natural epidemic focus的用法和樣例：
例句
- As one of the oldest identifiable diseases known to man, plague remains endemic in many natural loci around the world.
鼠疫作為人所共知的一種最古老可確定的疾病，在世界上許多自然疫源地仍呈地方性流行。 - Conclusion The findings of the present study imply that the natural foci of human monocytic ehrlichiosis may exist in northwestern Fujian Province.
結論福建西北部林區可能存在人單核細胞埃立克體病的自然疫源地。
