Impact of Drought on the Spatial Pattern of Transmission of Sehistosoma haematobium in Coastal Kenya

We analyzed temporal changes in spatial patterns of active Schistosoma haematobium infection in different age groups and associated them with ponds infested with Bulinus snails. A major drought between 2001 and 2009 resulted in drying of ponds that were known sources of infection, and we detected very few or no snails in ponds that were infested in the past. The household-level spatial pattern of infection for children of various age groups in 2009 was contrasted with historical data from 2000. The significant local clustering of high- and low-infection levels among school-aged children that occurred in 2000 was absent in 2009. We attribute the disappearance of significant clustering around historical transmission hot spots to a decade-long drought in our study area. The implications of extreme weather and climate conditions on risk and transmission of S. haematobium and their relevance to control strategies are discussed. Copyright © 2011 by The American Society of Tropical Medicine and Hygiene

The risks of malariainfection in Kenya in 2009

BACKGROUND: To design an effective strategy for the control of malaria requires a map of infection and disease risks to select appropriate suites of interventions. Advances in model based geo-statistics and malaria parasite prevalence data assemblies provide unique opportunities to redefine national Plasmodium falciparum risk distributions. Here we present a new map of malaria risk for Kenya in 2009. METHODS: Plasmodium falciparum parasite rate data were assembled from cross-sectional community based surveys undertaken from 1975 to 2009. Details recorded for each survey included the month and year of the survey, sample size, positivity and the age ranges of sampled population. Data were corrected to a standard age-range of two to less than 10 years (PfPR2-10) and each survey location was geo-positioned using national and on-line digital settlement maps. Ecological and climate covariates were matched to each PfPR2-10 survey location and examined separately and in combination for relationships to PfPR2-10. Significant covariates were then included in a Bayesian geostatistical spatial-temporal framework to predict continuous and categorical maps of mean PfPR2-10 at a 1 x 1 km resolution across Kenya for the year 2009. Model hold-out data were used to test the predictive accuracy of the mapped surfaces and distributions of the posterior uncertainty were mapped. RESULTS: A total of 2,682 estimates of PfPR2-10 from surveys undertaken at 2,095 sites between 1975 and 2009 were selected for inclusion in the geo-statistical modeling. The covariates selected for prediction were urbanization; maximum temperature; precipitation; enhanced vegetation index; and distance to main water bodies. The final Bayesian geo-statistical model had a high predictive accuracy with mean error of -0.15% PfPR2-10; mean absolute error of 0.38% PfPR2-10; and linear correlation between observed and predicted PfPR2-10 of 0.81. The majority of Kenya's 2009 population (35.2 million, 86.3%) reside in areas where predicted PfPR2-10 is less than 5%; conversely in 2009 only 4.3 million people (10.6%) lived in areas where PfPR2-10 was predicted to be > or =40% and were largely located around the shores of Lake Victoria. CONCLUSION: Model based geo-statistical methods can be used to interpolate malaria risks in Kenya with precision and our model shows that the majority of Kenyans live in areas of very low P. falciparum risk. As malaria interventions go to scale effectively tracking epidemiological changes of risk demands a rigorous effort to document infection prevalence in time and space to remodel risks and redefine intervention priorities over the next 10-15 years

Age-Stratified Profiles of Serum IL-6, IL-10, and TNF-α Cytokines Among Kenyan Children with Schistosoma haematobium, Plasmodium falciparum, and Other Chronic Parasitic Co-Infections.

In a study of children having polyparasitic infections in a Schistosoma haematobium-endemic area, we examined the hypothesis that S. haematobium-positive children, compared with S. haematobium-negative children (anti-soluble worm antigen preparation [SWAP] negative and egg negative) have increased systemic production of pro-inflammatory cytokines (interleukin [IL]-6, tumor necrosis factor [TNF]-α) and decreased down-regulatory IL-10. A total of 804 children, 2-19 years of age, were surveyed between July and December 2009 and tested for S. haematobium, Plasmodium falciparum, filariasis, and soil-transmitted helminth infections. Plasma levels of IL-6, TNF-α, and IL-10 were compared for S. haematobium-positive and S. haematobium-negative children, adjusting for malaria, filaria, and hookworm co-infections, and for nutritional status, age group, sex, and geographic location. IL-10 was significantly elevated among children infected with S. haematobium, showing bimodal peaks in 7-8 and 13-14 years age groups. IL-10 was also higher among children who were acutely malnourished, whereas IL-10 levels were lower in the presence of S. haematobium-filaria co-infection. After adjustment for co-factors, IL-6 was significantly elevated among children of 5-6 years and among those with P. falciparum infection. Lower levels of IL-6 were found in malaria-hookworm co-infection. High levels of TNF-α were found in children aged 11-12 years regardless of infection status. In addition, village of residence was a strong predictor of IL-6 and IL-10 plasma levels. In adolescent children infected with S. haematobium, there is an associated elevation in circulating IL-10 that may reduce the risk of later morbidity. Although we did not find a direct link between S. haematobium infection and circulating pro-inflammatory IL-6 and TNF-α levels, future T-cell stimulation studies may provide more conclusive linkages between infection and cytokine responses in settings that are endemic for multiple parasites and multiple co-infections

An Outbreak of Rift Valley Fever in Northeastern Kenya, 1997-98

In December 1997, 170 hemorrhagic fever-associated deaths were reported in Carissa District, Kenya. Laboratory testing identified evidence of acute Rift Valley fever virus (RVFV). Of the 171 persons enrolled in a cross-sectional study, 31(18%) were anti-RVFV immunoglobulin (Ig) M positive. An age-adjusted IgM antibody prevalence of 14% was estimated for the district. We estimate approximately 27,500 infections occurred in Garissa District, making this the largest recorded outbreak of RVFV in East Africa. In multivariate analysis, contact with sheep body fluids and sheltering livestock in one’s home were significantly associated with infection. Direct contact with animals, particularly contact with sheep body fluids, was the most important modifiable risk factor for RVFV infection. Public education during epizootics may reduce human illness and deaths associated with future outbreaks

Evaluation of the health-related quality of life of children in Schistosoma haematobium-endemic communities in Kenya: a cross-sectional study.

BACKGROUND: Schistosomiasis remains a global public health challenge, with 93% of the ~237 million infections occurring in sub-Saharan Africa. Though rarely fatal, its recurring nature makes it a lifetime disorder with significant chronic health burdens. Much of its negative health impact is due to non-specific conditions such as anemia, undernutrition, pain, exercise intolerance, poor school performance, and decreased work capacity. This makes it difficult to estimate the disease burden specific to schistosomiasis using the standard DALY metric. METHODOLOGY/PRINCIPAL FINDINGS: In our study, we used Pediatric Quality of Life Inventory (PedsQL), a modular instrument available for ages 2-18 years, to assess health-related quality of life (HrQoL) among children living in a Schistosoma haematobium-endemic area in coastal Kenya. The PedsQL questionnaires were administered by interview to children aged 5-18 years (and their parents) in five villages spread across three districts. HrQoL (total score) was significantly lower in villages with high prevalence of S. haematobium (-4.0%, p<0.001) and among the lower socioeconomic quartiles (-2.0%, p<0.05). A greater effect was seen in the psychosocial scales as compared to the physical function scale. In moderate prevalence villages, detection of any parasite eggs in the urine was associated with a significant 2.1% (p<0.05) reduction in total score. The PedsQL reliabilities were generally high (Cronbach alphas ≥0.70), floor effects were acceptable, and identification of children from low socioeconomic standing was valid. CONCLUSIONS/SIGNIFICANCE: We conclude that exposure to urogenital schistosomiasis is associated with a 2-4% reduction in HrQoL. Further research is warranted to determine the reproducibility and responsiveness properties of QoL testing in relation to schistosomiasis. We anticipate that a case definition based on more sensitive parasitological diagnosis among younger children will better define the immediate and long-term HrQoL impact of Schistosoma infection

Interepidemic Rift Valley Fever Virus Seropositivity, Northeastern Kenya

Exposure is associated with long-term retinal disease and is most common in rural settings among older men who have contact with aborting animals

Postepidemic Analysis of Rift Valley Fever Virus Transmission in Northeastern Kenya: A Village Cohort Study

RVFV infection causes significant disease in both human and animal populations, resulting in significant agricultural, economic and public health consequences. We conducted a cohort study on residents of a high-risk area to measure human anti-RVFV seroprevalence, to identify risk factors, and to estimate the durability of prior RVFV immunity. One hundred two individuals tested for RVFV exposure before the 2006–2007 RVF outbreak were restudied to determine interval anti-RVFV seroconversion and persistence of humoral immunity since 2006. Ninety-two additional subjects were enrolled from randomly selected households to help identify risk factors for current seropositivity. Seroprevalence in the region was high (23%). 1/85 at-risk individuals restudied in the follow-up cohort had seroconverted since early 2006. 29% of newly tested individuals were seropositive. After adjustment in multivariable logistic models, age, village, and drinking raw milk were significantly associated with RVFV seropositivity. Visual impairment (defined as ≤20/80) was much more likely in the RVFV-seropositive group. Among those with previous exposure, RVFV titers remained at protective levels (>1∶40) for more than 3 years. This study highlights the high seroprevalence among Northeastern Kenyans and the ongoing surge in seroprevalence with each RVF outbreak

Impact of insecticide-treated bed nets on malaria transmission indices on the south coast of Kenya

<p>Abstract</p> <p>Background</p> <p>Besides significantly reducing malaria vector densities, prolonged usage of bed nets has been linked to decline of <it>Anopheles gambiae </it>s.s. relative to <it>Anopheles arabiensis</it>, changes in host feeding preference of malaria vectors, and behavioural shifts to exophagy (outdoor biting) for the two important malaria vectors in Africa, <it>An. gambiae </it>s.l. and <it>Anopheles funestus</it>. In southern coastal Kenya, bed net use was negligible in 1997-1998 when <it>Anopheles funestus </it>and <it>An. gambiae </it>s.s. were the primary malaria vectors, with <it>An. arabiensis </it>and <it>Anopheles merus </it>playing a secondary role. Since 2001, bed net use has increased progressively and reached high levels by 2009-2010 with corresponding decline in malaria transmission.</p> <p>Methods</p> <p>To evaluate the impact of the substantial increase in household bed net use within this area on vector density, vector composition, and human-vector contact, indoor and outdoor resting mosquitoes were collected in the same region during 2009-2010 using pyrethrum spray catches and clay pots for indoor and outdoor collections respectively. Information on bed net use per sleeping spaces and factors influencing mosquito density were determined in the same houses using Poisson regression analysis. Species distribution was determined, and number of mosquitoes per house, human-biting rates (HBR), and entomological inoculation rate (EIR) were compared to those reported for the same area during 1997-1998, when bed net coverage had been minimal.</p> <p>Results</p> <p>Compared to 1997-1998, a significant decline in the relative proportion of <it>An. gambiae </it>s.s. among collected mosquitoes was noted, coupled with a proportionate increase of <it>An. arabiensis</it>. Following > 5 years of 60-86% coverage with bed nets, the density, human biting rate and EIR of indoor resting mosquitoes were reduced by more than 92% for <it>An. funestus </it>and by 75% for <it>An. gambiae </it>s.l. In addition, the host feeding choice of both vectors shifted more toward non-human vertebrates. Besides bed net use, malaria vector abundance was also influenced by type of house construction and according to whether one sleeps on a bed or a mat (both of these are associated with household wealth). Mosquito density was positively associated with presence of domestic animals.</p> <p>Conclusions</p> <p>These entomological indices indicate a much reduced human biting rate and a diminishing role of <it>An. gambiae </it>s.s. in malaria transmission following high bed net coverage. While increasing bed net coverage beyond the current levels may not significantly reduce the transmission potential of <it>An. arabiensis</it>, it is anticipated that increasing or at least sustaining high bed net coverage will result in a diminished role for <it>An. funestus </it>in malaria transmission.</p

Age-targeted chemotherapy for control of urinary schistosomiais in endemic populations

Severity of urinary tract morbidity increases with intensity and duration of Schistosoma haematobium infection. We assessed the ability of yearly drug therapy to control infection intensity and reduce S. haematobium-associated disease in children 5-21 years old in an endemic area of Kenya. In year I, therapy resulted in reduced prevalence (66% to 22%, P < 0.001) and intensity of S. haematobium infection (20 to 2 eggs/10 mL, urine), with corresponding reductions in the prevalence of hematuria (52% to 19%, P < 0.001). There was not, however, a significant first-year effect on prevalence of urinary tract abnormalities detected by ultrasound. Repeat therapy in years 2 and 3 resulted in significant regression of hydronephrosis and bladder abnormalities (41% to 6% prevalence, P< 0.001), and further reductions in proteinuria. Repeat age-targeted therapy was associated with decreased prevalence of infection among young children (< 5yr) entering into the target age group. Two years after discontinuation of therapy, intensity of S. haematobium infection and ultrasound abnormalities remained suppressed, but hematuria prevalence began to increase (to 33% in 1989). Reinstitution of annual therapy in 1989 and 1990 reversed this trends. We conclude that annual oral therapy provides an effective strategy for control of morbidity due to S. haematobium on population basis, both through regression of disease in treated individuals, and prevention of infection in untreated subjects