Biased distribution of pathogenic Entamoeba histolytica

近年来，溶组织内阿米巴被认为由致病种和非致病种组成。这意味着常规的粪便标本镜检方法不能确定从公共卫生角度更重要的致病性溶组织埃希氏菌的流行情况。由于从包囊中提取的DNA的聚合酶链式反应方法被证明是区分溶组织埃希氏菌和差异组织埃希氏菌的有效方法，它与显微镜方法相结合被用来阐明菲律宾吕宋岛不同地区两种细菌之间的传播方式的差异。研究结果如下：1)尽管贫民窟地区的寄生虫感染率接近70%，但两种寄生虫的流行率在所调查的所有地方都不超过15%。这说明内阿米巴的传播方式不如某些蠕虫有效。2)致病种、溶组织内阿米巴和非致病内阿米巴的流行率不到非致病种的一半。3)两种内阿米巴的流行因地而异。在公共卫生条件相近的情况下，较冷的气候为内阿米巴的传播提供了较好的条件。4)致病物种的分布比非致病物种的分布更加多样化。据推测，人与人之间的传播主要通过家庭中的亲密接触来维持。5)5)5岁至14岁儿童的患病率较高，女性的患病率高于男性。这可能是由于它们生活习性的差异所致。6)在日本大分县高崎山的日本猴子中发现了高流行率。这表明猴子比人类更适合作为致病埃希氏菌的宿主。

Recently, Entamoeba histolytica has been recognized to consist of a pathogenic species, E. histolytica and a non-pathogenic species, E. dispar. This means that the conventional method using microscopic examination of fecal samples can not determine prevalence of pathogenic E. histolytica that is more important from the viewpoint of public health. Since the PCR method using extracted DNA from cysts has been shown to be useful for differentiation of E. histolytica from E. dispar, it was used in combination with the microscopic method to clarify the difference of the transmission mode between two species at various parts of Luzon in the Philippines. The following results were obtained.1) The prevalence of two species was not over 15% in all the places examined, although the prevalence of helminthic infection reached nearly 70% in the slum area. This indicated that the transmission mode of Entamoeba is less effective than some helminths.2) The prevalence of a pathogenic species, E. histolytica was less than a half of that of a non-pathogenic species, E. dispar in all the areas examined.3) Both species showed a with variety of prevalence according to places. If the condition of public health is similar, the colder climate provides the better condition for transmission of Entamoeba.4) The distribution of the pathogenic species was more varied than the non-pathogenic. Transmission from a human to a human is inferred to be maintained mainly by intimate contact in a family. Consequently the highest prevalence was found in the slum area.5) Higher prevalence was found in children aged from 5 to 14 years, and in women than in men. This may be caused by differences of their living habits.6) High prevalence of E. dispar was found in Japanese monkeys at the Takasaki mountain, Oita prefecture, Japan. This indicated that monkeys are more fitting hosts for E. dispar than humans.