Sympatry influence in the interaction of Trypanosoma cruzi with triatomine

Abstract INTRODUCTION: Trypanosoma cruzi, the etiologic agent of Chagas disease, is widely distributed in nature, circulating between triatomine bugs and sylvatic mammals, and has large genetic diversity. Both the vector species and the genetic lineages of T. cruzi present a varied geographical distribution. This study aimed to verify the influence of sympatry in the interaction of T. cruzi with triatomines. Methods: The behavior of the strains PR2256 (T. cruzi II) and AM14 (T. cruzi IV) was studied in Triatoma sordida (TS) and Rhodnius robustus (RR). Eleven fifth-stage nymphs were fed by artificial xenodiagnosis with 5.6 × 103 blood trypomastigotes/0.1mL of each T. cruzi strain. Every 20 days, their excreta were examined for up to 100 days, and every 30 days, the intestinal content was examined for up to 120 days, by parasitological (fresh examination and differential count with Giemsa-stained smears) and molecular (PCR) methods. Rates of infectivity, metacyclogenesis and mortality, and mean number of parasites per insect and of excreted parasites were determined. RESULTS: Sympatric groups RR+AM14 and TS+PR2256 showed higher values of the four parameters, except for mortality rate, which was higher (27.3%) in the TS+AM14 group. General infectivity was 72.7%, which was mainly proven by PCR, showing the following decreasing order: RR+AM14 (100%), TS+PR2256 (81.8%), RR+PR2256 (72.7%) and TS+AM14 (36.4%). CONCLUSIONS: Our working hypothesis was confirmed once higher infectivity and vector capacity (flagellate production and elimination of infective metacyclic forms) were recorded in the groups that contained sympatric T. cruzi lineages and triatomine species.

引言：克氏锥虫（Trypanosoma cruzi）是恰加斯病（Chagas disease）的病原体，在自然界广泛分布，可在锥蝽（triatomine bugs）与野生哺乳动物（sylvatic mammals）之间循环传播，且具有丰富的遗传多样性。克氏锥虫的媒介物种与遗传谱系均呈现多样化的地理分布特征。本研究旨在验证同域分布（sympatry）对克氏锥虫与锥蝽互作的影响。方法：本研究针对静锥猎蝽（Triatoma sordida，TS）和健壮红猎蝽（Rhodnius robustus，RR），探究了克氏锥虫II型虫株PR2256与IV型虫株AM14的相关行为。通过人工异体感染试验（artificial xenodiagnosis），将5.6×10³个血液锥鞭毛体/0.1mL的各克氏锥虫虫株接种至11只5龄若虫体内。分别在接种后每20天检测其排泄物（持续至接种后100天）、每30天检测其肠道内容物（持续至接种后120天），检测手段包括寄生虫学方法（湿片镜检及吉姆萨染色涂片分类计数）与分子生物学方法（聚合酶链反应，PCR）。统计各组的感染率、后环发生率、死亡率，以及每只昆虫的平均寄生虫数与排泄寄生虫数。结果：同域组合RR+AM14与TS+PR2256的四项检测参数均表现为更高水平，仅死亡率例外：TS+AM14组的死亡率达27.3%，为各组最高。整体感染率为72.7%，该结果主要通过PCR验证，各组感染率由高到低依次为：RR+AM14（100%）、TS+PR2256（81.8%）、RR+PR2256（72.7%）以及TS+AM14（36.4%）。结论：本研究的工作假说得到验证：在携带同域分布克氏锥虫谱系与锥蝽物种的实验组中，其感染率与媒介能力（鞭毛体增殖及感染性后环鞭毛体的排泄量）均显著更高。