Browsing by Author "Okoth, S. O."
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Item Diurnal Activity of Allopatric Populations of Glossinapallidipes and Hosts and their Implications on Risk of Transmission of Sleeping Sickness in Kenya(2007) Okoth, S. O.; Kokwaro, E. D.; Kiragu, J. M.; Murilla, A. G.; Kenya Trypanosomiasis Research InstituteVector-host contact IS a key epidemiological parameter in vector transmitted parasitic infections the interaction between vectors and hosts IS influenced by both environmental and endogenous factors that regulate their diurnal activity. In this study, effects of temperature, relative humidity and lax on the activity on tsetse flies and hosts were evaluated in two a110patnc populations of G. pallidipes to estimate vector-host contact and risk of disease transmission within the dry and wet seasons Results showed that vector activity was majority influenced by temperature and relative humidity and the activity pattern was sensitive to seasons. Host movement significantly influenced vector movement in both dry and wet seasons at Nguruman, but only to a limited extent during the wet season at Busia. Host movement correlated positively with vector activity at high host densities while there was no definite correlation at low host densities. Vector-host contact was independent of prevailing weather conditions and seasons but was explained largely by random variability ascribable to innate spontaneous circadian rhythm of the vectors and the hosts. This implies that management of transmission risk in these two areas would largely depend on avoidance of contact between the vectors and hosts. This would require strategic livestock grazing patterns that is out-of-phase with peak vector activity periods to minimize contact.Item Glossina pallidipes and Host Interactions: Implications of Host Preference on Transmission Risk of Rhodesian Sleeping Sickness in Kenya(2007) Okoth, S. O.; Kokwaro, E. D.; Kiragu, J. M.; Murilla, A. G.; Kenya Trypanosomiasis Research InstituteHost preference by tsetse flies, tsetse-host interaction and host diversity and abundance were evaluated in relation to transmission risk of Rhodesian sleeping sickness in two tsetse subpopulations in Kenya. Bovidae provided the highest proportion of blood meals (58%) to tsetse at Busia while that from humans was 4.9%. Contrastingly, the highest proportion of blood meals at Ngururnan (35%) was from Warthogs, while no blood meals were obtained from humans at Ngururnan. The bushbuck Tragelaphus criptus, Pallas, an important reservoir host of T.h. rhodesiense, provided 2.5% of bleeds meals at Busia and 5% of blood meals at Nguruman Hosts were more diverse and abundant at Ngururnan than Busia. Host activity did not significantly influence vector activity at both Busia and Nguruman during the dry season. However, there was a significant influence of host activity on vector activity (F IOII =7.27; p<0.022) at Nguruman during the wet season. The diversity and abundance of reservoir hosts at Nguruman is a potential risk in maintenance of sleeping sickness, unlike at Busia where the reservoir hosts are fewer and less diverse. The occurrence of Bovidae, especially livestock, as the major alternative source of blood meal at Busia pose higher risk to humans as the livestock are constantly in close contact with humans Risk control would therefore aim at contact avoidance and sustained suppression of vector population.Item Identification of trypanosomes in Glossina pazzidipes and G. longipennis in Kenya(2004) Njiru, Z. K.; Makumi, J. N.; Okoth, S. O.; Ndungu, J. M.; gibson, C. W.; Kenya Trypanosomiasis Research Institute (KETRI), P.O. Box 362, Kikuyu, Kenya School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK Division of Health Sciences, School of Veterinary and Biomedical Sciences, Murdoch University, South Street, WA 6150, AustraliaThe polymerase chain reaction (PCR) was used to identify trypanosomes in Glossina pallidipes and C. longipennis caught in Kenya. Of 3826 flies dissected, 188 (4.9%) were parasitologically positive overall. The infection rate in C. pallidipes was 5.7% (187 of 3301 flies), but only one of 525 C. longipennis was infected (infection rate 0.2%). There was a higher infection rate in female C. pallidipes flies than male flies (X2 = 18.5, P < 0.001) and odds ratio = 2.5 (95% 1.6, 3.7). The infected flies were analysed by PCR using 10 sets of primers specific for species and subgroups within the subgenera Nannomonas, Trypanozoon and Duttonella. Of 188 parasitologically positive samples, PCR identified 137 (72.9%), leaving 51 (27.1 %) non-identified. We recorded infection rates of 47.2% for Trypanosoma congolense savannah, forest and kilifi subgroups, 20.9% for T. simiaelT. Simiae tsavo/T. godfreyi, 14.9% for T. brucei ssp. and 13.8% for T. vivax. Thirty-nine (26.7%) flies had mixed infections, with a minor association between T. congolense savannah/to simiae tsavo/T. godfreyi (X2 = 6.93, dJ. = I, P < 0.05). The relative proportion of each trypanosome species or subgroup varied between fly belts with T. congolense (all subgroups) being the most abundant and T. godfreyi the least. Statistical analysis showed that dissection method and PCR test classified infections independently (X2 = 10.5, d.f. = I, P < 0.05 and K = 0.38). This study shows that pathogenic trypanosomes are widespread in all sampled testes fly belts with C. pallidipes as the main vector. Further, PCR test is more reliable in detecting and identifying trypanosomes than dissection method.Item Transmission Dynamics And Epidemiology Of Rhodesian Sleeping Sickness In Allopatric Populations Of Glossina Pallidipes Of Kenya(Sylvance Okeyo Okoth, 2007) Okoth, S. O.Trypanosoma brucei rhodesiense causes rhodesian sleeping sickness in humans. The disease is transmitted by tsetse flies and the distribution of the disease is highly localised to traditional foci. In Kenya, despite widespread distribution of Glossina pallidipes, rhodesian-sleeping sickness is only restricted to western parts of the country. Factors restricting disease distribution to traditional foci are not well understood. A comparative assessment of transmission dynamics and epidemiology of the disease was carried out in two G. pallidipes subpopulations of Kenya in an attempt to understand causes of the focalized distribution. Entomological, socio-economic, cultural and epidemiological risk indicators were studied. Results showed that tsetse flies from the Busia subpopulation had higher survival, longevity, and susceptibility and transmission success than those from Nguruman subpopulation. Vector-host contact in both areas did not depend on prevailing weather conditions and, the influence of host movement on vector activity only became important at high host densities. Bovidae and suids were the most preferred hosts of G. pallidipes at Busia and Nguruman respectively. Livestock keeping was a higher risk activity than crop farming in both areas and, while women were more exposed by cultural activities at Busia, men were the most exposed by the same at Nguruman. Land use patterns showed that tsetse habitats have been significantly reduced by economic activities at Busia than Nguruman. Transmission risk at Nguruman was high during the dry season while that at Busia was high during the wet season. Although survival rates of the two subpopulations were similar, vector-host contact, teneral density and overall transmission risk were higher among the Busia subpopulation than the Nguruman subpopulation. Transmission risk projections showed that with increased contact, Nguruman subpopulation would pose significantly higher transmission risk than Busia subpopulation. The risk would however be reduced slightly by suppressed fly density but significantly by low teneral density. Results of this study therefore indicated significant differences in human-fly contact and in vectorial capacity of the two subpopulations. The differences sufficiently explain current epidemiological variations in disease occurrence in the two areas. Management of transmission risk would therefore require sustained suppression of vector population and avoidance of vector-host contact through strategic livestock grazing patterns that is out-of-phase with peak vector activity periods within respective seasons.
