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- 7 September 2005 at 1:30 pm #3240Martin WParticipant
Two Promed posts here; second notes how wild birds were first blamed, then found not guilty, for 5 bird flu outbreaks in Australia (poultry) – suggests that need further examination of recent spread in n Asia “with an open mind”.Quote:AVIAN INFLUENZA – ASIA (21): MIGRATORY BIRDS
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Sponsored in part by Elsevier, publisher of
Journal of Clinical Virology
Date: Mon, 5 Sep 2005
From: Nick Honhold
Regarding the previous ProMED-mail post Avian influenza – Asia (17):
Mongolia, migratory birds, H5N1, OIE,] the important news is that an H5N1
— most likely the same one currently circulating in South East Asia — has
extended its geographic range.
According to a ProMED-mail posting of 28 Oct 2004 [20041028.2911], H5N1 was
isolated in 2004 from migratory birds in Novosibirsk, situated northwest of
Mongolia, so this recent result “fills in” the gap between south Siberia
and South East Asia, reflecting (welcome) increased vigilance and
intensified surveillance, rather than a change in the geographical
distribution of the virus.
I believe that almost all of the human cases in South East Asia have been
due to direct or indirect (but mostly the former) contact with backyard
poultry — that is, small scale non-commercial or semi-commercial flocks.
Perhaps the moderator meant “domestic” rather than “commercial”, but even
so it is worth distinguishing between backyard poultry — which are usually
in small and free-ranging flocks — and (usually large and housed)
If HPAI (highly pathogenic avian influenza) enters a commercial flock, the
effects are usually obvious and quickly identified; contact between humans
and sick birds is likely to be less intense. Deaths in backyard poultry are
rarely investigated by veterinarians. If an epidemic disease enters a
village, and birds in a single holding start dying, other owners may rush
to slaughter or sell their birds before they have the opportunity to die,
but perhaps not before they are infected. Such a situation might enhance
human exposures and spread.
I am not trying to imply that strict controls or culling should be imposed
on village poultry; apart from the logistical problems that would occur,
village poultry are too important to those who own them for drastic actions
to either be supportable or even feasible. Birds would be hidden or sent
elsewhere. What is needed is a heat-stable AI vaccine for village poultry
and the means to deliver it.
Veterinary epidemiologist, DARD
Date: Mon, 5 Sep 2005
Source: George Arzey [edited]
Migratory birds: an easy explanation or sound epidemiology?
Previous ProMED-mail postings [Avian influenza – Eastern Asia (58):
waterfowl 20050625.1786; Avian influenza – Asia (10): migratory birds
20050824.2492] raised concerns about the need for sound science in drawing
conclusions about the involvement of migratory birds in the spread of H5N1
to domestic poultry.
Considering the reported widespread infection with H5N1 in SE Asia and the
recent findings in Central Asia attributed to migratory birds, Australia
and NZ are indeed an enigma: 2 islands endowed with wild aquatic birds, on
the migration zone of several flyways in and out of SE Asia, and yet
untouched by the subtype ravaging this continent.
Since the emergence of the AIV Goose/GD/96 in the province of Guangdong in
1996, it is estimated that approximately 27 million migratory birds have
visited Australian shores, approximately 3 million birds per year
(according to Wetlands International 2002, Waterbirds population estimates
3rd Ed., Global Series 2002 no 12).
Another intriguing aspect is that while both countries are on the migration
route of several flyways, Australia has experienced 5 outbreaks in chicken
flocks but NZ has experienced none.
In the 5 outbreaks in Australia, all in intensive poultry units, the H7
subtype was involved, and in all 5 outbreaks migratory/aquatic birds were
considered the source. This conclusion was largely based on (1) the premise
that aquatic wild birds are a significant reservoir of AIV and (2)
anecdotal evidence that suggested presence of aquatic wild birds in the
vicinity of an infected farm or inhabiting a body of water that supplied
water to the infected farm. AIV of the H7 subtypes were never reported in
Australia or NZ in wild waterfowl before, during, or after the outbreaks
(Arzey G. The role of aquatic wild birds in the epidemiology of avian
influenza in Australia. Aust Vet J 2004; 82(6), Jun). Several other AIV
subtypes were found in wild waterfowl during surveys over the years, but
none of those was ever found in the infected chicken flocks. During the
last outbreak in Australia (1997), the same AIV subtype which was found in
chicken (but of lower virulence) was isolated from farmed emus adjacent to
the infected biosecured index chicken shed. The emu as a possible source of
infection was largely ignored in favour of the water from the river being
the source of the infection in the chicken, despite the fact that it was
chlorinated (albeit with fluctuating levels of chlorine).
Considering the repeated outbreaks in Australia with H7 and the uniqueness
of emus to Australia, this population should perhaps receive more
consideration as a potential reservoir of AIV infection in Australia.
While it is acknowledged that absence of evidence is not necessarily
evidence of absence of infection with H7 subtype in Australian and NZ
aquatic wild birds, it is highly significant that the H7 subtypes isolated
from the AI outbreaks in Australia between 1985 to 1994 were all
phylogenetically delineated from H7 subtypes found in other regions of the
globe and the Australian H7 subtype formed a separate sublineage (Aust Vet
J 2004; 82(6), Jun). Would this delineation persist for such a long period
if migratory birds were responsible for the AI outbreaks in Australia?
Unlike Europe, Australian and NZ Anatides are considered nomadic within
their respective countries and generally do not migrate internationally or
intercontinentally. While the European data (see Avian influenza – Europe
(03): migratory birds, northern Europe 20050821.2463) may point to a strong
association between migratory birds and outbreaks in domestic poultry, this
has not been consistently the case, for example, in North America, where
the infections were, in significant numbers of outbreaks, related to local
bird markets. When the spread of the current epidemic in SE Asia occurred,
migratory waterfowl were almost instantaneously blamed as the source,
although the timing and distribution of several new outbreaks did not fit
any known migratory pattern for any species including terrestrial birds
(Melville DS & KF Shortridge. Reflection and reaction. Lancet Infect Dis
2004; 4: May). The presence of H5N1 in live bird markets as early as 1999
(Hong Kong in geese) and 2001 in Vietnam in Geese imported from China
(Nguyen, et al. Isolation and characterisation of Avian Influenza viruses,
including HP H5N1 from poultry in live bird markets in Hanoi, Vietnam in
2001. J Virology 2005; 79(7): 4201-12), provided a credible alternative
explanation for H5N1 outbreaks in domestic poultry. The paper by Nguyen et
al (2005) identified the domestic duck as being the major reservoir of the
AIV pool in nature and the live bird markets in Asian countries as a
suitable environment for reassortment and transmission.
Perhaps the Australia and NZ scenario provides another reason to examine
the possible association between migratory birds and outbreaks in domestic
poultry with an open mind.
Requiring a thorough examination of the evidence that links migratory birds
or other wild waterfowl and AI outbreaks in domestic poultry is not aimed
to weaken or to question the concept of biosecurity. The promotion of the
concept of biosecurity and exclusion of wild birds from poultry enterprises
should be viewed as a tool to reduce disease risks rather than as an
undisputed epidemiological association and acceptance of the direct role of
wild birds in all AI outbreaks on poultry farms.
Senior Veterinary Officer (Avian Health)
NSW Department of Primary Industries
Elizabeth Macarthur Agricultural Institute
[Dr Arzey’s data from Australia and New Zealand on the monitoring of avian
influenza in wild birds — as compared to isolates from domestic poultry —
are a valuable contribution to the current discussion on the significance
of migratory birds for the spread of avian influenza, particularly H5N1.
Similar comparative observations from other parts of the globe, especially
from landing sites of aquatic birds along their migration routes, will be
Dr Arzey’s observations fall in line with DEFRA’s decision that the UK will
not follow the Dutch example of moving all domestic poultry indoors, on the
grounds that no H7N7 virus appeared in the UK notwithstanding the frequent
movement of free-living birds between northern Europe and the UK. – Mod.CP]
Avian influenza – Asia (17): Mongolia, migratory birds, H5N1, OIE
Avian influenza – Asia (16): Mongolia, migratory birds,H5N1 20050831.2578
Avian influenza – Asia (15): migratory birds 20050827.2536
Avian influenza – Asia (10): migratory birds 20050824.2492
Avian influenza – Europe (03): migratory birds, no… 20050821.2463
Avian influenza – Asia (06): Mongolia, migratory b… 20050819.2443
Avian influenza – Asia(02): Kazakhstan (North), poultry, H5N1 20050817.2407
Avian influenza, migratory birds – Mongolia: OIE (03) 20050813.2367
Avian influenza, migratory birds – Mongolia (02) 20050812.2362
Avian influenza, migrating birds – Asia 20050812.2354
Avian influenza, migratory birds – Mongolia: OIE 20050808.2317
Avian influenza – Russia (Siberia)(10): H5N1, OIE 20050808.2315
Avian influenza A/H5N1, migratory birds – Russia (Siberia) 20041028.2911]
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