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Fact or Fallacy? Vector control is a major part of malaria interventions.

November 18, 2013 - 09:15 -- Mark Benedict

Veiled behind a bednet is a simple truth: no vector control technology has been implemented in Africa. Billions of dollars are being spent on malaria control in Africa, and numerous entomologists are enlisted to advise about deployment of two mainstays of “vector control” efforts, bednets and IRS. In spite of this, if one were designing a vector control method and these were proposed, would they even rank among the top ten list of effective possibilities?

On the contrary, bednets primarily prevent human/mosquito contact. The effect of local mosquito population suppression when they are intensively used was not their intent nor planned and is merely a secondary effect.

Similarly, IRS targets indoor-resting females. Again, the purpose is not to suppress mosquito populations but to kill those that are likely to have fed on human blood and become infective. IRS is an anti-parasite measure.

Both of these tools are poor excuses for mosquito population suppression methods. They can be considered vector control as rightly as finger pricks can be considered a method of reducing parasite load.

If one wanted to suppress vector populations, what possibilities are available for Africa? Therein lies the rub. There is simply no intervention in use – and possibly in existence - that is appropriate and designed to control mosquitoes effectively, but pretending that IRS and LLIN are vector control methods distracts researchers from developing the real thing.

This fact has implications for investment in research to develop new methods. Developing new insecticides that will extend the value of LLINs and IRS should not be thought of as vector control efforts since the vehicles by which they are applied are not methods chosen to suppress vector populations. Only if such chemicals will be applied in different ways that are designed for vector control will they bring something new to the table. Exploring methods, including insecticides, for area-wide larval or adult control would in fact be a true vector control implementation. Similarly, the promising - but not yet delivering – method of genetic control might eventually offer a true malaria vector control method.

Malaria is a three-legged stool resting on humans, mosquitoes and parasites. Remove any one and the stool will not stand. At present, only one of the two potential vulnerable legs is being attacked. Isn’t it time to quit believing that we are attacking the mosquito leg with LLIN and IRS and to think more creatively of new vector control methods? That recognition would elevate the perception that there is a huge unexploited vulnerability.

In spite of their weak anti-vector effects, LLIN and IRS are effective malaria interventions. What would be possible if a true vector control program were developed and implemented?

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Comments

William Jobin's picture
Submitted by William Jobin on

Hi Mark,

I share your irritation with the folks who pretend that bednets and spraying inside houses are vector control methods. But there is some recent good news out of Dar es Salaam. A community-based larviciding program was effective there in reducing malaria prevalence during a four year attack with microbial larvicides. This also avoided the resistance trap of chemical biocides.

Ref: Maheu-Giroux M and Castro M. (2013) Impact of community-based larviciding on the prevalence of malaria infection in Dar es Salaam, Tanzania. PLoS One 8(8): e71638. doi:10.1371/journal.pone.0071638

Their 4-year field study included two years of pretreatment data collection, plus a treated vs untreated area analysis.

During their data analysis they also determined that clearing of street drains was equally effective. They also found that these anti-larval methods supplemented the bednet and house-spraying efforts occuring sporadically in Dar.

This information was present at our African Malaria Dialogue at the Harvard School of Public Health in Boston, by Prof. Marcia de Castro on 9 October.

What was particularly interesting about her analysis of the impact of clearing of street drains was the subsequent comment from a former US State Department official who recounted the drainage work they supported in Maputo, Mozambique during a period of intense rains and multiple cyclones. They did this to reduce problems with cholera, but found to their delight that they had also eliminated malaria transmission during that year when they kept the drains open. The entire program was conducted with picks and shovels.

So there is some vector control going on, we just need to organize and expand it.

Bill, ready with pick and shovel

William Jobin Director of Blue Nile Associates

Jeff Juel's picture
Submitted by Jeff Juel on

Another excellent post Bill!

Imagine if you showed two people in Mozambique how to use a pick and shovel to improve drainage - or how to clean a storm drain. And they showed two people, etc etc. 1 2 4 8 16 32 64 128 256 512 1024... A geometric progression is an impressive thing!

On the other hand, in the 1930's during the Great Depression, the Works Progress Administration (WPA) hired thousands of unemployed Americans to dig ditches for mosquito vector control. Some of the work done was counter-productive and actually created breeding sites. Valuable wetland habitats were severely damaged and some never recovered.

Proper engineering is vitally important for this work.

There are too few engineers involved in vector control and the engineering can be extremely challenging. I think about drainage for vector control every day. It is not a simple problem.

Flood control is also worthy of attention as a means for vector control. Where drainage infrastructure crosses dikes is where flap-gated culverts (tide gates) come in.

Jeff, ready with pick and shovel... and surveying equipment... and tide gates!

Jeff Juel, PE
Juel Tide Gates

Jeff Juel, PE
www.jueltide.com

William Jobin's picture
Submitted by William Jobin on

If you would like to add a little New Year's joy to your day,
look up the article by Daniel Sledge recently featured in a major news release by
National Public Radio in the US, entitled:

Backhoes may be more important than bednets.

What Sledge - a political scientist from Univ Texas at Austin, reports is that drainage works in the southern USA were the key factor in eliminating malaria from the US in the 1930's. It is nice to have independent confirmation of our understanding of the importance of attacking the mosquito breeding sites.

"Eliminating malaria in the American South: An Analysis of the Decline of Malaria in 1930s Alabama
by Daniel Sledge and George Mohler

American Journal of Public Health Aug 2013 v103 no 8 pp 1381-1392

doi: 10.2105/AJPH.2012.301065

I got this from this same MalariaWorld site, but just thought it was worth emphasizing.

Bill Jobin in a blizzard better than the one in Jerusalem

William Jobin Director of Blue Nile Associates

Bart G.J. Knols's picture
Submitted by Bart G.J. Knols on

Hi Mark,
As always, good food for thought, thank you. I am in Tanzania at the moment, where we have started in a village called Igombati with eave tubes, which I reported on during MIM. Very exciting stuff, about which I will be reporting here on MW in due course...hang in there, new things are coming along that will fill the toolbox.
Best, B

Submitted by William Jobin (not verified) on

Like the ancient prophet Jeremiah, it is easy to see disaster coming in a year or two in the fight against malaria, but we must do more than just predict the end, which is near. We should have a backup plan for WHO and the US PMI and RBM to use.

I can suggest three things to do when we see spreading of resistance to the pyrethroids and to Artemisinin, both of which seem to be only a few years away:

1. WHO should institute annual sampling of malaria prevalence using blood smears, in a randomly selected sentinel population of school children, every year during the peak month of transmission. NMCPs should use this data to detect outbreaks of resistance, and WHO should use it in aggregate to monitor and report on progress. Administrative reports sent to Geneva are not adequate, we need to measure the prevalence.

When resistance shows, the spray programs should switch to the next effective biocide, usually bendiocarb. Apparently in South Africa they have found that rotating the biocides can deter further development of resistance. Usually the new biocides will cost more, so extra funds will be needed.

In urban areas, attacks on the larvae should begin now, to decrease the pressure toward resistance. Microbial larvicides, clearing of street drains, and filling of swamps can be done now, with available tools.

These additions to the attack on the mosquitoes will slow and perhaps stop the development of resistance, thus allowing for permanent improvements to housing including screens, to gradually build out the mosquitoes. Also, as economies rise due to more healthy labor forces, provision of more affordable and available electricity will make sleeping in closed or screened rooms tolerable during the transmission seasons. As this kind of reinforcing improvement occurs, African countries will progress toward the safer situation seen in South Africa and in the Maghreb and in Israel, where malaria is built out of the ecology because people sleep under screens, and mosquito breeding sites gradually disappear.

Jeremiah's prophesy of doom came true because the people did not listen. I pray that the malaria people will open their ears in 2014, and listen before the disaster occurs.