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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