Institut National de la Recherche Agronomique, UMR1300 Biologie, Epidémiologie et Analyse de Risque, Atlanpôle La Chantrerie, Nantes, France.
J Theor Biol. 2011 Sep 7;284(1):130-41. doi: 10.1016/j.jtbi.2011.06.017. Epub 2011 Jun 24.
Coxiella burnetii is the bacterium responsible for Q fever, a worldwide zoonosis. Ruminants, especially cattle, are recognized as the most important source of human infections. Although a great heterogeneity between shedder cows has been described, no previous studies have determined which features such as shedding route and duration or the quantity of bacteria shed have the strongest impact on the environmental contamination and thus on the zoonotic risk. Our objective was to identify key parameters whose variation highly influences C. burnetii spread within a dairy cattle herd, especially those related to the heterogeneity of shedding. To compare the impact of epidemiological parameters on different dynamical aspects of C. burnetii infection, we performed a sensitivity analysis on an original stochastic model describing the bacterium spread and representing the individual variability of the shedding duration, routes and intensity as well as herd demography. This sensitivity analysis consisted of a principal component analysis followed by an ANOVA. Our findings show that the most influential parameters are the probability distribution governing the levels of shedding, especially in vaginal mucus and faeces, the characteristics of the bacterium in the environment (i.e. its survival and the fraction of bacteria shed reaching the environment), and some physiological parameters related to the intermittency of shedding (transition probability from a non-shedding infected state to a shedding state) or to the transition from one type of shedder to another one (transition probability from a seronegative shedding state to a seropositive shedding state). Our study is crucial for the understanding of the dynamics of C. burnetii infection and optimization of control measures. Indeed, as control measures should impact the parameters influencing the bacterium spread most, our model can now be used to assess the effectiveness of different control strategies of Q fever within dairy cattle herds.
贝氏考克斯氏体是引起 Q 热的细菌，这是一种全球性的人畜共患病。反刍动物，特别是牛，被认为是人类感染的最重要来源。尽管已经描述了产仔牛之间存在很大的异质性，但以前的研究尚未确定哪些特征（如脱落途径和持续时间或脱落的细菌数量）对环境污染以及由此产生的人畜共患病风险影响最大。我们的目的是确定关键参数，这些参数的变化极大地影响了牛布鲁氏菌在奶牛群中的传播，特别是那些与脱落异质性相关的参数。为了比较流行病学参数对牛布鲁氏菌感染不同动态方面的影响，我们对描述细菌传播并代表脱落持续时间、途径和强度以及畜群人口统计学个体变异性的原始随机模型进行了敏感性分析。这种敏感性分析包括主成分分析和方差分析。我们的研究结果表明，最具影响力的参数是控制脱落水平的概率分布，特别是在阴道黏液和粪便中，细菌在环境中的特征（即其存活和脱落到达环境的细菌比例），以及一些与脱落间歇性相关的生理参数（从非脱落感染状态到脱落状态的转变概率）或从一种脱落者转变为另一种脱落者的转变概率（从血清阴性脱落状态到血清阳性脱落状态的转变概率）。我们的研究对于理解牛布鲁氏菌感染的动力学和优化控制措施至关重要。事实上，由于控制措施应该影响影响细菌传播的参数最大，因此我们的模型现在可以用于评估在奶牛群中不同 Q 热控制策略的有效性。
