全球島嶼鼠媒人畜共通傳染病的特性

Abstract

動物和人類間可以互相傳播的人畜共通傳染病，對人類社會、經濟和健康有很大的影響。全球旅遊與貿易的盛行增加了動物擴散到世界各地的機會，包括囓齒類動物。囓齒類動物可以藉由直接與節肢動物病媒兩種不同的途徑傳播鼠媒人畜共通傳染病。囓齒類動物會傳播許多鼠媒人畜共通傳染病，當牠們有機會入侵島嶼時，可能會同時引入病原體或寄生在囓齒類動物身上的節肢動物病媒。相較於大陸，島嶼較容易出現哪些類型的鼠媒人畜共通傳染病，鮮少受到關注。傳染病要在島嶼上持續出現，必須同時存在病原體、宿主與合適的生態環境，因此島嶼本身的地理生態特性和社會經濟因素，可能也會影響島嶼出現的鼠媒人畜共通傳染病數量和種類。本研究透過PubMed資料庫，收集記錄全球重要島嶼的各種鼠媒人畜共通傳染病、囓齒類動物宿主和節肢動物病媒種類，並比較病毒、細菌和寄生蟲三種不同病原類型和兩種傳播方式(直接vs.節肢動物病媒)的鼠媒人畜共通傳染病於島嶼上的出現率是否不同。考量大陸性和海洋性島嶼的生態特性不同，因此將島嶼分成兩種類型進一步進行比較。最後再收集島嶼相關的自然和社會因子，除了島嶼類型外，還包括島嶼面積、島嶼與大陸的距離、海拔最高點、人均國民所得、人口數、人口密度、平均年均溫、平均年雨量，並分析這些因子與鼠媒人畜共通傳染病數量的關係。共收集到557篇相關文獻資料，發現全球805個島嶼中，有155個島嶼紀錄有鼠媒人畜共通傳染病，以臺灣出現23種鼠媒人畜共通傳染病為最多。全世界59種鼠媒人畜共通傳染病，有41種在島嶼上出現過，出現頻度最高為鉤端螺旋體病，共出現在71個島嶼。複迴歸分析顯示，島嶼的傳染病數量和島嶼上的海拔最高點、人口數、人均國民所得均呈現正相關；人口數和島嶼與大陸之間的距離有顯著的交互作用，隨著島嶼人口數的增加，相較於較遠的島嶼，較近島嶼的傳染病數量增加的速度會較快；最後，島嶼類型、面積、與距離三者之間也存在顯著交互作用，在大陸性島嶼，隨著島嶼面積的增加，較近島嶼的傳染病數量增加的速度較較遠的島嶼快；相反地，在海洋性島嶼，隨著島嶼面積的增加，較遠島嶼的傳染病數量增加的速度較較近的島嶼快。檢測到傳染病的宿主中，以玄鼠(Rattus rattus)這個外來鼠種記錄到的傳染病種類最多。大陸性島嶼出現的鼠媒人畜共通傳染病數量顯著高於海洋性島嶼，且蜱所傳播的傳染病較容易在大陸性島嶼出現；海洋性島嶼較容易出現直接傳播的傳染病，島嶼上的宿主以外來鼠種為主，且出現的傳染病種類大多相同；相對地，大陸性島嶼出現的傳染病種類則較為不同。島嶼上和鼠媒人畜共通傳染病相關的節肢動物病媒有6種，其中又以蜱可以傳播的傳染病種類為最多有12種。最後，成對島嶼之間的距離越近，傳染病組成相似度越高。本研究詳盡記錄了全球島嶼出現的鼠媒人畜共通傳染病，並發現島嶼類型會影響鼠媒人畜共通傳染病數量和種類，以往普遍認知的氣候因子，如高溫多雨並未發現會影響島嶼鼠媒人畜共通傳染病的數量，其他因子，例如富裕程度，可能也會同時影響島嶼被發現鼠媒人畜共通傳染病的機率。未來應再探討其它因子，如囓齒類動物體重如何影響鼠媒人畜共通傳染病的盛行率，以得知更完整影響島嶼出現鼠媒人畜共通傳染病的原因。

Zoonotic diseases that can be transmitted between animals and humans have significant impacts on human society, economy, and health. Prevalence of global travel and trade has increased the opportunities for animals, including rodents, to spread around the world. Rodents can transmit a variety of zoonotic diseases via two different pathways: direct transmission and arthropod-vectored transmission. When rodents invade islands, they may simultaneously introduce pathogens or arthropod vectors parasitic to rodents. What type of rodent-borne zoonotic diseases is more likely to appear on islands has received little attention. For diseases to persist on islands, pathogens, hosts, and suitable ecological environments must coexist (for arthropod-vectored diseases, also competent vectors). Therefore, the geographical and ecological characteristics of islands, as well as socio-economic factors, may also affect the number and types of rodent-borne zoonotic diseases on islands. Related studies on rodent-borne zoonotic diseases on islands, as well as the rodent hosts, and arthropod vectors were retrieved from the PubMed database. Occurrence of rodent-borne zoonotic diseases on islands among three different types of pathogens (viruses, bacteria, parasites) and between two transmission pathways (direct vs. arthropod vectors) was compared. Considering the difference in ecological characteristics between continental and oceanic islands, islands were further classified into two different types for comparison. Lastly, natural and social factors related to islands were also compiled, including island type, area, distance from the continent, the highest point, GNI per capita, population size, population density, average annual temperature, and average annual precipitation. Relationship between these factors and the number of rodent-borne zoonotic diseases was then analyzed. A total of 557 references were collected, revealing the occurrence of rodent-borne zoonotic diseases on 155 of the global 805 islands. Taiwan had the highest number of rodent-borne zoonotic diseases among all islands (23 diseases). Out of the 59 global rodent-borne zoonotic diseases, 41 have been documented on islands, with leptospirosis being the most frequently reported disease, appearing on 71 islands. Multiple linear regression showed positive correlations between the number of diseases and the highest point, population size, and GNI per capita. There was a significant interaction between population size and distance from the continent: as island population size increased, the rate of increase in the number of diseases was higher on closer than further islands. Lastly, there was also a significant interaction among island type, area, and distance from the continent. The rate of increase in the number of diseases was higher on larger than smaller continental islands, while the opposite was true for oceanic islands. The most frequently recorded host species was the exotic house rat (Rattus rattus). There were significantly more rodent-borne zoonotic diseases on continental than on oceanic islands, and tick-borne diseases are more also likely to be reported on continental islands. Relative to continental islands, directly transmitted diseases were more likely to appear on oceanic islands, where the hosts were composed mainly of exotic species and composition of diseases were more similar. In contrast, composition of diseases was more distinct on continental islands. A total of six arthropod vectors that can transmit rodent-borne zoonotic diseases was identified on islands, with tick-borne diseases being the most common, accounting for 12 diseases. Lastly, the closer the distance between two islands, the higher the similarity in composition of diseases between them. This study documented the occurrence of rodent-borne zoonotic diseases on global islands and found that island type affects the number and types of rodent-borne zoonotic diseases. Climatic factors such as high temperatures and heavy precipitation that were conventionally considered to affect rodent-borne zoonotic diseases were not correlated to rodent-borne zoonotic diseases on islands. Factor, such as income, may also play a role in determining the number of rodent-borne zoonotic diseases detected on islands. In the future, other factors, such as how the body weight of rodents affects the prevalence of rodent-borne zoonotic diseases, should also be investigated to more comprehensively understand the causes for rodent-borne zoonotic diseases on islands.