Newsletter No. 268

Advice f r o m a Microbiologist A number of countries are reporting cases of avian influenza, commonly referred to as 'bird flu' in their domestic and wild bird populations. The vast majority of the known human cases have resulted from direct contact with poultry, and there is limited evidence to suggest possible human-to-human transmission. Concerns about the possibility of an avian influenza pandemic have prompted international and national efforts to institute pandemic preparedness measures. Human Influenza Viruses versus Avian Influenza Viruses Prof. Pau l Chan , professo r i n th e Departmen t o f Microbiology, explaine d tha t ther e ar e three type s o f influenza viruses : A , B and C . Influenz a type A viruses can infec t people , birds , pigs, whales and other animals , but wil d bird s ar e th e natura l host s fo r thes e viruses . Typically wild birds do not get sick when they are infected with influenz a virus. However , domestic poultry , such as turkeys and chickens, can get very sick and die from avian influenza, and some avian viruses also can cause serious disease and death i n wild birds . Influenz a type A viruses are divided int o subtype s base d on two protein s on the surface of the vims. There are over 20 subtypes, includin g the H5N 1 whic h cause s severe disease i n domesticate d fowl, bu t only some are currently i n genera l circulatio n among people. Other subtypes are found most commonly in other animal species . Influenza B viruses ar e normall y foun d onl y i n humans. Unlike influenza A viruses, they are not classified according to subtype. Although influenz a type B viruses can caus e huma n epidemics , the y hav e no t cause d pandemics. Influenza type C viruses cause only mild illness in humans and do not spark epidemics . Prof. Chan said while species barrier prevents the virus from bein g spread betwee n species , breache s do occu r under special circumstances. And once that happens, the results are usually severe as the human immune system is naive to the attack. There hav e been confirmed case s of bird-to-huma n transmissions o f avian influenz a i n Southeast Asia, many of which hav e resulted i n death. Bu t Prof. Chan believe s that th e proces s o f bird-to-huma n transmissio n i s stil l inefficient as the human respirator y tract does not favour the growt h o f the virus. Huma n t o huma n transmission , he continued, is even more inefficient at this stage although there have been a few suspected cases of human-to-human transmission. Th e critical issu e is if the virus has mutated to such a stage that makes human-to-human transmissio n efficient, then we can expect a pandemic.' Medication The two groups of medication use d to treat avian flu include conventional drugs, Amantadine and Rimantadine, which were used to treat avian flu i n Hong Kong in 1997 , and new drugs, Tamiflu and Relenza. Prof. Chan said the effects of the new drugs are limited and certain conditions apply. The y hav e to b e administered withi n two day s of infection to achieve maximum effectiveness. Their clinical effect o n avia n influenz a i s uncertai n du e t o th e smal l number of cases and there is a chance of resistance for all anti-viral agent s with the chance increasing in proportio n to the amount of usage. 'Stockpiling o f anti-viral agent s i s only on e elemen t of a pandemi c pla n an d it' s no t th e mos t importan t element. I t cannot replace other measures such as a good surveillance syste m a t th e nationa l level , and , a t th e individual level , being clear about modes of transmission and takin g precautions, ' advise d Prof . Chan . H e als o warned again drug misuse. 'Using the drugs unnecessarily and inappropriatel y wil l lea d to communit y resistance . Also, peopl e wit h avia n fl u wh o rel y to o muc h o n th e drugs may delay seeking medical help. ' Vaccination Currently influenz a vaccine s protec t agains t thre e circulating huma n strains — influenza A subtypes H1N 1 and H3N2 , an d influenz a B — but non e hav e prove n protection agains t avia n flu . Prof . Chan i s also worrie d that vaccinated individual s ma y develop a false sense of security and become too relaxed about avian influenza as a result. The effects of flu vaccine s ar e also short-lived , lasting not more than 9 to 1 2 months . Symptoms The symptoms of bird flu includ e fever, sore throat, and coughing. The illness usuall y strikes very suddenly . Infected person s hav e a high chanc e o f progressin g t o pneumonia, respirator y distress and multi-organ failure , and othe r lif e threatenin g complications . Althoug h i f you hav e flu-like symptoms , the chances of you havin g bird fl u ar e extremely small , i t does no t hur t to wea r a mask when i n publi c an d wash you r hand s frequently , as the viru s ca n surviv e fo r severa l hour s an d eve n overnight. Piera Chen 微生物學家的忠告 香港分別在一九九七和二零零三年錄得十八宗和兩宗人 類感染 H5N1 禽流感的個案。隨著世界各地今年陸續發現禽 鳥死於 H5N1 和人類受到感染，世界衛生組織不時警告禽流 感可演變至人傳人，各國都全力監察和防止禽流感爆發。 流感與禽流感 微生物學系陳基湘敎授表示，流感分為甲、乙、丙三 型。甲型的宿主是野鳥，但可感染人、鳥、豬、鯨等，火雞 和雞等家禽一旦染上，死亡率高，部分甲型流感更可使野鳥 重病以致死亡。甲型流感根據病毒表面的兩種蛋白質細分， 約有二十種，包括 H5N1 禽流感。 乙型流感通常只存活於人體，可致病和引起季節性流 感，但不會導致疫症。至於丙型流感只會令人體不適。 陳敎授指出，雖然東南亞確實有人患上禽流感並因而病 逝，但鳥傳人的傳播途徑效率不高，因為人體呼吸管道並不 適合 H5N1 的生長。至於人傳人的效率就更低，萬一不幸病 毒變異而可普遍地人傳人，則會成為疫症。 藥物 治療禽流感的最新藥物特敏福（ Tamiflu) 和樂感清 (Relenza) 的效用有限制，例如要在染病兩天之內服食才能 發揮最大藥效。陳敎授説，由於個案數目太少，科學家仍未 掌握它們的臨床效果。一般來説，抗病毒藥會隨著應用越廣 而越易使病毒產生抗藥性。所以，庫存藥物只是疫症應變計 劃的一環，亦不是最重要的。藥物的效用絕不能代替有效旳 全國疾病監察系統，也不能取代個人的良好衛生習慣。 他更關注濫用這類藥物的後果，不必要地或不適當地服 用，可能使社區有抗藥性。另外，若患上禽流感的人太倚賴 這些藥物，可能延誤了送院診治。 防疫 現行的流感疫苗針對甲型的 H1N1 和 H3N2 ，以及乙型 流感——對禽流感沒有效，「最怕注射了疫苗的人，誤以為有 了保障而放鬆對禽流感的警戒。」 感染禽流感初時的徵狀與普通流感差不多，包括發燒、 喉嚨痛和咳嗽，但病情每每急轉直下，很易引致肺炎、呼吸 衰竭、多種器官衰竭和死亡。就算身體出現流感徵狀，也不 必恐慌，畢竟感染禽流感的風險是很低的。我們日常加強衛 生習慣，多洗手，避免到人多擠迫的地方，或是戴上口罩才 去，受到感染的風險會降得更低。 蔡世彬 校方大力滅蚊 物業管理處主任譚必成先生表示，自去年初香港出現 登革熱和日本腦炎病例後，該處即戮力加強防治蚊患。首 先由校園環境衛生小組主席黃子惠敎授安排，帶領該處職 員參觀食物環境衛生署蟲鼠組的工作及硏究。校方又派遣 安全事務處的職員到食環署受訓，學習辨認各種蚊子，以 分析校園內蚊的數目和種類。 物業管理處亦參考食環署的經驗，實施了多項防政措 施。譚先生説：「治標方面，我們去年已裝設了近百部滅蚊 燈和捕蚊器，今年添加至一百八十六部。每星期又清理沙 井和溝渠沉澱位，並噴上蚊油；更會經常剪草，滅少蚊蟲 滋生的機會。此外，我們又盡力維持校園的自然生態，因 為雀鳥是蚊蟲的天敵，如大學圖書館的雨燕，每隻一天能 吃掉百多隻蚊子。 「治本方面，我們會定期巡查校園建築物和溝渠，改善 設計，減少積水。根據捕蚊器所得的成蚊數目，找出蚊患 黑點，針對處理，在溪流靜水處放置食蚊的魚類。電器組 的同事更特別設計了自動灑蚊油器，安裝於沙井的隔沙或 隔氣位置，定時自動噴灑蚊油。」 人人有責 經過這些努力後，校園蚊患大幅減少，有關的投訴亦 減少了。不過，譚先生強調，減蚊需要校方和大學同人的 合作，「所以，大家如果發現積水，或是蚊蟲滋生，請即致 電物業管理處熱線（二六零九六六六六），我們會盡量在二 十四小時內清理積水。」 彭醫生補充説：「保健處會不時舉辦講座和印製海報， 介紹防蚊知識和相關的傳染病，並透過電郵發放最新資 訊，請同人多留意。另外，大家亦可瀏覽中大網頁內的『環 境及健康』一欄 ( h t t p : / / www . c u h k . e d u . h k / v 5 / b 5/ environment.htm) ，了解最新情況；更歡迎大家提供預防 蚊患或其他傳染病的方案。如外遊回港後發燒或有其他病 徵，一定要通知保健處。」 陳偉珠 Eliminate Mosquitoes for a Healthier Campus It's no w autumn an d the mosquit o breedin g seaso n i s over, but Dr. Kenneth Pang, ex-director of the Universit y Health Servic e warn s agains t relaxin g vigilance . Th e Department o f Healt h announced i n early October that there have been 20 cases of imported dengue fever this year. The UHS disseminates information about mosquito- transmitted diseases regularly through talks, posters, and email. Universit y member s ca n also access update s at hup:/ /www.cuhk.edu.hk/v5/en/environment.htm. Mr. Benny Tam, director o f the Estates Management Office , also urge d member s o f th e Universit y communit y t o report stagnant water to the office's hotline at 2609 6666. The office will try to send staff to clear the problem within 24 hours . 4 第二六八期 二零零五年十一月十九日