《媒體觀察》致命的跳躍：不是「如果」，而是「何時」
資料來源：www.thelancet.com/infection Vol 23 October 2023
致命的跳躍：追蹤流行病的起源/ Leslie Reperant / John Hopkins University Press, 2023
隨著 COVID-19 大流行慢慢開始放鬆對人類和國際醫療保健的控制，一些問題正在出現。然而，有兩個問題反覆出現，也許是最關鍵的：SARS-CoV-2 從何而來，以及我們如何預防另一場疫情？有證據顯示 SARS-CoV-2 可能是從華南海鮮市場出售活體野生動物的區域出現的，科學家推測該病毒可能是從動物傳播給人類的。從動物到人類的致病性跳躍一直是歷史上幾次流行病的核心。在《致命的跳躍：追蹤流行病的起源》一書中，萊斯利·雷佩蘭特引導讀者了解這些生物體的進化和傳播——它們如何在宿主體內生存和繁衍，它們如何從一個宿主跳到另一個宿主，最重要的是，是什麼決定了它們的成功。
人類與我們的微生物鄰居有共生關係。我們的發展是由於早期真核生物的分化和演化。生物體（例如細菌和病毒）造成的環境壓力也是大多數現有生命形式中廣泛存在的有性生殖的原因。有性繁殖比無性繁殖在後代中產生更大的遺傳變異，這使得後代能夠更好地應對物種互動造成的威脅。這種變異是物種生存的重要決定因素。這種關係是「一場錯綜複雜的精心設計的遊戲」，其中在人類進步和發展的願望與自然世界之間保持微妙的平衡至關重要。
雷佩蘭特不僅涉及寄生蟲和病原體進化生存的生物學解釋，還涉及更廣泛的社會、政治和環境決定因素如何維持它們。最近記憶中的流行病和大流行病凸顯了航空旅行是疾病全球傳播最成功的媒介之一。 2015 年的玆卡 (Zika) 疫情席捲了拉丁美洲和加勒比海地區，最初於兩年前在法屬玻里尼西亞爆發。隨後，玆卡病毒傳播到了南太平洋的其他群島，之後巴西病例的激增讓玆卡病毒的存在聞名於世。由於國際航空旅行，SARS 能夠傳播到二十多個國家。隨著世界變得更加互聯，有必要製定協議來減輕新出現的病原體跨越國界的能力。
氣候變遷和城市化是疾病爆發的其他重要驅動因素。 2018 年，西尼羅病毒腦炎 (West Nile virus encephalitis) 病例爆發了有史以來最嚴重的一次，病例數比 2017 年增加了 7 倍。其關鍵決定因素之一是氣候變遷。在歐洲，2018 年是有記錄以來最熱的四年之一，繼特別潮濕的春季之後又出現了嚴重的夏季乾旱。潮濕的泉水增加了蚊子的數量，而隨後天氣變暖引起的乾旱使蚊子和鳥類集中在剩餘的水源處。同樣，城市發展將人類推入了埃及虎蚊的有利棲息地，埃及虎蚊是黃熱病攜帶者，黃熱病每年在非洲和南美洲造成近 20 萬例病例和 5 萬人死亡。隨著這些地區人口密度的增加，黃熱病的爆發可能是災難性的。這些地區的疫苗接種率低，加劇了這個問題。 2016年，需要為生活在拉丁美洲黃熱病流行國家的多達2億人和非洲的4億人接種疫苗，才能達到世衛組織80%疫苗接種覆蓋率的目標。然而，全球黃熱病疫苗製造商只生產了約 8000萬– 1 億劑。差距是顯而易見的，潛在的後果也很嚴重。
與病原體的競賽正在加劇。在過去的二十年裡，人類目睹了無數流行病和大流行性健康危機：SARS、流感大流行、伊波拉病毒、中東呼吸道症候群 (MERS) 和黃熱病等。當然，我們仍在從 COVID-19 大流行的影響中恢復。兩年內，有 5 億人感染了 COVID-19，據通報超過 600 萬人死亡。世界各地的政治家向 COVID-19 宣戰；但是「歷史上瘟疫和戰爭一樣多，但瘟疫和戰爭總是同樣讓人感到驚訝」（卡繆，《鼠疫》）。儘管這些話最初寫於 1946 年，但今天仍然和寫下時一樣真實。隨著全球疾病的驅動因素有可能增加流行病和大流行病的盛行率，人類如何從以前的錯誤中吸取教訓並為下一個新出現的健康威脅做好準備？
在整本書中，雷佩蘭特引導讀者踏上跨越大陸和穿越時空的旅程。她獨特的聲音將看似難以理解的生物學術語與現實世界中可理解的生物學實例進行了對比。她的告知能力，加上她提出的問題多於答案的能力，巧妙地凸顯了我們現有的關於寄生蟲和病原體的知識只是冰山一角。然而有一件事是明確的：當涉及病原體時，人們必須隨時準備好應對意外情況。
傑西卡·波普
《Media Watch》A fatal jump: not if, but when
www.thelancet.com/infection Vol 23 October 2023
Fatal jump: tracking the origins of pandemics / Leslie Reperant / John Hopkins University Press, 2023
As the COVID-19 pandemic slowly begins to loosen its grip on humanity and international health care, several questions are emerging. Two, however, occur repeatedly, and are perhaps the most crucial: where did SARS-CoV-2 come from, and how do we prevent another pandemic? With evidence indicating that SARS-CoV-2 might have emerged from the area of Huanan Seafood market where live wild animals were sold, scientists postulate that the virus might have been transmitted from animals to humans. A pathogenic jump from animals to humans has been at the heart of several historical pandemics. In Fatal jump: tracking the origins of pandemics, Leslie Reperant guides the reader through the evolution and propagation of these organisms—how they survive and thrive within their hosts, how they jump from one host to another, and, pivotally, what determines their success.
Humankind exists in a symbiotic association with our microbial neighbours. We developed due to the differentiation and evolution of early eukaryotic organisms. The environmental pressures posed by living organisms (eg, bacteria and viruses) are also responsible for widespread sexual reproduction seen in most existing lifeforms. Sexual reproduction generates greater genetic variation in offspring than asexual reproduction, which allows future generations to better respond to threats posed by interacting species. This variation is an essential determinant of species’ survival. The relationship is “an elaborate game of intricacies” in which maintaining a delicate balance between humanity’s desire for progress and development with the natural world is paramount.
Reperant touches not only on the biological explanations of parasites and pathogens evolutionary survival, but also how they are sustained by wider social, political, and environmental determinants. Epidemics and pandemics within recent memory highlighted air travel as one of the most successful vectors for the global spread of disease. The 2015 Zika epidemic, which tore through swathes of Latin America and the Caribbeans, originally began two years earlier in French Polynesia. It then travelled to other archipelagos of the South Pacific before an explosion of cases in Brazil made Zika’s presence known globally. SARS was able to spread to over two dozen countries due to international air travel. As the world becomes more connected, protocols are necessary to mitigate the ability of emerging pathogens to transcend borders.
Climate change and urbanisation are other crucial drivers of disease outbreaks. 2018 saw the greatest outbreak on record for cases of West Nile virus encephalitis, with a sevenfold increase in cases compared with those in 2017. One of the key determinants of this was climate change. In Europe, 2018 was one of the four hottest years on record, with a severe summer drought succeeding a particularly wet spring. Wet springs boost mosquito populations, and a subsequent drought caused by the warmer weather concentrates mosquitoes and birds at the remaining water sources. Similarly, urban development has pushed humans into the preferential habitats of the Egyptian tiger mosquito, the carrier of yellow fever, which causes close to 200 000 cases and 50 000 deaths each year in Africa and South America. As population density increases in these areas, an outbreak of yellow fever could be catastrophic. Low uptake of vaccinations in these areas compounds this problem. In 2016, the vaccination of up to 200 million individuals living in yellow fever endemic countries in Latin America and 400 million in Africa was needed to reach WHO’s target of 80% vaccination coverage. However, the manufacturers of yellow fever vaccine worldwide produced about 80–100 million doses. The disparity is obvious, and the potential consequences severe.
The race against pathogens is intensifying. In the past two decades, humans have witnessed numerous epidemic and pandemic health crises: SARS, the flu pandemic, Ebola virus, Middle East respiratory syndrome, and yellow fever to name but a few. And, of course, we are still recovering from the effect of the COVID-19 pandemic. Within 2 years, 500 million individuals were infected with COVID-19, and over 6 million deaths were reported. Politicians worldwide declared a war on COVID-19; but “there have been as many plagues as wars in history, yet always plagues and wars take people equally by surprise” (Camus A, The Plague). Although originally penned in 1946, these words remain as true today as they were when they were written. As global drivers of disease threaten to increase the prevalence of epidemic-level and pandemic-level disease, what will it take for humanity to learn from our previous mistakes and prepare for the next emerging health threat?
Throughout the book, Reperant guides readers on a journey across continents and through time. Her unique voice contrasts what could be considered impenetrable biological jargon with real world, understandable examples of biology in action. Her ability to inform, juxtaposed by her ability to present more questions than answers, deftly highlights how our existing knowledge of parasites and pathogens is merely the tip of the iceberg. Yet one thing is clear: when it comes to pathogens, one must always be ready to expect the unexpected.
Jessica Pope