbreak of African swine fever spread through China and its neighbors.

Dr. Clayton Johnson, a partner and veterinarian with Carthage Veterinary Service in Carthage, Illinois, has spent time on affected farms in China.

“I don’t feel comfortable that we’re going to find ASF quickly when it gets into the country,” Dr. Johnson said. “The first cases will die before we diagnose it, I’ve no doubt about that.”

Veterinarian examines pigs

Dr. Johnson, who described biosecurity strategies during a lecture at the American Association of Swine Veterinarians meeting in March, expects any outbreaks in the U.S. will be tough to end. Maintaining trade may require designating only certain areas of the U.S. as free from the disease.

“I think, unfortunately, regionalization may be a concept coming to the United States at some point, as much as I would love to say we’re going to eradicate it, stomp it out right away,” he said.

Dr. Johnson noted the virus is spreading in Asia and Europe. Russia has had some of the best success in containing the virus, yet the country still has outbreaks on more farms every year, he said.

“When we lose ground to ASF—when we lose a country—we don’t get it back, right?” Dr. Johnson said. “How many times have you heard of a cleanup story that’s been successful? We are only adding to the list of active countries.”

Biosecurity for pigs, people

But Dr. Tim Snider, health director for breeding company PIC’s operations in Europe, Russia, and Africa, indicated Belgium and the Czech Republic seemed to be containing outbreaks among their feral swine. In written remarks read by a conference moderator, as well as in his conference proceeding notes, Dr. Snider said those countries’ experiences indicated the degree of challenge in controlling an outbreak depends, in part, on the size of an affected area and its proximity to high-density swine farms. Both factors raise concerns about an ongoing outbreak in a region of Poland near high-density production units in Poland and Germany.

Dr. Snider, who is based in Spain, was unable to attend the meeting because of travel restrictions from Europe related to COVID-19.

The AASV hosted this year’s meeting March 7-10 in Atlanta, soon before public health officials responded to the viral pandemic with warnings against social gatherings and the federal government declared a national emergency and halted entry from Europe. The AASV meeting organizers designated the meeting a handshake-free zone.

The viral disease threatening swine emerged in 2007 in the Caucasus in Georgia. It spread through wild boar and domesticated pigs in Eastern Europe and Russia.

The virus then emerged in 2018 in China. The Food and Agriculture Organization of the United Nations indicated at least 10 more countries in Asia have since developed outbreaks, including Vietnam, which had outbreaks in all 63 provinces and culled about 6 million pigs.

I don’t feel comfortable that we’re going to find ASF quickly when it gets into the country. The first cases will die before we diagnose it, I’ve no doubt about that.

Dr. Clayton Johnson, swine veterinarian with Carthage Veterinary Service in Illinois 

On March 5, Reuters reported that cover-ups, denials, and downplaying hindered China’s response to the ASF outbreak and aided the spread of the virus. The report indicates ASF may have shrunk China’s 440-million hog herd by more than half.

Staying vigilant

Dr. Clayton Johnson expressed worries veterinarians could become complacent while the virus keeps spreading into more countries. Porcine epidemic diarrhea and porcine reproductive and respiratory syndrome still circulate among U.S. herds, showing the swine industry has gaps in biosecurity, he said.

Pork production companies reduce their risk, he said, if they prohibit workers from bringing pork in their lunches, provide those workers shoes and clothes to be worn only inside barns, and make international visitors wait days between arriving in the U.S. and visiting farms. The common expectation is visitors will wait five nights, he said, but he noted a lack of research on that number.

Dr. Johnson wants to see U.S. veterinarians fight African swine fever in other countries, rather than wait to fight it at home. After the meeting, he said veterinarians’ roles can include defining protocols, training farm workers, auditing farms, describing actions to correct deficiencies, and supervising on farms when the risk is highest.

One lecturer described ASF virus sampling at Vietnamese feed mills, where test results identified the virus in truck cabs, a driver rest area, and a cloth shroud that hangs down from spouts where feed bags are filled. Others described limited biosecurity in transportation in the U.S., efforts to improve truck washes and keep drivers from spreading disease, and protocols that heat trucks to kill the virus.

Philip C. Olsen, consultant to the water treatment industry through Water Think Tank LLC, said viruses on the ground surface slip through the 0.5- to 0.8-micron openings between particles of silt and clay with room to spare. Rain carries them in cascades into groundwater aquifers, where they migrate in concentrated plumes, and can remain viable up to three years.He has helped farms install smaller-scale versions of the water treatment systems used by cities.

Meeting attendees said they also have worked to reduce the risk on farms.

Dr. Jenna Scott, a veterinarian in Trenton, Missouri, and colleagues are working to improve biosecurity by, for example, reducing movements between areas on farms. That includes defining lines of separation, adding buffer areas, and reinforcing those separations with added signs—interventions that also fight PRRS.

Dr. Michael Mohr of Blomkest, Minnesota, said he was at the meeting to learn how to better keep farms and businesses secure from ASF. He noted lectures he attended on using ultraviolet light as a disinfectant and seeing how debris and potential contaminants move across the areas where farm employees move swine.

Dr. Lucas Pantaleon, who advises veterinary industries through his company, Pantaleon PLLC, said veterinarians can help the most by teaching people to follow biosecurity protocols.

Viruses in feed

In 2013, porcine epidemic diarrhea emerged and began spreading across the U.S., killing about 10% of the U.S. swine herd within a year, said Dr. Megan Niederwerder, an assistant professor at Kansas State University. That virus uncovered a vulnerability to viruses spread through feed, she said.

“When we think about feed as a potential transboundary viral disease vector, we first have to think about those risky agricultural practices that may put certain feed ingredients at risk for being contaminated,” she said.

American farms import millions of kilograms of feed ingredients from countries with circulating animal diseases foreign to the U.S., she said.

Dr. Niederwerder’s research team used meteorological data and environmental chambers to simulate combination ocean-crossing and overland voyages of contaminated feed ingredients and other materials shipped from Warsaw, Poland, and Beijing to Des Moines, Iowa. The results showed African swine fever and pseudorabies viruses remained viable in most substances tested.

In further study results, Dr. Niederwerder’s team calculated estimated half-lives for virus in nine feed ingredients, finding they ranged from 9.6 days to 14.2 days. Her team described those findings in a December 2019 issue of Emerging Infectious Diseases. Dr. Niederwerder thinks protein, fat, and moisture content of certain ingredients might help viruses remain viable.

“The feed ingredients, all of them that we tested, actually enhanced viral stability,” she said. “The half-lives were all longer in the feed ingredients that we tested compared to the media that’s used in a laboratory setting for cell culture.”

Reducing the viable virus by 99.99% requires 13 half-lives, or 125-168 days. By those figures, depleting the virus by that much requires that farms or feed mills hold untreated feed ingredients up to six months after they depart from Poland or China.

Dr. Scott Dee, research director for Pipestone Applied Research, is leading a team evaluating 15 products that may reduce viral loads in feed ingredients. He said in a lecture, 14 of 15 products seemed to reduce the amounts of viable virus in feed or stimulate immune responses.

Using pig feed contaminated with a mixture of PED virus, PRRS virus, and Senecavirus A, some of the mitigants reduced or prevented deaths, whereas a control group had a 6% death rate. Further studies could validate holding times to reduce virus viability.

In an interview after his presentation, Dr. Dee said some ingredients—such as fat-soluble vitamins—are time sensitive and could decay if they are held for extended periods to reduce infection risk. He also said some of the products under testing can require precise formulations to remain palatable to pigs, especially products containing formaldehyde.

Diagnostics, vaccines

On March 24, Department of Homeland Security officials announced they developed the first field-use test that identifies ASF virus DNA in pigs and pork—whether the samples come from oral fluid, blood, muscle tissue, bone marrow, or spleen tissue. The product is a collaboration of researchers with the federal Plum Island Animal Disease Center and MatMaCorp of Lincoln, Nebraska.

And days before the AASV meeting, a research team reported in Science China Life Sciences it had developed a promising gene-deleted ASF virus vaccine. Investigators wrote that the candidate is safe and effective.

One of Dr. Dee’s co-workers at Pipestone Veterinary Services, Dr. Joseph Yaros, said in a lecture that he has visited his company’s operations in China about 20 times since 2017. He said vaccines available on the black market in China, at $5-$20 per dose, might save half a herd.

“That sounds like not necessarily that effective,” he said. “But if you consider, today, a weaned pig is worth $285 and that the margin of profit per finishing pig is more than $420, there’s a lot of opportunity to make a substantial profit in China.”

Some farms had luck with a “tooth extraction” strategy: isolating pigs that might be sick for testing, euthanizing those positive for the virus, and keeping the herd alive without more infections. Some farms in China take extraordinary measures to keep the disease out, such as making staff live on the farm for months and bathe in disinfectant, Dr. Yaros said.

“ASF is going to be in China for a very long period of time,” he said. “Unless there was a vaccine that’s going to be 100% effective, I don’t necessarily see how it’s going to get out of China.”


Researchers map ASF genome

Researchers in Europe have mapped the transcriptome—the initial products of genome expression—of the virus that causes African swine fever in pigs, raising hopes of controlling the disease.

A report published online Feb. 19 in the Journal of Virology by scientists from the University College of London, the Pirbright Institute in England, and the University of Warsaw in Poland indicates their study found new genes and uncovered the order in which genes of the virus are activated, giving information that they think could aid antiviral drug development, according to an announcement from the Pirbright Institute.

ASF kills 90% of affected pigs and is spreading among domestic and wild pigs in Eastern Europe and Asia. Its 2018 emergence in China alone killed millions of pigs, with some reports estimating the disease cut the country’s previous pig population of 440 million in half.

Alhough the U.S. remained free of the virus as of this spring, swine veterinarians predict it’s arrival is imminent (see above).

The study results published in February indicate the ASF virus has complex, mammal-like gene controllers, using specific promoters to have RNA polymerase express genes at different stages of infection, according to an announcement from the University College of London. The study also identified 30 novel genes, it states.