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Topic: Wild birds "victims not vectors" 野鳥是受害者，不是播毒者 (Read 1554 times) |
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Carrie Ma
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Wild birds "victims not vectors" 野鳥是受害者，不是播毒者
« on: Dec 9th, 2005, 8:17am » |
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Source of information:
BirdLife news release
http://www.birdlife.org/news/news/2005/12/flu_migration.html
Wild birds "victims not vectors"
08-12-2005
As the year draws to a close, millions of wild birds have flown to their wintering sites across, Asia, Africa, Europe and the Americas without the widely predicted outbreaks of H5N1 bird flu associated with their migration routes.
"The most obvious explanation is that migrating wild birds are not spreading the disease," said Dr Michael Rands, Director & Chief Executive of BirdLife International.
"Migratory wild birds were blamed for spreading bird flu west from Asia, yet there been no spread back eastwards, nor to South Asia and Africa this Autumn. The limited outbreaks in eastern Europe are on southerly migration routes but are more likely to be caused by other vectors such as the import of poultry or poultry products. The hypothesis that wild birds are to blame is simply far from proven," said Dr Rands. "Wild birds occasionally come into contact with infected poultry and die: they are the victims not vectors of H5N1 bird flu."
BirdLife maintains that better biosecurity is the key to halting the spread of bird flu. In particular, BirdLife is urging governments and relevant agencies to concentrate their efforts on the poultry and cage bird trades and to ban the movement of poultry and poultry products from infected areas, and restrict the international movement of captive birds in trade.
The Government of Vietnam has warned local residents against the risk of dumping tonnes of chicken faeces into rivers and lakes as fish food.
BirdLife is also strongly urging governments to ban the use of untreated poultry faeces as fertiliser and feed in fish-farms and in agriculture. Domestic bird waste is widely used as food and fertiliser in fish farming and in agriculture, yet infected poultry are known to excrete virus particles in their faeces.
The use of untreated faeces in fish farming was recently described by the United Nation Food and Agriculture Organization as a 'high risk production practice'. Russian fish farms have begun using chicken faeces as fish farm fertiliser, and this practice is employed in Eastern Europe where poultry faeces are also spread onto agricultural land. The Government of Vietnam has warned local residents against the risk of dumping tonnes of chicken faeces into rivers and lakes as fish food; one boy has died of bird flu after swimming in a river where infected chicken carcases were discarded. This October, Mute Swans died at fish farms in Croatia and Romania.
"Implementing measures like these are proven to work," says Dr Rands. "For example, Malaysia and South Korea both experienced bird flu outbreaks through importing infected poultry products, but stamped the disease out and have remained disease free through improved biosecurity. In the mean time, hundreds of thousands of waterbirds have arrived to winter in, or migrated through South Korea, and many migrant waders have passed through Malaysia."
"Better biosecurity is the key to controlling the disease's spread," said Dr Rands. "But the virus can rapidly mutate, so it's important to monitor wild bird populations to look for evidence of new strains arising."
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Carrie Ma
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Re: Wild birds "victims not vectors"
« Reply #1 on: Dec 13th, 2005, 9:21am » |
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More information from BirdLife international on AI
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Migrating wild birds are victims not vectors of avian flu
BirdLife International, 8 December 2005
Over the last few months, millions of waterbirds have been pouring out of their northern breeding grounds, moving along traditional flyways on their vast and complex annual migrations. Migrating birds face numerous hazards: strong winds can blow them off course, predators and hunters lie in wait where they land to rest and feed, and there are big stretches of hostile territory, such as desert or ocean, to cross. This year they have faced an additional danger—a deadly strain of the avian influenza virus.
Originating in poultry, the high-pathogenicity avian influenza (HPAI) virus H5N1 caused deaths among wild waterbirds at several sites over the northern summer (Box 1). As waterbirds started to move south and west on their autumn migration, there was a widespread presumption that they would carry and spread the virus as they went.
Now, with migration nearing an end, there is little or no sign that this has happened. Migrating waterbirds have not spread HPAI H5N1 over a wide area, and may not have been responsible for any recorded outbreak. Importantly, the virus has not so far been reported from the birds' wintering areas in India and Africa. Unfortunately, unbalanced reporting by some official bodies, reflected by some of the media, has spread groundless panic, confused thinking and misguided attempts at culling wild birds.
We know that several species of wild birds can catch HPAI H5N1; we know this because these species have been found sick or dead, and subsequently shown to be infected with the virus. What we don’t know is to what extent infected birds are capable of migration.
However, we can make some inferences from the pattern of outbreaks in wild and domestic birds (Box 2). All the evidence suggests that H5N1 is highly lethal to these species, and kills them quickly; that infected wild birds cannot move long distances; and that the virus is most likely to be contracted locally, close to the site of deaths.
The pattern and timing of spread of HPAI H5N1 among domestic birds—from SE China to NW China and on to southern Russia—do not fit with the pattern and timing of wild bird migrations.
All this suggests that wild birds overwhelmingly remain victims, not vectors, of the HPAI H5N1 virus.
This conclusion is further supported by the (as yet, limited) information on prevalence of the HPAI H5N1 virus in LIVING wild birds. Well over 100,000 healthy wild birds have been tested across South-east Asia in the last two years. Out of 16,000 living wild birds (mainly migratory) tested at the Mai Po Nature Reserve in Hong Kong between 1997 and 2004, none tested positive for HPAI H5N1. Of 850 samples (mainly faecal) from living wild birds tested at Lake Erhel, Mongolia in August 2005, none were positive. In Eurasia, just 13 apparently healthy wild migrant birds have “tested positive” for HPAI H5N1—and doubts have been raised as to whether any of these birds were healthy, or indeed actually carrying HPAI H5N1. The UN’s FAO website, on an undated page from at earliest August 2005, states “To date, extensive testing of clinically normal migratory birds in the infected countries has not produced any positive results for H5N1 so far.” In currently uninfected areas, several thousand migratory waterbirds recently tested in New Zealand, Australia and Canada were all found to be negative for HPAI H5N1.
We may assume that many other tests of this kind have been carried out around the world, but that the results have not been made public. In the interests of all those attempting to control the spread of HPAI H5N1, all such results, whether positive or negative, should be published and made freely available to researchers.
But if wild birds aren't spreading H5N1, what is? There are at least three likely transmission routes:- Movements of untreated poultry and poultry products
- The trade in wild birds
- Use of infected poultry manure as fertiliser in agriculture and agriculture, and as feed in fish-farms and pig farms
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Carrie Ma
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Re: Wild birds "victims not vectors"
« Reply #2 on: Dec 13th, 2005, 9:25am » |
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Movements of poultry and poultry products
Most outbreaks in south-east Asia can be linked to movements of poultry and poultry products (or infected material from poultry farms, such as mud or soil, on vehicles, or peoples’ shoes). Live animal or ‘wet’ markets have played a major part in spreading the virus in south-east Asia. The UN Food and Agriculture Organisation (FAO), OIE and WHO have recognised the role that live animal markets have played in the emergence of avian influenza: “In 1992, live poultry markets in the USA were considered the “missing link in the epidemiology of influenza”. They were identified as the source of the H5N1 infection in chicken farms in Hong Kong in 1997 when approximately 20% of the chickens in live poultry markets were found to be infected. The same situation was seen in Viet Nam, where the circulation of H5N1 in geese in live bird markets in Hanoi had been documented three years before the 2004 outbreaks in chicken farms.” (FAO/OIE/WHO Consultation on avian influenza and human health: Risk reduction measures in producing, marketing, and living with animals in Asia, Kuala Lumpur, Malaysia July 2005)
There is also a huge international trade in poultry—both legal, unregulated and illegal. Recently it was revealed that poultry meat is being illegally imported from Asia into the USA; in October 2005 3,000 chickens were intercepted by Italian customs after being smuggled into the country from China; and in November the UK authorities revealed that large quantities, possibly hundreds of tonnes, of chicken meat had been illegally imported from China, and fraudulently relabelled before being sold on to food manufacturers across the country.
Illegal trade in cage birds
There is a widespread illegal trade in cage birds, that has been demonstrated to have transported flu infected birds over large distances. For example, customs in Taiwan have recently intercepted two consignments of infected birds being smuggled from mainland China, and an outbreak of H5N1 at a bird quarantine station in the UK may also be attributable to smuggled birds ‘laundered’ into a legally imported consignment. Last year a pair of Mountain Hawk-eagles smuggled in hand luggage from Thailand to Belgium were found to have the disease. The most likely source of infection in captive birds is at live animal ‘wet’ markets, where domestic and wild-caught birds are kept in close proximity posing a high-risk of bird flu cross-contamination.
Faeces as fertiliser and livestock feed
Also alarming, and needing closer investigation, is the widespread practice of using poultry manure (chicken, duck and other poultry faeces) in agriculture and aquaculture as fertiliser, and in untreated form as food for pigs and fish. Birds infected with the H5N1 virus excrete virus particles in their faeces: putting untreated faeces from infected birds into fish ponds provides a new source of infection. Although recognised as early as 1988, the risks of this practice for spreading influenza viruses remain little investigated. In Vietnam, the state media recently told residents of Ho Chi Minh City that the practice of using tonnes of chicken faeces every day to feed fish in a lake which flows into the city’s water supply should be stopped immediately. The Deputy Director of Ho Chi Minh City’s Pasteur Institute warned of the dangers of using chicken faeces as fish food “during the period when bird flu is evolving into a pandemic”. One local boy died of bird flu after swimming in a river where chicken carcases were discarded.
Initial investigations reveal that Russian fish farms have recently started using chicken faeces as fertiliser, and this practice is widespread in Eastern Europe where poultry faeces are also spread onto agricultural land and discharge inevitably runs off into waterways. Where untreated poultry manure is collected, transported and sold, this could be a highly effective way of spreading the virus. The FAO/OIE/WHO consultation recommended that “chicken faeces should only be used as fertilizers or livestock feed after appropriate treatment”.
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Carrie Ma
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Re: Wild birds "victims not vectors"
« Reply #3 on: Dec 13th, 2005, 9:27am » |
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Prevention and control
So preventive measures need to concentrate on better bio-security—surveillance and testing of poultry, controlling the movements and sale of poultry, poultry products and cage birds, ensuring that all poultry manure used in aquaculture and agriculture is treated prior to application, and stepping up national and international efforts to control the illegal trade in poultry, poultry products and wild birds.
The current focus on wild birds is misplaced and a potentially dangerous diversion of energy, effort and resources. Attempts to cull wild birds are even more misguided—the target is wrong and the approach is completely ineffective.
But we need to keep monitoring wild birds too. The H5N1 virus, like other forms of avian ‘flu, can change rapidly and unpredictably, and different genotypes can have very different effects from each other. Better global monitoring of the movements, populations and health of migratory birds is vital for their conservation. It may also be important for preventing future threats to public health.
Risks to people
Although H5N1 can cause serious disease in people, the virus is hard to catch and so far does not seem to spread from person to person. The concern is that it might evolve into a form that is transmitted easily between people.
In the last 100 years there have been four major pandemics of human influenza A, which killed many people around the world. It is thought that these deadly virus strains arose when bird flu and human influenza viruses came together, possibly in pigs, and reassorted their genetic material. Continued outbreaks of H5N1 increase the chances of this happening again, especially as the current strain of H5N1 is exceptional in that it has demonstrated that it can pass directly from poultry to humans, without the intervention of an intermediate host.
However, there is no evidence that H5N1 infection in humans have been acquired from wild birds. Human infections have occurred in people who have been closely associated with poultry. Given the number and distribution of outbreaks in domestic poultry and waterfowl, the number of human cases is very small, indicating that the transmission of the virus from poultry to man remains inefficient
Activities such as bird watching and feeding garden birds are completely safe, if simple common sense precautions are followed. These include avoid touching carcasses of wild birds, and washing hands with soap and water after filling or cleaning bird feeders. Both measures are advisable as birds can carry potentially dangerous pathogens.
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Carrie Ma
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Re: Wild birds "victims not vectors"
« Reply #4 on: Dec 13th, 2005, 9:28am » |
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Box 1. Recent outbreaks of HPAI H5N1 avian influenza among wild birds
Apart from caged birds, three types of wild bird species have been involved in outbreaks so far:- Savenging species (that are likely to forage around poultry farms) such as crows and magpies
- Species that often feed (and scavenge) in polluted waterways near towns and farms, including fish-farms, such as some herons, egrets and gulls
- Colonially-nesting or flocking waterfowl that feed in water bodies or in nearby farmland.
Japan, Korea: 2004
Crows and magpies found dead close to poultry outbreaks
Hong Kong: 2004 & 2005
Three birds in two incidents, first associated with deaths of semi-captive birds in park and poultry outbreaks
Lake Qinghai, China: May-July 2005
c. 6,000 deaths, mainly Bar-headed Geese but also ducks, gulls and cormorants, over two months in localised parts of the lake. Virus genotype linked to a poultry outbreak in southern China.
Russia/Kazakhstan: July/August and November 2005
A few wild birds reported dead, associated with poultry outbreaks along major transport routes. Virus genotype linked to the same strain as at Lake Qinghai.
Lake Erhel, Mongolia: August 2005
80 swans and geese died within a few days. Virus genotype linked to the same strain as at Lake Qinghai.
Romania: October 2005
Localised deaths (one of 537 swans over a few days, another of two geese, one swan, one heron); poultry outbreak at same time, and subsequently. Virus genotype linked to the same strain as at Lake Qinghai.
Croatia: October 2005
Localised deaths at fishponds (one of 15 out of 1,500 swans; another of 15 out of 244 swans; both over a few days). Not known if contracted virus at the fishponds or elsewhere, since became sick immediately after arrival. One swan that died at the fishponds was ringed in Hungary five weeks earlier, when apparently healthy. No poultry outbreak reported. Virus genotype much close to viruses isolated in China and Siberia than from outbreaks in Romania and Turkey. Other Croatian samples (c. 2,000, from wild and domestic birds, including ducks, coots and cormorants on the same fish ponds) all negative for H5N1.
Kuwait: November 2005
Single flamingo, which was a captive bird according to unconfirmed reports: the official OIE report describes samples being taken from “neighbouring enclosures”. According to media reports, Kuwait had a few weeks earlier allowed in a cargo of birds apparently infected with avian influenza.
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Carrie Ma
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Re: Wild birds "victims not vectors" 野鳥是受害者�
« Reply #5 on: Dec 13th, 2005, 9:30am » |
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Box 2: The effects of H5N1 infection on migrant wild birds
There are a number of different possible scenarios.
First, perhaps migrants are infected by H5N1 but show mild, or no, symptoms (as demonstrated experimentally in captive Mallards for some specific viral genotypes). If this were the case, infected birds would not die, but would shed the virus in their breeding grounds, on migration and in their non-breeding areas. Poultry outbreaks would accompany the birds in both breeding and non-breeding grounds and on migration. In contrast, we have seen limited and localised deaths of wild birds on breeding grounds, but no evidence of poultry outbreaks following the main migratory routes.
If H5N1 were deadly to most wild birds, but some could carry it without symptoms, we would expect a slightly different pattern. Wild birds would die in their breeding and non-breeding areas and along the migration routes of carrier species. Poultry should become infected at the same time and same sites as wild birds. Some wild birds could die at sites where there are no poultry; and where wild birds don’t die, poultry shouldn’t either. None of these patterns is apparent in the way the virus has spread. There have been wild bird deaths at two apparently isolated sites (Lake Qinghai, China and Lake Erhel, Mongolia), but not at migration time – and infection from poultry or other sources cannot be ruled out.
If wild birds were carrying and shedding the virus for a short time before dying, the pattern would be different again. As successive groups of migrants became infected and died, we would expect the virus to spread continuously along migration routes. Both wild bird deaths and poultry deaths should follow these routes, without isolated concentrations of dead birds. Again, the patterns don’t bear this out.
If infected wild birds all died rapidly, we would expect localised concentrations of deaths that soon burn themselves out, with no trails of deaths of either wild or domestic birds along migration routes. This is exactly what the pattern of most outbreaks shows.
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