AVIAN INFLUENZA, HUMAN - EAST ASIA (105): CDC UPDATE
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Date: Sun 24 Jul 2005
From: ProMED-mail <promed@promedmail.org>
Source: Centers for Disease Control and Prevention (CDC), Avian Influenza
update, Thu 21 Jul 2005 [edited]
<http://www.cdc.gov/flu/avian/outbreaks/asia.htm>
Recent avian influenza outbreaks in Asia - as of 21 Jul 2005
------------------------------------------------------------
Background
----------
Outbreaks of highly pathogenic avian influenza A (H5N1) [virus infection]
occurred among poultry in 8 countries in Asia (Cambodia, China, Indonesia,
Japan, Lao, South Korea, Thailand, and Viet Nam) during late 2003 and early
2004. At that time, more than 100 million birds either died from the
disease or were culled. From 30 Dec 2003 to 17 Mar 2004, 12 confirmed human
cases of avian influenza A (H5N1) [virus infection] were reported in
Thailand and 23 in Viet Nam, resulting in a total of 23 deaths. By late
February, however, the number of new human H5 cases being reported in
Thailand and Viet Nam slowed and then stopped. Within a month, countries in
Asia were reporting that the avian influenza outbreak among poultry had
been contained. No conclusive evidence of sustained human-to-human
transmission was found.
Recent Developments
-------------------
Beginning in late June 2004, however, new lethal outbreaks of avian
influenza A (H5N1) virus infection among poultry were reported by several
countries in Asia: Cambodia, China, Indonesia, Malaysia (first-time
reports), Thailand, and Viet Nam. In late March 2005, state media in the
Democratic People's Republic of Korea (North Korea) officially reported the
country's first outbreak of avian influenza in poultry. There has not been
a resurgence of avian influenza in South Korea and Japan, and the outbreaks
are reported to have been controlled in those countries. It is unknown to
what extent H5N1 outbreaks in the other countries may be ongoing. For more
information about outbreaks in poultry, visit the World Organization for
Animal Health website.
During August to October 2004, sporadic human cases of H5N1 were reported
in Viet Nam and Thailand. Of particular note is one isolated instance of
probable limited human-to-human transmission occurring in Thailand in
September 2004. Since December 2004, a resurgence of poultry outbreaks and
human cases have been reported in Viet Nam. On 2 Feb 2005, the first human
case of avian influenza A H5N1 infection from Cambodia was reported. On 21
Jul 2005, the first laboratory-confirmed human case of avian influenza A
H5N1 in Indonesia was reported.
As of 21 Jul 2005, there have been 109 human cases of avian influenza A
(H5N1) in Viet Nam (87), Thailand (17), Cambodia (4) and Indonesia (1)
resulting in 55 deaths. For more information about H5N1 infections in
humans, visit the World Health Organization (WHO) website.
Assessment of current situation
-------------------------------
The avian influenza A (H5N1) epizootic outbreak in Asia is not expected to
diminish significantly in the short term. It is likely that H5N1 infection
among birds has become endemic to the region and that human infections will
continue to occur. So far, no sustained human-to-human transmission of the
H5N1 virus has been identified, and no evidence for genetic reassortment
between human and avian influenza virus genes has been found; however, the
epizootic outbreak in Asia poses an important public health threat.
If these H5N1 viruses gain the ability for efficient and sustained
transmission between humans, there is little preexisting natural immunity
to H5N1 infection in the human population, and an influenza pandemic could
result, with high rates of illness and death. In addition, genetic
sequencing of influenza A (H5N1) virus samples from human cases in Viet Nam
and Thailand shows resistance to the antiviral medications amantadine and
rimantadine, two of the medications commonly used for treatment of
influenza. This would leave two remaining antiviral medications
(oseltamivir and zanamivir) that should still be effective against
currently circulating strains of H5N1 virus. Efforts to produce a vaccine
that would be effective against this strain of influenza A (H5N1) virus are
under way. Vaccine reference virus strains already have been made and
provided to manufacturers to produce pilot lots for human clinical trials
as well as to produce a larger quantity of H5N1 vaccine, but mass
production and availability of such a vaccine is some time off.
Recent research findings give further cause for concern. New research
suggests that currently circulating strains of H5 viruses are becoming more
capable of causing disease (pathogenic) for mammals than earlier H5 viruses
and are becoming more widespread in birds in the region. One study found
that ducks infected with H5N1 are now shedding more virus for longer
periods of time without showing any symptoms of illness. This has
implications for the role of ducks in transmitting disease to other birds
and possibly to humans as well. Additionally, other findings have
documented H5 infection among pigs in China and H5 infection in felines
(experimental infection in housecats in the Netherlands and isolation of
H5N1 viruses from infected tigers and leopards in Thailand), suggesting
that cats could host or transmit the infection. These findings are
particularly worrisome in light of the fact that reassortment of avian
influenza genomes is most likely to occur when these viruses demonstrate a
capacity to infect multiple species, as is now the case in Asia.
Notable findings of epidemiological investigations of human H5N1 cases in
Viet Nam during 2005 have suggested transmission of H5N1 viruses to 2
people through consumption of uncooked duck blood. Possible
person-to-person transmission of H5N1 viruses is being investigated in
several clusters of cases in Viet Nam.
One atypical fatal case of encephalitis in a child in southern Viet Nam in
2004 was identified retrospectively as H5N1 influenza through testing of
cerebrospinal fluid, fecal matter, and throat and serum samples. Further
research is needed to ascertain the implications of such findings.
CDC response to outbreaks - domestic activities
-----------------------------------------------
In February 2004, CDC issued recommendations for enhanced domestic
surveillance of avian influenza A (H5N1). Following the reports of human
deaths in Vietnam in August, CDC issued a follow-up Health Alert Network
(HAN) message on August 12 reiterating criteria for domestic surveillance,
diagnostic evaluation, and infection control precautions for avian
influenza A (H5N1). The HAN also detailed laboratory testing procedures for
H5N1. CDC collaborated with Association of Public Health Laboratories on 2
training workshops for state laboratories on the use of molecular
techniques to identify H5 viruses. Planning for a third training workshop
is under way.
CDC is working collaboratively with Council of State and Territorial
Epidemiologists and others to assist states with pandemic planning efforts.
CDC is working with other agencies such as the Department of Defense and
the Veterans Administration on antiviral stockpile issues.
CDC response to outbreaks - international activities
----------------------------------------------------
CDC worked collaboratively with WHO to conduct investigations of H5N1 in
Viet Nam and to provide laboratory diagnostic and training assistance. CDC
has performed laboratory testing of H5N1 viruses from Thailand and Viet
Nam. CDC has implemented a USD 5.5 million initiative to improve influenza
surveillance in Asia. CDC has conducted or taken part in 9 training
sessions to enhance local capacities to conduct surveillance for possible
human cases of H5 and to detect influenza A H5 viruses by using laboratory
techniques. CDC has developed and distributed a reagents kit for the
detection of the currently circulating influenza A H5 viruses. CDC is
monitoring the situation and remains in close contact with WHO and other
international partners. In addition, CDC continues to work collaboratively
with WHO and the National Institutes of Health (NIH) on safety testing
vaccine seed candidates and the development of additional vaccine virus
seed candidates for influenza A (H5N1).
More information
----------------
(H5N1), visit <www.cdc.gov/flu/avian/professional/han081304.htm>. For more
information about infection in birds, visit the and Agriculture
Organization of the United Nations For CDC's surveillance, diagnostic
evaluation, and infection control precautions for avian influenza A
website. For more information about infections in humans, visit the World
Health Organization (WHO) website. World Organization for Animal Health
website or the Food
Bird import ban
---------------
On 4 Feb 2004, CDC and USDA issued an order for a ban on the import of all
birds (Class: Aves) from affected areas in South East Asia. On 10 Mar 2004,
CDC, in coordination with USDA, lifted the embargo of birds and bird
products from Hong Kong. On 28 Sep 2004, the list of countries affected by
the embargo of birds and bird products was expanded to include Malaysia.
Information on influenza A (H5N1)
--------------------------------
Influenza A (H5N1) is a subtype of the type A influenza virus. Wild birds
are the natural hosts of the virus -- hence, the name avian influenza or
bird flu. The virus was first isolated from birds (terns) in South Africa
in 1961. The virus circulates among birds worldwide. It is very contagious
among birds and can be deadly to them, particularly domesticated birds like
chickens.
The virus does not typically infect humans. In 1997, however, the first
instance of direct bird-to-human transmission of influenza A (H5N1) virus
was documented during an outbreak of avian influenza among poultry in Hong
Kong; the virus caused severe respiratory illness in 18 people, of whom 6
died. Since that time, there have been other instances of H5N1 infection
among humans. However, H5N1 viruses thus far have not been capable of
efficient human-to-human transmission; health officials continue to monitor
the situation closely for evidence of H5N1 transmission between people.
Infected birds shed virus in saliva, nasal secretions, and feces. Avian
influenza viruses spread among susceptible birds when they have contact
with contaminated excretions. It is believed that most cases of H5N1
infection in humans have resulted from contact with infected poultry or
contaminated surfaces.
--
ProMED-mail
<promed@promedmail.org>
[see also:
Avian influenza, human - East Asia (93): CDC advice 20050622.1744
Avian influenza, human - East Asia (79): WHO update 20050519.1376
Avian influenza, human - East Asia (59): CDC guide... 20050328.0892
Avian influenza, human - East Asia (34): CDC Updates 20050220.0558
Avian influenza, human - East Asia (09): CDC update 20050116.0144]
........................cp/sh
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