Researchers said this certainly underestimates the actual number because standard flu tests cannot detect infection with the mutant virus. Most infections fail without further human transmission, probably because humans have strong immunity to similar influenza viruses.
However, if the pig virus appears and is easily spread in humans, it can trigger a pandemic. "It's as real as any zoonotic threat," said Martha Nelson, an evolutionary biologist at the National Institutes of Health, who has worked with Bowman for seven years.
has occurred before the epidemic. Nelson, who works at the National Center for Biotechnology Information at the National Institutes of Health and also studies highly deadly avian flu, is part of a team that found convincing evidence of , which proved that the 2009 flu pandemic infected hundreds of millions of people around the world, began with a new flu virus jumping out of commercial pigs on farms in central Mexico.
Although many epidemiological organizations believe that viruses from birds triggered three flu pandemics in the 20th century, including the infamous flu pandemic that began in 1918 and killed about 50 million people - but some believe that pigs may be the key intermediary between birds and humans.
"While people want to downplay it, I think the risk of a pig-to-human flu pandemic is much greater than that of avian flu ," said Gregory Grey Gray, an epidemiologist at the University of Texas Medical Division.
Concerns about the next pandemic are often concentrated in Asia, where markets sell live poultry and exotic animals such as palm civets, raccoon dogs and bamboo rat .
To assess this risk, Bowman and his colleagues have become regular visitors to exhibitions and fairs across the country. To win the trust of sometimes alert organizers and contestants, the researchers visited about 1,000 events and collected samples from about 40,000 pigs to analyze them for clues about how the novel influenza virus spread through performance circuits and the shuttle between pigs and people.
From their more than 20 studies, “we have learned a lot about how swine flu spreads in that particular niche,” said Richard Webby, a virologist at St. Jude Children’s Research Hospital.
Bowman and Nelson are also designing simple steps to protect pigs and people, including testing entrants and limiting pig-to-person contact. “Our goal is to try to figure out how to make small tweaks throughout the system, which will have a huge downstream impact,” Nelson said.
Pigs occupy a special position in the influenza ecology . Two types of influenza viruses, A and B, make humans sick, and as many as 650,000 people died worldwide in a bad year. Influenza B virus only spreads in humans, but type A can infect many species.
Waterfowl has the most diversity , with 16 varieties, one surface protein hemagglutinin and nine other neuraminidase , leading researchers to conclude that waterfowl is the main influenza A host.
The seasonal influenza A virus that is frequently infected with humans today is limited to variants of the H1N1 and H3N2 subtypes. But other type A viruses often spread to poultry, horses, dogs and pigs.
As the virus spreads, it will change and continue to bring new challenges to the immune system. One source of the change is its highly variable RNA genome, allowing “drift” during each round of viral replication. But influenza has another strategy to accelerate its own evolution. Viral RNA is divided into eight fragments that can be exchanged between relevant subtypes.
So if one type A virus enters human cells that have infected another virus, their two genomes can be mixed as they replicate. This recombination or "transfer" produces viral progeny with RNA fragments from both strains.
Drift forces vaccine developers to launch a new vaccine every year to fight the spread of seasonal flu.When metastasized viruses appear from animal hosts, these changes can sometimes greatly enhance transmission and increase immune escape, and may even trigger a pandemic. “The flu is an acrobat,” Nelson said. "You have to think from eight dimensions.
pigs are the main place for these acrobatics. When infected with pigs, avian influenza virus can reclassify viruses that are already in pigs that are more likely to infect humans. The result may be a new strain, not related to the human immune system, and spread more easily in the human body than the original bird virus. A series of troubles like
started in 1979, when a bird influenza H1N1 virus in Europe from Wild ducks spread to pigs. Decades later, after jumping from Mexican pigs to humans around March 2009, some of its genes were found in H1N1, which triggered the 2009 pandemic.
Just five months after the virus known as pH1N1 surfaced, the Minnesota expo showed the pig's nasal swab highlighted the threat of cross-species transmission by showing that 12% of animals were infected with the virus. This time, humans infected pigs. When the then Minister of Agriculture Tom Vilsack (Tom Vilsack) reported pig infections at the show, pork prices plummeted.
"The industry was very angry with us," said Gray, who led the study at the University of Florida . "We were just doing science, but it got very fast politically. "
The risk of the flu virus with pandemic potential spreading to humans through bird-infected pigs remains as real as ever. However, large commercial farms that raise thousands of live pigs may not be the biggest threat.
In large farms in the United States and many other countries, bioprotection measures limit human-pig contact, Pig veterinarian James at the University of Illinois at Urbana-Champaign Lowe said he studied flu in commercial pig herds. Instead, he was worried about shows like the Expo where young trainers compete for belt buckles, banners and ribbons because they raised the best-looking Duroc , Hampshire , Landress, Berkshire or hybrid pigs.
2009, Bowman has worked as a pest veterinarian at Ohio 2019. Bowman was , an ovarian school professor at at Oregon State University, contacted him and asked if he was considering coming back to pursue his PhD, focusing on testing flu display pigs at the fair.
Bowman hesitated to go back to academia, but the challenge attracted him. "We don't know what happened to the flu and these pigs," he said.
Initially, his request for nasal swabs to collect at the pig show was met with a lot of suspicion. "Worried that we would use this information and close them," Bowman said. Others were worried that the swabs would somehow hurt the pigs and cause the judges to "show them the door" -- the lingo that was eliminated.
"Of course we have, my pigs Will win until you wipe its nose,'" Bowman said. Early on, he took samples in the middle of the night to avoid conflict.
pig nose carries the flu virus
but the scientific value of this work is undisputed. In 2012, the CDC recorded 307 cases of human infection with mutant influenza strains, the highest number in a single year, most of which were related to the agricultural fair.
"Suddenly, I took all these samples from county fair pigs and we had all these kids infected with pig lineage flu at the same fair we attended," Bowman said. "It's the case that I was in the right place at the right time."
In 2012, many human cases occurred in Indian , and the following year, organizers of the state fair asked Bowman to wipe the nose of the pigs entering to better understand how many pigs were infected at the beginning. Organizers also measured the pig's rectal temperature, slowing the speed of entry into the exhibition venue and angered exhibitors, who mistakenly accused Bowman. The complaint reached Indiana governor and the National Pork Commission.
Nevertheless, Bauman slowly convinced more and more exhibition organizers and exhibitors that their love for display pigs is not far from his research, which aims to educate people and reduce diseases of animals, processors and visitors. "They are a blessing," said Kelly Morgan, a teacher at Columbus , who organized the jackpot show and raised about thirty display pigs with her family.
Bowman is "a solid veterinarian, a solid scientist, a pig man, so he was able to bridge the gap," said Luo. “What he achieved, building relationships with the population, allowing him to access the website and do this data collection was a miracle.
Bowman and Nelson talked for the first time at the influenza research web conference organized by the National Institute of Allergy and Infectious Diseases (NIAID) in 2015. “In the first few minutes, we realized that our interests were as appropriate as gloves,” Nelson recalled.
She has been studying the evolutionary origins of the mutant virus that led to the human outbreak at the 2012 show, but she only has samples of commercial pigs. “I salivated when I found someone tasted a show pig myself,” she said.
Since then, Bowman’s practical expertise in pig sampling is combined with Nelson’s core focus on the evolutionary biology of the virus they found. As Lo said, “Martha can’t do what Andy does, and Andy can’t do what Martha does.”
The resulting study of transmission between humans and pigs is "totally different levels", says Elodie Ghedin, who conducted parasite genome studies at NIAID. "These are very important studies to understand the dynamics and understand what happens every year. The first study by Bowman and Nelson was published in January 2016 in Journal of Infectious Diseases , which used the gorgeous family tree created by Nelson from Bowman's virus samples to track the four seasonal cycles of virus movement between pigs and humans.
It began in winter when the seasonal flu virus spreads among people and occasionally infects pigs. On small farms , human pig infections will soon disappear. But when humans infect commercial herds, this is still happening despite bioprotection measures, with the virus moving between animals and reclassifying throughout the spring.
They can then spread to pigs in different pig houses on the same property, and even through the wind to neighboring farms. By the summer, when the display pigs gathered in the exhibition, the human flu season was over. But pigs are prone to infect each other, leading to new recombinant viruses and occasional human infections of mutated influenza viruses.
"If there were no commercial pigs, there would be no flu virus in the pigs," Nelson said. Bowman's huge order Leku also lets them see that jumps from commercial pigs to display pigs can happen many times a year. "In performance pigs, the genetic diversity of influenza viruses is amazing because their populations are so small and only gather in large quantities during the short summer performance season," Nelson said.
Meanwhile, as Nelson and Bowman reported in December 2016 in the Journal of Virus , animals sometimes carry the same virus in exhibitions in distant counties and states. "It's a A headache-inducing moment, we realized there must be something else spreading these viruses so quickly between fairs,” Nelson said.
Big Prize shows like the Fair are key to spreading these viruses, Nelson and Bowman realized. Pigs at county fairs must come from the county, and the same geographical restrictions apply to state fairs. But the jackpot shows attracted contestants from all sides.
To understand how they affect virality, researchers participated in an early exhibition in Iowa , which hosted exhibitors from 17 states. They wouldn't name the show to avoid humiliating it.Four different flu viruses spread on the show, one of which accounts for 80% of pig infections.
When the pigs in the show were scattered into their hometown, they carried the virus with them. Through later sampling, researchers found swine flu at markets in 38 counties and states, with 94% of the variants dominating the jackpot. This variant also led to 90% of influenza cases associated with humans that year. The
fair, rather than the grand prize show, is where the pig variant is most likely to jump to humans. Although Bowman’s team’s sample survey over the years only detected flu in about 30% of exhibitions, the exhibition usually lasts longer than 80% of the jackpot shows. Therefore, the market starting with infected pigs will eventually end up with up to 80% of pigs infected, a prevalence rate far higher than the jackpot show.
There are more people interacting with pigs at the market, increasing the risk of zoonotic jumps. “You’re going to see human cases usually have to do with the end of the fair because if you have 250 pigs that get out of the virus, it’s just a ball of flu,” Bowman said.
Bowman, Nelson and others say that in order to reduce the risk of to humans, it should be standard to conduct regular testing of exhibition pigs that only account for 1.5% of the American pig herd. But there is no such "active monitoring" plan. Instead, the United States has a passive system that relies on farms to sample sick pigs and then voluntarily report their findings to Agriculture Department .
Bowman has convinced several pig show organizers to stop the children from sleeping near their animals. During a show, the children hang hammocks on their precious pigs. In the vendor hall of this year's expo, Bowman's team set up a station to directly educate children to reduce the spread of influenza.
The project was launched seven years ago by his collaborator Jacqueline Nolting, who holds a PhD in Agricultural Education, encourages kids to join Oregon State’s “swientist” program, offering free popsicles and stickers with a pig in a lab coat.
A " pathogen gun battle" lets children kill the flu with spray guns and shoot down plastic viruses from the base. They can pick up biosafety buckets containing soap, brushes, disinfectants, gloves and other essentials. “I won’t convince parents to do things differently, but I think I can get kids,” Bowman said. "So it's really a long game. Ten years later, I think I can change some behaviors.
Bowman's team also recruited people aged 5 to 21 for a long-term study to track any flu infection they're infected, which requires immediate blood samples.
"I'd love to see what they found in my blood," said Sam Fox, 18, who lives in Indiana and has seen most of his childhood for pigs. "I bet that I haven't been with pigs for only a few weeks in the last 8 years."
Morgan said the education program helped calm initial concerns about their pig sampling. “Andy and Jacqueline are nothing to do except improve the health of pigs and kids,” said Morgan, whose son showed up the pigs and participated in the swientist program.
Bowman and Nelson's more ambitious ideas include requiring all animals to be vaccinated with influenza, which can reduce transmission if matched with variation in circulation. The researchers even proposed that pigs participating in the national or regional jackpot show no longer appear within 2 weeks, and pressing the pause button can give any virus in the infected pig enough time to burn before it has a chance to spread.
But Bowman said the idea has zero appeal, partly because those who win pigs in the jackpot hope to be exhibited at state and county fairs in the coming weeks, which is understandable. “It’s hard,” he said. “We are making changes, and it’s pandemic prevention.But how do you quantify the impact of these changes?
Bowman said the most urgent need at present is to collect enough data to correctly evaluate the risks of this precious American tradition. "Will this show kick off?" he asked about the expo held in June. "I don't know, because we've mastered the pulse for a long time. But what else is there outside?
