Mosquito and Malaria Control (43)
Sorry this is rather long ... but it is a big subject.
I would like to follow up on a message that Chris White sent last September
about Mosquito/Malaria Control. Chris made the point that interventions that
are used in the United States are wrong for Africa ... but in all honesty, I
don't think he made a strong case for this.
The discussion had talked about the use of aerial spraying in the USA in the
aftermath of the Katrina hurricane ... and he correctly pointed out that this
was not spraying against malaria, but against various other mosquito borne
diseases (yellow fever, dengue and west nile virus). Since malaria has not been
a problem in the area since around 1950, spraying against malaria is not done
... which seems to make sense! My conclusion is that aerial spraying is a very
appropriate and cost effective way of delivering anti-mosquito pesticide,
especially with modern understanding of pesticide and the use of ultra low
volume (ULV) technology. I have made some cost estimates for aerial treatment
and it is very low cost per acre ... and depending on population density can be
very low cost per capita of human population.
Chris talks about the mosquito (specifically anopheles gambiae s.s.) breeding
in all sorts of small, transient rain-fed pools ... and how it is unrealistic
and uneconomic to expect that larvaciding can be effective. I am not at all
sure that Chris is right. From a practical scientific point of view,
larvaciding works ... though it is difficult to organize over a big area. I
don't think this problem is insurmountable, though it must not be ignored.
Arguably cleaning up the environment and larvaciding is the best way to break
the cycle of mosquito population rebuilding. Building the Panama Canal 100
years ago was done in the face of virulent malaria, in large part by cleaning
up the environment where the work was going on and where workers were living.
Spatial information seems to suggest that not all water has the same breeding
I have not been able to find much cost and result information that convinces me
that insecticide treated bednets is the best way to go for effective mosquito
malaria control interventions. While an individual seems to get less malaria
when they use a bednet ... the cumulative experience in the community does not
seem to change very much. This may not be the right conclusion, because the
information available is not very clear. Rather than having a focus on costs
and results (as measured by reduction in the prevalence of malaria in the
community), much of the cost performance information relates to merely the cost
and the scale of distribution of bednets into the community ... an interesting
metric, but not a metric that helps determine the effectiveness of bednets as
an anti-malaria intervention. I think it is fair to conclude that bednets on
their own do not make much of a difference, even when they are widely
distributed. I would love to know more about costs and reduction in malaria
parasite prevalence using the bednet approach.
There seems to be a lot of information that shows that interior residual
spraying (IRS) does have a significant impact on the prevalence of malaria in
the community ... and especially when DDT is used as the pesticide. The cost of
a large scale IRS program is substantial, but the results seem to justify the
expenditure, especially if DDT is permitted. Sadly use of DDT in a country has
the possibility of creating trade issues with Europe, not so much because of
prevailing legislation but because of corporate environmental sensitivities and
concern that there might be adverse consumer impact.
The role of medical interventions is not insignificant. Remove the parasite
from the human host and malaria transmission will be reduced ... though it is
not easy to get the reduction in malaria transmission low enough so that the
parasite population gets reduced. It can be done ... but it is not the norm for
Africa at the moment.
Clearly resistance is an issue in any chemical intervention ... whether against
the mosquito or the malaria parasite. A modern management information system
for any intervention should take this into consideration and collect
appropriate data and use it to manage the interventions.
Lastly ... the information I have been able to collect seems to suggest that a
variety of interventions going on together and coordinated gives the best
results at least cost. A data driven program, including spatial information
about all the interventions and all the results can be used to keep costs down
and to deliver better than "average" results. But in order for data to be
useful, they must be organized as "management information" for decision making
and not merely to satisfy academic criteria.
I would love to get more information that will help move me along in the design
of an integrated mosquito malaria control model ... and a program that can be
helpful in Africa to optimise mosquito and malaria control interventions.
Transparency and Accountability Network