**5. Conclusion**

*Vector-Borne Diseases - Recent Developments in Epidemiology and Control*

vector control intervention measures.

would be a question of validation.

ecological setups.

cannot intercept malaria transmission. Thus, zooprophylaxis would advance the effectiveness of malaria interventions if used in an integrated way with other

Either data are unavailable or no previous attempts were made about the impact of IRS on SR in Ethiopia. However, studies from other African countries [27, 28] demonstrated that the implementation of IRS reduced SR to non-detectable level, which is consistent with the results of the present study. And these would substantiate the contribution of IRS implementation in reducing malaria transmission risks in general and SR in particular in the present study area and others having similar

In the present study, *P. falciparum* was more prevalent than *P. viva* in *A. arabiensis.* No *A. arabiensis* was found positive for either *P. falciparum* or *P. vivax* in sprayed villages after IRS. Although too few *A. arabiensis* were recorded in sprayed villages after IRS, it would have been necessary to process thousands of mosquitoes to find any of them were infected by malaria parasites. There was no any mixed infection detected. The proportion of plasmodium-infected *A. arabiensis* was also low in non-sprayed villages indicating that SR might be low in naturally occurring vector population. Contradictory results about the prevalence of *P. falciparum* and *P. vivax* in *A. arabiensis* have been reported from different parts of Ethiopia at different times. Massebo et al. [21] reported the dominance of *P. falciparum* over *P. vivax*, while [6] reported the dominance of *P. vivax* over *P. falciparum* in South West Ethiopia. Animute et al. [29] reported the dominance of *P. vivax* over *P. falciparum* in South Central Ethiopia. Differing from all these, [30] reported that no *A. arabiensis* was found positive either for *P. falciparum* or *P. vivax* in South West Ethiopia. Except Taye and his colleagues [30], other investigators used either CDC or PSC mosquito sampling method so that the differences observed in the prevalence of malaria parasites in *A. arabiensis* could be potentially justified by the differences in ecological setups of the study sites and time period in which the study was conducted. Otherwise, this

Malaria transmission intensity, which is normally expressed by EIR, is highly variable with annual EIRs ranging from < 1 to >1000 infective bites per person per year in Africa [31]. Variations in EIR in malaria vectors could be due to different factors such as ecological heterogeneity at continental, regional, and country level [29, 32, 33] and season (dry or wet) [29, 34, 35]. For example, the burden of malaria is high in tropical countries having warm temperature, heavy rainfall, high humidity, and efficient *Anopheles* vectors than nontropical countries [36]. Previous studies indicated that the impact of wet or dry season on EIR is inconsistent, i.e., published reports indicated

In the present study, a very high *Pf*-EIR was observed in the vector in both years and study villages although SR and HBI were low. The trend was also similar for *Pv*-247 EIR in both study villages before IRS in 2013. These findings would be justified by the occurrences of high mosquito density during the study periods. The level of EIR of both parasites went to zero in sprayed villages after the implementation of IRS suggesting that IRS application is 100% effective to control disease transmission. In contrast, previous studies reported that EIR was 90% lower in the ITN community and 93% lower in the IRS community, relative to the community without intervention. The differences observed between the present and previous studies would be

that EIR is higher during wet season [15, 35, 37] or vice versa [38, 39].

attributed to heterogeneity in the ecology and behavior of the vector.

Variation in EIR could also differ by mosquito collection methods [40]. [41] indicated that PSC might underestimate the HBR, which again underrates EIR. Previous studies also reported CDC light traps were more efficient than PSC to estimate EIR [21, 42–44]. Contrary to these, a study from Bioko Island, Equatorial Guinea, demonstrated that CDC light traps failed to determine the human-biting

**62**

This study was linked with IRS application to assess its effect on EIR and other entomological risk factors for malaria transmission. The results illustrated that IRS was strong enough to reduce mosquito abundance, sporozoite rate, and EIR in areas having similar ecological setup with the present study villages [48].
