Influenza updates
Bird ‘flu again spreads across Asia
Pandemic ‘flu unlikely to spread through water systems Cornell researchers studied the related virus, called H5N2, to see whether a hypothetical mutated form of H5N1 could infect people through drinking and wastewater systems. Researchers at Cornell and the US Military Academy at West Point collaborated on the study, published in a recent issue of Environmental Engineering Science. H5N2, a low-pathogenic avian influenza virus that is not contagious for humans, is physically similar to H5N1, which has been lethal to millions of birds globally and more than half of the almost 200 infected people mostly through handling infected birds, since 2003. Researchers and officials are concerned that if H5N1 mutates to transmit easily between people, a global pandemic could occur. Because H5N1 requires high-level biosafety facilities, Lucio-Forster and colleagues used H5N2 as a surrogate virus. Given the similarities between the two viruses, Lucio-Forster believes that if H5N1 entered the water treatment system, "the virus should be inactivated, which means treated water may not be a likely source of transmission," said Lucio-Forster. To test the effectiveness of UV radiation for killing the H5N2 virus, the researchers exposed the virus in drinking water as well as in wastewater effluents to UV light at varying levels. The treatment was very effective in killing H5N2 at levels well within industry standards (and at lower levels than are used for killing Cryptosporidium and Giardia in water). For chlorine, which is mostly ubiquitous in US drinking water, the results were less definitive. Inactivation of H5N2 depends on both chlorine concentrations and time of exposure. On average, US treatment plants treat drinking water with chlorine concentrations of 1 milligram per liter for 237 minutes. Under these conditions, the researchers found that H5N2 (and probably H5N1) would be mostly inactivated, but further studies are needed to see if the viruses stay active when they come out of feces or are at different pH and salinity levels. Similarly, the small laboratory-scale study found that bacterial digesters also reduced H5N2 to undetectable levels after 72 hours, which is consistent with industry standards. The researchers also found that higher digester temperatures inactivated the virus more quickly.
Ramifications of widespread use of Tamiflu Since the World Health Organization’s first warning of a potential ‘flu pandemic, nations worldwide have been stockpiling Tamiflu for treatment and outbreak prevention. The drug, which minimizes ‘flu symptoms and duration, inhibits the movement of the influenza virus from the cells it infects, and also helps uninfected people avoid contracting ‘flu. However, Tamiflu’s active agent, the metabolite oseltamivir carboxylate (OC) would be excreted into sewers for several weeks during a pandemic and is expected to withstand biodegradation. According to the researchers in the current study, once birds drink OC-laced water from catchments receiving treated wastewater, they could produce Tamiflu-resistant strains and pass them on to other birds who share the same waters. The investigators analyzed 11 waterway catchments in the United States and five in England using a metabolic pathway prediction system to determine the potential biodegradability of OC. They also measured wastewater discharges into the catchments. They estimated the number of clinically infected people in each catchment area treated with a full 5-day course of Tamiflu with 100 percent compliance, assuming that 80 percent of the ingested Tamiflu was released into sewer systems as OC and that all of the OC entering each catchment was flushed out in one day. Their estimates showed a maximum concentration well above that required for development of resistance in vitro for 62 consecutive days in the arid Lower Colorado River catchment area. Overall, the researchers say that because of the lower population density for many of the US catchments, peak concentrations of OC in a pandemic would be approximately 10 times less than the concentrations in British rivers. All but one of the American catchments studied are larger than those in Britain and, with the exception of the Lower Colorado River flow area, have more available dilution per person in each given population. There were no specific ecotoxicological risks from Tamiflu identified at the time the drug was submitted for approval to the European Medicines Agency. The authors, however, suggest that the ecotoxicological risk associated with Tamiflu use needs to be reassessed in light of the hundreds of millions of courses that would be consumed globally during a pandemic. The authors warn that, with the release of the uniquely structured, biochemically resistant OC antiviral into river water, "the range of OC concentrations predicted . . . will have uncharacterized ecotoxicological consequences." They call for more detailed water contamination modeling, especially in high-risk areas of the world such as Southeast Asian countries, where there is more frequent human-to-waterfowl contact and where future use of Tamiflu would be significant. They also recommend development of methods to minimize the release of OC into wastewater systems, such as biological and chemical pretreatment in the toilet. The lead author of the study was Andrew C. Singer. Other authors included Miles A. Nunn, Ernest A. Gould, and Andrew C. Johnson.
•Date: 17th January 2007 • Region: World •Type: Article •Topic: Pandemic planning
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