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Response to Bousema and Sauerwein

Posted by pbio on 07 May 2009 at 22:11 GMT

Author: Jacob Koella
Position: Professor
Institution: Imperial College London
Additional Authors: R Lacroix, WR Mukabana, LC Gouagna
Submitted Date: November 15, 2005
Published Date: November 20, 2005
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

We appreciate the comments on our article "Malaria Infection Increases Attractiveness of Humans to Mosquitoes" [1]. Indeed, they raise some important issues (some of which were already mentioned in the article). However, we feel that our conclusions are valid. Perhaps the most important points are as follows.

i) Rotating children among tents would have indeed improved the experimental design, in particular as the repeatability of attractiveness of individual children could have been estimated. However, this would be rather difficult for logistic reasons. In addition, our design suffices to reach our conclusion. While we did not move individual children (within a group of 3 children) among tents, we ensured that the infection status among groups was allocated randomly. Therefore, there is no bias according to the position of the children in the tents.

ii) Although we did not mention this in the article, the children within a group were matched according to age, size and gender.

iii) Although Fansidar can indeed induce gametocytogenesis, this is not relevant in our study, as after treatment we evaluated only those groups within which each child was parasite-free (according to microscopy). Indeed, we had to remove several groups from the analysis, as at least one of the children had parasites (gametocytes or asexual stages) in the second round.

iv) The most interesting potential problem is that children might have low levels of parasites, and in particular gametocytes, even if they were not detected by microscopy [2]. Therefore, what we showed is that levels of parasitaemia that are sufficiently high to be detected can manipulate attractiveness. This suggests that a certain density of gametocytes is necessary to be able to manipulate their hosts. A future experiment could test the idea of density-dependent effects explicitly, but our experiment was not powerful enough to do that. Similarly, that carriers of asexual stages might also have harboured a few gametocytes does not invalidate our results. It just suggests that the few gametocytes are not enough to manipulate the host.

Again, we appreciate the comments and thank the authors of the comments and the editor for allowing us to clarify certain points.


[1] Lacroix R et al. (2005) PLoS Biol 3(9): e298

[2] Nassir E et al. (2005)Int J Parasitol 35: 49-55.

Competing interests declared: We declare that we have no competing interests.