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April 15, 2021

Swine veterinarians find disease lessons in COVID-19

Response to pandemic could influence responses to future swine diseases
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Updated April 1, 2021

When sow farm managers left COVID-19 safeguards unenforced, their employees increasingly disregarded those measures, Dr. Larry Coleman said.

Fellow swine veterinarians told him their clients were uncertain whether they needed to, for instance, mandate masks among employees or require social distancing in break rooms. When they added such measures, compliance by employees depended on leadership on the farms.

Indoor housing swine farm

In a presentation March 2 for the American Association of Swine Veterinarians annual meeting, Dr. Coleman, who is a swine practitioner in Broken Bow, Nebraska, said he repeatedly heard from veterinarians about their clients’ difficulties staffing sow farms during the pandemic. And he worries that the instances where employees didn’t comply with measures meant to protect them and their families could provide a warning about their future compliance with controls meant to prevent disease outbreaks in swine.

“It makes me shudder when I think about swine biosecurity measures because, if we let fatigue set in, eventually, we lose,” he said.

Outbreaks challenged farms

As of mid-March, Purdue University’s Department of Agricultural Economics estimated, about 500,000 farmworkers had developed COVID-19, including people working in animal and crop industries. In an article published in December 2020 in the Proceedings of the National Academy of Sciences, authors from Columbia University and the University of Chicago estimated livestock plants had been associated with 236,000-310,000 COVID-19 cases and 4,300-5,200 deaths.

Ahead of the AASV meeting, Dr. Coleman called 14 colleagues and, in what he describes as an informal survey, asked each what proportion of their clients had taken specific actions—such as mandating masks or adding hand sanitizing protocols—to protect employees on sow farms from COVID-19. Those veterinarians told Dr. Coleman about 37% of their client farms required face masks in spring 2020, and 19% did in the summer and fall. About 40% required physical distancing in break rooms in the spring, and 22% did by the fall.

“All veterinarians surveyed reported difficulties getting employees to comply with safeguards at work and home,” he said.

Between Dr. Coleman and his colleagues, their clients covered by the informal survey account for 30 swine production systems with 1.1 million sows, about one-sixth of the U.S. breeding herd.

Dr. Paul Yeske, veterinarian for the Swine Vet Center in St. Peter, Minnesota, and Dr. David Bomgaars, president and CEO of RC Family Farms, jointly described control efforts such as staggering worker shifts and breaks, monitoring employee temperatures, cleaning surfaces in offices, and increasing use of telemedicine.

“When we started to hear about the problems that were occurring around the country, never did we imagine—the first month especially—that slaughter capacity would soon be the biggest challenge that many of our producers and veterinarians had ever had to deal with,” Dr. Bomgaars said.

Outbreaks among slaughter plant workers in spring 2020 led to plant shutdowns and slowdowns, backing up production systems with pigs lined up for slaughter. Farms depopulated thousands of swine with no place to go.

Lee Schulz, PhD, associate professor in the Department of Economics at Iowa State University, said the backlog of hogs peaked in late May or early June, affecting 1.5 million to 2 million hogs. The pork industry reduced that backlog through early September.

Dr. Schulz said a report available this spring from the U.S. Department of Agriculture may show the extent of losses from depopulation. That report was unavailable at press time.

Testing, understanding reduce transmission

Kim VanderWaal, PhD, an assistant professor of population medicine at the University of Minnesota College of Veterinary Medicine, worked on a model that examined COVID-19 in three slaughter facilities. The results indicated the size of outbreaks in individual plants depended most on spread of the SARS-CoV-2 virus within the community and transmission rates within the plant. Although plant managers have little control over community infection rates, they can influence in-plant transmission rates by adding physical barriers and implementing other practices to reduce contact.

As testing revealed the extent of infections, she said, workers changed their behaviors and the infection rate plummeted.

In her presentation at the AASV meeting, Dr. VanderWaal said that, in the three slaughter plants examined in the studies, a typical worker infected early in the pandemic could be expected to spread the disease to two to four co-workers. But that rate rapidly declined as plants implemented safety measures and workers complied with protocols to prevent infections, plus people who had already been infected developed immune system protections.

Antibody testing added later also revealed far more workers had been infected than had been reported through disease-based testing, although the gap was smaller at the one plant that offered in-house COVID-19 testing. Those results, Dr. VanderWaal said, seem to illustrate the effects of asymptomatic transmission and differences in access to testing.

The model also found that conducting polymerase chain reaction–based testing on all workers every three days could reduce COVID-19 cases 25%-40%, whereas testing every seven days could reduce cases about 20%, and testing every two to four weeks provided little benefit.

Dr. Bomgaars also recounted working with public health officials to expand COVID-19 testing among slaughter plant employees, which he said helped build confidence they could return to work.

“Plants that kept harvesting near capacity took rapid steps both to decrease the spread and to show they cared for staff,” Dr. Bomgaars said.

The pandemic emphasized how important it is to understand and find effective ways to modify people’s attitudes and behaviors to reduce disease spread. These same concepts apply to getting producers to understand and use effective livestock biosecurity measures to halt the spread of high-consequence animal diseases.

Dr. Jack A. Shere, associate administrator, U.S. Department of Agriculture Animal and Plant Health Inspection Service

Disease responses improve

Dr. Jack A. Shere, associate administrator for the USDA Animal and Plant Health Inspection Service, said containing a disease of animals or people requires a fast, coordinated response. The USDA has been planning how to lead a response in case of an incursion of African swine fever, a viral disease that has devastated swine herds in Asia and Europe (see story).

In the response to COVID-19 and the slowdown in pork production, Dr. Shere said, members of some ASF working groups turned discussions toward how to find marketing channels for swine and depopulate when necessary. National Veterinary Stockpile funding paid for new mobile depopulation and disposal equipment, he said, and federal COVID-19 relief funding helped some swine producers pay for depopulation and carcass disposal.

“The pandemic emphasized how important it is to understand and find effective ways to modify people’s attitudes and behaviors to reduce disease spread,” Dr. Shere said. “These same concepts apply to getting producers to understand and use effective livestock biosecurity measures to halt the spread of high-consequence animal diseases.”

States also made great strides in improving disease testing and adding laboratory equipment that could be used in an ASF or foot-and-mouth disease outbreak, Dr. Shere said.

“If we can proactively identify and close the remaining gaps, particularly in the areas of biosecurity implementation and validation of mass depopulation and disposal protocols, we can better be prepared for the next threat,” he said.

Dr. VanderWaal said the worker protections added inside slaughter plants in response to COVID-19 could help protect workers against not just the pandemic but also seasonal colds and influenza.

“I do think that some of the additional practices and measures that have been put in place at these plants should help reduce the transmission of other respiratory diseases and also promote a healthier workforce,” she said.

Dr. Coleman, who himself developed mild COVID-19 in early May 2020 after working closely with an infected swine farm employee, sees a need for leadership in response to diseases on farms, whether they affect animal or human health. That leadership determines whether employees see the disease as a threat, he said.

“It’s not so much about making rules as it is making sure leadership drives home the message of what is really a threat and what isn’t a threat—and then trying to really control things that are controllable,” he said.

Ventilation shutdown on AVMA delegates’ agenda

In spring 2020, slaughter plants closed or reduced production to contain COVID-19 outbreaks among workers.

The resulting loss of production led to backups on swine farms, leaving too little room for both growing pigs and pigs ready to be sent to slaughter. Among pork producers who decided to depopulate excess swine, some opted for ventilation shutdown: sealing a barn, often with added heat, steam, or carbon dioxide, to kill the animals through suffocation and hyperthermia.

This summer, members of the AVMA House of Delegates will consider a resolution to amend the AVMA Guidelines for the Depopulation of Animals to list ventilation shutdown as “not recommended,” effectively discouraging its use under any circumstances. The current guidelines say ventilation shutdown may be used only under constrained circumstances and describe it as a method of last resort.

“The most compelling reason to use VSD when all other methods have been ruled out is that, when done properly, it may provide a quicker death, potentially eliminating the chance for the animals to die over a longer period of time from distressing and devastating disease,” the guidelines state.

The delegates will consider the resolution during their regular annual session, held July 28-29, ahead of AVMA Convention 2021.