Know Your Mosquitoes

Recently we have seen some online discussion about mosquitoes biting 24/7, and while this is true, it is not all species of mosquitoes that bite all the time – only that anytime during the day/night one might be bitten, but by different types of mosquitoes, carrying different diseases at different times. Below is a chart that tries to draw some of the distinctions among the different types of mosquitoes.  It is not all inclusive. Some references are listed at the end. Finally there is an abstract about possible changes in malaria mosquito biting behaviors, although we should use caution in that this has not been verified universally.

mosquito-types-sm.jpg

Reference Links

  • How Mosquitoes Work. http://science.howstuffworks.com/zoology/insects-arachnids/mosquito1.htm
  • Be vigilant to different mosquito breeding grounds. http://www.fehd.gov.hk/english/safefood/images/Pestnews_9e.pdf
  • Biological Notes on Mosquitoes. http://www.mosquitoes.org/LifeCycle.html
  • Mosquito. From Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Mosquito
  • Anopheles Mosquitoes. http://www.cdc.gov/malaria/about/biology/mosquitoes/
  • Differentiate Culex, Anopheles and Aedes Mosquitoes. http://profwaqarhussain.blogspot.com/2012/10/differentiate-culexanopheles-and-aedes.html
  • Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus. http://www.ncbi.nlm.nih.gov/pubmed/15266751

Effects of changing mosquito host searching behaviour on the cost effectiveness of a mass distribution of long-lasting, insecticidal nets: a modelling study. Malaria Journal 2013, 12:215 doi:10.1186/1475-2875-12-215. Olivier JT Briët (olivier.briet@unibas.ch). Nakul Chitnis (nakul.chitnis@unibas.ch)

Abstract: Background The effectiveness of long-lasting, insecticidal nets (LLINs) in preventing malaria is threatened by the changing biting behaviour of mosquitoes, from nocturnal and endophagic to crepuscular and exophagic, and by their increasing resistance to insecticides. \

Methods: Using epidemiological stochastic simulation models, we studied the impact of a mass LLIN distribution on Plasmodium falciparum malaria. Specifically, we looked at impact in terms of episodes prevented during the effective life of the batch and in terms of net health benefits (NHB) expressed in disability adjusted life years (DALYs) averted, depending on biting behaviour, resistance (as measured in experimental hut studies), and on pre-intervention transmission levels.

Results: Results were very sensitive to assumptions about the probabilistic nature of host searching behaviour. With a shift towards crepuscular biting, under the assumption that individual mosquitoes repeat their behaviour each gonotrophic cycle, LLIN effectiveness was far less than when individual mosquitoes were assumed to vary their behaviour between gonotrophic cycles. LLIN effectiveness was equally sensitive to variations in host-searching behaviour (if repeated) and to variations in resistance. LLIN effectiveness was most sensitive to preintervention transmission level, with LLINs being least effective at both very low and very
high transmission levels, and most effective at around four infectious bites per adult per year. A single LLIN distribution round remained cost effective, except in transmission settings with a pre-intervention inoculation rate of over 128 bites per year and with resistant mosquitoes that displayed a high proportion (over 40%) of determined crepuscular host searching, where some model variants showed negative NHB.

Conclusions: Shifts towards crepuscular host searching behaviour can be as important in reducing LLIN effectiveness and cost effectiveness as resistance to pyrethroids. As resistance to insecticides is likely to slow down the development of behavioural resistance and vice versa, the two types of resistance are unlikely to occur within the same mosquito population. LLINs are likely cost effective interventions against malaria, even in areas with strong resistance to pyrethroids or where a large proportion of host-mosquito contact occurs during times when LLIN users are not under their nets.

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Finally please note that one malaria intervention alone will not solve our problems so we need to apply a mix that includes Nets, Indoor Residual Spraying, Diagnosis with mRDTs, Appropriate treatment with Artemisinin-based Combination Therapy, Intermittent Preventive Treatment, one day a vaccine and others …

One thought on “Know Your Mosquitoes

  1. Very very useful. As a Malaria Technical Supervisor I want to update my knowledge always. Under 5 children, ANCs & PNCs are in High Risk Category. To create awareness among them is a very tough task. However I am trying my level best through IPC.

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