Division of Pathway Medicine and Centre for Infectious Diseases, School of Biomedical Sciences, College of Medicine and Veterinary Medicine, The University of Edinburgh, Edinburgh, UK.
PLoS Negl Trop Dis. 2012 Jan;6(1):e1501. doi: 10.1371/journal.pntd.0001501. Epub 2012 Jan 31.
Measuring the prevalence of transmissible Trypanosoma brucei rhodesiense in tsetse populations is essential for understanding transmission dynamics, assessing human disease risk and monitoring spatio-temporal trends and the impact of control interventions. Although an important epidemiological variable, identifying flies which carry transmissible infections is difficult, with challenges including low prevalence, presence of other trypanosome species in the same fly, and concurrent detection of immature non-transmissible infections. Diagnostic tests to measure the prevalence of T. b. rhodesiense in tsetse are applied and interpreted inconsistently, and discrepancies between studies suggest this value is not consistently estimated even to within an order of magnitude.
METHODOLOGY/PRINCIPAL FINDINGS: Three approaches were used to estimate the prevalence of transmissible Trypanosoma brucei s.l. and T. b. rhodesiense in Glossina swynnertoni and G. pallidipes in Serengeti National Park, Tanzania: (i) dissection/microscopy; (ii) PCR on infected tsetse midguts; and (iii) inference from a mathematical model. Using dissection/microscopy the prevalence of transmissible T. brucei s.l. was 0% (95% CI 0-0.085) for G. swynnertoni and 0% (0-0.18) G. pallidipes; using PCR the prevalence of transmissible T. b. rhodesiense was 0.010% (0-0.054) and 0.0089% (0-0.059) respectively, and by model inference 0.0064% and 0.00085% respectively.
CONCLUSIONS/SIGNIFICANCE: The zero prevalence result by dissection/microscopy (likely really greater than zero given the results of other approaches) is not unusual by this technique, often ascribed to poor sensitivity. The application of additional techniques confirmed the very low prevalence of T. brucei suggesting the zero prevalence result was attributable to insufficient sample size (despite examination of 6000 tsetse). Given the prohibitively high sample sizes required to obtain meaningful results by dissection/microscopy, PCR-based approaches offer the current best option for assessing trypanosome prevalence in tsetse but inconsistencies in relating PCR results to transmissibility highlight the need for a consensus approach to generate meaningful and comparable data.
衡量采采蝇种群中传播性布氏冈比亚锥虫的流行率对于了解传播动态、评估人类疾病风险以及监测时空趋势和控制干预措施的影响至关重要。尽管这是一个重要的流行病学变量，但识别携带传染性感染的苍蝇具有挑战性，因为存在低流行率、同一只苍蝇中存在其他锥虫物种以及同时检测到不成熟的非传染性感染等问题。用于测量采采蝇中传播性布氏冈比亚锥虫流行率的诊断检测方法的应用和解释不一致，并且研究之间的差异表明，即使在数量级内，也不能一致估计该值。
方法/主要发现：在坦桑尼亚塞伦盖蒂国家公园，我们使用三种方法来估计斯温纳顿氏采采蝇和棕尾褐麻蝇中传播性布氏冈比亚锥虫和布氏罗得西亚锥虫的流行率：（i）解剖/显微镜检查；（ii）感染采采蝇中肠的 PCR；和（iii）从数学模型推断。使用解剖/显微镜检查，传播性布氏冈比亚锥虫的流行率为 0%（95%CI 0-0.085），G. swynnertoni 和 0%（0-0.18）G. pallidipes；使用 PCR 的传播性布氏罗得西亚锥虫的流行率分别为 0.010%（0-0.054）和 0.0089%（0-0.059），通过模型推断分别为 0.0064%和 0.00085%。
结论/意义：解剖/显微镜检查的零流行率结果（由于其他方法的结果，实际上可能大于零）并不罕见，通常归因于灵敏度差。应用其他技术证实了布氏冈比亚锥虫的低流行率，这表明零流行率结果归因于样本量不足（尽管检查了 6000 只采采蝇）。鉴于解剖/显微镜检查获得有意义结果所需的样本量过高，基于 PCR 的方法是评估采采蝇中锥虫流行率的当前最佳选择，但将 PCR 结果与传染性相关联的不一致性突出表明需要采用共识方法来生成有意义且可比较的数据。
