Entomological Aspects of Vector Control A baseline entomological survey was conducted in Mozambique in December 1999, prior to the floods in the
region. Mosquitoes were collected through knock down pyrethrum spray catches. From the molecular identification of mosquitoes that were collected
during this baseline survey, Anopheles funestus was shown to be a major
malaria vector species in southern Mozambique and Anopheles arabiensis,
the second most common malaria vector in the area. The discovery of insecticide resistant An. funestus
in South Africa in 1999 raised the question of the status of insecticide resistance
among this mosquito species in Mozambique. Studies conducted showed that An.
funestus was resistant to synthetic pyrethroids. However, these mosquitoes
were still found to be susceptible to DDT. Extensive entomological collections were carried out during 1999
and 2000 at nine localities in Mozambique. Susceptibility tests indicate that
pyrethroid resistance is widespread in the southern Mozambique province of Maputo.
Results from the area north of Maputo city show resistance to pyrethroids at
Chokwe, but two collection sites further north at Quelimane and C-Delgado indicated
complete susceptibility. Three additional collections sites between C-Delgado
and Chokwe have been identified, and sampling will be extended to these sites
to assess the geographical extent of pyrethroid resistance in An. funestus. From the outset, pyrethroids were identified as the insecticide
to be used in the spraying component of the LSDI. However, with the discovery
of high levels of pyrethroid resistance in An. funestus, meetings
were held with the RMCC, national and international experts to recommend an
alternative to the use of this family of insecticides. Based on scientific data,
it was unanimously agreed the best course of action would be to use DDT. In
the light of Mozambique not agreeing to the use of DDT, an alternative recommendation
was that a carbamate such as Bendiocarb be used. Ongoing research indicates
levels of carbamate resistance outside the Zone 1 area and collections within
the study area have been completed towards evaluating selection in this regard
following spraying with a carbamate. Increasing levels of insecticide resistance and the limited
number of available insecticides, restricts what can be used in the residual
house spraying programme in southern Mozambique. Given the discovery of pyrethroid
and possibly carbamate resistance in the LSDI area the only remaining group
of insecticides are the organophosphates which have a high mammalian toxicity.
Since the use of DDT alone has not been approved by Ministry of Health in Mozambique,
a rotational method of spraying is proposed, using different insecticides, as
the way forward. DDT would need to be one of the insecticides used during such
a rotational insecticide spraying programme. Due to the discovery of insecticide resistant An. funestus,
biochemical assays have been conducted to determine the mechanism of resistance
responsible for insecticide resistance in this malaria vector. Biochemical analysis
highlighted the presence of two resistance mechanisms, namely, metabolic and
target-site mechanisms which correlated with the organophosphate and pyrethroid
resistance detected during susceptibility testing. Bioassays were conducted on the sprayed walls of houses to monitor
the residual insecticide effect of Bendiocarb towards determining when respraying
would be required. Bioassays were conducted using susceptible An. arabiensis
reared in the insectaries at the MRC and the Ministry of Health in Mozambique.
Monthly bioassays have been conducted in seven areas in Mozambique. The wide range in mortalities indicate the residual efficacy
of the insecticide on the different type of surfaces sprayed such as reed or
cement. Decreased mortalities are indicative of the waning effectiveness of
the insecticide and indicate the need to respray these structures. Respraying
was scheduled for April but financial constraints have delayed this. The window trap data clearly shows that An. funestus is
the predominant species found in all these areas with Catuane, Boane, Bela Vista
and Changalane yielding the greatest number of mosquitoes respectively. In all
areas fitted with window traps, the greatest number of mosquitoes of both species
were collected before October 2000 and before spraying activities were initiated.
Entomological Aspects
Since vector control forms the mainstay of the malaria control programme that was implemented in
southern Mozambique, extensive entomological surveys were undertaken to determine the status of mosquito vectors of malaria in this region prior to the implementation of a residual house spraying
programme. Entomological studies have been ongoing in the region to monitor and evaluate the effectiveness of the spraying programme.
Window
trap data was collected from the sentinel sites spread over a large geographical
area, with vastly different local ecological and climatological conditions affecting
not only malaria transmission but also the mosquito vectors themselves. This
is evident from the wide range in numbers of mosquitoes caught at the different
localities. During the December 1999 baseline survey, window traps were fitted
to four randomly selected houses in each of the eight sentinel localities
in Mozambique where the baseline was conducted. During November 2000, four additional
traps per locality were installed in houses in Boane, Bella Vista and Catuane.
Window trap data was collected along the eastern area at Bella Vista, Salamanga,
Zitundo and Ponto du Ouro. Data was also collected from the western border regions
of the LSDI area from Boane, Namaacha, Changalane and Catuane.
