Maurice R. Odiere

Anopheles gambiae: historical population decline associated with regional distribution of insecticide-treated bed nets in western Nyanza Province, Kenya

BackgroundHigh coverage of insecticide-treated bed nets in Asembo and low coverage in Seme, two adjacent communities in western Nyanza Province, Kenya; followed by expanded coverage of bed nets in Seme, as the Kenya national malaria programme rolled out; provided a natural experiment for quantification of changes in relative abundance of two primary malaria vectors in this holoendemic region. Both belong to the Anopheles gambiae sensu lato (s.l.) species complex, namely A. gambiae sensu stricto (s.s.) and Anopheles arabiensis. Historically, the former species was proportionately dominant in indoor resting collections of females.MethodsData of the relative abundance of adult A. gambiae s.s. and A. arabiensis sampled from inside houses were obtained from the literature from 1970 to 2002 for sites west of Kisumu, Kenya, to the region of Asembo ca. 50 km from the city. A sampling transect was established from Asembo (where bed net use was high due to presence of a managed bed net distribution programme) eastward to Seme, where no bed net programme was in place. Adults of A. gambiae s.l. were sampled from inside houses along the transect from 2003 to 2009, as were larvae from nearby aquatic habitats, providing data over a nearly 40 year period of the relative abundance of the two species. Relative proportions of A. gambiae s.s. and A. arabiensis were determined for each stage by identifying species by the polymerase chain reaction method. Household bed net ownership was measured with surveys during mosquito collections. Data of blood host choice, parity rate, and infection rate for Plasmodium falciparum in A. gambiae s.s. and A. arabiensis were obtained for a sample from Asembo and Seme from 2005.ResultsAnopheles gambiae s.s. adult females from indoor collections predominated from 1970 to 1998 (ca. 85%). Beginning in 1999, A. gambiae s.s decreased proportionately relative to A. arabiensis, then precipitously declined to rarity coincident with increased bed net ownership as national bed net distribution programmes commenced in 2004 and 2006. By 2009, A. gambiae s.s. comprised proportionately ca. 1% of indoor collections and A. arabiensis 99%. In Seme compared to Asembo in 2003, proportionately more larvae were A. gambiae s.s., larval density was higher, and more larval habitats were occupied. As bed net use rose in Seme, the proportion of A. gambiae larvae declined as well. These trends continued to 2009. Parity and malaria infection rates were lower in both species in Asembo (high bed net use) compared to Seme (low bed net use), but host choice did not vary within species in both communities (predominantly cattle for A. arabiensis, humans for A. gambiae s.s.).ConclusionsA marked decline of the A. gambiae s.s. population occurred as household ownership of bed nets rose in a region of western Kenya over a 10 year period. The increased bed net coverage likely caused a mass effect on the composition of the A. gambiae s.l. species complex, resulting in the observed proportionate increase in A. arabiensis compared to its closely related sibling species, A. gambiae s.s. These observations are important in evaluating the process of regional malaria elimination, which requires sustained vector control as a primary intervention.

Malacological survey and geographical distribution of vector snails for schistosomiasis within informal settlements of Kisumu City, western Kenya.

BackgroundAlthough schistosomiasis is generally considered a rural phenomenon, infections have been reported within urban settings. Based on observations of high prevalence of Schistosoma mansoni infection in schools within the informal settlements of Kisumu City, a follow-up malacological survey incorporating 81 sites within 6 informal settlements of the City was conducted to determine the presence of intermediate host snails and ascertain whether active transmission was occurring within these areas.MethodsSurveyed sites were mapped using a geographical information system. Cercaria shedding was determined from snails and species of snails identified based on shell morphology. Vegetation cover and presence of algal mass at the sites was recorded, and the physico-chemical characteristics of the water including pH and temperature were determined using a pH meter with a glass electrode and a temperature probe.ResultsOut of 1,059 snails collected, 407 (38.4%) were putatively identified as Biomphalaria sudanica, 425 (40.1%) as Biomphalaria pfeifferi and 227 (21.5%) as Bulinus globosus. The spatial distribution of snails was clustered, with few sites accounting for most of the snails. The highest snail abundance was recorded in Nyamasaria (543 snails) followed by Nyalenda B (313 snails). As expected, the mean snail abundance was higher along the lakeshore (18 ± 12 snails) compared to inland sites (dams, rivers and springs) (11 ± 32 snails) (F1, 79 = 38.8, P < 0.0001). Overall, 19 (1.8%) of the snails collected shed schistosome cercariae. Interestingly, the proportion of infected Biomphalaria snails was higher in the inland (2.7%) compared to the lakeshore sites (0.3%) (P = 0.0109). B. sudanica was more abundant in sites along the lakeshore whereas B. pfeifferi and B. globosus were more abundant in the inland sites. Biomphalaria and Bulinus snails were found at 16 and 11 out of the 56 inland sites, respectively.ConclusionsThe high abundance of Biomphalaria and Bulinus spp. as well as observation of field-caught snails shedding cercariae confirmed that besides Lake Victoria, the local risk for schistosomiasis transmission exists within the informal settlements of Kisumu City. Prospective control interventions in these areas need to incorporate focal snail control to complement chemotherapy in reducing transmission.

High prevalence of schistosomiasis in Mbita and its adjacent islands of Lake Victoria, western Kenya

BackgroundIntestinal schistosomiasis continues to be a significant cause of morbidity among communities located around Lake Victoria and on its islands. Although epidemiological surveys have been conducted in other areas bordering the lake in western Kenya, Mbita district and its adjacent islands have never been surveyed, largely due to logistical challenges in accessing these areas. Consequently, there is a paucity of data on prevalence of schistosomiasis and soil-transmitted helminth (STH) infections that are endemic in this region.MethodsThis cross-sectional study determined the prevalence, intensity of infection and geographical distribution of schistosome and STH infections among 4,065 children aged 5–19 years in 84 primary schools in Mbita and nearby islands of Lake Victoria (Mfangano, Ringiti, Rusinga and Takawiri), in western Kenya. Single stool samples were collected and examined for eggs of Schistosoma mansoni and STHs (Hookworms, Ascaris lumbricoides and Trichuris trichiura) using the Kato-Katz technique. Primary schools were mapped using geographical information system data on PDAs and prevalence maps generated using ArcView GIS software.ResultsOverall, 65.6% (95% CI = 64.2-67.1%) of children were infected with one or more helminth species; 12.4% (95% CI = 11.4-13.4%) of children were infected with one or more STH species. Mean school prevalence of S. mansoni infection was 60.5% (95% CI = 59.0-62.0%), hookworms 8.4% (95% CI = 7.6-9.3%), A. lumbricoides 3.3% (95% CI = 2.7-3.8%), and T. trichiura 1.6% (95% CI = 1.2-2.0%). Interestingly, the mean S. mansoni prevalence was 2-fold higher on the islands (82%) compared to the mainland (41%) (z = 5.8755, P < 0.0001). Similarly, intensity of infection was 54% higher on the islands (217.2 ± 99.3) compared to the mainland (141.3 ± 123.7) (z = 3.9374, P < 0.0001). Schools in closest proximity to Lake Victoria had the highest S. mansoni prevalence while prevalence of STHs was more homogenously distributed.ConclusionsThe very high prevalence of schistosomiasis in Mbita and the 4 islands is quite alarming, and indicates an urgent and critical need for control interventions. Findings from this survey indicate the need to implement treatment in remote areas not previously covered by mass drug administration programs.

Geographical distribution of schistosomiasis and soil-transmitted helminths among school children in informal settlements in Kisumu City, Western Kenya

This cross-sectional study determined the prevalence and distribution of schistosome and soil-transmitted helminth (STH) infections among 1,308 children aged 10-18 years in 34 primary schools in 8 informal urban settlements in Kisumu City, western Kenya. Stool samples were collected and examined for eggs of Schistosoma mansoni and STH (Hookworms, Ascaris lumbricoides and Trichuris trichiura) using the Kato-Katz technique. Haematuria was used as a proxy indicator of urinary schistosomiasis. Schools and water bodies were mapped using a geographical information system. Overall, 34% of children were infected with one or more helminth species whereas 16·2% of children were infected with one or more STH species. Schools in closest proximity to Lake Victoria and River Nyamasaria had the highest S. mansoni prevalence while schools with STH were more homogenously distributed. Mean school prevalence of S. mansoni infection was 21% (range=0-69·7%), S. haematobium 3·6% (range=0-12%), hookworms 6·1% (range=0-20%), A. lumbricoides 4·9% (range=0-18·4%), and T. trichiura 7·7% (range=0-18·6%). Helminth-related morbidities were not associated with infection. Our study demonstrates that schistosomiasis and STH are important health priorities among schools in informal settlements of Kisumu City, and highlights the need for routine deworming in similar settings.

Low Levels of Awareness Despite High Prevalence of Schistosomiasis among Communities in Nyalenda Informal Settlement, Kisumu City, Western Kenya

Introduction Intestinal schistosomiasis is widely distributed around Lake Victoria in Kenya where about 16 million people in 56 districts are at risk of the infection with over 9.1 million infected. Its existence in rural settings has been extensively studied compared to urban settings where there is limited information about the disease coupled with low level of awareness. This study therefore assessed community awareness on existence, signs and symptoms, causes, transmission, control and risk factors for contracting schistosomiasis as well as attitudes, health seeking behaviour and environmental antecedents that affect its control so as to identify knowledge gaps that need to be addressed in order to strengthen schistosomiasis control interventions in informal urban settings. Methods The study was carried out in an informal urban settlement where the prevalence of intestinal schistosomiasis was previously reported to be the highest (36%) among the eight informal settlements of Kisumu city. The study adopted cross-sectional design and purposive sampling technique. Eight focus group discussions were conducted with adult community members and eight key informant interviews with opinion leaders. Data was audio recorded transcribed, coded and thematically analyzed using ATLAS.ti version 6 software. Results Most respondents stated having heard about schistosomiasis but very few had the correct knowledge of signs and symptoms, causes, transmission and control of schistosomiasis. However, there was moderate knowledge of risk factors and at high risk groups. Their attitudes towards schistosomiasis and its control were generally indifferent with a general belief that they had no control over their environmental circumstances to reduce transmission. Discussion/Conclusion Although schistosomiasis was prevalent in the study area, majority of the people in the community had low awareness. This study, therefore, stresses the need for health education to raise communitys awareness on schistosomiasis in such settings in order to augment prevention, control and elimination efforts.

Faecal contamination of public water sources in informal settlements of Kisumu City, western Kenya

High levels of environmental contamination, often associated with improper waste and excreta management, are widespread among informal settlements within urban areas in developing countries. We determined the level of faecal contamination in domestic water sources and evaluated the potential contribution of these water sources to intestinal helminthiases in seven informal settlements of Kisumu City, western Kenya. Membrane filtration technique was used for enumeration of total and faecal (Escherichia coli) coliform bacteria in water samples collected from dams, rivers, springs and wells. Out of the 80 water sources sampled, 76 (95%) were highly contaminated with E coli. All water samples from unprotected wells (26) and 92.6% of samples from protected wells (25) were positive for E. coli. The highest and lowest E. coli densities were observed in samples from dams (3,800 ± 1,807 coliforms per 100 ml) and boreholes (419 ± 223 coliforms per 100 ml), respectively (p = 0.0321). Distance from pit latrines was negatively associated with E. coli coliform density for wells (r = -0.34, n = 53, p = 0.0142). Untreated well-water may not be suitable for human consumption, and its continued use constitutes a major health risk for the inhabitants of these informal settlements.

Tetanus Immunity Gaps in Children 5–14 Years and Men ≥ 15 Years of Age Revealed by Integrated Disease Serosurveillance in Kenya, Tanzania, and Mozambique

Recent tetanus cases associated with male circumcision in Eastern and Southern Africa (ESA) prompted an examination of tetanus immunity by age and sex using multiplex serologic data from community surveys in three ESA countries during 2012-2013. Tetanus seroprotection was lower among children 5-14 years versus 1-4 years of age in Kenya (66% versus 90%) and Tanzania (66% versus 89%), but not in Mozambique (91% versus 88%), where children receive two booster doses in school. Among males ≥ 15 years of age, tetanus seroprotection was lower than females in Kenya (45% versus 96%), Tanzania (28% versus 94%), and Mozambique (64% versus 90%). Tetanus immunity from infant vaccination doses wanes over time, and only women of reproductive age routinely receive booster doses. To prevent immunity gaps in older children, adolescents, and adult men, a life-course vaccination strategy is needed to provide the three recommended tetanus booster doses.

Effect of Repeated Anthelminthic Treatment on Malaria in School Children in Kenya: A Randomized, Open-Label, Equivalence Trial

Background. School children living in the tropics are often concurrently infected with plasmodium and helminth parasites. It has been hypothesized that immune responses evoked by helminths may modify malaria-specific immune responses and increase the risk of malaria. Methods. We performed a randomized, open-label, equivalence trial among 2436 school children in western Kenya. Eligible children were randomized to receive either 4 repeated doses or a single dose of albendazole and were followed up during 13 months to assess the incidence of clinical malaria. Secondary outcomes were Plasmodium prevalence and density, assessed by repeat cross-sectional surveys over 15 months. Analysis was conducted on an intention-to-treat basis with a prespecified equivalence range of 20%. Results. During 13 months of follow-up, the incidence rate of malaria was 0.27 episodes/person-year in the repeated treatment group and 0.26 episodes/person-year in the annual treatment group (incidence difference, 0.01; 95% confidence interval, −.03 to .06). The prevalence and density of malaria parasitemia did not differ by treatment group at any of the cross-sectional surveys. Conclusions. Our findings suggest that repeated deworming does not alter risks of clinical malaria or malaria parasitemia among school children and that school-based deworming in Africa may have no adverse consequences for malaria. Clinical Trials Registration. NCT01658774.

Experiences and perspectives of community health workers from implementing treatment for schistosomiasis using the community directed intervention strategy in an informal settlement in Kisumu City, western Kenya

BackgroundThe Community Directed Intervention (CDI) strategy has been used to conduct various health interventions in Africa, including control of Neglected Tropical Diseases (NTDs). Although the CDI approach has shown good results in the control of onchocerciasis and lymphatic filariasis with respect to treatment coverage using community drug distributors, its utility in the control of schistosomiasis among urban poor is yet to be established. Using a longitudinal qualitative study, we explored the experiences, opportunities, challenges as well as recommendations of Community Health Workers (CHWs) after participation in annual mass drug administration (MDA) activities for schistosomiasis using the CDI approach in an urban setting.MethodsUnstructured open-ended group discussions were conducted with CHWs after completion of annual MDA activities. Narratives were obtained from CHWs using a digital audio recorder during the group discussions, transcribed verbatim and translated into English where applicable. Thematic decomposition of data was done using ATLAS.ti. software, and themes explored using the principle of interpretative phenomenological analysis (IPA).ResultsFrom the perspective of the CHWs, opportunities for implementing CDI in urban settings, included the presence of CHWs, their supervisory structures and their knowledge of intervention areas, and opportunity to integrate MDA with other health interventions. Several challenges were mentioned with regards to implementing MDA using the CDI strategy among them lack of incentives, fear of side effects, misconceptions regarding treatment and mistrust, difficulties working in unsanitary environmental conditions, insecurity, and insufficient time. A key recommendation in promoting more effective MDA using the CDI approach was allocation of more time to the exercise.ConclusionFindings from this study support the feasibility of using CDI for implementing MDA for schistosomiasis in informal settlements of urban areas. Extensive community sensitization and provision of incentives may help address the aforementioned challenges associated with implementing MDA using the CDI strategy. Opportunities highlighted in this study may be of value to other programmes that may be considering the adoption of the CDI strategy for rolling out interventions in the urban setting.

A Persistent Hotspot of Schistosoma mansoni Infection in a Five-Year Randomized Trial of Praziquantel Preventative Chemotherapy Strategies

During a trial of preventive chemotherapy strategies, a hotspot of Schistosoma mansoni infection was found. Significant differences between hotspot and nonhotspot villages were found after 1 year. Villages meeting endpoints at year 5 were predicted from prior data with accuracy.