Boyd Orr Centre for Population and Ecosystem Health, University of Glasgow, Glasgow, UK.
Malar J. 2012 Apr 3;11:106. doi: 10.1186/1475-2875-11-106.
There has recently been a substantial decline in malaria incidence in much of Africa. While the decline can clearly be linked to increasing coverage of mosquito vector control interventions and effective drug treatment in most settings, the ubiquity of reduction raises the possibility that additional ecological and associated evolutionary changes may be reinforcing the effectiveness of current vector control strategies in previously unanticipated ways.
Here it is hypothesized that the increasing coverage of insecticide-treated bed nets and other vector control methods may be driving selection for a shift in mosquito life history that reduces their ability to transmit malaria parasites. Specifically it is hypothesized that by substantially increasing the extrinsic rate of mortality experienced in vector populations, these interventions are creating a fitness incentive for mosquitoes to re-allocate their resources towards greater short-term reproduction at the expense of longer-term survival. As malaria transmission is fundamentally dependent on mosquito survival, a life history shift in this direction would greatly benefit control.
At present, direct evaluation of this hypothesis within natural vector populations presents several logistical and methodological challenges. In the meantime, many insights can be gained from research previously conducted on wild Drosophila populations. Long-term selection experiments on these organisms suggest that increasing extrinsic mortality by a magnitude similar to that anticipated from the up-scaling of vector control measures generated an increase in their intrinsic mortality rate. Although this increase was small, a change of similar magnitude in Anopheles vector populations would be predicted to reduce malaria transmission by 80%.
The hypothesis presented here provides a reminder that evolutionary processes induced by interventions against disease vectors may not always act to neutralize intervention effectiveness. In the search for new intervention strategies, consideration should be given to both the potential disadvantages and advantages of evolutionary processes resulting from their implementation, and attempts made to exploit those with greatest potential to enhance control.
在非洲的大部分地区，疟疾发病率最近大幅下降。虽然在大多数情况下，这种下降显然与蚊子媒介控制干预措施的覆盖率增加和有效药物治疗有关，但这种普遍下降使得人们有可能认为，额外的生态和相关进化变化可能以以前未预料到的方式加强当前媒介控制策略的有效性。
这里假设，不断增加的驱虫蚊帐和其他媒介控制方法的覆盖率可能导致蚊子生活史的转变，从而降低其传播疟原虫的能力。具体来说，有人假设，通过大幅增加媒介种群中经历的外显死亡率，这些干预措施为蚊子创造了一种适应力，使其将资源重新分配到短期繁殖上，而牺牲长期生存。由于疟疾传播从根本上依赖于蚊子的生存，因此这种方向的生活史转变将极大地有利于控制。
目前，在自然媒介种群中直接评估这一假说存在一些后勤和方法上的挑战。与此同时，从以前对野生果蝇种群的研究中可以获得许多启示。对这些生物进行的长期选择实验表明，通过与预期的媒介控制措施扩大规模相似的程度增加外显死亡率，会导致其内在死亡率增加。虽然这种增加很小，但在按蚊媒介种群中，类似幅度的变化预计将使疟疾传播减少 80%。
这里提出的假说提醒人们，针对疾病媒介的干预措施所引发的进化过程并不总是会使干预措施的有效性失效。在寻找新的干预策略时，应考虑到由于实施这些策略而导致的进化过程的潜在劣势和优势，并努力利用那些最有可能增强控制效果的优势。
