UNIVERSITY PARK – Swine flu is no mystery to scientists in Penn State’s College of Agricultural Sciences, who have been keeping a wary eye on the virus in pigs for decades and researching better vaccines to prevent it, methods to limit its spread and ways to predict and gauge the risks it poses to human health.
The disease in pigs is relatively mild and rarely kills the animals, but when the swine virus combines with genes from human and avian influenzas — as it seems to have done in the current outbreak causing so much fear around the world — all bets are off.
“It is unclear at this point, given considerable information about previous outbreaks, where this particular virus will end up,” said Vivek Kapur, a renowned microbiologist who heads Penn State’s Department of Veterinary and Biomedical Sciences. “It is too soon in the outbreak to be sure. Influenza A viruses are notorious for re-assorting and mutating, and based on our understanding of previous outbreaks, this virus may come back with a vengeance this winter, or simply disappear over the next few weeks or months.
“When the virus jumps to humans, it becomes a different organism altogether — unpredictable and potentially dangerous. Several times in the last 100 years, influenza has proved deadly, and so we must always remain vigilant.”
Kapur pointed out that influenza, or what is commonly called the flu, annually kills about a million people worldwide (between 30,000 and 50,000 in the United States die of flu each year). Typically, flu is a late-fall, early-winter phenomenon. “There are probably hundreds or thousands of localized outbreaks that don’t turn into pandemics,” Kapur noted. “From an influenza perspective, most are mild and peter out, and they don’t get the publicity that the current outbreak has.”
However, the involvement of swine influenza and perhaps avian influenza in the current outbreak could make this flu different, contends extension veterinarian Dave Wolfgang, who said it is not unusual to have a few pigs suffering with flu. But he is quick to point out that the mixed virus strain identified in the current outbreak has not been seen in pigs in the United States or Pennsylvania.
“The real fear, of course, is that this strain will spread rapidly among the human population because people have no immunity to swine and avian flu, and that has the potential to start a pandemic. But what we are seeing right now is that this flu has a high attack rate — meaning it spreads easily — but it doesn’t seem to have a high mortality rate.”
If the disease infects hundreds of thousands or millions of people, even if only a very small percentage become quite ill, that could still lead to many deaths, Wolfgang said. A high attack rate but very low mortality rate is characteristic of swine flu, compared to a low attack rate with a high mortality rate for the current H5N1 avian flu. It is a lethal combination of the two — a virus strain that would have a high attack rate and high mortality rate, with human influenza genes somehow rolled in — that keeps scientists up at night.
“In the modern world with people traveling so much, we are always going to have influenza and infectious diseases,” Wolfgang said. “Small reassortments in influenza happened all the time, every day, every year, but most turn out to be insignificant.”
Veterinary scientist Lester Griel has been investigating ways to influence the immune systems of swine to resist influenza. He currently is conducting contract research for a company that is interested in ways to reduce aerosol distribution of influenza and limit the spread of disease among pigs.
“These viruses change rapidly, with mutations and recombinations,” he said. “The reason this was originally called swine flu is that the overall background of this new organism is definitely swine but it does have elements of human and bird flu.
“These type of influenzas circulate in birds, pigs and humans,” Griel added. “The reason many of these new strains originate in places like Southeast Asia and Mexico is that the pig houses and chicken houses are often closely attached to human houses and there is much more intimate contact between animals and humans than there are in other parts of the world.”
The current flu outbreak shows how closely linked animal health is to human health, Griel said. “The American Medical Association has stated that of the 1,500 diseases that can affect people, about 50 percent of them are transmissible between animals and humans,” he said. “The American Medical Association and the American Veterinary Medical Association have been working on the theme for the last three years, ‘One World, One Health, One Medicine.’ There is not as much difference between animal medicine and human medicine as most people think.
“Because of these zoonotic diseases (animal diseases which can infect humans), a lot of the disease-protection activities that veterinarians are involved in have a significant effect on human health.”
A virologist in the college, Biao He, studies the genetic material of viruses and is working to develop a viral vehicle to deliver antigens in vaccines, mostly targeting the H5N1 avian flu virus. “Swine are considered to be a reservoir for flu virus where swine, avian and human influenza combine and reassemble. The pig is the mixing vessel to create many different kinds of virus. We worry most about a completely new strain emerging to which humans would have no immunity.”
He believes that veterinary scientists play a huge role in protecting human health. The insight and knowledge they provide about flu is critical. “In the college, we have people who keep a close eye on what flu strains are circulating,” he said. “If we know what is coming we can prepare. If we don’t do surveillance we will get blindsided.
“So animal diagnostics are vital. One of the difficulties is the time it takes to make vaccine. We need to make hundreds of millions of doses. There is a possibility that this strain will come back next winter, but now we have the virus and we can make the vaccine.”
In the College of Agricultural Sciences, researchers are uniquely positioned to monitor zoonotic diseases, He noted. Obvious examples of human-health threats that have proved particularly menacing in recent years are HIV, which came from monkeys, and Ebola, which came from bats. “The odds are that the next emerging disease epidemic will come from animals,” He said. “If a virus only infects humans we have a chance to get rid of it — like smallpox. But we will never get rid of flu because there are reservoirs of influenza in animal populations.
“Our college is really at the front line of defending against emerging viruses,” He said. “People traditionally value agriculture from an economic perspective, but perhaps a more important aspect is protecting animal health by minimizing the threat from emerging viruses to guard human health.”
Molecular mechanisms that allow viruses to adapt to and thrive in new environments are the focus of biologist Mary Poss’s research. Although she has not worked with influenza viruses, because of her work with other pathogens, she has considerable insight into how emerging diseases such as swine and avian flu spread.
Poss noted that epidemiological modeling currently being done in the college will help experts to predict the spread and impact of the disease if it emerges this winter in a deadly way, and how susceptible people are to being infected. Because the H1N1 virus has “multiple parentages,” Poss worries it could have a significant effect on the human population.
“Historically, we know that an out-of-season outbreak, known as the Spanish flu, in the summer of 1918 was followed by a severe winter pandemic that proved to be fatal for many thousands of people,” she said. “So perhaps we should not be comforted by the mild nature of this spring outbreak. Only time will tell.
“But this outbreak is a very good example of why we need to study more than just the genes,” Poss added. “We also must understand wildlife movement such as bird migrations and agricultural practices that involve animals like swine because we now know that everything we do on this planet is connected and has an impact on human health.”