Department of Mathematical Sciences, University of Bath, Bath BA2 7AY, UK.
Epidemics. 2010 Mar;2(1):1-10. doi: 10.1016/j.epidem.2010.01.001. Epub 2010 Jan 22.
In many regions dengue incidence fluctuates seasonally with few if any infections reported in unfavourable periods. It has been hypothesized that vertical transmission within the mosquito population allows the virus to persist at these times. A review of the literature shows that vertical infection efficiencies are 1-4%. Using a mathematical model we argue that at these infection rates vertical transmission is not an important factor for long term virus persistence. In endemic situations, increases in reproductive number, half-life and persistence times of the disease only become significant when vertical infection efficiency exceeds 20-30%. In epidemic situations vertical infection accelerates the course of the outbreak and may actually reduce persistence time. These results stem from the fact that the mosquito life-cycle is relatively rapid and vertically acquired infections are multiplicatively diluted with every generation. When the efficiency of vertical infection is as low as reported from empirical studies, the virus is rapidly lost unless there is regular amplification in the human population. Processes such as asymptomatic human dengue cases are therefore more likely to be important in persistence than transmission within the vector population. The empirical data are not, however, unequivocal and we identify several areas of research that would further clarify the role of vertical transmission in the epidemiology of dengue.
在许多地区，登革热的发病率呈季节性波动，在不利时期几乎没有或没有报告任何感染病例。有人假设，蚊子种群内的垂直传播使病毒在这些时候得以持续存在。对文献的回顾表明，垂直感染效率为 1-4%。我们利用数学模型证明，在这些感染率下，垂直传播不是病毒长期持续存在的重要因素。在流行地区，当繁殖数、疾病半衰期和持续时间增加时，只有当垂直感染效率超过 20-30%时，才会变得显著。在流行情况下，垂直感染会加速疫情的爆发，并可能实际上缩短疾病的持续时间。这些结果源于蚊子的生命周期相对较快，垂直获得的感染会在每一代中被倍数稀释的事实。当垂直感染的效率像从经验研究中报告的那样低时，除非在人群中经常出现放大，否则病毒会迅速消失。因此，无症状人类登革热病例等过程比在媒介种群中的传播更有可能在持续存在中发挥重要作用。然而，经验数据并非明确无误，我们确定了几个研究领域，这些领域将进一步阐明垂直传播在登革热流行病学中的作用。
