# 5860
Being of swine origin, the pandemic producing 2009 H1N1 virus – to no great surprise – moved easily from human hosts back into pig populations around the globe.
By the fall of 2009 we’d seen reports of pigs in Canada, the US, Japan, Ireland, Norway, Australia, Argentina, Iceland, and China showing infection with the humanized H1N1 virus.
Since humans are far more traveled than your average pig, a virus that might have remained confined to swine herds in one region of the world for years soon spread to every continent via international travel.
Each year, more than 17 million commercial airline flights transport hundreds of millions of people across the globe (see Pathological Flyers).
You can literally travel from just about any two cities (with airports) anywhere in the world in 24 hours or less. No longer are the oceans, or distance, a protection against diseases normally seen only in remote areas of the world.
Which is why the pandemic of 2009 spread so quickly around the globe.
Given the very limited animal testing and surveillance in the United States and around the world (see Swine Flu: Don’t Test, Don’t Tell) the true scope of the spread of the H1N1 virus back into the pig population remains unknown.
The concern is that once `humanized’, and then reintroduced back into the swine population, the virus will have enhanced opportunities to meet up with – and reassort with – other flu viruses.
Reassortment happens when two different influenza viruses co-infect the same host, swap genetic material, and produce a hybrid virus.
We’ve already seen multiple reports of pdmH1N1 reassortments, although none have emerged that pose a renewed pandemic threat.
With global pig production growing rapidly to meet the demands of a hungry world, each year we add millions more `mixing vessels’ to natures laboratory. And the bulk of the predicted growth in hog farming is expected in developing countries where testing is pretty much non-existent.
Credit – FAO
Illustrating the problem is a report yesterday from UCLA on the prevalence of the pandemic H1N1 virus among pigs in Cameroon.
In one village, nearly all of the pigs tested showed evidence of current or past infection.
I’ve a small excerpt from a much longer UCLA Newsroom background article, along with a link to the study.
UCLA scientists find H1N1 flu virus prevalent in animals in Africa
By Stuart Wolpert September 22, 2011
UCLA life scientists and their colleagues have discovered the first evidence of the H1N1 virus in animals in Africa. In one village in northern Cameroon, a staggering 89 percent of the pigs studied had been exposed to the H1N1 virus, commonly known as the swine flu.
"I was amazed that virtually every pig in this village was exposed," said Thomas B. Smith, director of UCLA's Center for Tropical Research and the senior author of the research. "Africa is ground zero for a new pandemic. Many people are in poor health there, and disease can spread very rapidly without authorities knowing about it."
The study appears (behind a pay wall) in Veterinary Microbiology.
Pandemic A/H1N1/2009 influenza virus in Swine, Cameroon, 2010
Kevin Y. Njabo, Trevon L. Fuller, Anthony Chasar, John P. Pollinger, Giovanni Cattoli, Calogero Terregino, Isabella Monne, Jean-Marc Reynes, Richard Njouom, Thomas B. Smith
The viruses detected in Cameroon were reportedly `virtually identical’ to the H1N1 viruses detected early in the pandemic in San Diego. Thomas B. Smith, the senior author of the research is quoted as saying:
"When different strains of influenza are mixed in pigs, such as an avian strain with a human strain, you can get new hybrid strains that may affect humans much more severely and can potentially produce a pandemic that can allow human-to-human infection. This is how a pandemic can arise; we need to be very vigilant.
Of course, it isn’t just the 2009 H1N1 virus in swine that we concern ourselves with. In recent years we’ve seen a variety of reassorted H1N1 and H3N2 viruses in pigs, and on rare occasions these have been passed on to humans.
Pigs in Indonesia have also been found to have contracted the H5N1 bird flu virus (see EID Journal: Asymptomatic H5N1 In Pigs).
Most recently, four cases of a reassorted H3N2 virus with the M gene from H1N1 turned up in children in Pennsylvania and Indiana (see CDC Update On Recent Novel Swine Flu Cases).
While the epidemiological investigation continues, so far we’ve no evidence of sustained human transmission.
It is likely that limited infection by novel influenza reassortments such as these occur occasionally (and largely unnoticed) all over the world. Since only a tiny fraction of influenza flu viruses are ever sequenced, we really don’t know how often these types of novel infections occur.
But it’s probably more often than we think.
These rare SOIV infections are important to monitor and analyze, and may give us an early warning about the next pandemic threat. But for now they pose a very low public health threat.
Admittedly, it may be years or even decades before another pandemic emerges and threatens the human population. The timing of these events is impossible to predict.
But surveillance studies like the one above show that flu viruses will literally go to the ends of the earth looking for new hosts and an evolutionary advantage.
For more on the reassortment potential of avian, swine, and human flu viruses, you can’t do better than Helen Branswell’s excellent Scientific American article from last December called Flu Factories, or her SciAm Podcast interview.
