Browsing by Author "Gebre, Teshome(PhD)"
Item Comparative studies on bionomics and behavior of phlebotomine sandflies in highland and lowland areas of kala-azar transmission, northwest Ethiopia(Addis Ababa University, 2015-06) Aklilu, Essayas; Gebre, Teshome(PhD)The aim of this study was to investigate and compare the bionomics, ecology and behaviors of the vector (s) of visceral leishmaniasis (VL) in two endemic and ecologically distinct areas of northwestern Ethiopia. This included species composition, population dynamics, habitat preference, host preference, vectorial potential and nocturnal activity studies in the field. Phlebotomine sandflies were collected using CDC light traps, sticky traps and pyrethrum space spray catches from Libo-Kemkem district (May 2011-April 2012) and Metema district (October 2012-September 2013). A total of 51,411 sandfly specimens were collected: 10,776 from highland and 40, 635 from the lowland areas. Seven species were found in the highland area: two Phlebotomus sandflies (P. orientalis and P. rodhaini) and five Sergentomyia species, whereas 19 species were found in the lowland area: six Phlebotomus (P. orientalis, P. rodhaini, P. bergeroti, P. duboscqi, P. papatasi and P. martini) and 13 Sergentomyia species. Of the Phlebotomus spp., P. orientalis was the predominant species in both the highland (99.9%) and lowland (93.7%) areas. In both areas, this species showed seasonal a occurrence and mainly abundant during the dry months (March-May/June) of the year and increasing in numbers till the rains began, when numbers dropped dramatically. In both areas, P. orientalis exhibits both strong exophilic and exophagic behaviors and its parous rates of the species were 45.6% and 66.2% in highland and lowland, respectively. Identification of blood meals in wild caught blood fed P. orientalis using cytochrome b polymerase chain reaction (Cyt b –PCR) and reverse iv line blotting (RLB) and enzyme linked immunosorbent assay (ELISA) showed that this species has strong predilection for bovine in both the highland (67.8%) and the lowland (49.8%) areas. A total of 1087 P. orientalis from the highland area and 344 Phlebotomus spp. from lowland area were dissected for detection of natural infection, but none of them was infected. A similar result was obtained in 347 P. orientalis females processed using PCR for detection of L. donovani from the highland area. Hourly activity period of the two populations of P. orientalis showed variation. The nocturnal activity of P. orientalis in the highland peaked between 22:00 and 23:00hours for both sexes; whereas in the lowland area, this peak was between 3:00 and 4:00hours. Although natural infection was not detected in the current study, P. orientalis is strongly implicated as vector of VL in both study areas due to its abundance and other circumstantial evidences. Therefore, control of the disease in these particular areas should involve tools that mainly target the vector of the disease by considering its seasonal abundance, ecology and behaviors in the respective areasItem Evaluation of Some Plants for their Repellency against Some Anopheline and Culicines Mosquitoes in Kolm-Negewo (Central Ethiopia)(Addis Ababa University, 2005-07) Atsbaha, AkIilu; Gebre, Teshome(PhD)To evaluate and compare the repellency of 7 different local plants against diflcrcnt mosquitoL's. investigations wcrc macle by using fleld experimcnts in Koka NegeIVo village ahoul ')';, repellency against All. arabiellsis rcspectively. Highest repcllcncy showed with the seed or II. cila//apellsis (1'<0.001). The seed or this plant showed similar effee( on AI/. plwmci/sis and Culicines. In the contrary All. araiJiellsis was more repelled by hurning thc kavcs 01'.\ /1/,,//,' (1'<0.05) than the leaves of R. cilallepellsis mid M azedarach. Direct burning J>. a/Jyssillica, 0. /alll(til!illlll showed remarkable repellency against All. arabiellsis (1'<0.05). However, less protection was exhibited to thc other two mosquito species. Less repellency against all the three mosquito species has been (,hlainL'" Iw F gl"h"/,,,\ in ,U)I (est methods. Burning or !lowers. leaves and seeds of L. C(fJI/(//'(/ exhihil similar bUI signiliL"lnl repellency (PItem Species composition, Ecology, Seasonal abundance and Vectorial importance of the sub-family Phlebotominae (Diptera: Psychodidae) in Diteta Village, Konso Woreda of Southern Ethiopia(Addis Ababa University, 2013-06) Worku, Amha; Gebre, Teshome(PhD)A survey aimed to study species composition, seasonal abundance and infection rate of phlebotomine sandfly species were carried out in a village called Diteta, where new cases of visceral leishmaniasis (VL) have been recently observed by researchers and health centers/hospitals in the region. Sandfly densities monitored for six months (January-June, 2012) using CDC light traps and sticky paper traps yielded a total of 8091 sandflies belong to two genera: genus Phlebotomus (n=118) and genus Sergentomyia (n=7873). Three Phlebotomus species representing two subgenera; Anaphlebotomus (P. rodhaini) and Synphlebotomus (P. martini and P. celiae) together with ten Sergentomyia species in three subgenera were identified. Among Phlebotomus species, P. (An.) rodhaini and P. (Sy.) martini were shown similar abundance with a slight dominance of the former species and P. celiae were the least. Five Sergentomyia species: S. (Sergentomyia.) schewtzi, S. (Se.) bedfordi, and S. (Sintonius) suberecta, S. (Parratomyia.) africana and S. (Se.) antennata were the most common species. A relative increase in population of the three Phlebotomus species were observed during the wet season (March-May) of the year. Fluctuations in sandfly densities were seen in four most common Sergentomyia species during the six month period with highest densities during the dry months (January-February and June) whereas S. suberecta had its peak in wet month (May). A marked habitat preference was observed in all Phlebotomus species collected by both traps. The termite mounds were found to be most preferable habitat for all Phlebotomus as well as for most Sergentomyia species. However, the observation of low densities of all three Phlebotomus during the study period does not seem to explain adequately the occurrence of( VL) in the area. More detailed epidemiological and entomological studies are thus required to reveal the real (VL )situation in the area.Item Studies on the Anopheline Mosquitoes of Metehara and \ Surrounding Areas in Relation to Malaria Transmission(Addis Ababa University, 2001-05) Balkew, Meshesha; Gebre, Teshome(PhD)The ecology and behaviour of Anopheles mosquitoes was studied in four selected sites in the Metehara area, Upper Awash Valley, Eastern Ethiopia. The sites represented two insecticide unsprayed villages (Metehara and Gelcha) and two sprayed villages (the Sugar Estate and Buse). Information on the prevalence of malaria cases was also gathered from the Metehara Sugar Estate Hospital and the East Shoa Malaria Control Sector (Nazareth). The results showed that a total of 24,799 microscopically diagnosed malaria cases out of 68,000 blood samples were registered between July 1999 and September 2000 in the two health service rendering organizations. Plasmodium falciparum and P. vivax were found to be responsible for the disease and occur nearly in equal proportions (52.7% P. falciparum and 47.3% P. vivax ). Larval collections from the different breeding habitats revealed the presence of four species of which Anopheles arabiensis was the predominant followed by. An. pharoensis. Similarly, a total of 3639 adult anophelines representing at least eight species were caught using different methods from July 1999 to September 2000. An. arabiensis was the predominant species, forming 95% of all collections followed by An. pharoensis (3.8%). The density of An. arabiensis resting indoors in the sprayed sites was much lower than the density in the unsprayed sites. Consequently, 18%, 21.3%, 66.1% and 69.4% of An. arabiensis exhibited exophily in Gelcha, Metehara, Buse and the Sugar Estate, respectively. The indoor to outdoor biting ratio of An. arabiensis varied between villages: 0.53 in the Sugar Estate, 1.97 in Buse, 0.75 in Gelcha and 2.12 in Metehara town, showing that the species was more endophagic in Buse and Metehara and more exophagic in Gelcha and the Sugar Estate, * : XI The highest man biting rate of 39.5, was recorded in Metehara town and the lowest 8.4 in Buse. An. pharoensis was mostly an outdoor feeder. Of 864 An. arabiensis and 63 An. pharoensis dissected from human bait collections, the average parous rate was 45.1% and 30.2%, respectively, showing An. arabiensis to be longerlived than An. pharoensis. The sporozoite rate of An. arabiensis was 0.77% in parous and 0.21% in nulliparous population, the overall being 0.46%. Similarly, An. pharoensis had sporozoite rate of 5.3% in parous and 2.3% in nulliparous population, the overall being 3.2%. The biting rhythm of An. arabienisis exhibited two to three peaks of activity before and after midnight . The highest biting density occurred after midnight indoors while variation was observed outdoors. The average daily entomological inoculation rate (EIR) of An. arabiensis was 0.05 while that of An. pharoensis was 0.01. The Human blood index (HBI) of An. arabiensis revealed variation between sites/villages being 1 in Metehara, 0.47 in Gelcha, 0.85 in Buse and 0.93 in the Sugar Estate, the overall being 0.65. The HBI varied also between dwelling conditions of mosquito sampling, being highest in human dwellings (0.78) and lowest in animal shelters (0.13) showing the opportunistic feeding behaviour of An. arabienisis. Clearly, An. arabiensis is the most important vector and An. pharoensis a secondaiy vector of malaria in the Metehara area. Insecticide susceptibility studies in Metehara showed that 30% arid 25% of An. \ arabiensis was resistant to DDT and pennethrin , respectively. The level of DDT and permethrin resistance in An. arabiensis does not seem to be epidemiologically dangerous, but requires frequent monitoring. An. arabiensis was found to be highly susceptible to propoxur (carbamate insecticide) .