Center for Biological Sequence Analysis, Department of Systems Biology, The Technical University of Denmark, Building 208, 2800 Lyngby, Denmark.
J Theor Biol. 2009 Nov 7;261(1):100-6. doi: 10.1016/j.jtbi.2009.06.028. Epub 2009 Jul 21.
By examining published, empirical data we show that men and women consistently differ in the shape of the distribution of the number of sexual partners. The female distribution is always relatively narrow-variance is low-with a big majority of women having a number of partners close to the average. The male distribution is much wider-variance is high-with many men having few sex partners and many others having more partners than most females. Using stochastic modelling we demonstrate that this difference in variance is, in principle, sufficient to cause a difference in the gender prevalence of sexually transmitted diseases: compared to the situation where the genders have identical sex partner distributions, men will reach a lower equilibrium value, while women will stay at the same level (meaning that female prevalence becomes higher than male). We carefully analyse model behaviour and derive approximate expressions for equilibrium prevalences in the two different scenarios. We find that the size of the difference in gender prevalence depends on the variance ratio (the ratio between the variances of the male and female sex partner distributions), on the expected number of life-time partners, and on the probability of disease transmission. We note that in addition to humans, the variance phenomenon described here is likely to play a role for sexually transmitted diseases in other species also. We also show, again by examining published, empirical data, that the female to male prevalence ratio increases with the overall prevalence of a sexually transmitted disease (i.e., the more widespread the disease, the more women are affected). We suggest that this pattern may be caused by the effect described above in highly prevalent sexually transmitted diseases, while its impact in low-prevalence epidemics is surpassed by the action of high-risk individuals (mostly males).
通过研究已发表的经验数据，我们表明，男性和女性在性伴侣数量的分布形状上始终存在差异。女性的分布通常相对较窄——方差较低——绝大多数女性的性伴侣数量接近平均值。男性的分布则更为广泛——方差较高——许多男性的性伴侣较少，而许多其他男性的性伴侣比大多数女性多。通过随机建模，我们证明这种方差差异原则上足以导致性传播疾病在性别上的流行率出现差异：与男女具有相同性伴侣分布的情况相比，男性将达到较低的平衡值，而女性将保持在同一水平（这意味着女性的流行率会高于男性）。我们仔细分析了模型行为，并推导出了两种不同情况下的平衡流行率的近似表达式。我们发现，性别流行率差异的大小取决于方差比（男性和女性性伴侣分布的方差比）、预期的终生伴侣数量以及疾病传播的概率。我们注意到，除了人类，这里描述的方差现象也可能在其他物种的性传播疾病中发挥作用。我们还通过研究已发表的经验数据表明，女性对男性的流行率比值随着性传播疾病的总体流行率而增加（即，疾病越广泛，受影响的女性就越多）。我们认为，这种模式可能是由上述在高度流行的性传播疾病中起作用的原因引起的，而在低流行率的流行中，高风险个体（主要是男性）的作用超过了其影响。
