In recent months, meatpacking companies in different parts of the world have been associated with large clusters of COVID-19 infections. The Tönnies meat-processing plant in North Rhine-Westphalia, Germany, was temporarily closed, and U.S.-based pork processor Smithfield became a major focus of the disease in South Dakota, one of the country’s least-populated states. In Brazil, complaints abound about COVID-19 at slaughterhouses: 20% of the industry’s workers have been infected, according to the National Confederation of Workers in Food and Related-Industries (CNTA).
These outbreaks, along with China’s global leadership as a pork producer, caught the attention of three researchers who started looking into the matter: Larissa Mies Bombardi, a geography professor at the University of São Paulo (USP), German pharmacist Immo Fiebrig, and Pablo Nepomuceno, a technician at USP’s Laboratory of Remote Sensing and Geoprocessing.
In two papers, they show the spatial correlation between increasing numbers of COVID-19 infections and intensive pig farming in Brazil, the U.S. and Germany. They also put forward a hypothesis, still unproven, that the current agriculture model, specifically industrial pig farming, may favor the spread of the virus, with the animals as contamination vectors. “This is a hypothesis, but the spatial correlation is very high,” Bombardi says.
They presented the state of Santa Catarina, which accounts for 25% of Brazil’s pork production and a high COVID-19 infection rate, as evidence in their first paper. The low population density in the state’s western region, compared to the more crowded coastal area where infection rates are high, should have slowed the spread of the coronavirus inland. But that wasn’t the case.
“The novel coronavirus is moving to smaller towns in Brazil, and that is highly connected to meatpackers,” Bombardi says. “This has to do with two things: unhealthy human labor and poor conditions in pig farming.” The paper warns about untreated pig excrement entering into water bodies, posing the risk of infecting drinking water and spreading disease. “Testing pigs’ waste would be crucial,” Bombardi says.
The spatial correlation between COVID-19, pig farming and low population density found in Santa Catarina is repeated in the other states in southern Brazil, a region that accounts for 66% of the country’s pork production. The same pattern is seen in the United States. Northwest Germany, which has the highest pig production in the country, repeats that spatial correlation but with a higher population density, unlike the other two countries analyzed in the second paper on the topic.
The widespread theory that the SARS-CoV-2, the virus that causes COVID-19, spread from a wet market in Wuhan, China, was challenged in research published in May. According to that study, the virus had been circulating in China before that, and the first animal-to-human transmission occurred before the outbreak linked to the Huanan market. Experts from the Wuhan Institute of Virology (WIV) also said the initial transmission of SARS-CoV-2 did not occur at the Huanan market, which served instead as the site where it was further disseminated. Scientists have also discounted the theory that the virus was genetically engineered in a lab and then somehow got out.
What many experts do believe, though, is that there was likely an intermediary host between bats, where the virus is suspected to originate from, and humans. China is the world’s largest pork producer, and Hubei province, where Wuhan is located, is one of China’s five largest pork producers.
“There are many similarities between pigs and us, from the respiratory system to the gastrointestinal system,” Bombardi says. Pigs can catch the avian flu virus and human influenza virus at the same time, and then engender novel combinations that can be transmitted again and infect human beings.
This happened in March 2009, when a flu including respiratory infection appeared in an area close to an industrial pig farm in Mexico. The following month, the World Health Organization (WHO) declared the H1N1 swine flu pandemic.
A recent study published in the journal Proceedings of the National Academy of Sciences (PNAS) describes the analysis of influenza viruses found in China’s pigs between 2011 and 2018. They include a version of H1N1 with potentially pandemic characteristics. According to the study, the virus poses no imminent threat, but scientists have called for urgent, rigorous monitoring of the virus and human populations, especially pork industry workers.