Photo Credit – FAO
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Last night Lisa Schnirring writing for CIDRAP NEWS brought us details on the first highly pathogenic bird flu outbreak in Mexico in nearly two decades. The last time was during the mid-1990s, and the virus was H5N2.
This time, the culprit it is H7N3.
Follow the link below to read Lisa’s excellent report, after which I’ll return with a bit more.
Tests reveal high-path H7N3 in Mexican poultry farm outbreaks
Lisa Schnirring
Staff Writer
Jun 26, 2012 (CIDRAP News) – Mexican veterinary authorities are intensifying avian influenza control efforts in a region that houses several large commercial farms after further tests determined that the strain responsible for more than 200,000 bird deaths at three farms is the highly pathogenic H7N3 subtype.
While there are a number of avian flu viruses circulating in the wild, the OIE only requires that H5s and H7s be reported due to their known ability to mutate from a low pathogenic virus to highly pathogenic virus.
When it comes to avian influenzas, the H5N1 virus gets the bulk of the headlines, and rightfully so. While a matter of some controversy (see Revisiting The H5N1 CFR Debate), among known human cases, the mortality rate has been a staggering 60%.
Other strains that have demonstrated at least some ability to infect humans include H7, H9, H10, and H11. Fortunately, most of the time these rare infections have produced only mild flu symptoms (sometimes only localized conjunctivitis).
Last April, in EID Journal: Human Infection With H10N7 Avian Influenza we looked at some recent H10 infections, and in 2011 we explored A Little Background On H11 Avian Influenzas.
For now, however, these viruses are primarily a threat to the poultry industry, and to a lesser extent, people working in direct contact with infected fowl.
Although global surveillance and reporting on novel avian viruses in humans is spotty at best, some known H7 cases include:
- In 2003 an outbreak of H7N7 at a poultry farm in the Netherlands went on to infect at least 89 people. Most of the victims were only mildly affected, but one person died.
- In 2004 two people in British Columbia tested positive for H7N3 (see Health Canada Report) during an outbreak that resulted in the culling of 19 million birds.
- In 2006 and 2007 there were a small number of human infections in Great Britain caused by H7N3 (n=1) and H7N2 (n=4), again producing mild symptoms.
For now, H7 avian influenzas are presumed to pose a low public health threat, which may leave you wondering why all this fuss over this outbreak of H7N3?
The H7s, like all influenza viruses, are constantly mutating and evolving.
While considered mild today, there are no guarantees that the virus won’t pick up virulence over time, or reassort with another virus and increase its affinity for humans.
Four years ago, we saw a study in PNAS that indicated that the H7 virus might just be moving more towards adapting to humans.
You can read more about this in a couple of blogs from 2008, H7's Coming Out Party and H7 Study Available Online At PNAS.
The last pandemic, you will recall, came out of left field; from a region of the world (North America), host species (swine), and influenza strain (H1N1) all considered unlikely to spark a global epidemic.
Which is why we pay attention whenever there is an outbreak of a novel flu virus for which mankind may have little or no immunity.
