MIVEGEC (Université de Montpellier 1 et 2 - CNRS 5290 - IRD 224), Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle, Institut de recherche pour le développement (IRD), Representation in Bolivia, La Paz, Bolivia ; Instituto Nacional de Laboratorios de Salud (INLASA), Department of Entomology, La Paz, Bolivia.
PLoS One. 2013 Nov 29;8(11):e82269. doi: 10.1371/journal.pone.0082269. eCollection 2013.
Trypanosoma cruzi, the causative agent of Chagas disease, is subdivided into six discrete typing units (DTUs; TcI-TcVI) of which TcI is ubiquitous and genetically highly variable. While clonality is the dominant mode of propagation, recombinant events play a significant evolutive role. Recently, foci of wild Triatoma infestans have been described in Bolivia, mainly infected by TcI. Hence, for the first time, we evaluated the level of genetic exchange within TcI natural potentially panmictic populations (single DTU, host, area and sampling time). Seventy-nine TcI stocks from wild T. infestans, belonging to six populations were characterized at eight microsatellite loci. For each population, Hardy-Weinberg equilibrium (HWE), linkage disequilibrium (LD), and presence of repeated multilocus genotypes (MLG) were analyzed by using a total of seven statistics, to test the null hypothesis of panmixia (H0). For three populations, none of the seven statistics allowed to rejecting H0; for another one the low size did not allow us to conclude, and for the two others the tests have given contradictory results. Interestingly, apparent panmixia was only observed in very restricted areas, and was not observed when grouping populations distant of only two kilometers or more. Nevertheless it is worth stressing that for the statistic tests of "HWE", in order to minimize the type I error (i. e. incorrect rejection of a true H0), we used the Bonferroni correction (BC) known to considerably increase the type II error ( i. e. failure to reject a false H0). For the other tests (LD and MLG), we did not use BC and the risk of type II error in these cases was acceptable. Thus, these results should be considered as a good indicator of the existence of panmixia in wild environment but this must be confirmed on larger samples to reduce the risk of type II error.
克氏锥虫，恰加斯病的病原体，被分为六个离散的 typing units（DTUs；TcI-TcVI），其中 TcI 无处不在且遗传高度多变。虽然克隆性是主要的繁殖方式，但重组事件在进化中起着重要作用。最近，在玻利维亚发现了野生 Triatoma infestans 的疫源地，主要感染 TcI。因此，我们首次评估了 TcI 天然潜在群体（单一 DTU、宿主、区域和采样时间）内的遗传交换水平。从属于六个种群的 79 个野生 T. infestans 的 TcI 株系在八个微卫星基因座上进行了特征描述。对于每个种群，我们通过使用总共七个统计量来分析 Hardy-Weinberg 平衡（HWE）、连锁不平衡（LD）和重复的多位点基因型（MLG）的存在，以检验完全混合（H0）的无效假设。对于三个种群，七个统计量中没有一个可以拒绝 H0；对于另一个种群，由于种群规模较小，我们无法得出结论；对于另外两个种群，检验结果相互矛盾。有趣的是，只有在非常有限的区域内才观察到明显的混合，而在仅相距两公里或更远的种群中则没有观察到。然而，值得强调的是，对于“HWE”的统计检验，为了最小化第一类错误（即错误地拒绝真实的 H0），我们使用了 Bonferroni 校正（BC），这会显著增加第二类错误（即未能拒绝错误的 H0）。对于其他检验（LD 和 MLG），我们没有使用 BC，在这些情况下第二类错误的风险是可以接受的。因此，这些结果可以作为在野生环境中存在完全混合的良好指标，但为了降低第二类错误的风险，必须在更大的样本中进行确认。
