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Topic: Avian Flu in OBC mailing list 來自東方鳥會的電郵 (Read 983 times) |
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Simba Chan
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Avian Flu in OBC mailing list 來自東方鳥會的電郵
« on: Feb 13th, 2004, 8:53pm » |
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Posted by Dr. Hugh Buck. Hope you'll find it useful:
This subject is undestandably occupying a great deal of discussion space in
recent weeks and it perhaps needs a summary to cut through some of the
conjecture and hysteria that surrounds it. I attempt this with credentials
as follows:
I am a veterinary doctor
I am, as many of you know, a serious birder
I work for an Animal Health Company which, amongst other things,
specialises in vaccines for domestic poultry and ducks
I will try to put this as best I can in layman's terms (because in may ways
I am, in this subject, a layman) but I have cleared it with my technical
staff before release. Much of the data comes from an excellent study
entitled "Avian Influenza: Ecology and risk factors for Humans and Poultry
production" by Mauro Delogu of the Department of Public Veterinary Health
and Animal Pathology at Bologna University in Italy. Mauro is a renowned
virologist with a great interest in wild birds and, although the study was
done in Italy, it is undoubtabl relevant to the rest of the world. He
presented this work at a Scientific Seminar arranged by our Comopany in
Budapest on 7 November 2003 and if anyone is SERIOUSLY interested I can
arrange copies. I have also referred to the chapter on Avian Influenza by
Easterday, Hinshaw and Halvorson in the standard work Diseases of Poultry
10th Edition (1997).
Firstly this disease is by no means new. It has been suspected for more
than 100 years (first described in Italy in 187 , was studied intensively
during the devastating flu epidemics following the 1st world war and has
caused epidemics in poultry and other birds in many countries (including
USA and several in Western Europe) all over the world throughout this and
the last century. It is likely it has also been overlooked in the face of
other epidemic poultry diseases in the past and only in recent years ( the
virus was finally identified in 1955), in a parallel with a lot of birding,
have the true identification techniques been worked out. Note that domestic
pigs in Asia have also long been incriminated in outbreaks of "Asian" flu
in humans so it should come as no surprise that intensivey reared birds can
also be a source. The virus has also been isolated from seals, a whale and
mink.
There is no question that Avian Influenza, as it's name suggests, largely a
disease of birds. It is also clear from studies done that the virus is
commonly found in wild birds but the evidence is that it is primarily found
in waterfowl and waders and only rarely or never in other families. The
presence of the virus does not mean that these birds suffer from Avian
Influenza as they are hughly resiarant, have obviously developed high
degrees of immunity over the millenia and overt disease is rarely found.
They are however carriers of the virus.
In Dr Delogu's study he sampled 21000 wild birds of 88 species, 22 families
and 12 orders. He found evidence of virus as follows (percentage of birds
sampled):
Anseriformes 15.2%
Charadriformes 2.2%
Passeriformes 2.9%
It is interesting to note the species breakdown in "anseriformes" (% of
species sampled positive for virus)
Mallards 63.9%
Other dabbling ducks 31.4%
Diving Ducks 22-8%
Coots 7.1%
In addition virus was demonstrated at a much higher level in post breeding
juvenile ducks that in wintering birds which is logical. There was also a
higher percentage in birds released from captive rearing than from birds
collected from the wild
(to be continued)
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Simba Chan
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Avian Flu posted on OBC mailing list (part 2)
« Reply #1 on: Feb 13th, 2004, 8:55pm » |
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Mauro also specifically sampled other groups eg
Terns 3.6% positive in 140 birds sampled
Gulls 18.8% positive in 101birds sampled
Pheasant Zero positive from 424 birds (both wild and domestically
reared)
Quail Zero positive from 258 birds trapped from the wild
Finally the virus is shed by birds' faeces in addition to other modes (eg respiratory)
The influenza virus is highly mutagenic ie it can change in type and
virulence very rapidly. This has long been known in human flu and is the
main reason why there have never been (and probably never will be) truly
effective influenza vaccines. The same is true of Avian Influenza -
vaccines do exist and are (and undoubtable will continue to be) widely used
in attempts to control this disease. Their efficacy remains doubtful.
The serotypes of virus so far isloted from wild birds including ducks have
been almost invariably low pathogenic and do NOT immediatly cause influenza
in domestic birds. In modern day intensive poultry units the virus has
however the distressingly rapid ability to mutate to high pathogenic forms
and this is the crux of the problem. This of course is a common phenomenon
in highly crowded intensive situations anywhere - humans in the outback fo
Australia are less likely to suffer nasty new strains of Asian flu that
residents of Wanchai etc . This pathogenic virus can spread from poultry to
humans although this is as yet rare. I stress that so far the human
infections have only been in people directly in contact with diseased
birds, there is no evidence at all that humans can spread this disease to
other humans.
As birders we have to accept that Avian Influenza can spread from wild
birds, especially dabbling ducks, into domestic poultry. This may be by
direct eg wild ducks coming into contact with domestic ducks which in turn
come into contact with domestic chickens or it may be spread by humans or
domestic dogs (it is documented) who wander over fields contaminated with
wild duck or geese droppings and carry the virus into a farm. The low
pathogenic virus then has the ability to mutate into the high pathogenic
form and off we go. Highly pathogenic virus has been found, rarely, in
wild birds (Mauro found it in one Herring Gull out of 100 sampled) but
this, like the publicised dead Peregrine in Hong Kong and Open-Billed
Storks in Thailand was probably caused by contact with the pathogenic virus
in poultry or poultry waste.
Hysterical conclusions, statements and reactions such as the outbreak in
Indonesia being caused by migratory birds from China in August, Bramblings
falling out of trees in Thailand etc are exactly that - hysterical and ill
informed responses. Avian Influenza can be spread into poultry from wild
birds and can mutate into a pathogenic form which can cause disease in both
intensively reared poultry and humans. But the major transmission from farm
to farm is unquestionably movement of infected poultry and poultry products
and wild birds are only a scapegoat.
At this moment the only veterinary solution to this problem is the rapid
cull (kill) of all infected and in contact birds but this depends (remember
the last outbreak of Foot and Mouth Disease in Britain) on an effective
mobilised infrastructure to carry this out. This is probably not present in
many of the countries where the disease is present and this inaction will
lead to epidemics. Vaccination of healthy non-infected birds is now being
widely recommended and is underway in many countries but we do not know the
true value of this. We also do not know trhe future of this current
"pandemic" and whether it will continue and get more serious or the virus
will change again and the crisis will die down. What is likely however is
that this disease will, like human flu, continue to occur in outbreaks from
now on. The structure of the modern poultry industry almost guarantees it.
I have gone on far longer then I perhaps intended but we finally come to
the question - what can we, as birders, do about it. Well firstly
understand what is going on which is what I have tried to "summarise"
above. Secondly spread this understanding both amongst our friends.
colleagues and wherever possible influential persons at Government and
other levels. Some of the reactions, eg in Thailand, do show some common
sense being spoken but we all know that this may not be the majority view.
The message is that culling wild birds will never stop Avian Influenza, we
might as well cull all the domestic chickens and pigs in the world and we
will still have human flu. There is however also, as several people have
pointed out, a possible benefit in all of this - reaction against the
hunting, trapping and keeping of wild birds as pets. As birders this
possible benefit may outweigh the disadvantage. As a vet who earns a fair
proportion of his earnings from domestic poultry I might have to disagree!
I hope this is of interest to many of you
Hugh Buck
e.mail: hugh.buck@ceva.com
Dr Hugh A. Buck
Regional Director
CEVA Animal Health (MOTI) Ltd
19 Arch. Macharios III Ave. 2324 Lakatamia, Cyprus.
Tel: 00 357 22 814 550
Fax: 00 357 22 324 553
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假鳥迷
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BBS God
Have fun...
Posts: 112
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Re: Avian Flu posted on OBC mailing list (part 1)
« Reply #2 on: Feb 16th, 2004, 2:35am » |
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這是中譯本，希望可以讓多些鳥友獲得這訊息。
[節錄 – 開始]
From: hugh.buck@ceva.com
Date: Fri, 13 Feb 2004 11:08:53 +0200
To: orientalbirding@yahoogroups.com
Cc: sylvain.comte@ceva.com
Subject: [OB] 禽流感
據理解，這事件近幾個星期以來引發起很多的討論，當中有不少猜測和不理性的態 度，也有也許讓我來作一個簡報。我先來申報個資料，如下：
我是一個獸醫
相信很多人都認識我，我亦是一個觀鳥迷
我在一個動物健康公司工作，特別是專責家禽和鴨疫苗的工作
我會嘗試以淺白的名詞 (這項內容對於我來說亦是初哥)來作寫以下內容，不過我在發出前已就技術方面向 同事請教。這裏大部份內容原自一項由意大利Bologna University Department of Public Veterinary Health and Animal Pathology (公眾防疫健康及動物病理學系)由Mauro Delogu博士名進行名為「Avian Influenza: Ecology and risk factors for Humans and Poultry production」的研究而來。Mauro是一個知名的的病毒學家，特別是野生鳥類。雖� M這項研究是於意大利進行，亳無疑問對全球是有關係的。他曾於2003年11月7日於 布達佩斯的一個我的機構安排的科學研討會中發表他的研究，如各人有興趣參閱有 關內容，請與我聯絡安排。此外，以下內容亦參考自Easterday，Hinshaw 和Halvorson《Avian Influenza (禽流感)》一書 (1997年，第10版)。
這個疾病對很多人來說是很新的。它可能已經存在了超過100年(第一次是在1878年 於意大利出現的)。在第一次世界大戰後才開始獲廣泛研究，過去一世紀至現今， 禽 流 感 曾 經肆虐多個國家(包括美國和西歐幾個國家)，影響的家禽和其他鳥種。當時以至近 年都普遍當作其他疾病處理(這種病毒是於1955年確定的)，隨著觀鳥的普及，從而 發展了確實的病毒辨識方法。請留意亞洲的豬隻曾引致亞洲流禽爆發，這反映密集 飼養的鳥類亦是一個途徑。不過這病毒仍未在海狗、鯨魚或水貂找到，這 可 能 是 距 離 太 遙 遠 的 關係。
單從名字來看，「禽流感」與鳥類疾病有關係。從研究顯示，這病毒經常於野鳥身 上找到，並已證實是從水禽和水鳥而來，其他鳥種的機會則極少。在這類型鳥類找 到病毒並不表示牠們正受禽流感影響，相反牠們已有一定程度的抗體，發病的機會 亦相對很低。不過牠們是病毒的攜帶者。
Delogu博士的研究曾捕捉21,000隻共88種野鳥，當中包括了22科11目。他找到證實 有病毒的比例如下(百分比)：
雁形目 15.2%
(行鳥)形目 2.2%
雀形目 2.9%
而在上述的雁形目，我們再細分為如下(病毒測試呈陽性的百分比)
綠頭鴨 63.9%
其他水鴨 31.4%
潛鴨22.8%
白骨頂7.1%
除此以外，這病毒較多在繁殖期過後仍未成年的鴨類找到，故此越冬鳥是一個合理 想法。此外，這病毒亦較多在曾被飼養的鳥類找到，在野鳥反而較少。
Mauro亦測試了以下鳥種，例如：
140隻燕鷗類找到3.6%呈陽性反應
101隻鷗類找到18.8%呈陽性反應
424隻雉類 (野生或飼養)找到0%呈陽性反應
258隻鵪鶉類找到0%呈陽性反應
這些病毒主要由鳥類的糞便或其他方式(例如呼吸)傳播。
這種病毒變種得很快，傳播性高。人類的流感亦是一樣，至今還未有完全有效的疫 苗(也許無可能)。同樣道理，現時是有疫苗對府禽流感且被廣泛使用，不過成效成 疑。
從野鳥包括鴨類取得的病毒抗原因子變異性和傳染性都很低，是不會引發家禽的 流 感 的。現今的禽蓄養殖以密集形式的，這會導致病毒加速變種，從而變得高傳染性， 這才是問題的根源，亦是高密度的環境下的現象 - 例如從居於澳洲感染較強的亞洲流感的機會遠低於灣仔 (?) 等地。當然這種病毒由禽蓄傳染給人類是可能的，不過機會郤很低。我強調人類受 感染主要原因是接觸了帶病的鳥而導致的，現時仍未證實人與人之間可互相感染。
作為觀鳥者，我們要接這個事實，禽感流是可以由野鳥尤其是水鴨傳播至家禽。有可能的是，例如一隻野鴨與家鴨接觸，再接觸家雞，然後再傳染給人類。亦有可能是狗隻(已有文獻)在田野遊蕩，受到野鴨、雁的糞便感染，然後帶回禽蓄養殖場。由此，這低傳染性的病毒會有機會變種成高傳染性，問題亦因而衍生。有研究指在野鳥中曾找到高傳染性的病毒，不過這是很罕見的例子 (Mauro曾在100隻海鷗中找到1隻)。這個可以最近香港報導的游隼、或泰國的鉗 嘴 鸛 來解釋，相信牠們是曾接觸受感染養殖禽蓄或養殖場的廢物。
最近一些虛構的結論、聲明或反應，例如印尼的爆發與八月期間來自中國的候鳥有 關、泰國的燕雀群從樹上掉下等等，都是資料不足的。禽流感是可以由家禽傳染給 野鳥，以及可以變種至高傳染性而使其他家禽或人類受感染。此外，禽蓄養殖場之 間傳遞受感染的家禽和家禽產品方面亦有可疑之處，野生鳥類在這事件上其實是受 害者。
在這情況下，作為獸醫的選擇是盡快殺死受感染或曾接觸的家禽，不過這方面要視 乎內部設施和運送的成效 (記得英國上次爆發手足口病的經驗)。若果不足，這種行動會反而導致疾病爆發， 現時很多國家還未採用這個方法。有很多國家鼓勵為未受感染的禽鳥注射疫苗，不 過實際價值仍然未知。我們不知道將來這個傳染病會否繼續發生、變得更加利害、 或導致更多危機。現時現代化的禽蓄養殖方式來看，可以肯的是，這疾病會像人類 的流感一樣，繼續發生。
說得太遠了，也許我想提出最後一個問題----作為觀鳥者，我們可以做甚麼呢？首 先是要理解現時發生的甚麼事情，可參閱以上的簡報。第二是將這個訊息帶給我們 的朋友、同事、以及具有影響力的相關政府或其他人士。有些反應，例如在泰國的 例子，具有一定的可明白性，不過這個可能不是一般看法。事實上殺掉野鳥是不能 阻止禽流感的，就算殺掉全球的家雞和豬隻，人類一樣會有流感。已有人指出，現 時可行而有益的方法是----反對捕獵、反對以鳥類為 寵 物。作為觀鳥者，我認識為這個益處多於壞處；作為獸醫，如果有人認為我是從家 禽中賺取利益的話，我不敢苟同！
盼望你這資料對你有用。
Hugh Buck
e.mail: hugh.buck@ceva.com
Dr Hugh A. Buck
Regional Director
CEVA Animal Health (MOTI) Ltd
19 Arch. Macharios III Ave. 2324 Lakatamia, Cyprus.
Tel: 00 357 22 814 550
Fax: 00 357 22 324 553
[節錄 – 結束]
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| « Last Edit: Feb 16th, 2004, 2:41am by 假鳥迷 » |
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