Highly Pathogenic H5N1 Increases Spread to EU Countries, Africa, and India
By Eric toner, MD, February 21, 2006
The last 2 weeks have brought troubling news about the continued rapid global spread of H5N1 highly pathogenic avian influenza (HPAI). It is worth remembering that although H5N1 HPAI was first isolated from a goose in Guandong, China in 1996, the current strain, genotype Z, only appeared 25 months ago. In those 25 months, the virus has spread throughout Asia and into Siberia, the Middle East, North and West Africa, the Mediterranean, Central Europe, India and now Northern and Western Europe (Map).
Migratory Water Fowl are Asymptomatic Carriers
In addition to being spread by the poultry trade, the virus is being carried by asymptomatic migratory water birds, primarily ducks, which are infecting other species, primarily swans and poultry. Although low pathogenic avian influenza viruses are commonly found in the guts of migratory water fowl, this is the first time that birds have been known to be asymptomatic carriers of a highly pathogenic virus, which has resulted in the first known highly pathogenic influenza panzootic. At this point, it seems increasingly likely that the virus will continue be transmitted from one migratory species to another, eventually finding its way to the Americas. That could happen as early as this year.
Infected Poultry Poses the Greatest Threat to Humans
To date, most of the 170 human cases have been associated with close contact with infected poultry. Water fowl, poultry and people each have different hemagglutinin attachment receptors for influenza A viruses. Poultry receptors are more similar to the human receptors than are those from wild water fowl. Therefore, the viruses that are most likely to infect humans are those that have adapted to poultry. Thus, although infected swans and other wild birds are good indicators of the geographic distribution of the virus, their infections with the H5N1 virus are not likely to directly result in many human infections. On the other hand, outbreaks among poultry, such as those seen in Asia, are likely to continue to cause occasional human infections. The extensive outbreaks in chickens in Nigeria, India and Egypt are also likely to result in human cases.
The HIV “Wild Card”
The biggest threat is the possibility of efficient human-to-human transmission either by continued gradual evolution of the virus, as has been seen in Turkey, or by a sudden reassortment event. In either case, every additional human case increases the risk that the virus will adapt to a human host. In many parts of the world, but particularly in Africa, an unpredictable wild card is the high rate of HIV infection. So far only one H5N1 patient has been reported to also be infected with HIV. The literature on HIV and human influenza suggests that HIV/AIDS patients are more susceptible to adverse complications, including both viral and bacterial pneumonia[4, 5]. They also shed the H5N1 virus longer--sometimes for months. In addition, antiviral resistance has recently been found to occur more frequently in immunocompromised patients . The interaction of H5N1 and HIV could have significant implications for the health of those who may be co-infected. Moreover, if HIV and H5N1 co-infection amplifies the spread of H5N1, it could cause a significant increase in the numbers of people infected with the avian flu virus.
Are You and Your Hospital Prepared?
Clinicians in two thirds of the world now face the real possibility of seeing human H5N1 cases in their own hospitals in the near future, even in the absence of an actual pandemic. Recent events underscore the likelihood the physicians in the western hemisphere may be faced with the same situation in the not too distant future as well. Clinicians should ask themselves, am I ready for human H5N1 in my hospital?
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