Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, St Mary's Campus, London, United Kingdom.
PLoS Negl Trop Dis. 2011 Apr 26;5(4):e1047. doi: 10.1371/journal.pntd.0001047.
Much of our current understanding of the epidemiology of Ascaris lumbricoides infections in humans has been acquired by analyzing worm count data. These data are collected by treating infected individuals with anthelmintics so that worms are expelled intact from the gastrointestinal tract. Analysis of such data established that individuals are predisposed to infection with few or many worms and members of the same household tend to harbor similar numbers of worms. These effects, known respectively as individual predisposition and household clustering, are considered characteristic of the epidemiology of ascariasis. The mechanisms behind these phenomena, however, remain unclear. In particular, the impact of heterogeneous individual exposures to infectious stages has not been thoroughly explored.
METHODOLOGY/PRINCIPAL FINDINGS: Bayesian methods were used to fit a three-level hierarchical statistical model to A. lumbricoides worm counts derived from a three-round chemo-expulsion study carried out in Dhaka, Bangladesh. The effects of individual predisposition, household clustering and household covariates of the numbers of worms per host (worm burden) were considered simultaneously. Individual predisposition was found to be of limited epidemiological significance once household clustering had been accounted for. The degree of intra-household variability among worm burdens was found to be reduced by approximately 58% when household covariates were included in the model. Covariates relating to decreased affluence and quality of housing construction were associated with a statistically significant increase in worm burden.
CONCLUSIONS/SIGNIFICANCE: Heterogeneities in the exposure of individuals to infectious eggs have an important role in the epidemiology of A. lumbricoides infection. The household covariates identified as being associated with worm burden provide valuable insights into the source of these heterogeneities although above all emphasize and reiterate that infection with A. lumbricoides is inextricably associated with acute poverty.
我们目前对人类蛔虫感染的流行病学的大部分了解是通过分析蠕虫计数数据获得的。这些数据是通过用驱虫药治疗感染个体收集的，这样蠕虫就会从胃肠道完整地排出。对这些数据的分析表明，个体容易感染少量或大量的蠕虫，同一家庭的成员往往携带相似数量的蠕虫。这些效应分别称为个体易感性和家庭聚集性，被认为是蛔虫病流行病学的特征。然而，这些现象背后的机制仍不清楚。特别是，个体对传染性阶段的异质暴露的影响尚未得到彻底探讨。
方法/主要发现：贝叶斯方法被用于拟合一个三层分层统计模型，该模型基于在孟加拉国达卡进行的三轮化学驱虫研究中的蛔虫蠕虫计数。同时考虑了个体易感性、家庭聚集性以及宿主（虫荷）每头蠕虫数量的家庭协变量的影响。一旦考虑到家庭聚集性，个体易感性就被发现对流行病学意义有限。当将家庭协变量纳入模型时，发现家庭内虫荷的变异性大约降低了 58%。与贫困程度降低和住房建筑质量相关的协变量与虫荷呈统计学显著正相关。
结论/意义：个体接触感染性卵的异质性在蛔虫感染的流行病学中具有重要作用。确定与虫荷相关的家庭协变量为这些异质性的来源提供了有价值的见解，尽管它们首先强调并再次表明，感染蛔虫与急性贫困密不可分。
