Journal of Mosquito Research 2015, Vol.5, No.14, 1-8
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Table 5
Plasmodium falciparum
infection in
Anopheles
mosquitoes in Mwea and Ahero rice study sites
Village
An. species
Indoor collected and Sporozoite positive (%) Outdoor collected and Sporozoite positive (%)
Mbuinjeru
Ndindiruku
Murinduko
An. arabiensis
(n=200)
An. arabiensis
(n=200)
An. arabiensis
(n=200)
0.00
0.00
3
0.00
0.00
0.00
Kamagaga
Kobura
Wagai
An. arabiensis
(n=52)
An. funestus
(n=148)
An. arabiensis
(n=180)
An. funestus
(n=20)
An. arabiensis
(n=18)
An. funestus
(n=182)
0.00
3
0.00
0.00
0.00
1
0.00
4
0.00
0.00
0.00
3
et al., (1975) where
An. gambiae
s.l. was present in a
higher proportion than members of
An. funestus
complex. This variation may be attributed to a gradual
change in malaria vector composition since 1975 with
unclear causes (Githeko et al., 2003).
Anopheles
rivulorum, An. leesoni
and
An. parensis,
which are
members of the
An. funestus
complex, had not been
reported in Ahero in earlier studies, mostly likely due
to the lack of molecular assays to differentiate
between members of the species complex.
In terms of resistance to insecticides, there was
evidence of reduced susceptibility of
An. arabiensis
to
insecticides in Mwea, especially to pyrethroids when
compared to studies of Kamau and Vulule (2006).
This indicates that resistance is spreading and is likely
to increase further with the continued use of
insecticide-based vector interventions.
An. arabiensis
sampled from Ahero were susceptible to the test
insecticides except for fenitrothion which indicated
reduced activity. Similarly, the use of permethrin and
bendiocarb in Ahero should be monitored as reduced
insecticidal activity has been demonstrated in Kamagaga
and Kobura villages. Therefore, insecticides based
malaria control programs can be effectively used in
this ecosystem with close monitoring for resistance
development or in integrated vector control programs.
In Mwea, only mosquitoes collected from one of the
three villages were positive for
P. falciparum
. In the
said village, Murinduko, malaria parasite rates were
much lower than those reported earlier, which were
three-fold higher (Muturi et al., 2008). The lower
malaria parasite rates in the current study are likely
due to the use of bed nets as reported by Kamau and
Vulule (2006) in which 93% of the 42 households they
surveyed used bed nets and also due to high zoophilic
behaviour of
An. arabiensis
(Muturi et al., 2009). In
Ahero, only members of
An. funestus
complex were
reported to be positive for
P. falciparum
. This
indicates the potential of these members to transmit
malaria parasites in this region.
In Mwea study site, assessment on the feeding pattern
indicated mixed feeding for a blood meal. These
findings compare well with those published earlier by
Muturi et al.
,
(2008). This phenomenon can be utilised
by individuals to keep animals around their homesteads
while themselves sleep under a treated mosquito net.
This is because; the vector in this site can still obtain a
blood meal from animals, especially bovines, as the
preferred host, and this will reduce malaria parasite
transmission to humans.
In Ahero, we found lower human blood indices for
both
An. arabiensis
and
An. funestus
mosquitoes
sampled compared to those reported by Githeko et al.
,
(1994). The entire mosquito samples from Kamagaga
showed animal preference. This should be further
investigated to determine if it is due to human
inaccessibility or intrinsic behaviour of the vectors. In
Kobura and Wagai villages,
An. funestus
obtained
their blood meal from both humans and animals thus a
potential vector for malaria parasite while
An.
arabiensis
from the same villages obtained their blood
meal from none of the test hosts. This calls for
investigations to determine the source of blood meal
by
An. arabiensis
in these villages.
Feeding on multiple hosts, including non-human hosts
in
Anopheles
populations, has been suggested as one
of the factors responsible for lower levels of malaria
transmission despite higher vector densities (Lincithicum
et al., 1999; Maria et al., 2005). However, because
An.
