Anderson T J, Romero-Abal M E, Jaenike J
Department of Biology, University of Rochester, NY 14627.
Parasitology. 1993 Sep;107 ( Pt 3):319-34. doi: 10.1017/s0031182000079294.
In Guatemalan villages people commonly rear pigs, and both hosts may be infected with Ascaris. This study was designed to ask whether both humans and pigs are potential hosts in a single parasite transmission cycle in such villages, or alternatively, if there are two separate transmission cycles, one involving pigs and one involving human hosts. Parasites were collected from both host species from locations in the north and south of Guatemala. Allelic variation in the nuclear genome of Ascaris was measured using enzyme electrophoresis, while mitochondrial DNA (mtDNA) sequence variation was quantified using restriction mapping. Low levels of enzyme polymorphism were found in Ascaris, but allele frequencies at two loci, mannose phosphate isomerase and esterase, suggest that there is little gene exchange between parasite populations from humans and pigs. MtDNA haplotypes fall into two distinct clusters which differ in sequence by 3-4%; the two clusters broadly correspond to worms collected from humans and those collected from pigs. However, some parasites collected from humans have mtDNA characteristic of the 'pig Ascaris' haplotype cluster, while some parasites collected from pigs have mtDNA characteristic of the 'human Ascaris' haplotype cluster. These shared haplotypes are unlikely to represent contemporary cross-infection events. Patterns of phylogenetic similarity and geographical distribution of these haplotypes suggest, instead, that they are the result of two historical introgressions of mtDNA between the two host-associated Ascaris populations. The results clearly demonstrate that Ascaris from humans and pigs are involved in separate transmission cycles in Guatemala.
在危地马拉的村庄里，人们普遍饲养猪，人和猪都可能感染蛔虫。本研究旨在探究在这样的村庄中，人和猪是否在单一寄生虫传播循环中都是潜在宿主，或者是否存在两个独立的传播循环，一个涉及猪，另一个涉及人类宿主。从危地马拉北部和南部的地点采集了这两种宿主的寄生虫。使用酶电泳测量蛔虫核基因组中的等位基因变异，同时使用限制性图谱定量线粒体DNA（mtDNA）序列变异。在蛔虫中发现了低水平的酶多态性，但在磷酸甘露糖异构酶和酯酶这两个位点的等位基因频率表明，来自人和猪的寄生虫种群之间几乎没有基因交换。mtDNA单倍型分为两个不同的簇，它们的序列差异为3-4%；这两个簇大致对应于从人类和猪身上采集的蛔虫。然而，一些从人类身上采集的寄生虫具有“猪蛔虫”单倍型簇的mtDNA特征，而一些从猪身上采集的寄生虫具有“人蛔虫”单倍型簇的mtDNA特征。这些共享的单倍型不太可能代表当代的交叉感染事件。相反，这些单倍型的系统发育相似性和地理分布模式表明，它们是两个宿主相关蛔虫种群之间mtDNA两次历史渐渗的结果。结果清楚地表明，危地马拉的人蛔虫和猪蛔虫参与了独立的传播循环。
