EID Weekly Updates:
Emerging and Reemerging Infectious Diseases, Region of the Americas
Vol. 2, No. 6—12 February 2004
Since our last update on 5 February 2004, 4 new human cases of avian influenza have been confirmed in Viet Nam—out of which 3 have died—and 1 more in Thailand who is still alive. To date, 2 countries have reported human cases of avian flu (Viet Nam and Thailand), with a total of 25 persons affected, 6 of whom are still alive. The scaling up of surveillance for the early detection of new cases, along with the availability of detailed information on current cases, are both essential in order to evaluate the pandemic potential of avian influenza virus H5N1. To this end, WHO has published its Guidelines for Global Surveillance of Influenza A/H5 as well as its Preliminary Clinical and Epidemiological Description of Influenza A (H5N1) in Viet Nam.
According to the WHO update of 11 February 2004 on possible person-to-person transmission, the results of the study carried out on the virus isolated in the 23-year-old person belonging to the group of cases from one Vietnamese family, indicate that the genetic material in this case—the same as with the rest of the family—is of avian origin and does not contain any of the genes from the human influenza virus.
Several countries experiencing poultry outbreaks have weak health infrastructures as well as a low level of capacity for case diagnosis and detection, particularly in rural areas where the majority of domestic birds are raised. Moreover, the full clinical spectrum of H5N1 illness is unknown. Milder cases of illness could be occurring yet fail to come to the attention of health-care staff. For this reason, the current number of laboratory-confirmed cases cannot be taken as an accurate indication of the magnitude of the disease nor of its potential threat to human health.
Of the 10 countries that have reported outbreaks of avian flu in birds, 4 have documented widespread epizootics. This week, China reported a new outbreak to WHO. No detailed plan has yet been formulated to control influenza in animals and thereby reduce the risk to the human population. Over the past four decades, only 18 outbreaks of highly pathogenic avian flu have been reported throughout the world, most of them caused by the different H5N1 strains. Previous outbreaks of highly pathogenic avian influenza associated with human infections occurred in areas, such as Hong Kong and The Netherlands, with industrial poultry production and well-developed health and agricultural infrastructures. Both outbreaks were eventually controlled through the immediate culling of infected flocks, quarantining and disinfecting farms, strict biosecurity, restrictions on the movement of animals, and compensation for farmers.
According to the present situation, controlling the outbreaks of highly pathogenic avian influenza is especially difficult. Rural areas in several countries have been affected, in places where raising domestic birds is a common practice. Therefore, H5N1 virus could become established in bird populations in this geographical region, making it possible for it to spread to other parts of the world. Existing evidence available up to now does not provide enough information on which to base any universal recommendations that could be applied to ensure rapid and effective response in the affected countries.
Therefore, any control measures taken should be tailored to each country’s unique epidemiological situation and unique capacity, with the health and agricultural sectors working together. The agricultural authorities are faced with the immediate challenge of rapidly eliminating the H5N1 poultry reservoir. The authorities from all the affected countries need to work in a coordinated manner.