Abundance of An. merus species composition
An. merus was the most abundant species sampled in Garithe, this could be because of the favourable larval habitats which are saline. Apart from being the abundant species it was found to exist in sympatry with other members of the An. gambiae complex, this shows that An. merus can co-exist with other members of the complex. These findings are similar to earlier observations made [11], which found An. merus to be one of the sibling species along the Kenyan coast.
Vector behaviour: resting, feeding and transmission potential
There were significant differences in the number of An. merus sampled indoors and outdoors, this shows that An. merus adults rested both indoors and outdoors; the findings of this paper contrasted with those reported in Jimbo valley where it was found that An. merus rested mainly outdoors [18].
An. merus bites both indoors and outdoors and showed a tendency to feed on both human and non-human blood, most of the An. merus fed on bovine, goat or on mixed blood feeding on goat and bovine and humans suggesting that, An. merus is both zoophagic and anthropophagic. These findings were also observed in Jimbo Valley on the behavioural studies of An. merus on the Kenyan Coast [18]. From Results of the study were shown to differ from previous observations in Garithe, where it was observed that An. merus primarily fed on humans despite the availability of cows and goats [8, 19], this could have been because their data was based on only blood meal analysis performed on mosquitoes collected by light traps placed indoors, therefore targeting those that feed on humans [8, 19].
An. merus showed positivity for P. falciparum sporozoites with a percentage of 0.3, these findings showed that An. merus can transmit malaria parasites, as shown in studies carried out in Garithe, where the sporozoite rate of An. merus was 2.41% [11]. This demonstrates that An. merus can play a minor but important role. In Tanzania An. merus plays an important role in malaria transmission, this was shown by a study in which An. merus had a sporozoite rate of 11.6% [10]. This was also the same in Madagascar, where the role of An. merus as a malaria vector was confirmed in the case of two human-biting females, which were ELISA-positive for Plasmodium falciparum[9]. However, studies carried out on blood meal analysis for the Anopheline mosquitoes sampled along the Kenyan coast showed that there were no sporozoite infections found in the An. merus tested [8]. The low sporozoite rate of An. merus in Garithe could be attributed to its feeding largely on non-human blood (bovine, goat), which were abundant in every homestead sampled, this could be attributed to use of bed nets and screened windows.
Risk of transmission
The extent of the entomologic inoculation rate is influenced by the rate at which vectors feed on humans and the sporozoite rate. In Garithe, the HBR generally was low and did not exceed previous findings in Garithe where the HBR was 2.45 infective bites per day [8], but in this study it was observed that the HBR averaged to 0.49 infective bites per day both indoors and outdoors, this in turn reduced the EIR.
Overall, the results of this study revealed the EIR for the six months was 0.003 infective bites per person both indoors and outdoors indicating that an individual would receive approximately 3 infective bites every 3 years. Thus the transmission potential for An. merus in Garithe was very low as compared to previous studies, [11]. These observations show that malaria transmission by An. merus has decreased, however, it should be taken into consideration that, it can be a significant vector at specific times of the year and that relatively high malaria parasite prevalence can occur at low or even below detectable levels of transmission [11, 19, 20].