Tuesday, March 31, 2009


The classic model for malaria is rural and tropical. That model is changing with recent demographic and ecological shifts, as malaria is becoming more and more an urban disease, with the expected alteration in required prevention tactics. Unfortunately, the urban lifestyle dictates less time spent at home and more time out-and-about in the city, meaning traditional and proven control mechanisms such as insecticide treated nets lose some of their effectiveness. In addition, traditional agricultural development that has been shown to be effective in curtailing malaria propagation is less relevant in urban centres (I suggest Randall Packard's great book on the history of malaria for more information on this). Therefore, new techniques are mandatory, mostly through mosquito control. While we wait for genetically engineered mosquitoes, good old fashioned mosquito killers will have to do.

The larvicides used in this study (Geissb├╝hler Y, Kannady K, Chaki PP, Emidi B, Govella NJ, et al. (2009) Microbial Larvicide Application by a Large-Scale, Community-Based Program Reduces Malaria Infection Prevalence in Urban Dar Es Salaam, Tanzania. PLoS ONE 4(3): e5107. doi:10.1371/journal.pone.0005107) published this week in PLOS One, are bacteria distributed in pellets that larval mosquitoes ingest. These bacteria release toxins that are toxic to the mosquito digestive tract, resulting in mosquito death. The pellets are effective for a few weeks after distribution, and there has been no documented side-effect of human danger from their dissemination. One of the challenges is the development of larval resistance to their toxins, something not seen yet, but potentially present in the future.

The researchers showed a fairly significant decrease in malaria incidence, and a decreased number of mosquito bites in general (with the rigorous bites/night methodology used by frequently-tested volunteers). A nice population level intervention, though it was relatively top-heavy with staff and infrastructure - for an urban centre, however, the cost-effectiveness is probably reasonable, given the huge economic effects of malaria incidence upon a population. The next step is to replicate this in another city - perhaps in Asia where the mosquitoes are slightly different, to see if this can be effectively scaled up for global dissemination.

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