墨林.塔特/病毒獵巫 誤解使蝙蝠扣上疫病帶原者帽子 威脅了經濟、生態系 | 環境資訊中心

墨林.塔特/病毒獵巫 誤解使蝙蝠扣上疫病帶原者帽子 威脅了經濟、生態系

2020年04月21日
文:Merlin D. Tuttle(國際蝙蝠保育組織BCI創辦人);翻譯:何英毅(中央研究院生物多樣性研究中心博士後研究員);稿源:Issues in Science and Technology

對蝙蝠來說,過去10年是一段糟糕的時光。在武漢肺炎(COVID-19) 出現前,牠們的數量已在全世界急劇下降。現在,即便病毒的來源與傳播途徑仍不明,牠們仍被歸咎為當代歷史中代價最慘痛的流行病之一的罪魁禍首。雖然科學家有義務即時披露新的威脅,但關於蝙蝠的過度臆測卻在用來吸引目光焦點的媒體標題中被誇大了。結果造成不必要的混亂,即使在最需要牠們的地方,也導致了蝙蝠被妖魔化,驅逐和屠殺。

截止3月中,仍未找到武漢肺炎的「零號病人」,感染此人的源頭仍是個謎。病毒從未知的中間宿主跳到人類身上是否發生在最初所確認的地點—中國武漢的華南海鮮市場,也仍有不確定性。儘管有這些不確定性在,但在科學家的不小幫助下,媒體常未佐以自身觀點,便直接認定蝙蝠是可能的禍首並大肆渲染其風險,進而使牠們成為病毒獵巫的目標。

科學家關於蝙蝠的過度臆測卻在媒體的標題中被誇大了。照片來源:Bruce Lim(CC BY-SA 2.0)

世界各地開始出現反對蝙蝠的聲音

在世界各地,蝙蝠正承受這種錯誤資訊帶來的效應。我的馬來西亞同行,Sheema Abdul Aziz,花了數年時間,記錄狐蝠這不可或缺的授粉者,在東南亞每年數十億美元產值的榴蓮作物中扮演的關鍵角色。果農們原本打算加入她的一項大眾教育活動,闡述蝙蝠的價值,但現在卻因擔心受到公眾強烈反對而不願支持她的努力。

當地的一處度假村曾表示,擔心鄰近的一處狐蝠群集會影響他們的生意。由於擔心她的研究會引發新的疫情,民眾甚至曾要求政府阻止她接觸蝙蝠並支持根除蝙蝠,這類事在鄰國印尼已有報導。我在中國的同行也對蝙蝠被妖魔化及消滅蝙蝠的呼籲深表關切。

即使在我的家鄉德州奧斯汀市,數十年來我們一直安全地享受與150萬隻蝙蝠共用一座市區橋樑的樂趣,也開始有越來越多人探詢疫病風險。儘管矇昧的衛生官員警告說那些蝙蝠有狂犬病且危險,但牠們至今未嘗傳播過一例病症。

牠們僅在每年夏天吸引數百萬美元的觀光財,每晚抑制數以噸計的農業害蟲。德州的蝙蝠每年產值超過10億美元。如今蝙蝠愛好者在掛置蝙蝠屋一事上卻遇到強烈反對,因為鄰居們說,他們害怕吸引蝙蝠的同時也會帶來疫病。

然而僅告訴人們蝙蝠很有價值,且不應將其殺死並無助於抵銷恐慌。我曾親自走訪了一些案例,在那些地方,對蝙蝠恐懼的人會焚燒、下毒或封閉洞穴,一次就除掉數百萬隻蝙蝠。根據我的經驗所得的結論是,因誤導而造成的恐懼,會導致人們無法容忍以及進而消滅蝙蝠,這才是最大的威脅。

只要不碰觸蝙蝠 感染風險其實極低 然而事實通常不太會被報導

被誇大的蝙蝠疫病風險警告不僅是誤導,還威脅著整個經濟和生態系的健康。印尼的研究人員保守估計,蝙蝠每年在避免蟲害上,為可可農省下7億多美元。在墨西哥,每年產值達數十億美元的龍舌蘭酒和梅斯卡爾酒,依賴能幫龍舌蘭授粉的蝙蝠。從東南亞到地中海,蝙蝠為稻農提供了關鍵的蟲害控制。在南非,種植夏威夷豆的農人因蝙蝠抑制臭蟲而受益。

儘管蝙蝠傳統上長期遭受誤解且令人恐懼—或許是因牠們的夜行性與飄忽的飛行方式,蝙蝠在與人類安全共處方面卻有傑出的記錄。事實證明,數百萬住在後院蝙蝠屋,城市公園和橋樑中的蝙蝠是安全的鄰居。超過60年的研究生涯、處理過世界上數百種蝙蝠、有時甚至被洞穴中數百萬隻蝙蝠圍繞,我從未被蝙蝠攻擊過,且依然健康。如同獸醫師,我接種狂犬病疫苗,因為我在處理對我不熟悉的動物時偶而會被牠們咬傷。

只要避免碰觸蝙蝠,因蝙蝠而感染任何疫病的機會都是小到不行。所有可歸咎到蝙蝠的疫病都可以輕易避免,即便蝙蝠就住在你家院子裡。

然而,這些事實通常不會被報導,而風險卻常被放大。3月11日的《科學人》(Scientific American) 提供了一個絕佳的例子。其談論武漢肺炎文章的副標題寫道:「武漢的病毒學家石正麗曾在蝙蝠洞中發現數十種致命的類SARS病毒,她警告那裡還有更多。」使用「致命」一詞,即是無端的臆測。

該文進一步聲稱,武漢爆發的疫情是過去26年中,第六次由蝙蝠所引發。事實上,文中所列的前四次(嚴重急性呼吸道症候群[SARS]、中東呼吸症候群 [MERS]、亨德拉病毒感染症 [Hendra]、伊波拉病毒感染 [Ebola]) 看起來都是由蝙蝠以外的其他動物傳染給人類——然而蝙蝠仍承受了主要的責難。文中的第五次,立百病毒(Nipah virus),可能是由狐蝠傳播給人,只要蓋好採集容器或用巴斯德法對受污染的生椰棗汁進行消毒,即可輕易地預防。

科學家不成比例地過度專注在蝙蝠上 恐使媒體風向一面倒

關於武漢肺炎的爆發曾有兩種可能的假設情境被提出。第一種是某種新的冠狀病毒先進入了中間宿主動物,例如穿山甲,並在其體內逐漸演化出對人類的威脅性。另一種是,當新的冠狀病毒首次進入人體時可能無害,但隨著時間逐漸演化出毒性。這些情境都很難在事前預料,目前正在審查中的一篇論文甚至還將小鼠和家豬當作可能的來源。

那麼媒體為何幾乎一面倒地怪罪蝙蝠呢?有部分是因為科學家不成比例地過度專注在蝙蝠身上採樣。

自從蹄鼻蝠身上的冠狀病毒於2005年被發現,並首次被假定為SARS冠狀病毒的祖先起,蝙蝠便受到遠比其他任何動物類群更多更密切的關注。例如,在一篇曾被媒體下過最聳動標題的研究中,研究人員所採樣的蝙蝠數量幾乎是其他囓齒類、鼩鼱及非人靈長類動物總和的兩倍,且甚至未包含食肉目或有蹄類動物。

由於不討喜,因此易責難。蝙蝠也是最容易快速進行大量採樣的哺乳動物。這有利研究成果的快速發表,當焦點落在已令人生畏的動物身上時,聳人聽聞的臆測也更容易被接受。

毫不意外地,相較於那些較少被調查的物種,蝙蝠身上被找到更多的病毒,因此偏頗的臆測成為了一種自我實現的預言。我們並不知道蝙蝠是否帶有比其他動物更多的病毒,因為我們未曾對其他動物做過類似的採樣。即便蝙蝠真帶有更多病毒,病毒的數量也不一定代表傳播風險。許多病毒是無害的,甚至可能有益。

病毒學家擬進行全球野生動物病毒普查 遭權威專家強烈反對

某些病毒學家利用對大流行病的恐懼,去爭取用於普查自然界中病毒的研究經費,以作為預防或減輕這些可怕事件的可能方式。他們說服美國國家過敏與傳染病研究所(US National Institute of Allergy and Infectious Diseases),在2019年編列了48億美元的預算用於普查潛在的高風險病毒。

關於武漢肺炎大流行,長期普查的支持者目前認為,預防未來疫病爆發的最好方法是先啟動尋找和登錄全球野生動物病毒的普查,並聚焦在包括蝙蝠等,他們所認定的高風險動物。

然而,也有許多權威專家強烈反對。他們認為,這項普查的成本極高,但卻幾無實用價值。病毒引起的疫病爆發極罕見,且其出現無法預測。演化病毒學家 Edward Holmes 及其夥伴指出,即使當下所有病毒都可分類及登錄,新的RNA病毒變異仍會不斷演化出來。他們直率地警告,承諾病毒普查可以預防甚至減輕大流行,不但會傷害信譽且是一種傲慢。

要了解為何病毒普查這策略終將失敗,可參考MERS、西尼羅熱(West Nile) 和茲卡病毒感染症(Zika) 的例子。MERS 是從一個看似不太可能的源頭—駱駝,跳到了人類身上,其發生地點—沙烏地阿拉伯,在過去也被認為是極不可能發生這類事件的地點。新興病毒專家 Robert Tesh 曾指出,西尼羅熱和茲卡病毒皆非新病毒。它們的溢出(spilled over) 僅是因為在輸送到新地區時發生了無法預期的事件。

越來越多的權威流行病學專家同意,預測下一次病毒爆發的動物起源是不可能的。不幸的是,大眾媒體很少報導他們的警告。真被報導時,也往往遭淡化處理。

從目前爆發的疫情中,找出零號病人的真正感染源和感染途徑,似乎遠較譴責蝙蝠或花費數十億美元去尋找潛在病原更重要。這樣的公衛基金若用在改善人類疫情的早期發現將會更好。

但是,我們人類也必須面對自己的罪責。在市場中,將形形色色的動物關籠與宰殺,差不多也保證了病毒感染的傳播。不顧科學上所確知蝙蝠為環境與社會所帶來的巨大利益,而去責怪不討喜的蝙蝠只是徒增牠們本已嚴重的生存威脅而已。不論是否關心蝙蝠,我們應將武漢肺炎視為一次嚴厲的提醒,人類福祉需基於對大自然負責任的照管,而非僅是主宰。

墨林.塔特(Merlin D. Tuttle)是蝙蝠研究的權威,創建並主持國際蝙蝠保育 (Bat Conservation International) 30年。他目前主持墨林塔特蝙蝠保育(Merlin Tuttle's Bat Conservation) 同時也是德州大學奧斯汀分校整合生物學系的研究員。
A Viral Witch Hunt
BY MERLIN D. TUTTLE

It has been a bad decade for bats. Prior to the emergence of COVID-19, they were already in severe decline worldwide. Now, they are blamed as the culprits behind one of the costliest pandemics in modern history, even though the source and method of transmission haven’t been identified. Although scientists have an obligation to promptly disclose new threats, premature speculation about bats has been exaggerated in attention-grabbing media headlines. The result has been needless confusion, leading to the demonization, eviction, and slaughtering of bats even where they are most needed.

As of mid-March, “patient zero” for COVID-19 still had not been found, and who or what infected that person remains a mystery. There is even uncertainty about whether the viral jump from an unknown intermediate host to humans occurred in the location initially identified, an animal and seafood market in Wuhan, China. Despite these uncertainties, the media, with no small assistance from scientists, has sensationalized the risks, often without providing perspective, settling on bats as the likely culprit and thus making them targets in a viral witch hunt.

Around the world, bats are feeling the effects of this misinformation. My Malaysian colleague, Sheema Abdul Aziz, has spent years documenting the key role of flying fox bats as essential pollinators of Southeast Asia’s multibillion-dollar-a-year durian crop. Growers were planning to join her in a public education campaign explaining the value of bats, but now they fear a public backlash and are reluctant to support her efforts. A local resort has expressed fear of loss of sales due to a nearby flying fox colony. Fearing her research will trigger a new disease outbreak, private citizens have even asked the government to stop her from handling bats and to support eradication, something already reported in neighboring Indonesia. My colleagues in China are also deeply concerned about the demonization of bats and calls for their eradication.

Even in my home city of Austin, Texas, where we have safely enjoyed sharing a downtown bridge with 1.5 million bats for decades, growing numbers of people are asking about disease risks. Despite warnings from poorly informed health officials that our bats were rabid and dangerous, they’ve yet to transmit a single case of disease. They simply attract millions of tourist dollars each summer and control tons of crop pests each night. Texas bats are worth more than a billion dollars annually. Now bat-lovers are experiencing a backlash against putting up bat houses because neighbors say they fear that attracting bats will bring disease.

But simply telling people that bats are valuable and shouldn’t be killed can’t counter panic. I have personally investigated instances where fearful humans had burned, poisoned, or sealed caves, killing millions of bats at a time. Based on my experience, I have concluded that there is no greater threat than the intolerance and eradication that results from misguided fear.

Exaggerated warnings of bat disease risks aren’t just misguided. They threaten the health of entire ecosystems and economies. Researchers in Indonesia conservatively estimate that bats save cacao growers more than $700 million annually in avoided insect damage. In Mexico, tequila and mescal production worth billions annually relies on bats that pollinate agaves. From Southeast Asia to the Mediterranean, bats provide key pest control for rice growers. In South Africa, macadamia growers benefit from bat control of stink bugs.

Despite a long tradition of being misunderstood and feared, perhaps because of their nocturnal habits and erratic flight, bats have an outstanding record of living safely with humans. Millions living in backyard bat houses, city parks, and bridges have proven to be safe neighbors. I have never been attacked and am still healthy after more than 60 years studying and handling hundreds of species worldwide, sometimes surrounded by millions in caves. Because, like veterinarians, I am occasionally bitten by unfamiliar animals I handle, I’m vaccinated against rabies.

For anyone who simply avoids handling bats, the odds of contracting any disease from one are incalculably small. All diseases attributed to bats are easily avoided, even when bats live in one’s yard.

However, these facts typically go unreported, while risks are often magnified. The March 11 issue of Scientific American provides an excellent example. Its COVID-19 article subhead reads, “Wuhan-based virologist Shi Zhengli has identified dozens of deadly SARS-like viruses in bat caves, and she warns there are more out there.” The use of “deadly” is unjustified speculation.

The article additionally claims that the Wuhan outbreak is the sixth outbreak caused by bats in the past 26 years. In fact, the first four listed (SARS, MERS, Hendra, Ebola) appear to have been transmitted to people by animals other than bats—yet bats still receive primary blame. The fifth, the Nipah virus, which likely is spread to people from flying fox bats, is easily prevented by simply covering collection containers or pasteurizing contaminated palm juice.

Two possible scenarios have been hypothesized for the COVID-19 outbreak. The first is that a new coronavirus entered an intermediate host animal, such as a pangolin, where it evolved over an undetermined period to gradually become a threat to people. Alternatively, the new coronavirus could have been harmless when it first entered humans, but over time evolved to become virulent. Such scenarios would be difficult to predict, and a publication currently under review even points to mice and domestic pigs as possible sources.

So why has the media almost universally blamed bats? In part because scientists have disproportionately focused on sampling them.

Since 2005, when coronaviruses in horseshoe bats were first hypothesized to be the ancestors of the coronavirus that caused SARS, bats have received far more scrutiny than any other group of animals. For example, in the study on which the scariest headlines were based, researchers sampled nearly twice as many bats as rodents, shrews, and nonhuman primates combined and didn’t even include carnivores or ungulates.

Easily blamed, due to their lack of popularity, bats are also the easiest mammals to quickly sample in large numbers. This led to rapid publication of the results, and sensational speculations were deemed more acceptable when focused on already-feared animals.

Not surprisingly, more viruses have been found in bats than in less-surveyed species, so biased speculation has become a self-fulfilling prophecy. We don’t yet know if bats have more viruses than other animals because we haven’t similarly sampled others. And even if bats do have more, the number of viruses isn’t necessarily indicative of transmission risk. Many viruses are innocuous or possibly even beneficial.

Some virologists have capitalized on the fear of pandemics to promote funding for viral surveys in nature as a possible means of preventing or mitigating these scary events. They convinced the US National Institute of Allergy and Infectious Diseases to budget $4.8 billion in 2019 for surveys searching for potentially high-risk viruses. Referring to the COVID-19 pandemic, longtime surveying proponents now argue that the best way forward is to prevent future outbreaks by beginning with surveys to find and catalog wildlife viruses globally, focusing on what they consider to be high-risk animals, including bats.

However, many leading experts strongly disagree. They argue that such surveys would be extremely costly and have little practical value. Viral-caused outbreaks are exceedingly rare, and their emergence is unpredictable. The evolutionary virologist Edward Holmes and associates note that even if all current viruses could be cataloged, new variants of RNA viruses are constantly evolving. They bluntly warn of arrogance and loss of credibility resulting from promises that viral surveys could prevent or even mitigate pandemics.

To understand why surveying will fail as a strategy, consider the examples of MERS, West Nile, and Zika viruses. MERS jumped to humans from a seemingly unlikely source, camels, in Saudi Arabia, previously believed to be an extremely improbable location for such an incident. Robert Tesh, an expert on emerging viruses, has pointed out that neither West Nile nor Zika viruses are new. They simply spilled over when transported to new areas in incidents that couldn’t have been predicted.

A growing number of leading epidemiologists agree that it isn’t possible to predict the animal origin of the next viral outbreak. Unfortunately, their warnings are seldom covered by public media. When they are, they tend to be de-emphasized.

Finding the true source and means of infection for patient zero in the current outbreak seems far more important than condemning bats or spending billions on searches for potential pathogens. Such public health funds would be much better directed toward improved early detection in humans.

But we humans must also address our own culpability. Caging and slaughtering a wide variety of animals in markets virtually guarantees the spread of viral infections. Blaming already unpopular bats only increases already severe threats to their survival, despite scientific certainty about the enormous benefits they provide to both the environment and societies. Care about bats or not, we should see COVID-19 as a grim reminder that human well-being requires responsible stewardship of nature, not just dominance.