Do malaria parasites manipulate mosquitoes?

Abstract

Malaria parasites have been suggested to alter the behavior of mosquito vectors to increase the likelihood of transmission. Some empirical evidence supports this hypothesis, yet the role of manipulation is ignored in most epidemiological models, and behavioral differences between infected and uninfected females are not considered in the development or implementation of control measures. We suggest that this disconnect exists because the link between behavioral alteration and actual transmission in the field has yet to be demonstrated or quantified fully. We review and discuss the current evidence for manipulation, explore its potential significance for malaria transmission, and suggest ways to move this hypothesis forward from theory to potential application in malaria control.

Figure 1. The effect of manipulation on transmission

The effect of increased number of bites per attempt (different colored bars) and the probability that a female feeds in a pre-infectious cycle (x-axis) on the force of malaria infection. For the left panel, daily mortality is assumed to be the most important source of mortality; in the right panel, mortality is assumed to be almost entirely feeding-associated. The dashed line indicates force of infection for unmanipulated females that always feed during the pre-infectious cycle and bite one person per feeding attempt. These two mortality extremes illustrate the interactions between mortality distribution and manipulation phenotypes. When mortality is evenly distributed through the feeding cycle and not associated with the feeding event, the biggest increase in force of infection comes from the number of bites per attempt (the differences between different colored bars). When mortality is attributed to feeding, the biggest increases in relative force of infection are mediated by the decreased mortality experienced by females in the oocyst-stage.