| dc.description.abstract | Malaria continues to be a health problem in Kenya, .. .
due to the growing resistance to insecticides among the
mosquito vectors (WHO, 1970) and increasing resistance
to drugs by the malaria parasites. Parasite resistance
to chloroquine as a common anti-malaria drug was first
reported in Kenya in 1982. These two facts, coupled
with inadequate national resources for mounting massive
malaria control programme calls for a simple, cheap,
sustainable and an appropriate vector control measure
such as using mosquito nets.
A field trial with mosquito bednets impregnated with
1% permethrin was carried out against malaria vectors in
Kisumu to assess the potential of this method as a means
of reducing vector densities thus reducing the risk of
transmission of malaria. For effective control
programmes to be conducted, the ecology and behaviour of
the vector should also be understood. Therefore their
breeding sites, seasonality and biting habits i. e. peak
biting rates were investigated. Host preference was
determined by bloodmeal analysis. The sporozoite rates
were also determined by dissec~ion and ELISA for
sporozoites methods.
Six species of anopheline mosquitoes were
identified in the area namely; Anopheles gambiae sensu
stricto Giles, Anopheles .arabiaensis Patton, Anopheles
funestus Giles, Anopheles pharoensis Theobald, Anopheles
pretoriensis Theobald and Anopheles necuIipennis
Theobald. Collected data showed that the predominant
mosquitoes in the region were An. gambiae s. s. and
Anopheles funestus, and were singled out as the main
malaria vectors in the area as earlier sited by
(Surtees, 1970). Anopheles pretoriensis and An.
maculipenis appeared only during the rainy seasons. The
two species together with An. pharoensis were of no
importance in malaria transmission.
Use of, permethrin treated bed nets led to a marked
decline in the mosquito densities when compared to the
use of untreated bed nets or the no-nets situation.
There was statistically, a significant difference found
in the house resting densities of mosquitoes in the
three study sites. Using the Analysis of variance F was
0.63, at degree of freedom (2,24), at probability level
P< 0.05, based on Pyrethrum Spray Catch data.
Rainfall had an influence on mosquito house
resting densities. Data collected by both the PSC and
night catch indicated a marked increase of both An.
gambiae 5.1. and An funestus in site 2 and 3 with
increased rains while in site 1 increase was negligible.
This increase in sites 2 and 3 was attributed to the
increased mosquito breeding sites. there was a decrease
in the mosquito densities during the short rains and the
dry season due to the limited breeding grounds in all
the three sites.
The bioassay experiments on -the permethrin
treated nets showed that the insecticide had a long
lasting residual effect as it was found effective up to
9 months after impregnation 1.e. it could knock down and
kill 70% of the exposed test mosquitoes and according to
WHO this would be the correct time for re-impregnation.
The malaria parasites found among 92 child~en
examined were predominantly Plasmodium falciparum
Welch, 1897, found in 56 children (64%), Plasmodium
malariae Grassi and Feletti, 1890, found in 27 children
(30%), and Plasmodium ovale Stephens, 1922, found in 8
children (6%). Children with P. 1!1alariae and P. ovale
infections' also had concurred infections of P.
falciparu1!1.Blood smears also showed a great decline of
parasitaemia amongst children between 0-10 years of age
in site 1 (the permethrin treated bed net site). At
site 1 Plasmodium falciparum percentage prevalence was
reduced from the original 98% during the baseline data
to an average of 20% throughout the 11 subsequent months
of the data collection period. Site 2 and 3 also had a
reduction from 83% to an average 40% and from 90% to an
average 60% respectively. There was a significant
difference P < 0.05 noted between the percentage
prevalence of P. falciparum in the three study sites
where by the Chi square was and degree of
freedom 2. | en |
