Friday, July 13, 2012

Updating Mexico’s H7N3 Outbreak



Photo Credit SENASICA


# 6432


Just over three weeks ago the OIE was notified by Mexico’s Director General of Animal Health Dr Hugo Sanchez Fragoso of an outbreak of highly pathogenic H7N3 avian influenza among poultry in the state of Jalisco (see Mexico: High Path H7 In Jalisco). 


A week later, Mexico’s Agricultural Ministry (Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación; SAGARPA) Declared a National H7N3 Animal Health Emergency as the H7N3 virus continued to spread.



Map Credit OIE



Since humans have only rarely been reported to have been infected by this strain of avian flu, the big concern right now is for poultry operations. Cesar de Anda, vice chairman of the International Egg Commission, was quoted by EFE news yesterday as stating:


"The industry will fail to produce $50 million, not only from the cost of the (dead) birds, but also from the intrinsic value of production, the generation of wealth and of indirect jobs in other fields."


According to Anda, if this outbreak is not brought under control, as many as 32,000 jobs could be at risk.


To date, 2.5 million poultry have either died, or been destroyed because of this virus, and according to a press release from SENASICA (Mexico’s Food Safety agency) as many as 17 million birds in the region may be at risk.


The latest OIE Filing (Follow-up report No. 3 ) states the source or origin of the virus remains unknown, and provides brief summaries of 31 separate outbreaks. 


Under Epidemiological comments, they list:


  • During the epidemiological surveillance carried out in response to the event, the National Food Quality, Food Safety and Health Service (SENASICA) has taken samples in the outbreaks and around the outbreaks in 148 poultry farms.
  • 31 farms were identified by viral isolation, diagnosis is ongoing in other 83 and 34 have tested negative to H7N3 highly pathogenic virus.
  • The population at risk in these 148 farms amounts to about 17 million birds, of which 86.1% of layers, 6.9% of broilers and 7% of breeders.
  • As part of the measures taken to reduce the risk, the buffer zone has been extended to 60 km around the index outbreak and includes 161 poultry farms at risk with a population of 25.8 million of birds.
  • Control measures on birds and their products movements have been strengthened in the quarantine area and eight check points have been established with the support of 26 health technicians with 9 vehicles that monitor the quarantine zone.
  • Epidemiological surveillance activities continue in the outbreaks, around the outbreaks and in the buffer zone. As a measure to reduce the risk, sampling will be carried out in neighbouring States and in poultry farms at risk outside the buffer zone.


In the first six months of 2012, 14 countries have reported outbreaks of high path avian flu with strains ranging from H5N1 and H5N2 to H7N3. Surveillance and reporting around the world is spotty at best, and so it is likely that we don’t hear about all of the outbreaks.


For now, however, these viruses are primarily a threat to the poultry industry, and to a far lesser extent, people working in direct contact with infected fowl.  While H7 viruses have been known to infect humans on rare occasions, most of the reported cases have produced only mild to moderate illness.


  • 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.  But H7s, like all influenza viruses, are constantly mutating and evolving.


In 2008 we saw a study in  PNAS that suggested the H7 virus might just be inching towards adapting to humans. For more details on that study, you may wish to revisit H7's Coming Out Party and H7 Study Available Online At PNAS.


So, while the H7 virus poses a minimal risk to human health at this time, it pays to keep an eye on outbreaks such as the one in Jalisco.


Influenza viruses are constantly changing, and evolving, always seeking an evolutionary advantage. So, what was true about a specific flu virus yesterday, may not hold true tomorrow.

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