wild birds not guilty re bird flu in australia

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    Martin W

    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”.

    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)
    commercial flocks.

    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.

    Nick Honhold
    Veterinary epidemiologist, DARD

    Date: Mon, 5 Sep 2005
    From: ProMED-mail
    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.

    George Arzey
    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
    helpful.- Mod.AS

    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]

    [see also:
    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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