Threat of H5N1 Avian Flu Pandemic Increasing

The H5N1 avian influenza virus is evolving and poses "a continuing and potentially growing pandemic threat," say experts convened recently in Manila by the World Health Organization (WHO) to study the pathogen. Changing patterns of cases, particularly in northern Vietnam, may indicate the virus is becoming more infectious for humans, the WHO said in a report....In addition, genetic analysis indicates that H5N1 viruses are becoming more antigenically diverse.

The report cites several differences between epidemiologic features of human cases this year in northern Vietnam, and those in southern Vietnam this year and overall last year.
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In addition, the report says the recent discovery of three asymptomatic cases in Vietnam suggests that milder infections are occurring. A few asymptomatic cases also were found in Japan and Thailand in the past year....

The report says the longer duration of recent clusters may signal a growing number of ways in which people contract the virus, including exposure to sick birds, environmental infection, lengthy exposure to asymptomatic birds that are shedding virus, and person-to-person transmission.

The avian virus had already vaulted to the top of the pandemic threat list because it had developed the ability to sicken and kill humans. The virus's inability to cause efficient, ongoing human-to-human transmission is the last barrier to a pandemic. Now experts appear worried that the barrier is crumbling.

'Investigators were not able to prove that human-to-human transmission had occurred. However, they expressed concerns, which were shared by local clinicians, that the pattern of disease appeared to have changed in a manner consistent with this possibility,' the assessment states.

At the same time, it says that in places where the disease in poultry has been controlled or eliminated, human cases have stopped. And thus far, the first case in most of the human clusters in Vietnam followed the person's exposure to infected poultry.

Hat tip: CIDRAP. More detail in the complete article.