禽流感最新消息28(WHO 2004-02-20)_中国质量新闻网移动版

禽流感最新消息28(WHO 2004-02-20)

2004-05-26 00:00:00 www.aqsiq.gov.cn

Avian influenza A(H5N1) - update 28

20 February 2004

Reports of infection in domestic cats (Thailand)

WHO is aware of reports of H5N1 infection in a single household ofdomestic cats in Thailand. Investigations are under way and no firmconclusions can be made at present. However, concern is great andseveral specific questions are being raised about risks to humansin close contact with infected cats and the need for surveillanceof disease in cat populations.

H5N1 infection in two out of three dead domestic cats was announcedtoday by the Faculty of Veterinary Sciences at Thailand’s University. The animals are part of a single household of 15 cats.Of these, 14 have died. Contact of one cat with dead chickens wasobserved by the owner.

Thailand’s Ministry of Public Health is investigating the incidentin cats and is monitoring the health of human contacts. FAO is alsocontributing expertise.

While conclusions are premature pending the results of theseinvestigations, confirmation of H5N1 infection in cats is notconsidered likely to enhance the present risks to human health. Noris it considered likely to influence the future evolution of theoutbreak in humans in any significant way.

Several studies have shown that a small number of mammalianspecies, including pigs, seals, whales, mink, and ferrets, aresusceptible to natural infection with influenza viruses that arepurely avian in their genetic make-up. Of these species, only thepig has significance for human health. Pigs can be co-infected withboth avian and human influenza viruses and can thus serve as the“mixing vessel” for the mingling of genetic material, possiblyresulting in the emergence of a new influenza virus subtype. Mostexperts agree that pigs played a role in the emergence of pandemicviruses in 1957 and 1968.

Up to now, domestic cats have not been considered susceptible todisease caused by natural infection with influenza viruses. Someolder studies, from 1970,1972, and 1981, reported experimentalinfection of domestic cats under laboratory conditions. Althoughinfection occurred (virus was recovered from the respiratorytract), all of the cats remained healthy. None developed typicalsymptoms of influenza, including fever, nasal discharge, coughingor sneezing. These findings are important in that they stronglysuggest that, should additional cats become infected with H5N1,they would not shed large quantities of the virus.

In contrast, H5N1 virus replicates in the intestines as well as therespiratory tract of birds. In the present outbreak, very largequantities of virus are being excreted in the faeces of infectedbirds, resulting in widespread contamination of the environment.This wide presence of the H5N1 virus in the environment creates oneof the most important risks for human exposure and subsequentinfection. Should domestic cats prove to be easily infected withH5N1, which is considered unlikely, their infection is not expectedto contribute in a significant way to the presence of H5N1 virus inthe environment.

Avian influenza viruses, including the specific strain implicatedin the present outbreak, lack the receptors needed to infectmammals efficiently. However, the infection of humans observed inthis and two previous H5N1 outbreaks demonstrates that transmissionfrom birds to mammals can occur despite this lack of receptors. Thevery small number of human cases – despite abundant and widespreadopportunities for exposure and subsequent infection – stronglysuggests that transmission of H5N1 from birds to mammals, includingcats as well as humans, is a rare event.

The reported infection of domestic cats with H5N1 is an unusualevent in what is an historically unprecedented situation. Resultsfrom the investigation undertaken by Thai authorities will shedcritical light on this unusual event.

Influenza viruses are highly unstable and their behaviour cannot bepredicted. Vigilance for suspected cases in various mammalianspecies is presently high and should be continued. Reporting byveterinarians of suspected or confirmed cases to nationalauthorities, as happened in the present situation, is a keycomponent of this continuing vigilance.

WHO is collaborating closely with FAO and OIE as part ofinternational efforts to understand the continuing evolution of theoutbreaks in humans and animals, which are closelyinter-related.

Situation (human) in Thailand

Since 23 January 2004, the Ministry of Public Health in Thailandhas reported 9 laboratory-confirmed cases of human infection withH5N1 avian influenza. Of these, seven have died. The situation isreviewed daily by a joint team of ministry officials and WHOstaff.

Preliminary epidemiological and clinical dataon the first fivecases were published last week by WHO. The subsequent four casesinclude two who have fully recovered (a 2-year old boy and a27-year-old woman), a thirteen-year-old boy, and a four-year-oldboy, who died on 3 February. All cases have been announced inprevious updates.

Thai authorities are currently investigating a further 147 reportsof patients admitted to hospital with suspicious symptoms. Ofthese, 21 are being considered as suspect cases of H5N1 infection.All have a clinical diagnosis of pneumonia. Eight have died, 8 havefully recovered, and 5 remain hospitalized.

The investigation of cases is following three lines: laboratorytesting, epidemiological tracing of likely sources of infection,and examination of clinical features of disease.

Final results of laboratory testing are pending for the additional126 patients under investigation. The results of virus isolationstudies are pending. These studies, which can take up to 14 days,are used to verify and supplement the initial PCR findings. Recentenhancement of laboratory facilities at Thailand’s NationalInstitutes of Health, including the addition of equipment forreal-time PCR testing, has expedited the processing of clinicalsamples, thus reducing the time from notification to obtaining theinitial laboratory diagnosis. In this group of 126 patients, 19 arestill being investigated to obtain more details about eitherpotential exposure to affected poultry or the clinical features ofdisease.

The surveillance system in Thailand is on high alert. To date, 510reports have been brought to the attention of health authorities.Of these, 354 have been excluded from consideration followingthorough laboratory, epidemiological, and clinicalinvestigation.

The most recently announced confirmed case was a four-year-old boyfrom the northeastern province of Khon Kaen. His family raisedchickens, and many died shortly before the onset of hissymptoms.

One of the most recently reported suspect cases is a two-year-oldgirl from a southern province. The family’s poultry died 7 daysprior to the onset of her symptoms. The case is not yet laboratoryconfirmed. As H5N1 infection in poultry has not been reported inthis province to date, the Ministry of Agriculture has beeninformed and is currently investigating animal illness in thearea.

To date, no evidence suggests that human-to-human transmission hasoccurred in Thailand.

The number of reports brought to the attention of Thai authoritieshas declined and the numbers this week are low. The Ministry ofAgriculture is currently responding to the detection, earlier thisweek, of the reappearance of infection in poultry in provinceswhere extensive culling was previously carried out. Rapid cullingin the newly affected areas is now under way to prevent furtherspread, and thus reduce opportunities for the disease to becomeendemic.

Thailand’s Ministry of Public Health, with the full support of WHO,is stressing the need for continued vigilance and intensivesurveillance.

Situation (poultry) in Japan

Japanese authorities have confirmed that the country’s secondoutbreak of avian influenza, detected in Oita Prefecture, is causedby the H5N1 strain.

Situation (poultry) in China

As of today, Chinese authorities have reported 53 outbreaks inpoultry in 16 provinces. Of these, 49 have been confirmed as causedby H5N1. To date, an estimated 1.2 million chickens, ducks, andgeese have been destroyed.

禽流感最新消息28

2004-2-20

家猫感染禽流感的报告（泰国）

世界卫生组织注意到泰国一个家庭家猫感染H5N1禽流感的报告。调查正在进行之中，目前尚不能做出确切结论。不过，这件事已经引起了极大的担忧，并且已经提出了许多有关密切接触病猫者感染禽流感的危险和在猫群开展禽流感监测需求的具体问题。

今天，泰国Kasetsart大学兽医科学系宣布在3只死家猫中2只感染了H5N1禽流感。养猫的这个家庭，共养了15只猫，14只已经死亡，这3只死猫是其中的一部分。主人观察到其中一只猫曾经接触过死鸡。

泰国公共卫生部正对这一事件进行调查，其中包括在猫中进行调查和对人类接触者的健康进行监测。世界粮农组织专家也提出了意见。

虽然调查尚未结束，做出任何结论都尚属太早，但是目前并不认为证实猫感染H5N1会增加禽流感对人类健康的威胁，也不认为会明显的影响将来人类流感爆发的演化。

许多研究已经表明，为数不多的哺类动物（其中包括猪、海豹、鲸鱼、貂和白鼬等对基因组成完全属于禽类流感的病毒易感，感染可在自然情况下发生。在这些动物中，只有猪感染禽流感对人类健康具有明显的意义。猪可能同时感染禽流感和人流感病毒，从而成为一个基因物质的混合容器，可能导致新流感病毒亚型的出现。大多数专家认为，猪与1957年和1968年导致流感大流行病毒的出现有关。

直到目前为止，尚不认为家猫对自然感染的流感病毒疾病易感。一些早前的研究（1970、1972和1981）曾报告在实验室的条件下家猫感染此病毒。虽然发生了这样的感染（从呼吸道重新获得病毒），但是所有的猫均一直健康，未发生疾病。没有一只出现典型的流感症状（包括发热、流涕、咳嗽或者打喷嚏）。这些发现是重要的，因为他们强烈地提示如果还有猫感染H5N1，那么他们也不会播散大量的病毒。

相比之下，H5N1病毒在禽类肠道以及呼吸道却进行复制。在目前这次爆发中，感染禽流感的禽类于粪便中排出了大量的病毒，从而导致环境的广泛污染。H5N1病毒在环境中的广泛存在形成了人类接触继之感染H5N1病毒的巨大危险。如果能够证明家猫很容易感染H5N1病毒（这种情况据认为不可能），预计猫的感染不会对环境中H5N1的存在产生明显的影响。

禽流感病毒，包括与目前爆发相关的病毒株，缺乏有效地感染哺乳类动物所需要的受体。然而，在此次禽流感爆发中和以前两次禽流感爆发中所观察到的人类感染H5N1禽流感病毒证实，尽管缺乏这种受体，还是能够发生禽流感病毒从禽类向哺乳类动物的传播。尽管存在大量的广泛的接触禽流感病毒继之感染禽流感病毒的机会，但是只有非常少量的人类病毒有力地表明H5N1病毒从禽类传播到哺乳类动物包括猫以及人都是非常罕见的事件。

已经报告的家猫感染H5N1这件事是一个史无前例的情况。泰国当局开展的调查的结果将为这一非常事件提供重要的解释。

流感病毒具有高度的不稳定性，而且其不能预测其变化的情况。目前对各种哺乳类动物疑似病例的警觉性都非常高，而且需要继续保持这种警觉性。象目前这样，兽医向国家当局报告疑似或确诊病例是这种继续保持警觉性的一个重要组成部分。作为全球努力遏制流感的工作的一部分，世界卫生组织现在正在与世界粮农组织和世界动物卫生组织密切合作了解密切相关的人类和动物中流感爆发的演化。

泰国禽流感态势

自从2004年1月23日以来，泰国公共卫生部已经报告了9例经实验室确证的H5N1禽流感人类病例。在这些病例中，7例已经死亡。由泰国公共卫生部和世界卫生组织官员联合组成的工作队每天都对该国的禽流感态势进行观察。

世界卫生组织上周公布了泰国前5例病例基本流行病学和临床学资料。后来的这4例病例包括两例已经康复的病例（一例两岁男孩，一例27岁妇女）、1位13岁男孩和1位4岁男孩，他们均于2月3日去世。所有这些病例都是上次信息更新时公布的。

泰国当局目前仍在调查另外147份具有具有疑似症状住院病人的报告。在这些病例中，21例被认为是H5N1疑似病例。所有这些病例均临床诊断为肺炎。8人已经死亡，8例已经康复，还有5例仍在住院治疗。

对这些病例正在以3种方式进行治疗：实验室检测、流行病学追踪传染源、疾病特征临床检查。

还有126例正在接受调查的病人的实验室结果还没有出来。这些研究可能需要14天的时间来证实和补充PCR初步检查的结果。最近，泰国国家卫生研究所得到了加强，其中包括增加了实时PCR的装备，从而加速了临床样本的加工程序，减少了从通知到获得实验室初步诊断的时间。在这组126位病人中，19位仍然在接受调查以便得到有关可能接触受侵袭家禽或者疾病临床特征的详细资料。

泰国监测系统已经处于高度警觉状态。到目前为止，510例报告已经受到卫生当局的注意。其中354例继全面实验室检查、流行病学和临床调查之后已经排除了禽流感。最近公布的这例确诊病例是一位KhonKaen东北省份的4岁男孩。他的家庭养鸡，就在病人出现症状之前许多鸡已经死掉。

最近报告的疑似病例之一是一位南方省份的2岁女孩。其出现症状的7天前其家庭饲养的家禽死亡。这个病例尚未得到实验室确证。由于到目前为止，该省份尚没有H5N1禽类中H5N1流感的报告，农业部已经得到通知并且目前正在调查这一地区动物疾病。

到目前为止，尚无证据表明泰国已经发生了禽流感人与人之间的传播。

受到泰国当局关注的报告数已经下降，而且本周报告数也低。农业部本周早期已经开始根据情况侦察以前实施过广泛扑杀的省份禽类中重新出现禽流感的问题。为了防止禽流感进一步传播，现在新受到禽流感侵袭的省份正在进行扑杀，从而减少这种疾病在当地形成地方性流行的可能性。

在世界卫生组织的全面支持下，泰国公共卫生部重点解决持续保持警觉和强化监测的需求。

日本禽流感态势

日本当局已经证实该国第二起禽流感爆发，这次爆发是在大分发现的，致病病原体为H5N1病毒株。

中国禽流感态势

到今天为止，中国当局已经在16个省份报告了53起爆发。其中，49起经确证是由H5N1病毒所导致的。到现在，估计已经有120万只鸡、鸭、鹅被消灭。

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