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A Faerie's Farthing

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Saturday, February 18, 2006

Keeping Up With Avian Flu

Keeping Up With Avian Flu

Flu season may be drawing to a close, but bird flu marches on. After Iraq reported its first cases from northern provinces a few weeks ago, the virus appears to be spreading through the country. Iraq's health minister has declared an alert for the southern province of Maysan, where one suspected case has been discovered.

The Iraqi cases are especially alarming because there were no reported animal cases first, which indicates a breakdown in monitoring and reporting of the disease. In a war-torn country lacking infrastructure, an outbreak could quickly prove unmanageable.

More alarming still, officials said, the finding suggests that the disease may be spreading widely - and undetected - among birds in countries of Central Asia that are poorly equipped to pick up or report infections. Bird flu has never been reported in animals in Iraq.

As in Turkey earlier this month, the spread of bird flu to a new part of the world was heralded by a human death, a death that was most likely avoidable. Bird flu only rarely infects humans, late in the course of an animal outbreak, and then only after intense contact with sick birds.

"We shouldn't be seeing human cases first, and this points to serious gaps in surveillance," said Maria Cheng, a spokeswoman for the World Health Organization in Geneva. "But given the situation in Turkey, I don't think we'd be surprised to see isolated humans cases in surrounding areas."

...For example, the local government in Sulaimaniya is monitoring commercial poultry flocks, "but they don't really have the ability to monitor what's going on in village flocks," said Rod Kennard, who is managing a year-old UN project to rebuild veterinary services in Iraq.

What do they mean by "the situation in Turkey"? One point is that even though efforts to contain the disease have been largely successful, Turkey has already identified 55 outbreaks in 15 provinces. Like Iraq, Turkey first detected the disease in humans, not animals. Most importantly, at least one patient was infected with what appeared to be a new mutation of the virus.

Mutations that could make it easier for the bird flu virus to infect humans have been found in a sample taken from a patient in Turkey, a report in the journal Nature said Friday.

The World Health Organization is monitoring the situation, but a spokeswoman said it is too early to know whether the virus is changing in ways that would signal the start of a human flu pandemic.

..."It's one isolate from a single virus from Turkey," WHO's Maria Cheng said in Geneva. One mutation found "suggests the virus might be more inclined to bind to human cells rather than animal cells," Cheng said, but there's no evidence that it's becoming more infectious.

The Nature report cites a second mutation that also "signals adaptation to humans."

...The mutations, which were detected by scientists at a lab in London, may "signify the virus is trying different things to see if it can more easily infect humans," Cheng said. "So far, we haven't seen that the virus has the ability to do this. But it's important that we continue monitoring."

Since the previous year's cases, the virus has already weakened the species barrier; it can now pass to humans from even casual contact with infected birds. Does this change have implications for human-to-human transmission? Maybe; maybe not. Nobody is sure what direction H5N1 evolution will ultimately take. But some scientists have been investigating its evolutionary mechanisms.

A recent development regarding bird flu evolution took place in October, 2005, when Dr. Jeffery Taubenberger and his associates published a letter in the science journal Nature, stating that the 1918 Spanish Flu did not evolve in the same way as two other 20th century pandemic strains: Asian Flu in 1957 and Hong Kong Flu in 1968.

The 1957 and 1968 pandemic strains evolved when a human with flu also contracted bird flu. Genetic material from the two viruses combined by what scientists call "reassortment" to create a flu that can pass between humans. It's believed that flu viruses created in this way are milder than flu viruses that evolve indepedently.

Taubenberger's work showed that the 1918 Spanish flu evolved by a process of "recombination." In other words, the virus mutated on its own to a form that humans could catch from each other.

...So far, the H5N1 bird flu virus has evolved only by recombination. And flus that evolve in this way are thought to be more deadly to their human hosts, as was the Spanish Flu of 1918, which killed millions around the globe.

The virus has recently spread to Nigeria, Egypt, Greece, and Germany, among other places. Currently, it meets all the criteria for causing a pandemic except human-to-human transmission. Hold on to your hats!

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