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Letter
Highly Pathogenic Avian Flu,
Japan
Kazuo Inoue*
*University of Tokyo, Tokyo, Japan
Suggested citation
for this article: Kazuo I. Highly pathogenic avian flu, Japan [letter].
Emerg Infect Dis [serial on the Internet]. 2004 Jul [date cited].
Available from: http://www.cdc.gov/ncidod/EID/vol10no7/04-0116.htm
To the Editor: More than 15,000 chickens on an egg farm in Yamaguchi
Prefecture (Chugoku area) have died since the end of 2003. A highly pathogenic
avian influenza virus, which had not appeared in Japan for 79 years, was
detected in the dead chickens. Of the 34,600 chickens on the farm, dozens
to hundreds have died daily since December 28. Moreover, the deaths have
increased during 2004. The Ministry of Agriculture, Forestry, and Fisheries
ascertained that the same H5N1 avian influenza virus had caused the bird
flu epidemic that started in 1997 in East Asia, including Hong Kong, Vietnam,
and South Korea. The H5N1 type is a virulent pathogen that can also infect
humans as demonstrated by the >20 deaths in Hong Kong, Vietnam, and
Thailand. After the influenza infection was confirmed, the ministry immediately
ordered the hennery to recall all eggs that had been shipped. The hennery
was then disinfected, and nonworkers were restricted from entering. Yamaguchi
Prefecture also restricted transfer of the chickens and eggs within a
30-km radius of the infected hennery. The hennery was the first facility
infected in Japan. Since mid-February, an additional three outbreaks have
occurred (one in Ohita Prefecture in Kyushu Island and two in Kyoto Prefecture
in the Kansai Area). In a big poultry farm in Kyoto, 40,000 deaths of
chickens, caused by H5N1, were confirmed. The H5N1 virus was also detected
by polymerase chain reaction in crows found dead near the chickens in
Kyoto. All four sites with infected chickens are in western Japan.
Modern stock raising that involves breeding a large number of domestic
animals and fowl in high density has become a risk factor for large-scale
outbreaks. The globalization of the marketplace and easy mobility of people
and goods have facilitated the spread of many pathogens. Avirulent pathogens
that mutate easily may acquire stronger infectious and toxic properties
as confirmed in the influenza pandemic of 1918 (1).
Several possibilities exist for the appearance of avian influenza virus
in Japan. First, migratory birds from epidemic disease areas might be
the primary vectors of the virus. Yamaguchi Prefecture is located 200
km southeast of South Cholla Province, South Korea, where avian influenza
is epidemic. The two areas are close enough for wild birds to cross the
Korean Strait. Ito et al. reported that avirulent viruses found in wild
waterfowl and bearing the consensus avirulence type sequence R-E-T-R have
the potential to become pathogenic when present in chickens (2).
Thus, migratory birds that are asymptomatic carriers may cross the Korean
Strait harboring the H5N1-type virulent viruses generated in Korea. Alternatively,
people, cars, and feed grains instead of migratory birds could carry the
virulent viruses. To identify the source of infection, the genetic sequence
of the virus will be compared with the sequences of viruses acquired in
other epidemic areas.
The avian influenza virus did not originally infect other animals, including
humans. The virus in Japan had different DNA sequencing from the viruses
responsible for human deaths in Hong Kong and Vietnam. However, mutations
of the virus in pigs as a result of hybridization are possible, since
both avian and human influenza viruses can infect pigs. According to the
Food and Agriculture Organization of the United Nations, the H5N1-type
virus was detected in pigs raised on farms that also raise chickens infected
with the virus in Vietnam. Thus, a new virus that can infect other animals
may emerge. In fact, a clouded leopard died of avian influenza in Thailand.
The worst scenario would be that the new virus could be spread from person
to person. An avian influenza vaccine is not available in Japan. Because
a vaccine may not be developed quickly enough, this new influenza might
become pandemic. Therefore, to prevent the virus from infecting humans,
bird-to-bird transmission must be stopped.
References
- Stevens J, Corper AL, Basler CF, Taubenberger JK,
Palese P, Wilson IA. Structure of the uncleaved human H1 hemagglutinin
from the extinct 1918 influenza virus. Science. [serial on the Internet]
2004 Feb [cited 2004 Feb 5]. Available from: http://www.sciencemag.org/cgi/content/abstract/1093373v1
- Ito T, Goto H, Yamamoto E, Tanaka H, Takeuchi M, Kuwayama M, et al.
Generation
of a highly pathogenic avian influenza A virus from an avirulent field
isolate by passaging in chickens. J Virol. 2001;75:4439–43.
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