Bio-environmental methods of malaria vector control in Africa
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Oh dear. Here's another suggestion that anti-malaria drugs, mosquito
nets and insecticides are all unnecessarily sophisticated, and that
environmental interventions such as bush-clearing offer a simple and
cheap method of preventing malaria in Africa. This time, it comes
from A. Odutola in his commentary on the Roll Back Malaria Summit.
[see: AFRO-NETS Mon, 5 Jun 2000> DATELINE HEALTH NIGERIA: Supplement
on Roll Back Malaria Summit]
Generally, the examples that are cited as demonstrating the feasibil-
ity of non-chemical control methods actually indicate the opposite.
Most are "exceptions which prove the rule". By this I mean that there
are exceptional circumstances, which make it unusually easy to find
all the breeding sites and eliminate them. Consider for example the
two cases where larvivorous fish have been shown to be effective as a
means of malaria control in Africa. These two cases are reported from
Somalia and the Comoros Islands. Both these places are arid, with
very little water in the dry season, so people collect water in the
wet season in large concrete tanks. These then form the only avail-
able breeding sites. In both countries, An. arabiensis has adapted to
breeding in this habitat (elsewhere it is extremely unusual to find
this species in any kind of container). The addition of larvivorous
fish to these tanks successfully controlled malaria transmission. The
point here is that the breeding sites in these two cases were ex-
traordinarily few in number, easy to identify, fixed in location and
homogenous in form. In most of its distribution, of course, this spe-
cies normally breeds in sites that are numerous, varied, scattered,
shifting, and hard-to-find.
A more balanced view of the potential for "naturalistic" methods of
control can be seen in an old paper which was written when expertise
in this field was at its peak - at the end of the 1930s, just before
the arrival of DDT.
Hackett LW, Russell PF, Scharff JW and Senior White R. (1938) The
present use of naturalistic measures in the control of malaria.
Bulletin of the Health Organisation of the League of Nations, Vol 7,
pp 1046-1064.
This may be old, but it was written by a panel of the world's most
highly experienced malariologists, just before the advent of syn-
thetic residual insecticides, when environmental approaches and tech-
niques were still "mainstream". Here is a sample:
"...The ERECTION OF BARRIER PLANTS is, as far as we can find out,
nothing more than a medieval myth. The ODOR OF PERSPIRATION may the
reason why certain rare individuals are not bitten by mosquitoes, but
no food or drug has been found which produces this effect. As or
DESTRUCTION OF SHELTERS, we know of no instance where a small radius
of clearing about houses or inhabited centres has done any good, but
many instances where it has done great harm. Nevertheless, the cut-
ting of underbrush and trees around dwellings is an obligatory anti-
malaria measure in many tropical settlements. Just the opposite has
also been suggested in the form of a TREE BARRAGE TO OBSTRUCT FLIGHT.
No serious attempt has been made to evaluate the results in either
case."
I know of only two subsequent attempts to carry out such an evalua-
tion, both of which confirmed the panel's sceptical comments. The
first was reported in...
Ribbands, C.R. (1946) The effects of bush clearance on flighting of
West African anophelines. Bulletin of entomological Research 37,
33-41...
...and showed convincingly that clearance was useless.
The second was the heroic effort by Gillies and Wilkes (1978, Bull.
ent. Res. 68:401-408) to test the idea of using barriers to isolate a
settlement from mosquitoes. They built a circular mosquito-proof
fence 65 metres in diameter and 6 (yes, six) metres high - and showed
that it failed to protect a bait inside the fence.
--
Jo Lines
London School of Hygiene & Tropical Medicine
Keppel St. London WC1E 7HT, UK
mailto:Jo.Lines@lshtm.ac.uk
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