RR\ID Evidence Scale rating by reviewer:
Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.
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Review: The information in this manuscript is intriguing and important enough to need corroboration, especially in terms of the implication that changing Anopheles vector species composition is one of the causative factors for a decrease in mono Plasmodium falciparum infections and an increase in mixed infections including higher frequencies of P. ovale and P. malariae. The association between an increased prevalence of An. funestus, coinciding with a decreased prevalence of members of the An. gambiae complex in the second phase of a trial, is not necessarily but may be partially causative of the shift in Plasmodium species prevalence. As the authors suggest, changing vector control interventions, diagnostics and anti-malarial drug regimens primarily directed at P. falciparum are also clearly important. Add to this variation in immune responses to Plasmodium infections in mosquito and human hosts, and increasingly complex interactions emerge. It is nevertheless likely that the higher feeding propensity of An. funestus s.s. will lead to higher frequencies of mixed infections, especially because An. funestus tend to blood feed several times during one gonotrophic cycle, notwithstanding the cited reference showing that An. gambiae may also multiple blood feed during one gonotrophic cycle. The assertion in the discussion that “An. gambiae s.l. are exposed to parasites upon blood feeding nearly twice as often as An. funestus” therefore seems somewhat counter-intuitive, but may point to the regional complexities of malaria transmission where multiple vector and parasite species occur, and where variations in the feeding propensities of vector populations are likely adaptations to localized conditions. It is quite unusual for An. funestus s.s. to feed extensively on cattle, although cattle-feeding is common in other members of this species group. The various hypotheses given toward the end of the discussion to explain these unusual data are therefore appreciated.
In terms of the Anopheles species composition comparisons and associations with shifting Plasmodium species infections, the data may be more informative if there was a greater emphasis on identification to species within the An. gambiae complex and An. funestus group collections. Although subsets from each group were identified to species, it is still not possible to find direct comparisons between anopheline collections by species and the prevalence of Plasmodium parasites by species. At some points in the text, it is unclear as to whether the authors are referring to An. funestus sensu stricto or An. funestus sensu lato. I nevertheless agree that there is differential vector competence between An. gambiae s.s. and An. funestus s.s, with An. funestus s.s. generally causing higher rates of infection (although not in this study?), especially of falciparum malaria.
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