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AVIAN INFLUENZA – ASIA (10): 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 International Journal of Microbial Agents Date: Wed 24 Aug 2005
From: Hon Ip Dead birds don’t migrate (re. ProMED 20050822.2475)
I am in complete agreement with the anonymous ProMED contributor for the request for more information on the role of H5N1 and wild birds in the evolving situation in Asia [see commentary to posting 20050822.2475]. Reports of the role of wild birds as the cause of new bird flu outbreaks occur almost daily, but at the present time, there is little evidence available to support such statements. So making that kind of material available to ProMED readers would be greatly appreciated. One of the few pieces of published data that addresses the question of H5N1 isolation from wild birds is from the work of colleagues in Hong Kong. H5N1 was isolated from clinically healthy birds in Penfold Park during the 2002 pathogenic [influenza] outbreak in Hong Kong SAR. In addition to the isolation of H5N1 from sick and dying birds at the park, the virus was isolated from apparently healthy birds, include 2 Canada geese (_Branta canadensis_), one bar-headed goose (_Anser indicus_) and 2 other geese of unspecified Anser species (Ellis et al., 2004. Avian Pathol 33:492-505). [Initially, the SAR authorities reported to the OIE that the affected population in the Penford Park included resident waterfowl (ducks, geese, and swans) and wild little egrets (_Egretta garzetta_); no reference was made to tests in clinically unaffected birds.
See 20030126.0236. – Mod.AS] It should be noted that, although the Canada goose and the bar-headed goose are migratory species, these birds were in a captive situation, and so the question of whether they are capable of migration remains unanswered. A further point illustrating the lack of data on the role of wild birds in HPAI H5NA transmission is the outbreak in Novosibirsk, Russia. The source of the outbreak has been attributed to wild birds. [See 20050725.2150 and .] But, in some of the limited information available on the nature of the Novosibirsk HPAI H5N1 virus, as provided by Russia to OIE [see 20050813.2369 and ], the 4 isolates of H5N1 from domestic poultry in 2 regions of Novosibirsk are similar, but one sample, which is from a wild duck, clearly has a different PCR electrophoreogram pattern (Figure 1 in the OIE report). While other data not included in the report may show that the virus in wild birds is related to those isolated from affected poultry in the Novosibirsk region, the available data suggest that such is not the case, and certainly no data that shows the wild birds were the vector of transmission has been made available at the present time. Movement of birds, including annual migration, is only one of several possible means of dissemination of the HPAI H5N1 virus. In many of the areas of recent outbreaks, there is a thriving trade of live birds and poultry products. Some of the areas such as Qinghai in China and Hovsgol, Mongolia are tourist destinations.
There is no evidence of sustained human to human transmission at the present time. But because the influenza virus can survive in poultry droppings for up to 2 weeks (Lu et al., 2003. Avian Dis 47:1015-1021), movement of people and contaminated farm equipment can rapidly spread the virus from one locale to another. Although much has been made of the recent pattern of spread as indicative of avian migration, many ornithologists have indicated that the spread of H5N1 does not fit with known behavior of the bird species in that area of the world (Butler, D. 2005. Nature: [sadly, seems this is for premium subscribers]): It should be noted that the same pattern of spread can just as easily be seen as from the major routes of human transportation. — Hon S. Ip United States Geological Survey National Wildlife Health Center Diagnostic Virology Laboratory Madison, WI USA [Those are valuable observations. Any available data on the detection of pathogenic H5N1 virus strains in subclinically infected uncaged wild birds will be appreciated. Subscribers are referred to a paper by FAO authors, published on 6 Aug 2005 in the Veterinary Record: Sims LD, Domenech J, Benigno C, Kahn S, Kamata A, Lubroth J, Martin V & Roeder P. (2005) Origin and evolution of highly pathogenic H5N1 avian influenza in Asia. Vet Rec. 157(6):159-64: "Abstract: Outbreaks of highly pathogenic avian influenza caused by H5N1 viruses were reported almost simultaneously in 8 neighboring Asian countries between December 2003 and January 2004, with a 9th reporting in August 2004, suggesting that the viruses had spread recently and rapidly.
However, they had been detected widely in the region in domestic waterfowl and terrestrial poultry for several years before this, and the absence of widespread disease in the region before 2003, apart from localized outbreaks in the Hong Kong Special Autonomous Region (SAR), is perplexing. Possible explanations include limited virus excretion by domestic waterfowl infected with H5N1, the confusion of avian influenza with other serious endemic diseases, the unsanctioned use of vaccines, and the under-reportingof disease as a result of limited surveillance. There is some evidence that the excretion of the viruses by domestic ducks had increased by early 2004, and there is circumstantial evidence that they can be transmitted by wild birds.
The migratory birds from which viruses have been isolated were usually sick or dead, suggesting that they would have had limited potential for carrying the viruses over long distances unless subclinical infections were prevalent. However, there is strong circumstantial evidence that wild birds can become infected from domestic poultry and potentially can exchange viruses when they share the same environment. Nevertheless, there is little reason to believe that wild birds have played a more significant role in spreading disease than trade through live bird markets and movement of domestic waterfowl. Asian H5N1 viruses were 1st detected in domestic geese in southern China in 1996. By 2000, their host range had extended to domestic ducks, which played a key role in the genesis of the 2003/04 outbreaks. The epidemic was not due to the introduction and spread of a single virus but was caused by multiple viruses which were genotypically linked to the Goose/GD/96 lineage via the hemagglutinin gene. The H5N1 viruses isolated from China, including the Hong Kong SAR, between 1999 and 2004 had a range of genotypes and considerable variability within genotypes.
The rising incidence and widespread reporting of disease in 2003/04 can probably be attributed to the increasing spread of the viruses from existing reservoirs of infection in domestic waterfowl and live bird markets leading to greater environmental contamination. When countries in the region started to report disease in December 2003, others were alerted to the risk and disease surveillance and reporting improved. The H5N1 viruses have reportedly been eliminated from 3 of the 9 countries that reported disease in 2003/04, but they could be extremely difficult to eradicate from the remaining countries, owing to the existence of populations and, possibly, production and marketing sectors, in which apparently normal birds harbor the viruses." During early stages of the outbreak, it was argued that the pattern of spread strongly suggested that the virus was carried by people smuggling poultry, a practice reportedly widespread in southeast Asia, rather than by migratory birds.
Though there were reports of mass die-offs of rare birds in zoos in Thailand, regular monitoring of migratory birds in Thailand did not reveal the virus. In regions with big outbreaks in poultry, local wild birds were affected; the question remained as to whether their infection did not originate from the domestic birds (see item 3 in 20040128.0335). Useful information on waterbird populations worldwide can be found on the web-site of Wetland International; the organization has recently published the drafted 4th edition (2005) of "Waterbird population estimates," – Mod.AS]
[see also: Avian influenza, migrating birds – Asia 20050812.2354 Avian influenza, migratory birds – Mongolia (02) 20050812.2362 Avian influenza, migratory birds – Mongolia: OIE 20050808.2317 Avian influenza, migratory birds – Mongolia: OIE (03) 20050813.2367 Avian influenza – Asia (06): Mongolia, migratory b… 20050819.2443 Avian influenza – Asia (09): Russia (Siberia), OIE 20050822.2475 Avian influenza, wild waterfowl – China 20050527.1462 Avian influenza, wild waterfowl – China (02): warn… 20050601.1529 Avian influenza, wild waterfowl – China (03) 20050604.1558 Avian influenza, wild waterfowl – China (04): (Xin… 20050622.1743 Avian influenza, wild waterfowl – China (05) 20050628.1828 Avian influenza, wild waterfowl – China (06) 20050629.1833 Avian influenza, wild waterfowl – China (07) 20050702.1872 Avian influenza, wild waterfowl – China (08) 20050707.1922 Avian influenza – Europe (03): migratory birds, no… 20050821.2463 Avian influenza – Russia (Siberia)(13): H5N1, OIE 20050813.2369 Avian influenza – Russia (Siberia)(04): OIE 20050725.2150 2004 —- Avian influenza – Eastern Asia (13) 20040128.0335 2003 —- Avian influenza – China (Hong Kong): OIE (02) 20030126.0236] ………………..arn/msp/mpp
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