Birds and the flu
From: ProMED Digest V2004 #19
Source: World Health Organization (WHO), WER and Epidemiological Bulletin
online, Tue Jan 13 2004 [edited]
Viet Nam: avian influenza A(H5N1) in humans and poultry
Laboratory results received on Sun 11 Jan 2004 have confirmed the presence
of avian influenza virus strain A(H5N1) in samples taken from humans. The
samples were taken from 2 children and one adult admitted to hospital with
a severe respiratory illness in Hanoi.
Since the end of October 2003, hospitals in Hanoi and surrounding provinces
have admitted 14 people with severe respiratory illness. The cases are 13
children and one adult, the mother of a deceased child. To date, 11 of the
children and the adult have died. It is not known whether all of these
cases were caused by the same pathogen.
At present, there is no evidence that human-to-human transmission has
occurred. No reports indicate that health care workers have been infected.
The presence of avian influenza A(H5N1) in samples from 3 of these cases
was confirmed by Hong Kong's National Influenza Center, which is a member
of the WHO Global Influenza Surveillance Network. Samples have also been
sent for analysis to Japan's National Institute for Infectious Diseases,
another member of the WHO influenza network. Results are awaited shortly.
WHO is providing support to Vietnamese health authorities in their
investigation of the cases and in the prevention of further spread to humans.
Avian influenza strains normally infect birds only. The first cases of
human infection with avian influenza A(H5N1) were identified in 1997 in
Hong Kong. The virus infected 18 people and caused 6 deaths. Genetic
studies subsequently linked the outbreak in humans to an outbreak of highly
pathogenic avian influenza in poultry. The immediate culling of around 1.5
million poultry in Hong Kong is thought to have averted a larger outbreak
Other recent outbreaks of avian influenza in humans have caused limited
disease. An outbreak of H5N1 in Hong Kong in February 2003 caused 2 cases
and 1 death. An outbreak of H7N7 avian influenza in the Netherlands caused
the death of one veterinarian in April 2003, and mild illness in 83 humans.
Mild cases of avian influenza A(H9N2) in children occurred in Hong Kong in
1999 (2 cases) and in mid-December 2003 (one case).
Highly pathogenic avian influenza in poultry
Last week, avian influenza virus A(H5N1) was identified as the cause of an
outbreak of highly pathogenic avian influenza in two southern provinces of
Viet Nam. To date, the virus, which spreads rapidly and has a mortality in
chickens approaching 100 per cent, has resulted in the deaths of 40 000
chickens and the culling of 30 000 more.
The relationship between the human and poultry outbreaks of avian influenza
A(H5N1) in Viet Nam is not fully understood at present. WHO and Viet Nam's
Ministry of Health are undertaking investigations to determine the source
of the human cases and whether human-to-human transmission has occurred.
The situation is also being followed closely by the country's Ministry of
Agriculture and Rural Development.
An outbreak of avian influenza A(H5N1) occurred in South Korea in December
2003. On Monday, Japanese authorities announced the death of 6000 chickens
at a single farm as due to infection with the same strain of the virus.
These outbreaks mark the first cases of avian influenza in South Korea, and
the first cases in Japan since 1925. No human cases of infection with the
avian influenza virus have been reported in either of these outbreaks.
WHO regards every case of transmission of an avian influenza virus to
humans as a cause for heightened vigilance and surveillance. The
circulation of highly pathogenic avian influenza viruses in large numbers
of poultry in a growing number of countries is of particular concern.
Influenza viruses are highly unstable. The co-circulation of highly
pathogenic animal viruses with human viruses could create opportunities for
different species-specific viruses to exchange genetic material, giving
rise to a new influenza virus to which humans would have little, if any,
[A ProMED-mail correspondent in Japan has forwarded the information that
Japanese media are reporting today that the Japanese Ministry of
Agriculture, Forestry and Fisheries has announced that the highly
pathogenic avian influenza virus responsible for the current outbreak in
Japan has been typed as avian influenza A (H5N1)virus. The recent spread of
avian influenza A (H5N1) virus through east Asia is an increasing cause for
concern, as are the isolated instances of transmission to humans. This may
reflects the expansion of poultry farming and greater opportunities for
contact between humans and domestic poultry. Although the present situation
is fairly stable, it may only be a matter of time before a reassortant
virus or mutant virus capable of human-to-human transmission evolves. -