Sunday, February 21, 2010

Malaria and Indoor Residual Spraying

Svenska Dagbladet published a long article* about malaria today. The disease, which has haunted the third world for generations, kills up to 1 000 000 human beings annually. But finally, thanks to among other Bill Gates, we have the means to eradicate the disease, the newspaper reports. One of these means is better medicines, developed by Swedish scientists. The two others are mosquito nets impregnated with intesticides and IRS - Indoors Residual Spraying. That means spraying the inside of people's homes with DDT. I was confused... isn't DDT poisonous? Well... I spent most of my sunday morning researching the issue, and in the afternoon a few things are obvious:


  • Malaria is an enormous health problem
  • DDT is a cheap and easy way to kill mosquitos carrying malaria
  • Mosquitos can become resistant to DDT
  • DDT might have health effects on humans
  • DDT and Malaria will be a hot topic in this springs Th!nk About it 3 blogging competition.
  • The interests behind the issue are roughly the same as behind the Climate debate - environmentalists against industrialists. Only that this time the UN, in the shape of WHO, is on the industrialist side.

In this post I will try to report on two texts about DDT use against malaria:

(PDF links)

First a brief background. Before the 20th century malaria was endemic in large parts of the world. It existed also in Sweden, where it dissapeared spontanously in the 1930's, due to rising living standards and change in land use - many wetlands disappeared as agriculture was modernized.

During the second world war, the allied forces used DDT against mosquitos spreading typhus among their troops, with impressive results. After the war, Indoor Residual Spraying (IRS) with DDT was depolyed against malaria.

IRS have some restrictions - notably that it requires a wall to spray on, and that this wall is not plastered. It must be a naked clay wall, for examle. Also, IRS requires 80% of all household in an area to be sprayed, in order to be efficient. The method requires consent from an entire community, voluntary or not.

DDT, which back then was seen as a panacea, was used in a wide range of situations. Agriculture made massive use of DDT to protect crops from insects.

The years after the second world war were successful in the fight against malaria. The disease was eradicated in western- and eastern Europe, and in many places in Asia and South America the spread declined. Some people, notably the authors of the WHO report I will refer to later, and the American Enterprise Institute whose reputation is flawed among environmentalists and climate believers, are convinced that these successes were due to DDT use.

Indoor Residual Spraying in an Ethiopian home Photo credits: Bonnie Gillespie, Voices for a Malaria Free Future

I suspect that other people will say something else. Obviously these countries also experienced a post-war economic boom, which may have made society less malaria-friendly for other reasons, similar to those eradicating the disease in Sweden before the war.

But no one is doubting that the DDT kills mosquitos. It does. And no one is doubting that mosquitos carrying malaria kill people. They do.

After using DDT for everything for 20 something years, a widening concern about environmental- and health effects and growing problems with DDT resistant mosquitos, DDT was phased out in the -70's. DDT use was banned in the US in 1972, and finally the Stockholm Convention, a UN body, in 2001 restriced use of DDT to public health only. That means - DDT can be used against malaria, but not in agriculture.

In 2006, the WHO revaluated the use of DDT for Indoor Residual Spraying, from now on I will write IRS. The WHO now reccomends the method, given that certain demands are met.

WHO's position statement on IRS is short and very easy to read. Already on the first page it is stated that "Effective implementation of IRS with DDT or other recommended insecticides should be a central part of national malaria control strategies where this intervention is appropriate." (italics are mine)

There is nothing that says that IRS must be done with DDT, the method could be deployed with various instecticides, but througout the document it is obvious that the subject matter is DDT, being a highly efficient, and very cheap insecticide.

The text continues with an historical background: "The efforts of the Malaria Eradication Programme (1955–1969) contributed to significantly reducing the global malaria burden, particularly in Asia, Latin America and Southern Africa. The eradication programme was based on IRS against the vector mosquitos, as endorsed by the WHO Kampala Conference of 1950."

Straightforward and uncomplicated. Not the shadow of a doubt about the role of DDT in the disappeareance of malaria.

Onfortunately, these programmes stopped due to the lack of government support and funding, and the worries about DDT resistance. "However, another important factor has been general disapproval of DDT use, due to fears of its harmful effects on the environment and on human health, fears which are unjustified when DDT is used appropriately for IRS."

To me - this is the argument that DDT usage stands or falls with. Is it dangerous for people, or is it not? Some researchers say that it is not. So why not use it also in agriculture? Because agricultural use would imply much larger volumes, and a quicker development of DDT resistant moquitos, is the answer from WHO.

The other paper I read, The Pine River Statement: Human Health Consequences of DDT Use, try to asses the health affects with a research overview. While also this paper approves of DDT use, it does not paint a rosy picture. The most troubling fact is how little we know about this insecticide, that is being sprayed on Africans' homes as I write.

Research indicates that DDT and/or DDE (DDE is a breakdown product from DDT) levels are higher among people whose home have been sprayed, than among people living in areas where DDT is used in agriculture, which can hardly be surprising. "...data suggest that indoor residual spraying results in high DDT exposure in humans, including vulnerable populations, such as pregnant women and fetuses."

Here I think - Before spraying, we should also consider who spends time in these houses. Men, or their pregnant wives? Is there a hidden gender issue here?

So IRS results in high levels of DDT/DDE in humans. What effects can these levels give? Very little research seems to be done and unfortunately a very little part of the existing research on DDT effects examines populations in areas where IRS has been deployed. These are the findings presented in Eskenazi et alt. , sorted by disease:

Cancer
There might be a link between cancer and DDT, but the data is notvery convincing. However, regarding breast cancer, one "study suggests that the prepubertal and pubertal years are critical periods of exposure",
Who will spend most time in these sprayed hosues? Most likely women, who also might have the most to fear from DDT exposure. Again, is there a gender issue in this?

Diabetes
The link seems to be stronger with diabetes: "studies from the United States and Sweden suggest that body burdens of DDT and/or DDE may be associated with the prevalence of diabetes. A variety of other persistent environmental chemicals also have been associated with diabetes prevalence (Lee et al. 2006). However, given the high correlation among various organochlorine exposures (Bradman etal. 2007), additional research is needed to delineate the specific contributions of DDT and DDE."

Does DDT affect childrens physical growth?
Maybe not. "Overall, the evidence for the relation of maternal DDT exposure and child physical growth is weak"


Sure enough, DDT does not kill humans instantly. The possible effects would be long term, which is also what causes the writers of the research review to advocate caution in their final conclusion:

"The use of DDT historically may have helped prevent millions of infections and deaths from insect-borne diseases. Based on recent studies, we conclude that humans are exposed to DDT and DDE, that indoor residual spraying can result in substantial exposure, and that DDT may pose a risk for human populations. However, few studies have measured body burdens of both DDE and DDT, and studies have rarely investigated the effects of DDT/DDE exposure at levels observed in populations exposed through indoor residual spraying. Furthermore, information on exposure to DDT/DDE during critical periods is limited for outcomes such as cancer.

We are concerned about the health of children and adults given the persistence of DDT and its active metabolites in the environment and in the body, and we are particularly concerned about the potential effects of continued DDT use on future generations. We recognize the serious implications of restricting DDT use given that an estimated 880,000 people die each year from malaria, most of whom are <5 years of age(WHO 2008)."

Isn't it remarkable how little we know, after more than 60 years of DDT usage? There are many "mays" and "mights"... Unlike the WHO text, even the succes story of DDT in the fifties is not completely sure here.

Let's go back to the WHO reccomendations. The WHO, stresses that DDT should nowadays be deployed in an appropriate way. Which means...

"In a single country, several epidemiological patterns and situations are com- monly found requiring different interventions or combinations of interventions. These must be taken into account when deciding whether to use IRS. IRS can be effective in almost all settings as long as certain conditions for implementa- tion are met.

  • In unstable, epidemic-prone malaria transmission areas, IRS will prevent
    seasonal increase in transmission, will prevent and control epidemics and
    can be used for the elimination of local transmission of malaria.
  • In stable-endemic malaria areas with moderately intense but seasonal trans-
    mission, IRS can prevent seasonal increase in transmission and reduce lev-
    els of infection prevalence and highly seasonal morbidity and mortality.
  • In stable-hyperendemic areas where very intense seasonal or perennial
    transmission occurs, IRS, with a higher frequency of application than in the
    above instances, can reduce the level of transmission and reduce levels of
    infection prevalence, morbidity and mortality.*
There are some situations in which IRS is not a suitable intervention, notably where there are no structures to spray. Therefore, IRS has almost no utility in the control of malaria in forested areas of South-East Asia and the Amazon region, where personal protection measures are the best option."

I find this the most disturbing part of the WHO text... In short: IRS is the best way to act in all situations, except when there is no wall to spray on. Isn't that giving a carte blanche for IRS, and implying that DDT is in deed not dangerous for humans? If this is the WHO standpoint, why only implying it, instead of speaking out?

Finally, there is one condition that must be met, according to the WHO. The usage MUST be restricted to public health use, to avoid the problem with resistant mosquitos. IRS is therefore not to be deployed in a country where the state can not guarantee that it is properly managed, and that DDT is not sold to farmers who use it or unintended use in agriculture etc. .I admit, I have never been to Africa, but there are several of EU governments I would not trust with this. And which African is actually able to control what happens with the DDT on the gound?

Maybe that is the point. If DDT use is actually impossible to restrict, governments will have to choose - either DDT is dangerous, and it should not be used, or it is not dangerous and should be sold and used freely. And I'll be damned if that is not what some of the people who have been lobbying the WHO into reccomending IRS want... among them the former Bush administration.

*Not avaliable online. "Spraytrupper i sista striden mot malaria", Svenska Dagbladet, 21/2 2010, s. 22-25

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