As avian flu continues its spread across the globe — killing nearly 60 million farmed and wild birds in the U.S. alone — researchers are keeping a close eye on the many other animal diseases with the potential to spark an outbreak in human populations. One possible threat is swine flu. For now, most cases occur at agricultural fairs but, like any zoonotic disease, the risk can change at any time.
What Is Swine Flu?
Crowded with animals and their waste, factory farms are especially conducive to the rapid spread of disease — a fact made all the more clear after recent mass avian flu outbreaks and resulting poultry culls. There are other influenza strains that originate in animals, including swine flu.
According to the CDC, swine flu is simply a variant of influenza that mostly infects pigs. While incredibly rare, humans can become infected. In recent years, most human infections of swine flu have occurred at agricultural fairs.
Throughout North America, 150 million people visit these events each year. Most infected cases are in animal exhibitors — the people with the closest and most prolonged interactions with pigs.
In 2012, Indiana experienced an eightfold rise in human swine flu cases tied to fairs over the course of just one week, with a 30-case outbreak in neighboring Ohio. That same year, an outbreak of 309 human cases ultimately led to the formation of a working group to recommend safety measures. Last updated in 2018, the guidelines are not mandatory, and may differ from regulations imposed by individual states and fairs.
Chief among the recommendations is to hire a veterinarian. Other guidelines include banning food or drinks in areas where people hold pigs, and — based on the findings of research led by Dr. Andrew Bowman of Ohio State University’s Department of Veterinary Preventive Medicine — limiting the duration of agricultural fairs to no more than 72 hours. Bowman, who has studied this topic for many years, said the restriction “can be the difference between a few animals catching the virus and most of them becoming infected.”
‘Assume Pigs Show Up at the Fair Infected’
On a CDC podcast, Bowman explained that “pigs at fairs are different from commercial swine” because they usually come from various locations and then are placed in close quarters together for a long period of time. It’s the “prolonged mixing of pigs and people” that spreads the disease — both between animals and from animals to humans.
Research of Ohio fairs found 22.6 percent of pigs tested positive. What’s more worrisome though, greater than 83 percent of infected animals were asymptomatic — making it near impossible to detect illness based just on observation. In further research, Bowman and others found evidence of “significant intra- and inter-species transmission.”
In yet another study, Bowman detected influenza A in 18.6 percent of air samples at agricultural fairs, and in 18.8 percent of surface samples. More recently, researchers detected flu in 13.9 percent of pigs at events known as “jackpot shows” that bring in pigs from longer distances and run for longer durations.
All told, agricultural fairs remain the leading hotspot for swine flu outbreaks in humans. “You have to pretty much assume pigs are going to show up at the fair infected with flu,” Bowman told The Frederick News-Post, after an outbreak in Maryland resulted in 40 human cases. Over 300 pigs were culled in Ohio that year.
Last August, 2 human infections of H3N2 swine flu were found among West Virginia fair workers. Just one month later, a case of H1N2 was reported in a Michigan fairgoer.
We May Be Underestimating All Strains of Influenza
The number of human cases of any influenza may be higher than we realize. Asymptomatic infections are common and there are other potential hotspots, like intensive agricultural operations. A 2020 study of large-scale European farms revealed 56 percent of facilities were host to influenza strains that could pass to humans. In that same research, 36 percent of pigs studied tested positive.
The BBC called the findings “a pandemic waiting to happen.”
Globally, over 284,000 deaths were caused by the 2009 H1N1 pandemic. While some believe the virus originated in pigs, other health officials strongly disagree. Still other researchers argue it began with strains found on U.S. factory farms as far back as 1998.
Regardless of the origin, the 2009 pandemic was severe — hitting infants, young children and the elderly the hardest — an estimated 80 percent of those killed were under the age of 65. Shots offered little protection at the time, and the U.S. saw 60.8 million cases between April of 2009 and 2010 — more than twelve thousand of which were fatal.
Today’s flu vaccines protect against H1N1 and other variants of influenza. Yet because the strain that became known as “swine flu” may not have originated in pigs, flu shots are “generally not expected” to protect against those particular strains.
Public Health Threat From Swine Flu, Explained
Health officials maintain there is little current risk of swine flu pandemic in humans. Just as with avian influenza, people who become infected with swine flu typically have direct contact with pigs.
Yet, according to the CDC, “limited human-to-human transmission” of swine flu is possible.
And there are other challenges. The U.S. public continues to underestimate influenza viruses writ large — think of the “COVID-19 is just the flu” narrative for instance.
Perhaps Americans pay little attention because the disease tends to disproportionately affect low-income nations and communities. Currently, India is facing an outbreak of H3N2, with more than 3,000 cases and at least 2 fatalities reported since January. The World Health Organization estimates 3-5 million severe cases of seasonal flu annually, and 290,000-650,000 deaths.
Ten years ago, the World Health Organization issued this warning: “the world is ill-prepared to respond to a severe influenza pandemic or to any similarly global, sustained and threatening public health emergency.” This statement came 7 years before the current coronavirus pandemic.
Since then, we’ve seen a dramatic uptick in pandemic risk — thanks in large part to how much meat we eat and its link to deforestation — yet little has changed to curb that risk. We haven’t done enough to prepare for future pandemics, public health experts warn, and on top of that, we’ve done nothing to change our global food system.
Jennifer is a writer and editor based near Washington, DC. Her background is in communications in the animal protection movement. She is also a contributing writer with Sentient Media.