Photo Credit – FAO
# 8312
With the recent imported case of H7N9 to Malaysia – and the prospect that we could see other such cases around the world - there are natural concerns that this might lead to the introduction of the virus to local poultry or livestock outside of Mainland China.
Today the FAO has published a reassuring news story with – in my humble opinion - a badly phrased headline.
While we’ve not seen any evidence of humans transmitting the H7N9 virus to other animal species – as Carl Sagan put it in Cosmos - “The absence of evidence is not the evidence of absence.”
So the headline below - stating that the possibility has been `ruled out’ - seems more than just a reach.
The body of the story, I would note, is slightly less adamant, stating that there is no evidence that humans can `transmit the virus to animals, including birds’ and “The highest risk of virus introduction is uncontrolled live poultry trade between affected and unaffected areas”.
First some excerpts, after which I’ll return with a bit more.
FAO rules out human-to-animal transmission of influenza A(H7N9)
After the first case of A(H7N9) outside China, FAO says there is no evidence that infected people could transmit the virus to poultry
Uncontrolled live poultry trade poses the highest risk of A(H7N9) introduction.
19 February 2014, Rome – FAO says there is no evidence that human patients infected with influenza A(H7N9), a low pathogenic virus in poultry, can transmit the virus to animals, including birds.
FAO referred to the first human case of A(H7N9) outside China, which was recently detected in Malaysia.
The patient, originally from Guangdong Province in China, where she is thought to have contracted the infection, was visiting Malaysia as a tourist and has now been hospitalized there. Guangdong is one of the Chinese provinces most affected by the A(H7N9) virus in 2014.
“This case does not come as a surprise and should not be a cause for increased concern, but should remind the world to remain vigilant," said FAO Chief Veterinary Officer Juan Lubroth.
“Humans that become ill with influenza A(H7N9) constitute no threat to poultry populations,” Lubroth underlined.
“In fact, we have no evidence that affected people could transmit the virus to other species, including birds. The highest risk of virus introduction is uncontrolled live poultry trade between affected and unaffected areas.”
People, on the other hand, become infected following close contact with infected live poultry, mostly in live bird markets or when slaughtering birds at home.
WHO risk assessments show that should infected people from affected areas travel internationally, community level spread is unlikely since the virus does not have the ability to transmit easily among humans.
Lubroth observed that "Such 'imported’ human cases, like the one reported in Malaysia last week, have been found in the past in previously unaffected areas of China, like Guizhou, Taiwan Province of China and Hong Kong SAR, and we will likely continue to see this in the not too distant future again. To date the virus has not been found in poultry populations outside affected areas in China."
Birds that have contracted A(H7N9) do not show clinical signs, which renders early detection of the virus in poultry populations more difficult. FAO therefore urges countries to adapt their surveillance programmes to include this recently emerged virus.
While no evidence of human-to-animal transmission of the virus has been established - that last paragraph, stating that birds that contract A(H7N9) remain asymptomatic (rendering the detection of the virus more difficult) – highlights the difficulties in making absolute statements like the one in the headline above.
Unless and until comprehensive post-human-exposure seroprevalence studies can be done on poultry, birds, and other livestock (and using all of the reassortant versions of the virus in circulation), I don’t see how we can `rule out’ the possibility.
Is it unlikely? Perhaps. But we won’t really know until we look.
We’ve discussed reverse zoonosis – the passing of an infection from a human to another species before, including Companion Animals & Reverse Zoonosis. While it doesn’t get much attention, it probably happens more often than we know.
During the 2009 H1N1 pandemic, the virus – which evolved in pigs – jumped to humans and spread rapidly. But humans also passed it on to new swine herds around the world, and to other animals as well. We saw reports of dogs, cats, turkeys, cheetahs, and pet ferrets falling ill with the virus (see US: Dog Tests Positive For H1N1, USDA Listing Of Animals With H1N1).
It is one of the reasons why people who work with, or raise swine are urged to get the seasonal flu vaccine each year, to prevent infecting pig herds with humanized flu strains – a possible route to creating a new reassortant flu virus. The following comes from the CDC.
Influenza Vaccination of Swine Workers
(Excerpt)
However, influenza vaccination of swine workers – regardless of whether or not they have a high risk condition – is important to reduce the risk of transmitting seasonal influenza viruses from ill people to pigs. Seasonal influenza vaccination of workers might also decrease the potential for people or pigs to become co-infected with both human and swine influenza viruses. Such dual infections could result in genetic reassortment of the two different influenza A viruses and lead to a new influenza A virus that has a different combination of genes, and which could pose significant public health concern. Employers should consider providing swine workers with access to annual seasonal influenza vaccination that follow the recommendations for the general public for Preventing Seasonal Flu With Vaccination.
For now, based on the evidence to date, I think its reasonable to say that the odds of humans transmitting the virus to other species is pretty low. But influenza viruses are notorious for not playing by the `rules’.
Often making absolute statements about their behavior subject to future revision.
