Saturday, April 22, 2017

WHO Avian Flu Risk Assessment - April 2017

















#12,401



The World Health Organization has released an updated Influenza at the human-animal interface report - one that reflects H7N9 cases officially notified to WHO by the Chinese government through April 20th of this year, along with a single H9N2 infection reported in a child from Gansu Province, China. 
This report is dated April 20th, but since China doesn't always notify WHO immediately of cases, today's report is running roughly 30 behind Hong Kong's most recent tally. 
Two HPAI H5 viruses with a track record of infecting humans (H5N1 & H5N6) were not diagnosed during this latest reporting period, with only 2 H5N1 cases reported thus far in 2017, and the last human H5N6 infection reported last November in China.


First some excerpts from today's report, then I'll return with a bit more.

Influenza at the human-animal interface

Summary and assessment, 16 March to 20 April 2017

  • New infections1: Since the previous update, new human infections with influenza A(H7N9) and A(H9N2) viruses were reported.
  • Risk assessment: The overall public health risk from currently known influenza viruses at the human-animal interface has not changed, and the likelihood of sustained human-to-human transmission of these viruses remains low. Further human infections with viruses of animal origin are expected.
  • IHR compliance: All human infections caused by a new influenza subtype are required to be reported under the International Health Regulations (IHR, 2005).2 This includes any animal and non-circulating seasonal influenza viruses. Information from these notifications is critical to inform risk assessments for influenza at the human-animal interface.

Avian Influenza Viruses

 
Avian influenza A(H5) viruses

 
Current situation:
Since the last update, no new laboratory-confirmed human cases of influenza A(H5) virus infection were reported to WHO. Influenza A(H5) subtype viruses have the potential to cause disease in humans and thus far, no human cases, other than those with influenza A(H5N1) and A(H5N6) viruses, have been reported to WHO. According to reports received by the World Organisation for Animal Health (OIE), various influenza A(H5) subtypes continue to be detected in birds in Africa, Europe and Asia.


Avian influenza A(H7N9) viruses


Current situation: During this reporting period, 86 laboratory-confirmed human cases of influenza A(H7N9) virus infection were reported to WHO from China. Case details are presented in the table in the Annex of this document. For additional details on these cases, public health interventions, and the recently detected highly pathogenic avian influenza (HPAI) A(H7N9) viruses, see the Disease Outbreak News.


As of 20 April 2017, a total of 1393 laboratory-confirmed cases of human infection with avian influenza A(H7N9) viruses, including at least 534 deaths3, have been reported to WHO (Figure 1).


1 For epidemiological and virological features of human infections with animal influenza viruses not reported in this assessment, see the yearly report on human cases of influenza at the human-animal interface published in the Weekly Epidemiological Record. www.who.int/wer/en/
2 World Health Organization. Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005). www.who.int/ihr/Case_Definitions.pdf

3 Total number of fatal cases is published on a monthly basis by China National Health and Family Planning Commission.

According to reports received by the Food and Agriculture Organization (FAO) on surveillance activities for avian influenza A(H7N9) viruses in China4, positives among virological samples continue to be detected mainly from live bird markets, and some commercial and backyard farms.

Risk Assessment

1. What is the likelihood that additional human cases of infection with avian influenza A(H7N9) viruses will occur? Most human cases are exposed to the A(H7N9) virus through contact with infected poultry or contaminated environments, including live poultry markets. Since the virus continues to be detected in animals and environments, further human cases can be expected. Additional sporadic human cases of influenza A(H7N9) in other provinces in China that have not yet reported human cases are also expected.
2. What is the likelihood of human-to-human transmission of avian influenza A(H7N9) viruses? Even though small clusters of cases have been reported, including those involving healthcare workers, currently available epidemiological and virological evidence suggests that this virus has not acquired the ability of sustained transmission among humans, thus the likelihood is low.

 
3. What is the risk of international spread of avian influenza A(H7N9) virus by travellers? Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
4 Food and Agriculture Organization. H7N9 situation update. www.fao.org/ag/againfo/programmes/en/empres/H7N9/situation_update.html

Avian influenza A(H9N2) viruses
Current situation:

 
One new laboratory-confirmed human case of A(H9N2) virus infection was reported to WHO from China in an eleven-month-old boy from Gansu province. The case developed mild illness on 6 February 2017, was hospitalized and has recovered. He had exposure to backyard poultry prior to illness onset. This is the first human case of avian influenza A(H9N2) virus infection reported to WHO since December 2016 and the first human case reported from Gansu province. Avian influenza A(H9N2) viruses are enzootic in poultry in China.

Risk Assessment:
1. What is the likelihood that additional human cases of infection with avian influenza A(H9N2) viruses will occur? Most human cases are exposed to the A(H9N2) virus through contact with infected poultry or contaminated environments. Human infection tends to result in mild clinical illness. Since the virus continues to be detected in poultry populations, further human cases can be expected.
2. What is the likelihood of human-to-human transmission of avian influenza A(H9N2) viruses? No case clusters have been reported. Currently available epidemiological and virological evidence suggests that this virus has not acquired the ability of sustained transmission among humans, thus the likelihood is low.
3. What is the risk of international spread of avian influenza A(H9N2) virus by travellers? Should infected individuals from affected areas travel internationally, their infection may be detected in another country during travel or after arrival. If this were to occur, further community level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
(Continue . . . )


While the risk assessments for H7N9 remains unchanged - and the virus has not demonstrated the ability to transmit efficiently from human to human -  it is fair to say that  recent developments with this virus have raised concerns world wide.

  1. This year's surge in human cases not only ends a two year decline in the number of  human infections, it is well on its way to more than doubling the size of its biggest previous epidemic (320 cases in the winter 2013-14).  
  2. H7N9 has recently split into two major lineages - Pearl River Delta and Yangtze River Delta - (see MMWR:Increase in Human Infections with Avian Influenza A(H7N9) In China's 5th Wave) This new (Yangtze River Delta) lineage will require a new vaccine - meanwhile the virus continues to evolve at an impressive rate.
  3. Previously only an LPAI virus, a new virulent (in birds) HPAI version of H7N9 emerged in Guangdong province this winter, and has demonstrated the ability to infect humans. 
  4. In a recent Eurosurveillance Research Article it was reported that despite better medical treatment for patients, the mortality rate remains high (30%+), and the authors report an`accelerated disease progression of H7N9 patients', which they note  `suggests that the viral pathogenicity might have become stronger'.
  5. The authors also noted  ` . . .  increased detection rate of H7N9 in environmental samples suggests that the virus might become more resistant to high ambient temperature.' - which you may recall was a concern raised last summer (see HK CHP: Additional Details On China's July H7N9 Cases) when we saw a dozen `out of season H7N9 cases'. 


While none of this guarantees that H7N9 will spark the next pandemic, the CDC's IRAT ( Influenza Risk Assessment Tool) ranks H7N9 as having the highest pandemic potential of 11 novel viruses currently being tracked.
And earlier this month renown virologist Dr. Guan Yi at the University of Hong Kong, in a recent interview (see NPR: A Pessimistic Guan Yi On H7N9's Evolution),  was quoted as saying  "I think this virus poses the greatest threat to humanity than any other in the past 100 years."
Add in the recent expansion of H7N9 to the north (Beijing) and west (Tibet) of China, and you have ample reasons to put H7N9 at the very top of our influenza pandemic threats list.


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