RFI: Adverse effects of impregnated bed nets (6)
It is true, as Torben Vestergaard says, that a treated net gives very
much better protection than an untreated net, especially when the net
has holes. But we are beginning to recognise that untreated nets are
indeed valuable in themselves. It seems that untreated nets give
roughly half the protection given by treated nets.
The evidence that treated nets are much better than untreated ones
comes mainly from the trials in The Gambia, where the intervention was
insecticide treatment of existing nets (no nets were distributed by
the project). The effect of the treatment was very impressive, and
this convinced many people that untreated nets must be pretty use-
The other big ITN trials did not shed light on this question, since
they compared treated nets with no nets - i.e. there was no group
with untreated nets. Thus, for a while, we were in the rather absurd
position of knowing a great deal about the benefits of treated nets
(our wonderful new preventive measure) and very little about the
benefits of untreated nets (the old familiar preventive measure).
There was some evidence that untreated nets are protective (e.g.
D'Alessandro et al. 1995 Trans Roy Soc Trop Med Hyg 89, 596-598), but
it was limited. However, recent work (for example by Sian Clarke and
her colleagues of the Danish Bilharzia Laboratory) has shown that un-
treated nets do indeed give good protection compared to not using a
net at all. This has been confirmed even more recently by evidence
(published in BMJ and Lancet) from Schellenberg and her colleagues in
No formal meta-analysis has yet been performed, but all these studies
suggest that untreated nets give roughly half the protection given by
London School of Hygiene & Tropical Medicine
Keppel St. London WC1E 7HT, UK
Send mail for the `AFRO-NETS' conference to `<email@example.com>'.
Mail administrative requests to `<firstname.lastname@example.org>'.
For additional assistance, send mail to: `<email@example.com>'.