# 5258
For all of the concerns over the pandemic potential of highly pathogenic H5N1 avian flu, the virus – thankfully – remains exceedingly difficult for humans to contract.
As of today, we know of just over 500 cases worldwide since 2003. If this were practically any other type of virus, it would hardly bear notice.
But influenza viruses are a special case.
We know that they are constantly mutating, and evolving, and over time have the ability to adapt to new hosts. When that host happens to be human, a virus can go from rare (or even non-existent) to a pandemic threat overnight.
And so we watch H5N1, along with a handful of other avian flu strains, for signs they may becoming better adapted to human physiology.
For now, the H5N1 virus remains primarily adapted to avian species, and to their avian (alpha 2,3) receptor cells.
Despite tens of thousands of contacts each year between infected birds (primarily poultry) and mankind, only rarely has the virus managed to latch onto a human host.
The big concern, of course, is that this virus – more so than with any influenza virus seen before – has an absolutely horrendous mortality rate.
Of the 500+ known human cases, just under 60% have died.
Unknown, of course, is whether this virus would retain that kind of CFR (Case Fatality Ratio) should it adapt to humans.
But even at 1/10th its current fatality rate, H5N1 has the potential to spark a formidable pandemic.
And so researchers spend a good deal of time watching H5N1, trying to detect – at the earliest opportunity – any changes to its threat level.
Which brings us to a study that appears in this week’s PloS One journal, that takes a detailed look at the risks, and pathways of human exposure, to the H5N1 virus.
I’ve provided the link, and the abstract, but the entire (open access) article makes for interesting reading.
Highly Pathogenic Avian Influenza (H5N1): Pathways of Exposure at the Animal‐Human Interface, a Systematic Review
Abstract
Background
The threat posed by highly pathogenic avian influenza A H5N1 viruses to humans remains significant, given the continued occurrence of sporadic human cases (499 human cases in 15 countries) with a high case fatality rate (approximately 60%), the endemicity in poultry populations in several countries, and the potential for reassortment with the newly emerging 2009 H1N1 pandemic strain. Therefore, we review risk factors for H5N1 infection in humans.
Methods and Findings
Several epidemiologic studies have evaluated the risk factors associated with increased risk of H5N1 infection among humans who were exposed to H5N1 viruses. Our review shows that most H5N1 cases are attributed to exposure to sick poultry. Most cases are sporadic, while occasional limited human-to-human transmission occurs. The most commonly identified factors associated with H5N1 virus infection included exposure through contact with infected blood or bodily fluids of infected poultry via food preparation practices; touching and caring for infected poultry; consuming uncooked poultry products; exposure to H5N1 via swimming or bathing in potentially virus laden ponds; and exposure to H5N1 at live bird markets.
Conclusions
Research has demonstrated that despite frequent and widespread contact with poultry, transmission of the H5N1 virus from poultry to humans is rare. Available research has identified several risk factors that may be associated with infection including close direct contact with poultry and transmission via the environment. However, several important data gaps remain that limit our understanding of the epidemiology of H5N1 in humans. Although infection in humans with H5N1 remains rare, human cases continue to be reported and H5N1 is now considered endemic among poultry in parts of Asia and in Egypt, providing opportunities for additional human infections and for the acquisition of virus mutations that may lead to more efficient spread among humans and other mammalian species. Collaboration between human and animal health sectors for surveillance, case investigation, virus sharing, and risk assessment is essential to monitor for potential changes in circulating H5N1 viruses and in the epidemiology of H5N1 in order to provide the best possible chance for effective mitigation of the impact of H5N1 in both poultry and humans.
