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Amantadine off the table in future avian flu pandemic?

Posted on Thursday, January 8, 2009 at 09:54AM by Registered CommenterScott McPherson in , | Comments1 Comment

The University of Colorado confirms what we always suspected - that the overuse of amantadine in Chinese poultry vaccines has rendered the M2 antiviral essentially useless if H5N1 "goes pandemic."

A brand-new paper from the University of Colorado at Boulder (Go Buffaloes!) has confirmed the resistance of at least 30% of the existing substrains of H5N1 avian flu to amantadine, an M2 antiviral. Further, this study declares that amantadine resistance is now (in laymens terms) part of the natural evolution of the virus, meaning it has become the norm; the standard; the template for virus evolution. Irreversible and permanent, this resistance to amantadine (and also rimantadine) is the direct result of Chinese farmers feeding it to their chickens in a futile effort to beat back H5N1. The presence of amantadine in feed and in vaccines simply hastened the virus's resistance to the antiviral.

Amantadine works against the M2 protein by preventing it from doing its duty; namely, dissolving the outer coating of the virus.  By denying the virus the chance to dissolve its coat, it cannot infect.

Researchers, using among other tools the famed Google Earth API (for Application Programming Interface), have created a template so they can watch in near real-time as viruses, including H5N1, begin to display resistance to certain antivirals and drugs. "Real time" would be defined as the time in which these findings are actually noted, meaning researcher and publication real time, and not time as the real world knows it. Further, real time in this universe is complicated by the lack of shared data, which can render this issue moot if researchers are denied information on drug resistant genetic changes and modifications in the virus itself.

Researchers also speak to the Elephant In The Room, which is Tamiflu resistance. So far, they say, there is no cause for concern. But they hasten to add that it is not yet under the influence of "positive genetic selection," meaning that it H5N1 has not yet settled in to any sort of observable trend toward Tamiflu resistance. Yet.

Of particular interest to us (and probably to Dr. Henry Niman) is the statement that resistance is not being conferred via reassortment, or the mixing of genes as the virus mingles with other copies of itself. Instead, the amantadine resistance is gaining momentum via novel genetic mutations rather than an exchange of RNA segments within cells, according to the author of the study.

Here's the news story:

Bird flu becoming more resistant to antivirals

The avian flu, an Influenza A subtype dubbed H5N1, is evolving a resistance to a group of antiviral drugs known as adamantanes, one of two classes of antiviral drugs used to prevent and treat flu symptoms, said CU-Boulder doctoral student Andrew Hill, lead study author. The rise of resistance to adamantanes -- which include the nonprescription drugs amantadine and rimantadane -- appears to be linked to Chinese farmers adding the drugs to chicken feed as a flu preventative, according to a 2008 paper by researchers from China Agricultural University, said Hill.

In contrast, resistance of the avian flu virus to the second, newer class of antiviral drugs that includes oseltamivir -- a prescription drug marketed under the brand name Tamiflu -- is present, but is not yet prevalent or under positive genetic selection, said Hill of CU-Boulder's ecology and evolutionary biology department. The CU findings should help health administrators around the world plan for the possibility of an avian flu pandemic.

The CU-Boulder study is the first to show H5N1 drug resistance to adamantanes arose through novel genetic mutations rather than an exchange of RNA segments within cells, a process known as re-assortment, said Hill. The research on the mutations, combined with molecular evolution tests and a geographic visualization technique using Google Earth, "provides a framework for analysis of globally distributed data to monitor the evolution of drug resistance," said Hill.

The CU-Boulder-led study appears online in the journal Infection, Genetics and Evolution . Co-authors included CU-Boulder Associate Professor Robert Guralnick, recent CU-Boulder graduate Meredith Wilson, Farhat Habib of Kansas State University and Daniel Janies of Ohio State University.

"As these adamantanes have gotten into nonhuman vectors like birds, the positive selection for resistance to avian flu is rising," said Hill. "If Tamiflu is ever used in the manner of adamantanes, we could conceivably see a similar resistance developing through positive selection."

The research team used an interactive "supermap" using Google Earth technology that portrays the individual gene mutations and spread of the avian flu around the globe, said Guralnick of CU-Boulder's ecology and evolutionary biology department. By projecting genetic and geographic information onto the interactive globe, users can "fly" around the planet to see where resistant H5N1 strains are occurring, said Guralnick, also Hill's doctoral adviser.

For the study, the researchers analyzed 676 whole genomes of Influenza A/H5N1 from National Institutes of Health databases of viruses isolated between 1996 and 2007. The team is comparing how often amino acid sequence changes in genes lead to mutations that affect drug resistance in the H5N1 virus and how often such changes evolve into random mutations that don't affect resistance, Hill said.

The next step is to analyze 2008 data, he said.

First detected in China in 1996, the avian flu has spread throughout Asia and to India, Russia, Pakistan, the Middle East, Africa and Europe by various carriers, including poultry and migratory waterfowl, Hill said. While H5N1 is not highly communicable to humans from birds or between humans, experts are concerned future evolution of this subtype or other subtypes, or genetic re-assortment between subtypes, could make an avian influenza strain more contagious with the potential to cause a pandemic.

"Even if H5N1 is not the flu subtype that develops into the next pandemic, this technique can help us understand the properties of flu viruses and we can use these methods to track mutations in other viruses," said Guralnick. "We can harvest genetic influenza data and monitor it in near real-time, which should give this project some traction to help governments make decisions on managing potential pandemics."

Like the legend of a road map, colors and symbols on the supermap indicate which types of hosts carry the virus or the distribution of genotypes of interest, said Hill. A click by users on viral "isolates" generates computer windows revealing H5N1 mutations linked to positive genetic selection resulting from the spread and use of adamantanes.



Reader Comments (1)

There are numerous strains of influenza virus that are present naturally in wild birds, yet only a few cause infections in domesticated birds and a lesser few in humans. Of all the subtypes of influenza virus, influenza A subtype H5N1 or simply H5N1 causes the most severe illness in both infected poultry and humans. This strain of highly pathogenic influenza virus has caused millions of dead poultry and the most severe cases of avian flu in humans. It is also responsible for the most number of deaths of avian flu patients.


March 3, 2009 | Unregistered Commenteravian

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