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Extract - an interesting respinse on ProMed to the Opinion article, Viewpoint: Leon Bennun on the BBC

http://www.promedmail.org/pls/promed/f?p=2400:1001:2942347053424217451::NO::F2400_P1001_BACK_PAGE,F2400_P1001_PUB_MAIL_ID:1000,32065
 
Date: Sat, 18 Feb 2006 08:05:04 +1000
From: Les Sims <apvis@bigpond.net.au>


The news articles reproduced in ProMED-mail posting 20060217.0516 highlight a
number of misconceptions about avian influenza that need to be challenged
before they become further entrenched in the minds of the public and policy
makers.

i) Blaming intensive poultry farms for the genesis of H5N1 avian influenza

There have been a number of attempts recently to attribute to intensively
reared poultry the root of the H5N1 problem. This fits neatly with the agenda
of some animal welfare lobbyists but does not accord with the facts, which
show that the vast majority of cases of H5N1 avian influenza are occurring in
village and smallholder poultry. A key factor in emergence of avian influenza
has been the expansion of the smallholder poultry sector without concurrent
enhancements in biosecurity. This sector is where control measures are being
focused at present. Few cases are seen in large intensive farms with properly
implemented biosecurity programs. [The opposite is reportedly the situation in
Laos -- see [1] above. - Mod.JW]

ii) Chickens are silently carrying avian influenza virus

A number of media stories based around the recent paper by Chen et al (2006)
(Establishment of multiple sublineages of H5N1 influenza virus in Asia:
Implications for pandemic control Proc Nat Acad Sci [PNAS] USA, 10 Feb 2006, e-
published) suggest that apparently healthy chickens are capable of silently
excreting virus.

However, the available data (see Table 4 in the supplementary information to
[Chen's] paper) do not entirely support these conclusions. These data are
based on swabs from poultry in live bird markets. Swabs were collected at a
particular point in time with no follow-up of the positive poultry to
determine whether they subsequently developed clinical signs, seroconverted,
or died. [It should be pointed out that while academically correct, it would
be extremely difficult and expensive to resample individually identified birds
(even if they had been microchipped on the 1st round) from a live bird market
anywhere, including in Asia or Queensland, thanks to subsequent dispersal and
the culinary arts. - Mod.MHJ]

Over an 18-month period over 22 000 faecal samples were collected from
chickens in 5 poultry markets in China. Only 58 positive faecal samples were
detected. Of these, 25 were detected in January 2004 when more than 20 percent
of duck samples collected in the same markets were positive for virus,
providing ample opportunities for cross-infection.

With the exception of 3 positive samples in May 2004, all other positive
samples were detected when virus was also detected at high levels in ducks and
geese in the markets.

We have known since 1999 that domestic waterfowl can silently excrete highly
pathogenic H5N1 viruses for a short period of time and pose a threat to
terrestrial poultry.  It is also well-recognised in Asia that dead chickens
are rarely presented to authorities in live poultry markets because birds
showing signs of illness are immediately slaughtered and dressed (and the same
can also happen with birds found dead).

The most plausible explanation for this small number of virus-positive
chickens in markets is that they had been recently infected in the market and
were incubating the disease.

These results certainly provide further justification for segregating
waterfowl from chickens but do not yet provide convincing evidence of
widespread silent infection in chickens.  This issue should be explored
further but until such time as additional studies are completed it is
important to keep these results in perspective.

iii) Failures in risk communication

The shunning of poultry meat by consumers following the detection of H5N1
avian influenza in wild birds in Europe is yet another demonstration of our
failure to provide clear information to the public regarding the risks
of "bird flu". Avian influenza is not a food-borne illness, given that
properly cooked meat and eggs pose a negligible risk, yet the public has not
taken this message on board. Much of this has probably arisen as a result of
confusion and hype in the media about the risks posed by "bird flu." This
remains a rare zoonotic disease occurring in people living in households with
infected poultry. The confusion between 'bird flu' and emergence of human
pandemic influenza also contributes to this problem.

iv) Wild birds versus poultry and bird trade as the source of infection

We have known for a long time that poorly regulated trade in poultry and
poultry products can spread avian influenza. Recent experiences in Western
Europe provide further incontrovertible evidence that wild birds can also
spread highly pathogenic H5N1 viruses over relatively long distances, adding
to the evidence already available from Mongolia.

The arguments about whether trade or wild birds are the main source of
infection are now essentially irrelevant from a disease control standpoint.
Both must be recognised as genuine threats. Any control program that does not
take into account the potential for both of these to spread highly pathogenic
H5N1 viruses will likely fail. The only ways to reduce these risks are to
strengthen border controls and farm biosecurity to prevent potentially
infected or contaminated material from getting onto farms and to create
barriers between poultry and wild birds.  For poultry reared outdoors the only
option available (other than moving poultry indoors) is vaccination.

v) Infected vaccinated birds can still shed virus and therefore vaccine should
not be used because of the lack of tests to detect infected vaccinated flocks

The main flaw in this line of argument used against vaccination is that there
is also no simple test to detect a recently infected flock of unvaccinated
poultry, other than testing of dead poultry for virus. Around the globe, we
have seen repeatedly that once H5N1 avian influenza emerges astute or
opportunistic smallholders and poultry farmers who detect early signs of a
disease sell their flocks before the disease becomes widespread. In most cases
this goes undetected until the disease appears in a new location. In my view,
in an emergency situation it is far better to have the high levels of flock
immunity provided by vaccination than to risk uncontrolled infection and
spread through movement of infected, non-immune flocks.

Experience from Hong Kong where a vaccinated, biosecure compartment has been
established shows that fears of silent infection are overblown. No cases of
infection have been detected in vaccinated flocks, in dead birds in wholesale
markets, or in cage swabs in retail markets since compulsory vaccination was
introduced some 3 years ago, despite the presence of H5N1 viruses in the
region.

Clearly, there are trade issues with vaccination that need to be resolved, but
these need to be kept in perspective, especially when considering the havoc
wreaked on trade by an outbreak of this disease in non-immune poultry.

--
Les Sims
Asia Pacific Veterinary Information Services
PO Box 353
Manunda
Queensland 4870, Australia
<apvis@bigpond.net.au>

[Among a number of blessings granted me in my life was to be taught
epidemiology at Tulane by Ken Newell, a superb teacher whose stutter no one
remembers except in exchanging yarns about when he did this or that with us,
his one-time students. One of his lectures was on how to carry out a field
epidemiology investigation, full of his experiences. Given limited facilities
and time, he told us that you should ignore the body of an epidemic and
investigate the outliers because how these occurred would provide the most
insight. Later this was defined by David Roger's 'Two Models' Rule: A
mathematical model to describe the core area of an epidemic will need some 20
parameters but for the margin you will only need 3 parameters. This is logical
because at the margins the disease is either present or it isn't; in the
centre the incidence is going up and down all over the place. This is what we
are seeing with H5N1 avian influenza; what is or is not happening in central
China may only be confusing the interpretation of long-distance spread.

Apropos Ken Newell, he did his doctoral research on 'joy-riding' pigs and how
the semi-quantified stress of travel to markets in Northern Ireland (his 3 pre-
infected experimental pigs traveled around on the back seat of his Morris car -
-- I don't know if he was married at the time) affected their shedding of
salmonella when at the market. The interpretation of simple prevalence studies
of market animals should be conservative, as the true events can be complex.

This is clearly an instance in which forensic molecular studies of the virus
isolates from inside and outside China would be invaluable. The results quoted
for PNAS above need to be rigorously confirmed by others, and it should
involve, if possible, purposefully collected samples, not opportunist
diagnostic laboratory survivors.

It is now mid-February and the migratory birds over-wintering in the Southern
Hemisphere will be heading north, back to their breeding grounds.

I am reliably informed that a commercial poultry breeding facility in Lanzhou,
China, was identified by FAO as the probable source for a H5N1 outbreak in
Tibet in 2005.  The parent company of one major breeding facility in Lanzhou --
according to information on its corporate website -- also controls 30-40
percent of the commercial poultry industry in Turkey.

The problem is not just identifying the risks for long-distance spread but
quantifying them so that they can be prioritised, and appropriate actions
taken in the most cost-effective manner and sequence. At the same time, farm
biosecurity and appropriate flock disease prevention/vaccination needs to be
implemented. The former is a national/international responsibility; the latter
is local.

A useful link:
Stock Photography and Assignment Images - OnAsia Images ...... Country:
Thailand  Area: Rayong
<http://www.onasia.com/system/preview.aspx?pvp=pch0791320.75,pch0791620.73>

This provides a wealth of images of Thai situations including poultry markets,
plus Dhanin Chearavanont, Chairman and CEO of Charoen Pokphand Group
(Thailand), inspecting one of his fighting cocks at his Native Chicken
Research and Development Center. In Thailand a special breed of chicken is
raised for cock fighting (see ref. below), and these birds can reach prices of
Baht 150 000 (US $3850) and more. One might assume that these beautiful birds
are sold with a health certificate. - Mod.MHJ]