A theoretical approach to predicting the success of genetic manipulation of malaria mosquitoes in malaria control

BACKGROUND: Mosquitoes that have been genetically modified to better encapsulate the malaria parasite Plasmodium falciparum are being considered as a possible tool in the control of malaria. Hopes for this have been raised with the identification of genes involved in the encapsulation response and with advances in the tools required to transform mosquitoes. However, we have only very little understanding of the conditions that would allow such genes to spread in natural populations. METHODS: We present here a theoretical model that combines population genetical and epidemiological processes, thereby allowing one to predict not only these conditions (intensity of transmission, evolutionary cost of resistance, tools used to drive the genes) but also the impact of the spread of refractoriness on the prevalence of the disease. RESULTS: The main conclusions are 1) that efficient transposons will generally be able to drive genes that confer refractoriness through populations even if there is a substantial (evolutionary) cost of refractoriness, but 2) that this will decrease malaria prevalence in the human population substantially only if refractoriness is close to 100% effective. CONCLUSIONS: If refractoriness is less than 100% effective (because of, for example, environmentally induced variation in the effectiveness of the mosquito's immune response), control programmes based on genetic manipulation of mosquitoes will have very little impact on the epidemiology of malaria, at least in areas with intense transmission

Variability in the Relationship Between Weight and Wing Length of Anopheles gambiae (Diptera: Culicidae)

The relationship between wing length and body weight of female Anopheles gambiae Giles reared at 3 densities and at 3 temperatures was examined. Although overall, weight was proportional to wing length raised to the 4th power, the relationship within treatments was linear. The slope of the regression line varied significantly among treatments. Therefore, wing length of mosquitoes caught from field populations may not be an adequate measure of body weight if the conditions under which the mosquitoes have developed are not know

Effects of shortened host life span on the evolution of parasite life history and virulence in a microbial host-parasite system

<p>Abstract</p> <p>Background</p> <p>Ecological factors play an important role in the evolution of parasite exploitation strategies. A common prediction is that, as shorter host life span reduces future opportunities of transmission, parasites compensate with an evolutionary shift towards earlier transmission. They may grow more rapidly within the host, have a shorter latency time and, consequently, be more virulent. Thus, increased extrinsic (i.e., not caused by the parasite) host mortality leads to the evolution of more virulent parasites. To test these predictions, we performed a serial transfer experiment, using the protozoan <it>Paramecium caudatum </it>and its bacterial parasite <it>Holospora undulata</it>. We simulated variation in host life span by killing hosts after 11 (<it>early </it>killing) or 14 (<it>late </it>killing) days post inoculation; after killing, parasite transmission stages were collected and used for a new infection cycle.</p> <p>Results</p> <p>After 13 cycles (≈ 300 generations), parasites from the <it>early-killing </it>treatment were less infectious, but had shorter latency time and higher virulence than those from the <it>late-killing </it>treatment. Overall, shorter latency time was associated with higher parasite loads and thus presumably with more rapid within-host replication.</p> <p>Conclusion</p> <p>The analysis of the means of the two treatments is thus consistent with theory, and suggests that evolution is constrained by trade-offs between virulence, transmission and within-host growth. In contrast, we found little evidence for such trade-offs across parasite selection lines within treatments; thus, to some extent, these traits may evolve independently. This study illustrates how environmental variation (experienced by the host) can lead to the evolution of distinct parasite strategies.</p