Health Protection Agency Malaria Reference Laboratory, Immunology Unit, London School of Hygiene and Tropical Medicine, London, United Kingdom.
J Infect Dis. 2010 May 15;201(10):1544-50. doi: 10.1086/652240.
Malaria in humans is caused by apicomplexan parasites belonging to 5 species of the genus Plasmodium. Infections with Plasmodium ovale are widely distributed but rarely investigated, and the resulting burden of disease is not known. Dimorphism in defined genes has led to P. ovale parasites being divided into classic and variant types. We hypothesized that these dimorphs represent distinct parasite species.
Multilocus sequence analysis of 6 genetic characters was carried out among 55 isolates from 12 African and 3 Asia-Pacific countries.
Each genetic character displayed complete dimorphism and segregated perfectly between the 2 types. Both types were identified in samples from Ghana, Nigeria, São Tomé, Sierra Leone, and Uganda and have been described previously in Myanmar. Splitting of the 2 lineages is estimated to have occurred between 1.0 and 3.5 million years ago in hominid hosts.
We propose that P. ovale comprises 2 nonrecombining species that are sympatric in Africa and Asia. We speculate on possible scenarios that could have led to this speciation. Furthermore, the relatively high frequency of imported cases of symptomatic P. ovale infection in the United Kingdom suggests that the morbidity caused by ovale malaria has been underestimated.
人类疟疾是由属于疟原虫属的 5 种锥虫寄生虫引起的。卵形疟原虫感染分布广泛，但研究甚少，其疾病负担也未知。在明确的基因中存在二态性，导致卵形疟原虫寄生虫分为经典和变异型。我们假设这些二态代表不同的寄生虫种。
对来自 12 个非洲和 3 个亚太国家的 55 个分离株的 6 个遗传特征进行了多位点序列分析。
每个遗传特征都表现出完全的二态性，并在这 2 种类型之间完全分离。在来自加纳、尼日利亚、圣多美、塞拉利昂和乌干达的样本中均发现了这 2 种类型，并且之前在缅甸也有描述。这 2 个谱系的分裂发生在 100 万至 350 万年前人类宿主中。
我们提出卵形疟原虫包括 2 个非重组种，它们在非洲和亚洲是同域的。我们推测了可能导致这种物种形成的可能情况。此外，英国输入性有症状卵形疟感染的相对较高频率表明卵形疟引起的发病率被低估了。
