This page contains notes as I read about malaria.
Some questions I’d like to address:
- If swamp-draining and DDT were the methods used to eliminate malaria in the United States, why are LLINs what we hear about nowadays?
- Why was DDT banned? What were the tradeoffs involved in the banning?
- Regarding a 1953 WHO antimalarial program in Liberia, Wikipedia says “these projects encountered difficulties that foreshadowed the general retreat from malaria eradication efforts across tropical Africa by the mid-1960s.” What happened? What were these difficulties?
DDT worked most effectively when sprayed on impermeable walls where it could continue to kill insects landing there for more than 3 months. But more than 50 percent of the interior house walls in Monrovia were constructed of laterite bricks, a natural hard claylike soil that is high in iron and aluminum. The DDT soaked through these walls, instead of staying on the surface, and thus was much less effective as a residual insecticide. At the time, there was no entomologist or chemist in Liberia who understood the issue, and work proceeded on an ad hoc basis. When the DDT seemed no longer to do the job—that is, to kill the mosquitoes inside the dwelling—the sprayers returned and sprayed again. The result was roughly a once-a-month spraying cycle with exceedingly high per capita costs.
- DDT not used “because of concerns over its effectiveness in coastal Liberia”.
- Fog generator attempted but “achieved limited success, owing to the difficulty of getting proper wind direction and movement and the need to release the fog before the sun’s heat became intense after 9 a.m. A technology that had worked reasonably well in the United States did not transfer well to coastal Liberia.”
Webb (2014, p. 94):
For African adults, malaria was largely perceived as an annoyance, an unpleasant reality of life like the seasonal flu, rather than a vital problem to be tackled with scarce resources. At independence, most African states declined to take up the “pre-eradication” programs – in essence, malaria control programs that would be developed to build capacity – recommended by the WHO.
“The ban of DDT did not cause millions to die from malaria” by Michael Palmer:
Malaria remains rampant because control efforts lack resources and political support, not because of the choice of insecticide. Where insect resistance to it is not yet widespread, DDT remains a legitimate weapon against malaria. However, DDT is not a panacea, and the limited restrictions imposed on its use are not a significant factor in the current deplorable state of affairs in malaria morbidity and mortality.
From this paper:
Knowledge of the role of mosquitoes in malaria transmission (11.8%) and cause of malaria (9.6%) was observed to be low among the study population. Comprehensive knowledge about malaria prevention measures was high (90%), but not reflecting in their practice (16%). They have good knowledge of mosquito behavior (breeding areas (64.5%), resting places (70%) and biting time (81%)). Seeking hospital care for a febrile child was a good practice (68.5%) observed. Attitudes regarding the best antimalarial therapy was limited (56.7%) to chloroquine.
The CDC says:
Most Anopheles mosquitoes are crepuscular (active at dusk or dawn) or nocturnal (active at night). Some Anopheles mosquitoes feed indoors (endophagic) while others feed outdoors (exophagic). After blood feeding, some Anopheles mosquitoes prefer to rest indoors (endophilic) while others prefer to rest outdoors (exophilic). Biting by nocturnal, endophagic Anopheles mosquitoes can be markedly reduced through the use of insecticide-treated bed nets (ITNs) or through improved housing construction to prevent mosquito entry (e.g., window screens). Endophilic mosquitoes are readily controlled by indoor spraying of residual insecticides. In contrast, exophagic/exophilic vectors are best controlled through source reduction (destruction of the breeding sites).
This paper notes some sensitivities for mosquitoes to temperature.
Dowling and Yap (2014, p 138):
Generally models of high mosquito infestation would involve differences in altitude, temperate, rainfall and time of year (seasonal variation). However, no one has been able to develop a general model that can predict well when an epidemic is likely to occur.
The details are provided by Yakob, Dunning and Yan (2011). They conclude that the most effective strategy is to treat as many houses as possible with bed nets and the remainder with IRS. It is not recommended to use both together. They act antagonistically. This recommendation comes after a rigorous testing experience of treating houses with combinations of IRS and INT in a controlled setting. Hopefully WHO and country officials will take note. It is also interesting to note that IRS has not been used in any of the countries with an epidemic of malaria as judged by the number of cases or deaths per annum.
To evaluate the impact of all the programs designed to reduce the incidence and mortality of malaria, UNICEF has constructed three maps of Africa with an estimated number of lives saved (see Figure 4.3). This is very good public relation and is certainly evidence of the overall success of malaria reduction in Africa. However, it does not give much detail about which program was responsible for how many lives saved and in which countries. Because all of these programs (bed nets, spraying and ACT) are relatively new, we are still at the evaluation stage. The effectiveness will have to be judged as they are evaluated over time. So far, as indicated in the analysis of mortality in the epidemic countries, there has been limited evidence of a decline in mortality.
Counterfeit antimalarial drugs:
- Counterfeit and Substandard Antimalarial Drugs
- The counterfeit anti-malarial is a crime against humanity: a systematic review of the scientific evidence
From Tren and Bate (p 13), an example of saying DDT was “banned” without being clear on the different use cases of DDT:
Despite a lack of scientific evidence, DDT was banned in many countries in the early 1970s following concerns about its environmental and human health impacts. However, the negative impacts from DDT use in agriculture, which led to the concerns, are vastly different from the impacts of DDT used in health control.
More on the DDT debate at claims about DDT.
Goldsmith (Battling Malaria on the Front Lines) mentions climate change and land use as two reasons for reemergence of malaria (and not just any two reasons – she mentions these two first as she explains the reemergence).
Hay and Snow writing in 2006:
The distribution of populations exposed to the risk of P. falciparum and P. vivax malaria is poorly understood at the global level. Considerable effort as part of MAP is required to improve our basic maps of malaria transmission intensity and help identify the global distribution of populations at risk of malaria. This will involve assembling the largest-ever collection of PR data and a significant parallel investment in establishing the required environmental, population, and malaria vector data.
DCP2 (p 422):
Despite its impact on mosquito density and its contribution to reducing transmission, larviciding is not as effective as IRS and ITNs in reducing mosquito longevity (Najera and Zaim 2002).
Do these FAQs adequately address the common questions? They probably address most of them, but some questions (especially those that might seem stupid) might be missing. Examples:
- Don’t mosquitoes need swamps to breed? And isn’t Africa full of desert regions? What gives?
- Why are there no malaria vectors in parts of northern Africa? It’s coastal so there can be mosquitoes, right? There must be some rainfall at least?
- What about the Arabian and Kalahari Deserts? They’re both deserts too, so why do we see malaria in countries located in those places?
- Classify each point on the Earth landmass surface by (desert, not desert), (
Classify the regions (smaller than countries) of the world by (desert, not desert) and
- Do non-mosquito vectors exist for malaria? If so why do we never hear about them?
What’s up with the push toward mosquito extinction?
Mosquitoes can’t fly that far, right? Why can’t we just create “safe zones” by draining all the swamps around cities? A better-formulated version of this is given in Dowling and Yap, Communicable diseases in Developing Countries (p 132):
On the surface, malaria looks like an easier target to control and eradicate than HIV-, TB- or cholera-type diseases. This is because malaria is borne by mosquitoes and should be easier to track and control than humans whose behavior is hard to predict and control and who are not subject to eradication using chemicals.
p 164 hints that something like this is possible in limited situations:
Locating the breeding ground is another initiative suggested by Abeku (2007), something that has been missing from most of the literature on malaria. Anopheles gambiae, one of the primary vectors of malaria in Africa, breeds in numerous small pools of water that form due to rainfall. The larvae develop within a few days and are able to escape from the water before it dries out. As a result it is difficult, if not impossible, to predict when and where the breeding sites will form, and to find and treat them before the adult mosquitoes emerge. Therefore, larval mosquito control for the prevention of malaria in Africa has not been attempted on a large scale. It may, however, be appropriate at specific settings such as urban environments or desert fringe areas where habitats are more stable and predictable. WHO has recommended larval control as appropriate only at areas where the larval habitats are “few, fixed and findable.” Otherwise a more ecologically damaging strategy would be to
- So I heard the Romans used sheep to attract mosquitoes away from humans. Why don’t we do that now? Can’t we just make some artificial warm-bodied thing?
- The CDC FAQ says “the eradication campaign never involved most of Africa, where malaria is the most common”. Why was this the case?
- What does the pie chart of spending within malaria look like?
- What does the pie chart of spending on malaria, seen in terms of all of global health, look like?
- Total malaria budget?
- Total spending on bednets? Total number of bednets?