Despite the fearsome reputation of H5N1 as a threat to human health, other H5 avian viruses have demonstrated a wide range of pathogenicity in people. Even among H5N1 clades, not all viruses are created equal. We’ve seen considerable variability in that subtype’s ability to infect, and kill around the globe (see Differences In Virulence Between Closely Related H5N1 Strains).
In Bangladesh, only 1 (14%) of 7 known H5N1 cases has died, while in Cambodia 37 of 56 (66%) have succumbed. In Egypt, the CFR is running about 35%, while in Indonesia, it is a stratospheric 83%.
Although there are likely many factors involved in causing this disparity in CFRs – including quality of, and delays in seeking medical care – it suggests that the H5N1 virus may be more virulent in some regions of the world than in others.
The recently emerged H5N6 is known to have killed at least two people (see WHO GAR Update – H5N6 In China), but the (old) H5N2 virus appears to have – at most – produced antibodies in a handful of poultry workers and The Human Risk From H5N2 Is Considered Low.
Over the past year we’ve watched the emergence of a new, robust Highly Pathogenic (in birds) H5N8 virus that has spawned several other reassortant subtypes – including a new H5N2 – which have spread quickly via migratory birds to poultry farms across Korea, China, Taiwan, Japan and have even made it into Europe and the Pacific Northwest.
Despite a good deal of infected-poultry-to-human contact, we’ve not seen any evidence of these new subtypes causing illness in humans.
Granted, cullers are using PPEs and some are probably receiving prophylactic antivirals, but many poultry workers have had unprotected exposure prior to detection and culling, and none have (as yet) become sick. Despite this reassuring track record, Taiwan public health authorities are monitoring nearly 3,000 people who have been exposed.
Below you’ll find a statement by Taiwan’s CDC on recent genetic analysis of their recently arrived H5N8 and H5N2 subtypes, that cautiously finds them to pose little threat to human health.
Gene sequence alignment of avian flu viruses shows transmission still limited to poultry; Taiwan CDC continues to closely monitor outbreak situation to ensure health and wellbeing of people in Taiwan ( 2015-01-26 )
In the afternoon of January 23, 2015, the Taiwan Centers for Disease Control obtained the genome sequences of the H5N2 and H5N8 viruses from the Council of Agriculture and submitted it to the National Influenza Center for gene sequence alignment. The results showed that both the H5N2 and H5N8 viruses are of avian origin. Based on the sequence data, the Taiwanese viruses were identified as closely related to the Japanese, the American, the Canadian, the German and the Republic of Korea H5N8 viruses.
Unlike the H7N9 virus, the H5N8 virus does not replicate well in mammalian cells and is not as fatal. Although several H5N8 outbreaks have been reported many countries around the world, no evidence of bird-to-human transmission has been found.
Taiwan CDC once again emphasizes that the H5N2 and H5N8 viruses are currently still limited to transmission among poultry and no bird-to-human transmission has occurred. As for treatment, the US Centers for Disease Control (US CDC) and the World Health Organization (WHO) currently recommend oseltamivir or zanamivir. Taiwan CDC will continue to closely monitor the development of the outbreaks and the viruses for new mutations in order to facilitate timely implementation of relevant disease control measures and ensure the health and wellbeing of the people in Taiwan.
In response to the ongoing avian influenza outbreaks among poultry, Taiwan CDC is monitoring everyone who has been exposed to the poultry farms where avian influenza outbreaks have occurred, including poultry farm workers and public health workers, for influenza-like symptoms for 10 days as a precaution. Those who develop influenza-like illness will be further evaluated and tested for influenza. As of January 24, 2015, a total of 2,906 people are being monitored. Of the people being followed up, 40 people have developed influenza-like symptoms. Specimens have been collected from 28 of them (1 is positive for seasonal influenza, the other 23 are negative and 4 tests results are pending),while the other 12 people are still being monitored for their health status. 76 other people have been removed from surveillance.
Taiwan CDC reminds poultry farm workers to take additional preventive measures to ward off infection. If fever or influenza-like symptoms develops,please put on a mask and seek immediate medical attention. Moreover, poultry farm workers must inform the physician of their exposure and job history to facilitate diagnosis and treatment. The general public is urged to practice good personal hygiene such as washing hands frequently and putting on a mask when coughing and take preventive measures such as avoiding direct contact with poultry and birds or their droppings/dead bodies, and consuming only thoroughly cooked poultry and eggs to prevent infection. For more information, please visit the Taiwan CDC website at http://www.cdc.gov.tw or call the toll-free Communicable Disease Reporting and Consultation Hotline, 1922 (or 0800-001922).
So far, good news indeed. The lack of replication in mammalian host cells is particularly encouraging.
The caveat being that flu viruses are constantly changing, and what we can say about their behavior today, cannot be guaranteed tomorrow.