Spatial and temporal dynamics of malaria transmission in rural western Kenya

ABSTRACT: BACKGROUND: Understanding the impact of reducing Plasmodium falciparum malaria transmission requires estimates of the relationship between health outcomes and exposure to infectious mosquitoes. However, measures of exposure such as mosquito density and entomological inoculation rate (EIR) are generally aggregated over large areas and time periods, biasing the outcome-exposure relationship. There are few studies examining the extent and drivers of local variation in malaria exposure in endemic areas. METHODS: We describe the spatio-temporal dynamics of malaria transmission intensity measured by mosquito density and EIR in the KEMRI/CDC health and demographic surveillance system using entomological data collected during 2002-2004. Geostatistical zero inflated binomial and negative binomial models were applied to obtain location specific (house) estimates of sporozoite rates and mosquito densities respectively. Model-based predictions were multiplied to estimate the spatial pattern of annual entomological inoculation rate, a measure of the number of infective bites a person receive per unit of time. The models included environmental and climatic predictors extracted from satellite data, harmonic seasonal trends and parameters describing space-time correlation. RESULTS: Anopheles gambiae s.l was the main vector species accounting for 86% (n=2309) of the total collected mosquitoes with the remainder being Anopheles funestus. Sixty eight percent (757/1110) of the surveyed houses had no mosquitoes. Distance to water bodies, vegetation and day temperature were significantly associated with mosquito density. Overall annual point estimates of EIR were 6.7, 9.3 and 9.6 infectious bites per annum for 2002, 2003 and 2004 respectively. Monthly mosquito density and EIR varied over the study period peaking in May during the wet season. The predicted and observed densities and EIR showed a strong seasonal and spatial pattern over the study area. CONCLUSIONS: Spatio-temporal maps of malaria transmission intensity obtained in this study are not only useful in understanding variability in malaria epidemiology over small areas but also provides a high resolution exposure surface that can be used to analyse the impact of malaria exposure on mortalit

Estimation of the national disease burden of influenza-associated severe acute respiratory illness in Kenya and Guatemala : a novel methodology

Background: Knowing the national disease burden of severe influenza in low-income countries can inform policy decisions around influenza treatment and prevention. We present a novel methodology using locally generated data for estimating this burden. Methods and Findings: This method begins with calculating the hospitalized severe acute respiratory illness (SARI) incidence for children <5 years old and persons ≥5 years old from population-based surveillance in one province. This base rate of SARI is then adjusted for each province based on the prevalence of risk factors and healthcare-seeking behavior. The percentage of SARI with influenza virus detected is determined from provincial-level sentinel surveillance and applied to the adjusted provincial rates of hospitalized SARI. Healthcare-seeking data from healthcare utilization surveys is used to estimate non-hospitalized influenza-associated SARI. Rates of hospitalized and non-hospitalized influenza-associated SARI are applied to census data to calculate the national number of cases. The method was field-tested in Kenya, and validated in Guatemala, using data from August 2009–July 2011. In Kenya (2009 population 38.6 million persons), the annual number of hospitalized influenza-associated SARI cases ranged from 17,129–27,659 for children <5 years old (2.9–4.7 per 1,000 persons) and 6,882–7,836 for persons ≥5 years old (0.21–0.24 per 1,000 persons), depending on year and base rate used. In Guatemala (2011 population 14.7 million persons), the annual number of hospitalized cases of influenza-associated pneumonia ranged from 1,065–2,259 (0.5–1.0 per 1,000 persons) among children <5 years old and 779–2,252 cases (0.1–0.2 per 1,000 persons) for persons ≥5 years old, depending on year and base rate used. In both countries, the number of non-hospitalized influenza-associated cases was several-fold higher than the hospitalized cases. Conclusions: Influenza virus was associated with a substantial amount of severe disease in Kenya and Guatemala. This method can be performed in most low and lower-middle income countries

Genomic signatures of population decline in the malaria mosquito Anopheles gambiae

Population genomic features such as nucleotide diversity and linkage disequilibrium are expected to be strongly shaped by changes in population size, and might therefore be useful for monitoring the success of a control campaign. In the Kilifi district of Kenya, there has been a marked decline in the abundance of the malaria vector Anopheles gambiae subsequent to the rollout of insecticide-treated bed nets. To investigate whether this decline left a detectable population genomic signature, simulations were performed to compare the effect of population crashes on nucleotide diversity, Tajima's D, and linkage disequilibrium (as measured by the population recombination parameter ρ). Linkage disequilibrium and ρ were estimated for An. gambiae from Kilifi, and compared them to values for Anopheles arabiensis and Anopheles merus at the same location, and for An. gambiae in a location 200 km from Kilifi. In the first simulations ρ changed more rapidly after a population crash than the other statistics, and therefore is a more sensitive indicator of recent population decline. In the empirical data, linkage disequilibrium extends 100-1000 times further, and ρ is 100-1000 times smaller, for the Kilifi population of An. gambiae than for any of the other populations. There were also significant runs of homozygosity in many of the individual An. gambiae mosquitoes from Kilifi. These results support the hypothesis that the recent decline in An. gambiae was driven by the rollout of bed nets. Measuring population genomic parameters in a small sample of individuals before, during and after vector or pest control may be a valuable method of tracking the effectiveness of interventions

Wash durability and optimal drying regimen of four brands of long-lasting insecticide-treated nets after repeated washing under tropical conditions

<p>Abstract</p> <p>Background</p> <p>The current study was undertaken to determine the optimal wash-drying regimen and the effects of different washing procedures on the efficacy, and durability of four brands of newly introduced long-lasting insecticide-treated nets (LLINs) under tropical conditions.</p> <p>Methods</p> <p>In the current study, the following four LLINs were tested: Olyset^®, PermaNet ^®2.0, BASF^®and TNT^®. Nets were divided into three sets; one set was washed by hand rubbing and air-dried either hanging or spread on the ground in direct sunlight or hanging or spread on the ground under the shade. A second set was washed using the WHO protocol (machine) and the third set was washed by beating the nets on rocks. The biological activities of the nets were assessed by a three-minute bioassay cone test and the residual insecticide contents were determined using high performance liquid chromatography (HPLC) procedure.</p> <p>Results</p> <p>Nets that were dried hanging under the shade retained more insecticide, 62.5% and recorded higher mortality compared to nets which were dried lying on the ground in direct sunlight 58.8%, nets dried under the shade spread on the ground 56.3%, and 57.8% for nets dried hanging in direct sunlight. It was also observed that nets washed by the standard WHO protocol, retained more insecticide and were more effective in killing mosquitoes compared to nets washed by local methods of hand rubbing and beating on rocks. There were significant differences between drying regimens (p < 0.0001) and between washing procedures (p < 0.001) respectively. However, the effect of net type was statistically insignificant. The statistical differences on individual nets were also compared, for PermaNet^®and TNT there were no significant differences observed between the four drying regimens (<it>p </it>= 0.7944 and 0.4703) respectively). For BASF and Olyset, the differences were significant (p < 0.001 and p > 0.0001).</p> <p>Conclusion</p> <p>The results of this study suggest that washing and drying regimen influence the insecticidal activity of LLINs. The standard WHOPES washing protocol underestimates the amount of insecticide washed from LLINs compared to the abrasive washing procedures that are used in the field. This suggests that there is need to educate net users to adopt a more gentle washing procedure while handling LLINs. The education should accompany net distribution campaigns.</p

Malaria mortality in Africa and Asia: evidence from INDEPTH health and demographic surveillance system sites.

BACKGROUND: Malaria continues to be a major cause of infectious disease mortality in tropical regions. However, deaths from malaria are most often not individually documented, and as a result overall understanding of malaria epidemiology is inadequate. INDEPTH Network members maintain population surveillance in Health and Demographic Surveillance System sites across Africa and Asia, in which individual deaths are followed up with verbal autopsies. OBJECTIVE: To present patterns of malaria mortality determined by verbal autopsy from INDEPTH sites across Africa and Asia, comparing these findings with other relevant information on malaria in the same regions. DESIGN: From a database covering 111,910 deaths over 12,204,043 person-years in 22 sites, in which verbal autopsy data were handled according to the WHO 2012 standard and processed using the InterVA-4 model, over 6,000 deaths were attributed to malaria. The overall period covered was 1992-2012, but two-thirds of the observations related to 2006-2012. These deaths were analysed by site, time period, age group and sex to investigate epidemiological differences in malaria mortality. RESULTS: Rates of malaria mortality varied by 1:10,000 across the sites, with generally low rates in Asia (one site recording no malaria deaths over 0.5 million person-years) and some of the highest rates in West Africa (Nouna, Burkina Faso: 2.47 per 1,000 person-years). Childhood malaria mortality rates were strongly correlated with Malaria Atlas Project estimates of Plasmodium falciparum parasite rates for the same locations. Adult malaria mortality rates, while lower than corresponding childhood rates, were strongly correlated with childhood rates at the site level. CONCLUSIONS: The wide variations observed in malaria mortality, which were nevertheless consistent with various other estimates, suggest that population-based registration of deaths using verbal autopsy is a useful approach to understanding the details of malaria epidemiology

Reproductive health issues in rural Western Kenya

<p>Abstract</p> <p>Background</p> <p>We describe reproductive health issues among pregnant women in a rural area of Kenya with a high coverage of insecticide treated nets (ITNs) and high prevalence of HIV (15%).</p> <p>Methods</p> <p>We conducted a community-based cross-sectional survey among rural pregnant women in western Kenya. A medical, obstetric and reproductive history was obtained. Blood was obtained for a malaria smear and haemoglobin level, and stool was examined for geohelminths. Height and weight were measured.</p> <p>Results</p> <p>Of 673 participants, 87% were multigravidae and 50% were in their third trimester; 41% had started antenatal clinic visits at the time of interview and 69% reported ITN-use. Malaria parasitemia and anaemia (haemoglobin < 11 g/dl) were detected among 36% and 53% of the women, respectively. Geohelminth infections were detected among 76% of the 390 women who gave a stool sample. Twenty percent of women were underweight, and sixteen percent reported symptoms of herpes zoster or oral thrush in the last two months. Nineteen percent of all women reported using a contraceptive method to delay or prevent pregnancy before the current pregnancy (injection 10%, pill 8%, condom 0.4%). Twenty-three percent of multigravidae conceived their current pregnancy within a year of the previous pregnancy. More than half of the multigravidae (55%) had ever lost a live born child and 21% had lost their last singleton live born child at the time of interview.</p> <p>Conclusion</p> <p>In this rural area with a high HIV prevalence, the reported use of condoms before pregnancy was extremely low. Pregnancy health was not optimal with a high prevalence of malaria, geohelminth infections, anaemia and underweight. Chances of losing a child after birth were high. Multiple interventions are needed to improve reproductive health in this area.</p

Plasmodium falciparum Spatial Analysis, Western Kenya Highlands

Parasite transmission is intense in the highlands, and these areas are vulnerable to epidemics

Entomological Surveillance of Behavioural Resilience and Resistance in Residual Malaria Vector Populations.

The most potent malaria vectors rely heavily upon human blood so they are vulnerable to attack with insecticide-treated nets (ITNs) and indoor residual spraying (IRS) within houses. Mosquito taxa that can avoid feeding or resting indoors, or by obtaining blood from animals, mediate a growing proportion of the dwindling transmission that persists as ITNs and IRS are scaled up. Increasing frequency of behavioural evasion traits within persisting residual vector systems usually reflect the successful suppression of the most potent and vulnerable vector taxa by IRS or ITNs, rather than their failure. Many of the commonly observed changes in mosquito behavioural patterns following intervention scale-up may well be explained by modified taxonomic composition and expression of phenotypically plastic behavioural preferences, rather than altered innate preferences of individuals or populations. Detailed review of the contemporary evidence base does not yet provide any clear-cut example of true behavioural resistance and is, therefore, consistent with the hypothesis presented. Caution should be exercised before over-interpreting most existing reports of increased frequency of behavioural traits which enable mosquitoes to evade fatal contact with insecticides: this may simply be the result of suppressing the most behaviourally vulnerable of the vector taxa that constituted the original transmission system. Mosquito taxa which have always exhibited such evasive traits may be more accurately described as behaviourally resilient, rather than resistant. Ongoing national or regional entomological monitoring surveys of physiological susceptibility to insecticides should be supplemented with biologically and epidemiologically meaningfully estimates of malaria vector population dynamics and the behavioural phenotypes that determine intervention impact, in order to design, select, evaluate and optimize the implementation of vector control measures

Effect of malaria transmission reduction by insecticide-treated bed nets (ITNs) on the genetic diversity of Plasmodium falciparum merozoite surface protein (MSP-1) and circumsporozoite (CSP) in western Kenya

Background Although several studies have investigated the impact of reduced malaria transmission due to insecticide-treated bed nets (ITNs) on the patterns of morbidity and mortality, there is limited information on their effect on parasite diversity. Methods Sequencing was used to investigate the effect of ITNs on polymorphisms in two genes encoding leading Plasmodium falciparum vaccine candidate antigens, the 19 kilodalton blood stage merozoite surface protein-1 (MSP-119kDa) and the Th2R and Th3R T-cell epitopes of the pre-erythrocytic stage circumsporozoite protein (CSP) in a large community-based ITN trial site in western Kenya. The number and frequency of haplotypes as well as nucleotide and haplotype diversity were compared among parasites obtained from children <5 years old prior to the introduction of ITNs (1996) and after 5 years of high coverage ITN use (2001). Results A total of 12 MSP-119kDa haplotypes were detected in 1996 and 2001. The Q-KSNG-L and E-KSNG-L haplotypes corresponding to the FVO and FUP strains of P. falciparum were the most prevalent (range 32–37%), with an overall haplotype diversity of > 0.7. No MSP-119kDa 3D7 sequence-types were detected in 1996 and the frequency was less than 4% in 2001. The CSP Th2R and Th3R domains were highly polymorphic with a total of 26 and 14 haplotypes, respectively detected in 1996 and 34 and 13 haplotypes in 2001, with an overall haplotype diversity of > 0.9 and 0.75 respectively. The frequency of the most predominant Th2R and Th3R haplotypes was 14 and 36%, respectively. The frequency of Th2R and Th3R haplotypes corresponding to the 3D7 parasite strain was less than 4% at both time points. There was no significant difference in nucleotide and haplotype diversity in parasite isolates collected at both time points. Conclusion High diversity in these two genes has been maintained overtime despite marked reductions in malaria transmission due to ITNs use. The frequency of 3D7 sequence-types was very low in this area. These findings provide information that could be useful in the design of future malaria vaccines for deployment in endemic areas with high ITN coverage and in interpretation of efficacy data for malaria vaccines based on 3D7 parasite strains