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Avian Influenza: Inadequate Surveillance Undermines Pandemic Preparedness

By Eric Toner, M.D. and D.A. Henderson, M.D., M.P.H., May 17, 2005

Reliable surveillance is the essential starting point for pandemic influenza response plans; however, several recent news items raise questions about the adequacy of the current epidemiological intelligence originating in South Asia.

  • According to a report in the May 10 issue of Nature, countries affected by avian influenza may be reluctant to share specimens of the H5N1 virus. Nature reported that the WHO had obtained only 6 samples of virus obtained from human sources and no samples of virus from poultry in the last eight months. The WHO denied the story, saying that, in fact, Viet Nam provided 100 clinical samples. However, the yield of viruses derived from these specimens is quite low, severely compromising the ability to track mutations in the virus. The ability to track genetic changes is crucial to vaccine preparation. In addition, monitoring for mutations known to be associated with human infection and lethality may give early warning of a shift to a pandemic strain. Given compelling evidence that the current H5N1 strain is both adapting to mammalian hosts and being spread ever more widely by birds, especially ducks, ongoing surveillance of viral samples is essential.

  • Last week it was reported by Canadian Press that PCR tests being used to test for human cases of H5N1 are not up to date, and may therefore produce false negative results. This corresponds with several incidences of apparent false negatives in Vietnam.

  • Indian Express reported last week that specimens taken from 3 poultry workers in India in 2002 tested positive for H5N1 antibodies. If confirmed, then despite the fact that there have been no recognized outbreaks of H5N1 infection in India, these results suggest that there is or was circulating H5N1 virus in a country that is more than 1,000 miles from countries where avian influenza is known to exist.

In addition to these news reports, we note that no large scale H5N1 serological studies have yet been published from the region. As a result it is impossible to tell the true extent of the outbreak of human H5N1 infection, the spectrum of disease it causes, the true case fatality rate or the degree to which it is being transmitted to others.

Many influenza experts have issued grave warnings of an imminent pandemic. The hope inherent in all planning for a pandemic is that if we are able to detect a pandemic early in its course, we may be able to undertake necessary preparations in both prevention and medical care. This will not be possible without comprehensive and reliable surveillance.

Polio Exported to Indonesia and Yemen

By Brad Kramer and Eric Toner, M.D.

In the past month, cases of polio have been detected in Yemen and Indonesia, countries which had been polio-free for nearly 10 years. Experts suspect the virus causing disease in Indonesia may have been carried by migrant workers or by pilgrims visiting religious sites in Saudi Arabia during the Hajj.

On April 20, 2005, four cases of polio due to wild poliovirus type 1 were confirmed in Yemen. Since then, at least 45 more cases have been confirmed across the country. On May 2, 2005, a global reference laboratory confirmed a wild poliovirus type 1 isolate from a patient in Western Java, Indonesia with acute flaccid paralysis. As of May 13th, eight cases had been confirmed by government sources. Prior to these occurrences, Indonesia had not seen a case of wild poliovirus since 1995, and Yemen had been polio-free since 1996. Genetic analysis of the viruses indicates that the Indonesian poliovirus was likely carried from Nigeria through Sudan, and is similar to viruses recently isolated in Saudi Arabia and Yemen.

In late May, Yemen will launch a nationwide immunization campaign to vaccinate all of the country’s 4.5 million children under the age of five. Indonesia has launched an initiative to vaccinate the 5.2 million children under the age of five living in west Java. Extension of this campaign to cover other areas of Indonesia will depend on surveillance data and the determination of wider spread.

Yemen and Indonesia are the 15th and 16th previously polio-free countries to be reintroduced to the virus within the past 2 years. In early 2003, only 6 countries were endemic for polio, and then late in the year, rumors that Western vaccines caused infertility in Muslim girls caused many individuals in Nigeria to resist vaccination, which allowed spread of the virus outside of Nigeria. The immunization program resumed after vaccine was secured from Indonesia, an Islamic country. World Health Organization (WHO) officials have indicated that northern Nigeria was the original source of poliovirus strains now causing disease in both Yemen and Indonesia.

In this age of widespread global travel, this multi-country re-emergence of polio highlights the need for increased vigilance in monitoring for all pathogenic microbes, even those thought to have been eradicated or brought under control.