Vector Biological Studies in Leishmaniasis

我们已经能够提供确凿的证据，证明利什曼原虫的无脊椎动物阶段在沙蝇媒介的生长和发育过程中完全有能力进行有性循环。2011年我们研究的重点一直是确定中肠内杂交形成的频率、时间和解剖位置，并将有性能力的发现推广到其他沙蝇媒介物种和利什曼原虫的其他物种和品系。我们已经能够从Lutzmyia long gipalpis中回收主要的杂交沙蝇，证明在新大陆发现的主要沙蝇属能够支持它们传播的利什曼原虫的有性繁殖周期。杂交种最早在感染后三天就被恢复，这表明早期发育阶段，如原环状和/或蜜腺单胞体，是具有性能力的形式。我们还成功地与来自西非和中东的主要亚株杂交，这些亚株在C57BL/6小鼠身上产生了本质上不同的皮肤病理，前者导致耳部真皮完全侵蚀，后者产生完全消失的皮肤损害。在F1后代和每个亲本之间产生的回交杂交将被产生，以定位控制这些临床结果的寄生虫基因。 为了确定在受感染的沙蝇种群中可靠地预测随后传播给哺乳动物宿主的利什曼原虫感染参数，我们在2011年对许多不同组的受感染苍蝇进行了采样，并比较了感染强度和后生细胞发育程度与传播频率的关系。中肠内属于后环前鞭毛体的寄生虫的百分比与传播频率的相关性最高。多个传输实验的荟萃分析使我们能够建立一个预测传输能力的百分比半周期截止值。传播时沙蝇产卵状况和环境条件的变化也会影响传播频率。这些观察结果对实验室中沙蝇媒介传播利什曼原虫具有重要意义，因为它们允许对受感染苍蝇种群中传播成功的预测用于关键实验，例如，涉及受感染沙蝇挑战以评估实验疫苗。这些发现还对自然界中沙蝇传播利什曼原虫具有重要意义，表明沙蝇从感染源获得的微生物数量可能会影响通过叮咬传播的寄生虫的剂量和感染的临床结果。

We have been able to provide conclusive evidence that the invertebrate stages of Leishmania are fully capable of a sexual cycle during their growth and development in the sand fly vector. The priority of our studies in 2011 has been to determine the frequency, timing, and anatomical location of hybrid formation within the midgut, and to extend the findings of sexual competence to other sand fly vector species and other species and strains of Leishmania. We have been able to recover L. major hybrids from Lutzomyia longipalpis, demonstrating that the main genus of sand flies found in the New World are capable of supporting the sexual reproductive cycle of the Leishmania parasties that they transmit. Hybrids were recovered as early as three days post infection, indicating that early developmental stages, e.g. procyclic and/or nectomonad promastigotes, are sexually competent forms. We have also been able to successfully cross L. major sub-strains from West Africa and the Middle East that produce substantially different cutaneous pathologies in C57Bl/6 mice, with the former producing complete erosion of the ear dermis and the later producing dermal lesions that fully resolve. Backcross hybrids generated between F1 progeny and each parental line will be generated to positionally map the parasite genes controlling these clinical outcomes. To identify parameters of Leishmania infection within a population of infected sand flies that reliably predict subsequent transmission to the mammalian host, in 2011 we sampled many different groups of infected flies and compared infection intensity and degree of metacyclogenesis with the frequency of transmission. The percentage of parasites within the midgut that were metacyclic promastigotes had the highest correlation with the frequency of transmission. Meta-analysis of multiple transmission experiments allowed us to establish a percent-metacyclic cutoff value that predicted transmission competence. Alteration of sand fly oviposition status and environmental conditions at the time of transmission also influenced transmission frequency. These observations have important implications for transmission of Leishmania by the sand fly vector in the laboratory, as they permit predictions of transmission success in a population of infected flies to be used for critical experiments involving, for example, infected sand fly challenge to evaluate experimental vaccines. The findings also have important implications for transmission of Leishmania by the sand fly in nature, indicating that the number of organisms acquired by the sand fly from an infection reservoir may influence the dose of transmitted parasites and the clinical outcome of infection following transmission by bite.