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Published Date: 2006-12-22 00:00:00
Subject: PRO/AH> Avian influenza (221) - EU update and overview
Archive Number: 20061222.3586

AVIAN INFLUENZA (221) - EU UPDATE & OVERVIEW
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Date: Thu, 21 Dec 2006
From: ProMED-mail <promed@promedmail.org>
Source: HPAI A/H5N1 - update and overview of
2006; Eurosurveillance weekly release, Vol 11,
Issue 12, 21 Dec 2006 [edited]
<http://www.eurosurveillance.org/ew/2006/061221.asp#1>

Animals still source of human infections
----------------------------------------
In 2003, highly pathogenic avian influenza
viruses type A/H5N1 (Asian strain) re-emerged and
spread rapidly, infecting poultry and some humans
in a number of Southeast Asian countries,
particularly Vietnam, Thailand, Cambodia and
Indonesia. The mechanism for this spread remains
unclear although it is suspected that it was as
much related to trade of poultry and poultry
products as the movements of wild birds. An
exceptional multi-species epizootic at Qinghai
Lake in northwest China in May 2005 seemed to
demonstrate a role of wild birds in the spread of
the viruses beyond Asia. From Qinghai, the virus
spread to Central Asia, Europe and some African
countries with human cases reported in Turkey,
Iraq, Azerbaijan, Djibouti and Egypt. Now, at the
end of 2006, the virus has been confirmed in
birds in over 50 countries, with birds (almost
entirely domestic poultry) being the source of
human infections in 10 of these.
Some countries are facing up to endemic infection
in their national poultry flock and consequent
ongoing risks to humans with domestic poultry,
while others are barely affected. At a recent
world conference on avian influenza and pandemic
preparedness [see footnote], field reports on
efforts to control avian influenza were presented
by national and international authorities. There
is evidence that H5N1 viruses have now become
entrenched in backyard poultry in Indonesia, and
perhaps also Egypt. Large-scale programmes of
poultry immunisation have been underway in China
and Vietnam where, since 2005 and until an
outbreak in the Mekong Delta this week in
Vietnam, poultry outbreaks had stopped being
reported. The scale of immunisation in China,
with potentially 14 billion poultry needing to be
vaccinated twice annually (in spring and autumn),
is the largest immunisation programme against
avian influenza ever attempted anywhere in the
world.
In the European Union (EU), the virus has not
become established in poultry nor have there been
there any human infections even though the virus
was found in wild birds in at least 15 countries
in the spring of 2006. Some cats and a pine
marten that fed on infected birds were also
infected. The bird movements to the EU may have
been exceptional following an unusually cold
spell of weather in Russia and Central Asia in
early 2006. After the spring wave, there has been
confirmation of sporadic H5N1 infections in birds
in only Spain and Germany.
Figure 2. Highly pathogenic avian influenza cases
in wild birds in the EU member states: 748 cases
notified in 2006.
The successful protection of domestic birds in EU
countries was primarily due to the robust and
consistent application of veterinary measures
directed under EU legislation. As a consequence,
only 5 poultry outbreaks occurred in the EU and
these were rapidly contained. However, the
continuing sporadic reports demonstrate that the
virus may still sometimes be present and
therefore, routine biosecurity measures and early
warning systems cannot be relaxed. There were
major outbreaks of infection in wild birds and
domestic poultry in the Danube delta in 2005 and
2006, and the Romanian authorities successfully
contained these. There will be an additional
challenge for EU authorities if it occurs here
again after Romania joins the European Union next
month.
Continuing evolution of the viruses
--------------------
There remains the risk of emergence of a human
pandemic strain through either mutation of the
H5N1 virus or incorporation of part of its
genome, through recombination, into a human
influenza virus. As well as extending their range
geographically the H5N1 viruses have diversified
genetically into clades and sub-clades. Clade 1
dominated in 2003-2004, then clade 2 became more
important. Clade 2 has subsequently developed
into 3 distinct sub-clades. The balance between
the types of virus continues to change, for
reasons that are not clear. For example, since
2005, the Fujian-like virus (clade 2, sub-clade
3) has become the dominant type found in
surveillance of market poultry across southern
China. Fortunately, despite genetic changes,
there has been no evidence of significant change
in the viruses' effects on humans. The genetic
differences and the fact that the virus is
continuing to change are, however, important
considerations since the clades have different
antiviral resistance profiles and continuing
genetic change will alter the necessary
composition of human H5N1 vaccines referred to as
"pre-pandemic vaccines."
Two countries have already committed to
purchasing these vaccines and others are
considering doing so, although it is by no means
clear that an H5-based pandemic is inevitable.
Discussion
------
There are many important unknown factors relating
to the spread of H5N1, including the current
distribution of the viruses. The pattern of H5N1
infection in Africa remains elusive because
surveillance is especially weak there, apart from
Egypt and some parts of Nigeria. The picture is
also incomplete in eastern Asia -- following 2
human cases in summer 2006, the situation has
improved in Thailand, but the risk remains.
A good picture of the zoonotic situation in China
is currently not available and it is also still
unclear whether the H5N1 vaccination programmes
in China and Vietnam have been successful in
eliminating or just reducing the level of
infection in poultry, and whether low levels of
circulating viruses pose a significant human
risk. One negative consequence of any success in
vaccination programmes is that surveillance for
sporadic human cases is made more difficult,
since now, when atypical pneumonias occur, there
is rarely the marker of local poultry deaths to
inform decisions on whether to test the patient
for H5N1 virus.
The relative role of the commercial movement of
animals and wild birds in the international
spread and local distribution of H5N1 viruses
remains controversial. However, it is local
preparedness and response that are most crucial
in determining the outcome in terms of domestic
animal and human health when countries are
challenged by the virus. Nationally organised
veterinary services, which would enable effective
surveillance/early warning and biosecurity
systems, are crucial so that authorities can
respond promptly when infections are first
suspected in either birds or humans. Where
biosecurity is poor and veterinary services
ineffective, viruses can become endemic and the
situation can be complicated by the virus cycling
between poultry and wild birds.
One challenge developing countries face is a lack
of financial support for the veterinary services
and biosecurity measures, even though avian
influenza has demonstrated that it is truly an
international problem. There has been some
progress towards a solution for the financial
issues by the involvement of the World Bank, the
European Commission and the United Nations System
Influenza Coordinator
(<http://www.undg.org/content.cfm?id=1482), which
have mobilised and released donations that had
been pledged by national and international donors.
The data indicate that H5N1 avian viruses remain
poorly adapted to humans. With a high enough
viral challenge and perhaps some genetic host
susceptibility the viruses can infect humans, in
which case they are then often lethally
pathogenic, although they are still unable to
transmit efficiently between humans. The H5N1
viruses have been around for nearly a decade and
it might be tempting to conclude that if they
were going to proceed to form or contribute to a
pandemic strain, they would have done so by now.
However, it should be remembered that it is
thought that the avian influenza virus which
contributed to the 1918-19 Spanish Influenza�
H1N1 pandemic strain had been around for some
years before it became part of a virus that could
efficiently transmit between humans and so be a
successful pandemic strain.
(Footnote. The Bamako conference was organised by
the African Union, the Interafrican Bureau for
Animal Resources and the European Union.
International Conference on Avian and Human
Pandemic Influenza, (Ministerial Meeting and
Pledging Conference) 6-8 Dec 2006, Bamako.
Documentation and presentations at the conference
are viewable at :
<http://www.avianinfluenzaconference4.org/index.php?id=61>).
Prepared by:
Influenza team <influenza@ecdc.eu.int>
European Centre for Disease Surveillance and Control, Stockholm, Sweden
--
ProMED-mail
<promed@promedmail.org>
[This is a timely, authoritative overview
touching upon the most crucial aspects of the
H5N1 panzootic; the above text does not include
parts of the document which deal exclusively in
human health. For references, tables and figures,
subscribers are referred to the original.
Rightly, the authors reemphasise the urgent need
for the upgrading of national veterinary services
in developing countries, without which no
effective surveillance and acceptable biosecurity
are achievable. - Mod.AS]

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