1. Figure 1: Map of Study Area
Diversity and Distribution of Rift Valley Fever and Malaria Transmitting Mosquitoes in Baringo County, Kenya
Ondiba, I M.1 Oyieke,F A.1 Ong’amo, G O. 1 Kobia , D A. 1 Oluoch, A O.2 Nanyingi, M.1,3 Kipruto E2, Loye,C.1 Nyamongo, I K.1 and Estambale, BB.2
1 University of Nairobi, 2 Jaramogi Oginga Odinga University of Science and Technology, 3 Colorado State University
ABSTRACT
Effective monitoring of vectors to estimate their diversity and distribution is important in determining the areas prone to VBD outbreaks. This study assessed diversity and distribution of mosquito vectors of Rift Valley Fever (RVF) and malaria in Baringo County, Kenya. It involved sampling of immature mosquitoes in aquatic habitats using a standard dipper and pipette. Three vectors of malaria and several secondary vectors of RVF were collected. Although vectors were present in all study sites their numbers varied indicating different levels of disease risk for the communities at different altitudes.
RESULTS
A total of 2691 immature mosquitoes belonging to 13 species were collected from all sites across the four zones. Of the 13 species, three of the anophelines; Anopheles gambiae s.l. (9.6%), Anopheles funestus (0.2%) and Anophels pharoensis (19.5%) are known vectors of malaria, while three Aedes species; Aedes aegypti (0.4%), Aedes taylori (0.2%) and Aedes africanus (0.04%) are implicated in the transmission of arboviruses. Culex quinquefasciatus, which was the most abundant species (35.5%), has also been incriminated in the transmission of RVF.
Lowland and riverine were ecologically similar in terms of species composition (Fig.4) however pairwise comparison between zones showed no statistical diference between highland and the two zones (Table 1).
Midland zone was different from all other zones (Table 1) and had the largest proportion of an. gambiae (Fig.4).
Highland had the largest number (5) dominant species
Figure 2: Larval collection and an inset of mosquito identification under a microscope
Figure 3: Mosquito identification
INTRODUCTION
Mosquitoes are responsible for transmission of human and animal vector borne diseases (VBDs) across the world particularly to vulnerable communities in the tropics (WHO, 1997).
Malaria and Rift Valley Fever (RVF) are among the VBDs which are transmitted by mosquitoes. Whereas malaria occurs seasonally, RVF is sporadic (Aniedu, 1997; Murithi et al., 2011).
Knowledge on larval vector species and distribution is necessary for targeted vector control measures to control RVF and malaria
DISCUSSION
All the 3 Aedes species collected are vectors of arboviruses (Gillett, 1972).
The Culex species collected have been reported as secondary vectors of RVF during epidemics (Sang et al., 2010).
Anopheles gambiae, An.phrroensis, An.funestus and An.coustani are the most predominant species in Baringo County (Mala et al., 2011).
The anopheline vectors of malaria were in all altitudinal zones though more at midlands than highlands similar to findings of Minakawa et al., 2002.
Culex species were equally distributed in all altitudinal zones while Aedes were found at high and lowland zones only.
OBJECTIVE
To determine the diversity and distribution of RVF and malaria vectors in Baringo County.
MATERIALS AND METHODS
Study Area: Baringo County
CONLUSION
There are more than 2 vector species for RVF and malaria in Baringo County.
The presence of Anopheline species in all study zones indicates risk of malaria more so at lowlands and midlands of the County.
The presence of Aedes and several Culex species previously reported as vectors indicate the potential for virus transmission in case of RVF outbreak.
Figure 1: Map of Study Area
Fig. 4 Species diversity and distribution between zones
MOSQUITO COLLECTION
The study was undertaken in four zones based on elevation within Baringo County, Kenya. Fig.1
It involved sampling of immature mosquitoes in aquatic habitats using a standard dipper and pipette.Fig.2
The collected specimens were morphologically identified to species level under a dissecting microscope using taxonomic keys. Fig. 3
Principle Component Analysis (PCA) was used to estimate species diversity for each zone and Shannon diversity t-test to compare zones.
KEY REFERENCES
WHO. Vector control methods for use by individuals and communities. World Health Organization. Geneva p.10-17
Sang, R. et al., Am J Trop Med Hyg, 83(2):28– 37.
Gillett JD. W.H. Med. Books Ltd. ISBN ; 1972.
Aniedu I. Indian J Med Res. 1997; 105:
Murithi et al., Epidemiol infect. 139(3):372-80
Mala et al., Parasites and Vectors, 4:25
Minakawa et al., J Med Entomol,39(6):833-41
Riverine
Lowland
Midland
t85.31=1.94; p=0.055
t74.08=3.87; p=0.000
t1685.5=4.31; p=0.012
Highland
t98.9=1.12; p=0.267
t1712.3=1.39; p=0.166
t1273.4=5.14; p=0.002
Table 1: Pairwise comparison of species diversity between the zones using Shannon t-test
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ACKNOWLEDGEMENTS
This research is funded by WHO/TDR-IDRC initiative on " Population Health Vulnerabilities to Vector-Borne Diseases: Increasing Resilience under Climate Change Conditions in Africa“
2. Division of Vector Borne Diseases Laboratory, Marigat/Baringo, Kenya
3. County government and Communities of Baringo, Kenya
Project ID: B20278