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Recent Avian Flu News—Pay Attention to the People, Not the Cats

By Eric Toner, M.D., March 9, 2006

Against a backdrop of daily reports of outbreaks of highly pathogenic H5N1 avian influenza in birds throughout Europe, Asia, and Africa and a report of the death of a H5N1-infected Chinese man in China’s Guangdong province [1], attention has been most sharply focused in the past week on the discovery of H5N1 in cats in Europe. Three cats, on Ruegen Island in northern Germany, died from H5N1 infection, and 3 others in an animal shelter in Austria were found to have non-lethal H5N1 infections [2]. In Austria, the cats were reportedly caged next to infected birds in the mistaken belief that the virus could not be transmitted from birds to mammals. While seemingly worrisome, the feline infections should not distract attention from the import of the news from China, which is genuinely troublesome for what it may signal.

There is no evidence, for instance, to suggest that the appearance of the H5N1 virus in cats is related to a change in the biology of the virus. The cats died in an area in Germany known to have a number of wild birds infected with H5N1. Furthermore, it has been known since early in the global outbreak that felines are susceptible to infection with H5N1: in 2004 several tigers died in a Thai zoo after being fed raw, contaminated chicken carcasses [3]. In addition, it has been shown that domestic cats are susceptible to the virus and able to transmit it to other cats [4].

While only one of 15 confirmed human infections with H5N1 in China, the case of the man who recently died is of greater concern than the feline infections in Europe for 3 reasons:

  1. There have been no reports of H5N1 infection in birds in Guangdong province in the past year.

  2. Unlike most other human cases of H5N1, this man had no apparent contact with farms, rural areas or backyard poultry.

  3. This man did have contact with the live animal “wet” markets, wherein all birds are supposedly screened and vaccinated against H5N1; these are the same live animal markets in Guangdong province that gave rise to the SARS virus.

There have been several other incidences of human infection in China in areas where no bird cases have been reported. It has been suggested that this may be attributable to the use of poor quality or counterfeit vaccine that produces only partial immunity in birds. With partial immunity, the birds can carry the H5N1 virus without becoming ill themselves. There was a report from ProMed in December of the arrest of 9 people who were selling fake vaccine that is believed to have contributed to an outbreak in northeastern China [5].

The SARS-related coronavirus was spread among civets and other fairly exotic and expensive animals in the wet markets in China, and then transmitted to people who handled and slaughtered them. Chicken is a staple of the Chinese diet and is eaten in far greater quantities than civets. If chickens and other birds in the wet markets are infected, despite vaccination, and without signs of illness, the risk of spread to large numbers of people may be greatly increased. The true extent of H5N1 infections in China is unknown. WHO officials have repeatedly suggested, that there may be many more human H5N1 infections in China than have been reported [6]. Since every human infection represents an opportunity for mutation that may result in effective human-to-human transmission of H5N1, a great increase in the numbers of infected people may increase the threat of a pandemic.

References

  1. China's latest bird flu death adds to worries for HK. Retuers AlertNet. March 7, 2006. Available at:  http://www.alertnet.org/thenews/newsdesk/HKG281322.htm.  Accessed March 6, 2006.
  2. Austrian cats get, then beat, bird flu; health experts plan for pandemic. Agence France Press. March 6, 2006. Available at: http://news.yahoo.com/s/afp/20060306/hl_afp/healthflu_060306230602.  Accessed March 6, 2006.
  3. Thanawongnuwech R, et al. Probable tiger-to-tiger transmission of avian influenza H5N1. Emerg Infect Dis. 2005;11:699-701.
  4. Rimmelzwaan GF, et al. Influenza A virus (H5N1) infection in cats causes systemic disease with potential novel routes of virus spread within and between hosts. Am J Pathol. 2006;168:176-83.
  5. ProMED-mail. Avian Influenza-Eurasia (88): China, Vaccines. ProMed-mail 2005; 1 Dec: 20051201.3468. Available at:  http://www.promedmail.org/pls/askus/f?p=2400:1001:11736603311717157397::NO::F2400_P1001_BACK_PAGE, F2400_P1001_PUB_MAIL_ID:10001,31229. Acessed March 7, 2006.
  6. ProMED-mail. Avian Influenza, human – worldwide (23): China. ProMed-mail 2006; 2 Mar: 20060306.0726. Available at: http://www.promedmail.org/pls/askus/f?p=2400:1001:11736603311717157397::NO::F2400_P1001_BACK_PAGE, F2400_P1001_PUB_MAIL_ID:1000,32261. Accessed March 6, 2006.