永利集团游戏网址

Secret of drug-resistant bird flu unveiled

作者:姚踟琐    发布时间:2019-03-02 06:08:03    

By Debora MacKenzie A strain of the H5N1 flu virus that resists the antiviral drug Tamiflu has been analysed by scientists. Tamiflu, known generically as oseltamivir, is expected to be almost the only defense against the virus in the early stages of any H5N1 pandemic. But New Scientist can reveal that this discovery does not mean the drug will become useless. The mutation that made the virus resistant is already well known in ordinary human flu, and it seems to make both ordinary flu – and now H5N1 – less able to cause further infections. The resistant strain was found in a 14-year-old girl in Vietnam. She had been put on one Tamiflu capsule a day in February, to protect her while she was caring for her 21-year-old brother who had H5N1 bird flu. This dose – half the normal therapeutic level – is commonly used as a preventative measure for people exposed to the virus. But after three days she fell ill. Her dose was doubled to normal treatment levels – and it worked. Doctors failed to isolate flu virus from the girl after she went on the full dose and she eventually recovered. But a sample of virus isolated just before she started full treatment contained some viruses that were sensitive to Tamiflu, and some that were a hundred times less sensitive, report Yoshihiro Kawaoka, at the University of Tokyo, Japan, and colleagues (Nature, vol 437, p 1108). This might suggest that in a pandemic with many people taking Tamiflu, the virus could become drug resistant. But the situation is not that simple. The mutation that made the girl’s H5N1 virus resistant also occurs in ordinary flu viruses among Japanese children who are treated with Tamiflu. And ordinary flu with that mutation rarely if ever goes on to cause a new infection in another person, says Frederick Hayden of the University of Virginia, US, an expert in antiviral drugs. “Becoming resistant to this class of drugs seems to impose a fitness penalty on the virus,” he told New Scientist. Sure enough Kawaoka found that the resistant H5N1 was much less virulent in ferrets, which developed levels of virus nearly a hundredfold lower than did ferrets infected with the Tamiflu-sensitive virus isolated from the girl. Her recovery after treatment also suggests that, while resistant virus was present, Tamiflu-sensitive viruses dominated her infection The observation may, however, cast doubt on plans by some governments to put “essential” workers on Tamiflu prophylaxis if a pandemic breaks out. Large numbers of people on low doses of the drug for a long time could cause new kinds of resistant strains to emerge,

 

Copyright © 网站地图