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Monday, June 20, 2005
Drug-Resistant Avian Flu In China From Inappropriate Medication Of Chickens Avian influenza (or bird flu) outbreaks have devastated the poultry industry in Asia in recent years. Since 2003, avian flu has swept through poultry populations of at least nine countries in Eastern Asia and Southeast Asia. Tens of millions of chickens have either died form infection or have been slaughtered to contain viral spread. Passage of the virus from birds to humans has resulted in at least 54 deaths in Cambodia, Thailand and Vietnam. Officials of the World Health Organization (WHO) have warned that the virus is highly mutable and could develop into a strain capable of a deadly pandemic affecting tens of millions worldwide. Therefore, it follows that health officials would want to have as many useful antiviral drugs as possible in their medical arsenal in order to battle this debilitating disease in humans. Well, it seems that the WHO might have lost one of their two best weapons. An article in the 18 June 2005 Washington Post reports that the Chinese government has been encouraging Chinese farmers to treat major bird flu outbreaks among chickens by giving the chickens amantadine, an important antiviral/anti-flu drug meant for humans. The result is that now strains of the bird flu are rapidly evolving that are immune to the drug. Treatment of chickens and other livestock with human-approved drugs is in violation of US and most international livestock guidelines. The Chinese, however, have apparently been using amantadine in chickens since the 1990s, well before China acknowledged bird flu infection of its poultry in 2004. International researchers now conclude that years of adaptation by the virus to amantadine have rendered the drug ineffective. For this reason, amantadine will no longer protect people in case of a worldwide bird flu epidemic. From the Washington Post article: Amantadine is one of two types of medication for treating human influenza. But researchers determined last year that the H5N1 bird flu strain circulating in Vietnam and Thailand, the two countries hardest hit by the virus, had become resistant, leaving only an alternative drug that is difficult to produce in large amounts and much less affordable, especially for developing countries in Southeast Asia. In fact, just days ago, USA Today and other media reported the first apparent human case of avian flu in Indonesia. It bears noting that bird flu infection is not universally fatal for humans. As noted in USA Today: …[W]hile most people who tested positive for bird flu showed symptoms of the disease, some did not. During a 1997 outbreak in Hong Kong, for example, about 10% of workers in poultry markets tested positive for the virus but were not ill… . The concerns of health officials, however, are far from alarmist. As more humans become infected with avian flu viruses, the chances increase for infection by a drug resistant form, which could lead to life-threatening illness and epidemic, or even global pandemic. If there are fewer pharmacologic tools available as a treatment because of viral resistance, then the public health implications are all the more serious. There is also an economic angle, as noted by The Post: "Amantadine is widely used in the entire country [of China]," said Zhang Libin, head of the veterinary medicine division of Northeast General Pharmaceutical Factory in Shenyang. …Zhang and other animal health experts said the drug was used by small, private farms and larger commercial ones. Amantadine sells for about $10 a pound, a fraction of the drug's cost in Europe and the United States, where its price would be prohibitive for all but human consumption. The way that amantadine acts to inhibit flu virus spread is not well understood. The drug appears to block an important protein pore (the M2 H+ channel) in the viral outer coat that is essential for allowing the virus to reproduce and spread from cell to cell in an infected animal or human. (It seems to help maintain the optimum viral pH, or acid/base balance.) Clever flu viruses have been engineering new ways to work around this channel blocker drug, rendering it ineffective in the resistant viral strains. I don't think it is clear yet exactly what mutations in the avian flu virus have led to recent widespread immunity of the virus to amantadine due to the Chinese government's imprudent action. Such investigation will aid researchers as they try to design new antivirals, but the drug development and approval process is a tedious and expensive one rife with failure. More to the point: This egregious error on the part of myopic and selfish Chinese authorities could have lasting repercussions outside of Asia, should an avian flu epidemic involving these newly resistant viral strains spread in humans. Since there are so few effective antiviral drugs available, the loss of any one as a potential treatment for human avian flu infection could have dire implications for worldwide public health. The MaryHunter blogs at TMH's Bacon Bits. This story was modified 6/20/2005 7:26:10 AM:Corrected final paragraph per original post http://www.tmhbaconbits.net/2005/06/20/resistant-bird-flu/ Blogger News Network is advertiser-supported, and your visits to our advertisers help BNN to meet its expenses. Help keep us afloat! posted by BNN Archive at 7:58 PM |
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