A socioenvironmental composite index as a tool for identifying urban areas at risk of lymphatic filariasis

Culex quinquefasciatus Density Associated with Socioenvironmental Conditions in a Municipality with Indeterminate Transmission of Lymphatic Filariasis in Northeastern Brazil

Lymphatic filariasis (LF) is a neglected tropical disease associated with poverty and poor environmental conditions. With the inclusion of vector control activities in LF surveillance actions, there is a need to develop simple methods to identify areas with higher mosquito density and thus a higher consequent risk of W. bancrofti transmission. An ecological study was conducted in Igarassu, which is in the metropolitan region of Recife, Pernambuco, Brazil. The mosquitoes were captured in 2060 houses distributed across 117 census tracts. The vector density index (VDI), which measures the average number of lymphatic-filariasis-transmitting mosquitoes per number of houses collected in the risk stratum, was constructed. Moreover, the social deprivation indicator (SDI) was constructed and calculated through principal component factor analysis. An average of 242 female C. quinquefasciatus were found in the high-risk stratum, while the average in the low-risk stratum was 108. The overall VDI was 6.8 mosquitoes per household. The VDI for the high-risk stratum was 13.2 mosquitoes per household, while for the low/medium-risk stratum, it was 5.2. This study offers an SDI for the density of C. quinquefasciatus mosquitoes, which can help reduce the costs associated with data collection and allows for identifying priority areas for vector control actions.

Ecological and Socioeconomic Predictors of Transmission Assessment Survey Failure for Lymphatic Filariasis

The transmission assessment survey (TAS) is recommended to determine whether cessation of mass drug administration (MDA) for lymphatic filariasis (LF) is warranted. Ministries of health typically implement TASs in evaluation units (EUs) that have had more than five rounds of annual MDA. Under TAS guidelines, sample size calculations determine a decision value: if the number of individuals testing positive exceeds this threshold, then MDA continues in the EU. The objective of this study was to determine whether fine scale geospatial covariates could be used to identify predictors of TAS failure. We geo-referenced 746 TAS EUs, of which 65 failed and extracted geospatial covariates using R to estimate odds of failure. We implemented stepwise backward elimination to select covariates for inclusion in a logistic regression to estimate the odds of TAS failure. Covariates included environmental predictors (aridity, distance to fresh water, elevation, and enhanced vegetation index), cumulative rounds of MDA, measures of urbanicity and access, LF species, and baseline prevalence. Presence of Brugia was significantly associated with TAS failure (odds ratio [OR]: 4.79, 95% CI: 2.52–9.07), as was population density (OR: 2.91, 95% CI: 1.06–7.98). The presence of nighttime lights was highly protective against failure (OR: 0.22, 95% CI: 0.10–0.50), as was an increase in elevation (OR: 0.36, 95% CI: 0.18–0.732). This work identifies predictors associated with TAS failure at the EU areal level, given the data presently available, and also identifies the need for more granular data to conduct a more robust assessment of these predictors.

Evaluation of lymphatic filariasis in endemic area of Brazil where mass drug administration is not required

Mass drug administration (MDA) is the main counter-transmission strategy of the Global Programme to Eliminate Lymphatic Filariasis. In endemic countries, there are areas where MDA is not required. However, there is no standard approach in these areas, and studies are important to evaluate the epidemiological status. This study aimed to investigate lymphatic filariasis and strategies developed for its control in an area where MDA is not required. Together with the 2018 morbidity evaluation, a survey was conducted using point-of-care immunochromatographic test-AD12 tests for diagnostic screening in an area where MDA is not required. The methodology also included desk research based on Health Department reports of the control activities for lymphatic filariasis during 2003-2016. Among the 934 cases investigated in 2018, there was a 0.64% prevalence of circulating filarial antigen positive, comprising five adults and one 2-year-old child. Six patients aged 39-63 years had filarial disease. Fourteen surveys have already been conducted as control activities, and since 2009, there have been no positive cases. This study showed that the prevalence of antigenemia decreased from 2.97% in 2003 to 0.64% in 2018. Moreover, the transmission of filariasis infection was under control in this area. Our study provides insights into the surveillance phase by identifying areas of low transmission and where MDA is not required. Although we have not identified cases of filarial infection, there is a need to provide services that will provide assist those already affected with morbidity and help reduce and prevent disability.

Mapping and monitoring for a lymphatic filariasis elimination program: a systematic review

Lymphatic filariasis (LF) is targeted for elimination by the year 2020. The Global Programme for Elimination of LF (GPELF) aims to achieve elimination by interrupting transmission through annual mass drug administration (MDA) of albendazole with ivermectin or diethylcarbamazine. The program has successfully eliminated the disease in 11 of the 72 endemic countries, putting in enormous efforts on systematic planning and implementation of the strategy. Mapping areas endemic for LF is a pre-requisite for implementing MDA, monitoring and evaluation are the components of programme implementation. This review was undertaken to assess how the mapping and impact monitoring activities have evolved to become more robust over the years and steered the LF elimination programme towards its goal. The findings showed that the WHO recommended mapping strategy aided 17 countries to delimit, plan and implement MDA in only those areas endemic for LF thereby saving resources. Availability of serological tools for detecting infection in humans (antigen/antibody assays) and molecular xenomonitoring (MX) in vectors greatly facilitated programme monitoring and evaluation in endemic countries. Results of this review are discussed on how these existing mapping and monitoring procedures can be used for re-mapping of unsurveyed and uncertain areas to ensure there is no resurgence during post-MDA surveillance. Further the appropriateness of the tests (Microfilaria (Mf)/antigenemia (Ag)/antibody(Ab) surveys in humans or MX of vectors for infection) used currently for post-MDA surveillance and their role in the development of a monitoring and evaluation strategy for the recently WHO recommended triple drug regimen in MDA for accelerated LF elimination are discussed.

Intraurban differentials of perinatal mortality: modeling for identifying priority areas

Abstract Objective: To analyze the intraurban spatial distribution of perinatal mortality, its avoidability, and relationship with socioeconomic indicators in Recife, Pernambuco, Brazil, in the period from 2013 to 2015. Method: An ecological study with data from the Information Systems on Mortality and Live Births and the Brazilian Institute of Geography and Statistics, using neighborhoods as the analysis unit. We elaborated an indicator of social deprivation formed by variables from the demographic census. We estimated the Kernel density of the deaths and calculated the Moran index of the perinatal mortality coefficients in the spatial analysis. We elaborated thematic maps of avoidable perinatal mortality and social deprivation. Results: The global statistical analysis of the mortality distribution indicated evidence of spatial aggregation. Moran's index was 0.18. We found clusters of perinatal mortality in neighborhoods of the Central, North, Northwest, and South Regions. In the North, Northwest, Southwest, and South Regions we identified neighborhoods with greater social deprivation and avoidable mortality coefficients. The primary cause of death was of fetuses and newborns affected by hypertensive maternal disorders. Conclusion: We demonstrated intraurban differentials in perinatal mortality among neighborhoods. The stratification of the urban space according to the social deprivation indicator presented a relation with the perinatal mortality and its avoidability.

Determinants of transmission hotspots and filarial infection in households after eight rounds of mass drug administration in India

OBJECTIVES

Lymphatic filariasis (LF) elimination through mass drug administration (MDA) of DEC and albendazole have resulted in very low levels of infection in most endemic districts in India. But small pockets with residual microfilaraemia in the community and antigeneamia in children ('hotspots') are a cause of concern. We aimed to identify the determinants of such transmission hotspots and filarial infection in households using data from 33 communities.

METHODS

The filariasis vector Culex quinquefasciatus was collected from 627 randomly selected households using gravid traps. Parallel data on environmental, entomological, demographical, socio-economical and behavioural factors were analysed to identify the determinants of hotspots and household-level infection.

RESULTS

Hotspots and non-hotspots did not differ significantly in terms of socio-economical and behavioural aspects, but did differ in terms of demographical and environmental factors. Logistic regression revealed that tiled and concrete houses increased the risk of an area being a hotspot by 2.0 and 2.9 times respectively. Presence of Culex breeding habitats was significantly associated with elevated risk of being a hotspot. Proximity of U-drains to a house increased the risk of filarial infection 5.8 times.

CONCLUSIONS

An environment suitable to Culex breeding influences continued transmission despite eight rounds of MDA, particularly in hotspots. Proximity to U-drains increases the risk of infection in households. Implementing localised vector control measures may help interrupt low-level transmission, thereby reducing the risk of resurgence in the absence of MDA.

Knowledge, attitudes and perceptions regarding lymphatic filariasis: study on systematic noncompliance with mass drug administration

The aim of this study was to investigate the epidemiological characteristics, antigenic profile, perceptions, attitudes and practices of individuals who have been systematically non-compliant in mass drug administration (MDA) campaigns targeting lymphatic filariasis, in the municipality of Olinda, State of Pernambuco, Northeastern Brazil. A pretested questionnaire was used to obtain information on socioenvironmental demographics, perceptions of lymphatic filariasis and MDA, and reasons for systematic noncompliance with treatment. A rapid immunochromatographic test (ICT) was performed during the survey to screen for filariasis. It was found that the survey subjects knew about filariasis and MDA. Filariasis was identified as a disease (86.2%) and 74.4% associated it with the presence of swelling in the legs. About 80% knew about MDA, and the main source of information was healthcare workers (68.3%). For men the main reasons for systematic noncompliance with MDA were that “the individual had not received the medication” (p=0.03) and for women “the individual either feared experiencing adverse reactions”. According to the ICT, the prevalence of lymphatic filariasis was 2%. The most important causes of systematic noncompliance were not receiving the drug and fear of side-effects. For successful implementation of MDA programs, good planning, educational campaigns promoting the benefits of MDA, adoption of measures to minimize the impact of adverse effects and improvement of drug distribution logistics are needed.

Pterodon emarginatus oleoresin-based nanoemulsion as a promising tool for Culex quinquefasciatus (Diptera: Culicidae) control

BACKGROUND

Preparation of nanoformulations using natural products as bioactive substances is considered very promising for innovative larvicidal agents. On this context, oil in water nanoemulsions develop a main role, since they satisfactorily disperse poor-water soluble substances, such as herbal oils, in aqueous media. Pterodon emarginatus, popularly known as sucupira, has a promising bioactive oleoresin. However, to our knowledge, no previous studies were carried out to evaluate its potential against Culex quinquefasciatus, the main vector of the tropical neglected disease called lymphatic filariasis or elephantiasis. Thus, we aimed to investigate influence of different pairs of surfactants in nanoemulsion formation and investigate if a sucupira oleoresin-based nanoemulsion has promising larvicidal activity against this C. quinquefasciatus. We also evaluated morphological alteration, possible mechanism of insecticidal action and ecotoxicity of the nanoemulsion against a non-target organism.

RESULTS

Among the different pairs of surfactants that were tested, nanoemulsions obtained with polysorbate 80/sorbitan monooleate and polysorbate 80/sorbitan trioleate presented smallest mean droplet size just afterwards preparation, respectively 151.0 ± 2.252 and 160.7 ± 1.493 nm. They presented high negative zeta potential values, low polydispersity index (<0.300) and did not present great alteration in mean droplet size and polydispersity index after 1 day of preparation. Overall, nanoemulsion prepared with polysorbate 80/sorbitan monooleate was considered more stable and was chosen for biological assays. It presented low LC50 value against larvae (34.75; 7.31-51.86 mg/L) after 48 h of treatment and some morphological alteration was observed. The nanoemulsion did not inhibit acetylcholinesterase of C. quinquefasciatus larvae. It was not toxic to green algae Chlorella vulgaris at low concentration (25 mg/L).

CONCLUSIONS

Our results suggest that optimal nanoemulsions may be prepared with different surfactants using a low cost and low energy simple method. Moreover, this prototype proved to be effective against C. quinquefasciatus, being considered an ecofriendly novel nanoproduct that can be useful in integrated control programs of vector control.

Burden of lymphatic filariasis morbidity in an area of low endemicity in Brazil

The Global Programme to Eliminate Lymphatic Filariasis has two main components: interrupting transmission of lymphatic filariasis (LF) and managing morbidity and preventing disability. However, interventions to prevent and manage LF-related disabilities in endemic communities have been of limited extent. The aim of this study was to describe the prevalence of morbidity and its correlation with filarial infection, thereby filling a gap that existed regarding the data on morbidity in Brazil. Presence of Wuchereria bancrofti microfilaria was investigated using the thick smear technique. Information on parasitosis-related clinical manifestations was obtained using a questionnaire applied by community health agents with previous training and capacitation to know about and identify the disease. To analyze correlations, Pearson's correlation coefficient was used with the corresponding statistical significance test. 23,673 individuals were investigated: 323 presented microfilaremia (1.36%) and 741 (3.13%) had clinical complaints that were attributable to LF. Acute dermatolymphangioadenitis (ADLA) was the most prevalent condition (2.2%). Lymphedema, ADLA and chyluria were more commonly reported among female patients. There were positive associations between all the clinical complaints reported and filarial infection. Hydrocele presented the most strongly positive association (r=0.699; p<0.001). The present study showed that there is an association between clinical condition reported and the rate of infection among people living in an area of low endemicity for LF. It contributes data that might provide support for healthcare systems and thus optimize disease management, through incorporating surveillance measures directed towards preventing disability and reducing the psychosocial and economic impact of the disease on poor populations living in areas endemic for LF.

Lymphatic filariasis among children and adolescents: spatial identification via socio-environmental indicators to define priority areas for elimination

BACKGROUND

The occurrence of lymphatic filariasis (LF) and its transmission dynamics among children and adolescents are still not clearly elucidated. The aim of this study was to describe the spatial distribution of microfilaremia and its relationship with socio-environmental variables, thereby identifying areas at greater risk of transmission.

METHODS

An ecological study was conducted, in which the analysis unit was formed by districts of the municipality of Jaboatão dos Guararapes in the state of Pernambuco, Brazil. The data source was a parasitological survey. Inadequate sewage disposal, number of people in the household and income of between 0.5 and 1 minimum salary were used to construct the socio-environmental indicator. The districts were then grouped according to the indicator into three risk strata, using the k-means clustering technique.

RESULTS

In the study, 96/8670 (1.1%) of the population were found to present microfilaremia. The high-risk stratum had a mean prevalence rate of 1.9% and a risk of 2.56 (p<0.05), in relation to the low-risk stratum. The middle stratum grouped the households that presented an intermediate risk of transmission, with a prevalence rate of 1.92%.

CONCLUSIONS

The indicator used is a promising tool that enables the precise measurement of the relationship between social deprivation and the prevalence of filarial infection among children. Thus, it can be used to plan control and elimination actions.

The global distribution and transmission limits of lymphatic filariasis: past and present

BACKGROUND

Lymphatic filariasis (LF) is one of the neglected tropical diseases targeted for global elimination by 2020 and to guide elimination efforts countries have, in recent years, conducted extensive mapping surveys. Documenting the past and present distribution of LF and its environmental limits is important for a number of reasons. Here, we present an initiative to develop a global atlas of LF and present a new global map of the limits of LF transmission.

METHODS

We undertook a systematic search and assembly of prevalence data worldwide and used a suite of environmental and climatic data and boosted regression trees (BRT) modelling to map the transmission limits of LF.

RESULTS

Data were identified for 66 of the 72 countries currently endemic and for a further 17 countries where LF is no longer endemic. Our map highlights a restricted and highly heterogeneous distribution in sub-Saharan Africa, with transmission more widespread in West Africa compared to east, central and southern Africa where pockets of transmission occur. Contemporary transmission occurs across much of south and South-east Asia and the Pacific. Interestingly, the risk map reflects environmental conditions suitable for LF transmission across Central and South America, including the southern States of America, although active transmission is only known in a few isolated foci. In countries that have eliminated LF, our predictions of environmental suitability are consistent with historical distribution.

CONCLUSIONS

The global distribution of LF is highly heterogeneous and geographically targeted and sustained control will be required to achieve elimination. This first global map can help evaluate the progress of interventions and guide surveillance activities.

Social deprivation index and lymphatic filariasis: a tool for mapping urban areas at risk in northeastern Brazil

This paper describes the construction and application of a social deprivation index that was created to explore the relationship between lymphatic filariasis and socioenvironmental variables in the municipality of Jaboatão dos Guararapes, Pernambuco, Brazil, thereby contributing towards identifying priority areas for interventions. This indicator was obtained from principal-component factor analysis. Variables available from the national census representing socioenvironmental conditions, household characteristics and urban services were used. Epidemiological data came from a parasitological survey on lymphatic filariasis. 23 673 individuals were examined and 323 were positive (1.4%). Two factors that together explained 80.61% of the total variance were selected. The social deprivation strata were capable of indicating a risk gradient, with 74.9% of the microfilaremia cases situated in the high-risk stratum. Principal-component factor analysis was shown to be sensitive for selecting indicators associated with the risk of lymphatic filariasis transmission and for detecting areas potentially at risk. The capacity of the social deprivation index for picking up social inequalities qualifies it as a new tool for use in planning interventions aimed at controlling lymphatic filariasis in urban spaces.

Residential characteristics aggravating infestation by Culex quinquefasciatus in a region of Northeastern Brazil

OBJECTIVE

Analyse how basic sanitation conditions, water supply and housing conditions affect the concentration of Culex quinquefasciatus

METHODS

Populations of C. quinquefasciatus in 61 houses in the municipality of Olinda, PE, were monitored between October 2009 and October 2010. Observations were carried out in homes without the presence of preferred breeding sites in order to identify characteristics that may be aggravating factors for the development of the mosquito. Five aggravating factors were analysed: vegetation cover surrounding the home, number of residents/home, water storage, sewage drainage and water drainage. These characteristics were analysed in terms of presence or absence and as indicators of the degree of infestation, which was estimated through monitoring the concentration of eggs (oviposition traps - BR-OVT) and adults (CDC light traps).

RESULTS

Sewage drainage to a rudimentary septic tank or to the open air was the most frequent aggravating factor in the homes (91.8%), although the presence of vegetation was the only characteristic that significantly influenced the increase in the number of egg rafts (p = 0.02). The BR-OVT achieved positive results in 95.1% of the evaluations, with the presence of at least one egg raft per month. A total of 2,366 adults were caught, with a mosquito/room/night ratio of 32.9. No significant difference was found in the number of mosquitoes caught in the homes.

CONCLUSIONS

Although the sanitation and water supply influence the population density of C. quinquefasciatus, residence features that are not usually considered in control measures can be aggravating factors in sustaining the mosquito population.

Urban lymphatic filariasis

Lymphatic filariasis (LF) is a disabling and disfiguring disease resulting from a mosquito-borne parasitic infection. It is a major public health problem in many countries with a warm climate. Research and control activities have mainly focused on LF in rural areas where it also has its major impact. However, with rapid and unplanned growth of cities in the developing world, there is a need also to consider LF transmission and control in urban settings. Here, we review currently available knowledge on urban LF and the environmental and socio-economic basis for its occurrence. Among the three parasite species causing LF in humans, only Wuchereria bancrofti has been documented to have a significant potential for urban transmission. This is primarily because one of its vectors, Culex quinquefasciatus, thrives and proliferates excessively in crowded city areas with poor sanitary, sewerage and drainage facilities. For this reason, urban LF also often shows a marked focality in distribution, with most cases clustered in areas inhabited by the less privileged city populations. More knowledge on urban LF is needed, in particular on its socio-economic and human behavioural context, on the potential for transmission in regions where other LF vector species predominate, and on rapid methods for identification and mapping of risk areas, to provide a strong evidence base for its control.

Epidemiological assessment of eight rounds of mass drug administration for lymphatic filariasis in India: implications for monitoring and evaluation

BACKGROUND

Monitoring and evaluation guidelines of the programme to eliminate lymphatic filariasis require impact assessments in at least one sentinel and one spot-check site in each implementation unit (IU). Transmission assessment surveys (TAS) that assess antigenaemia (Ag) in children in IUs that have completed at least five rounds of mass drug administration (MDA) each with >65% coverage and with microfilaria (Mf) levels <1% in the monitored sites form the basis for stopping the MDA. Despite its rigour, this multi-step process is likely to miss sites with transmission potential ('hotspots') and its statistical assumptions for sampling and threshold levels for decision-making have not been validated. We addressed these issues in a large-scale epidemiological study in two primary health centres in Thanjavur district, India, endemic for bancroftian filariasis that had undergone eight rounds of MDA.

METHODOLOGY/PRINCIPAL FINDINGS

The prevalence and intensity of Mf (per 60 µl blood) were 0.2% and 0.004 respectively in the survey that covered >70% of 50,363 population. The corresponding values for Ag were 2.3% and 17.3 Ag-units respectively. Ag-prevalence ranged from 0.7 to 0.9%, in children (2-10 years) and 2.7 to 3.0% in adults. Although the Mf-levels in the survey and the sentinel/spot check sites were <1% and Ag-level was <2% in children, we identified 7 "residual" (Mf-prevalence ≥ 1%, irrespective of Ag-status in children) and 17 "transmission" (at least one Ag-positive child born during the MDA period) hotspots. Antigenaemic persons were clustered both at household and site levels. We identified an Ag-prevalence of ~1% in children (equivalent to 0.4% community Mf-prevalence) as a possible threshold value for stopping MDA.

CONCLUSIONS/SIGNIFICANCE

Existence of 'hotspots' and spatial clustering of infections in the study area indicate the need for developing good surveillance strategies for detecting 'hotspots', adopting evidence-based sampling strategies and evaluation unit size for TAS.

Using kernel density estimates to investigate lymphatic filariasis in northeast Brazil

After more than 10 years of the Global Program to Eliminate Lymphatic Filariasis (GPELF) in Brazil, advances have been seen, but the endemic disease persists as a public health problem. The aim of this study was to describe the spatial distribution of lymphatic filariasis in the municipality of Jaboatão dos Guararapes, Pernambuco, Brazil. An epidemiological survey was conducted in the municipality, and positive filariasis cases identified in this survey were georeferenced in point form, using the GPS. A kernel intensity estimator was applied to identify clusters with greater intensity of cases. We examined 23 673 individuals and 323 individuals with microfilaremia were identified, representing a mean prevalence rate of 1·4%. Around 88% of the districts surveyed presented cases of filarial infection, with prevalences of 0-5·6%. The male population was more affected by the infection, with 63·8% of the cases (P<0·005). Positive cases were found in all age groups examined. The kernel intensity estimator identified the areas of greatest intensity and least intensity of filarial infection cases. The case distribution was heterogeneous across the municipality. The kernel estimator identified spatial clusters of cases, thus indicating locations with greater intensity of transmission. The main advantage of this type of analysis lies in its ability to rapidly and easily show areas with the highest concentration of cases, thereby contributing towards planning, monitoring, and surveillance of filariasis elimination actions. Incorporation of geoprocessing and spatial analysis techniques constitutes an important tool for use within the GPELF.

Mapping of Wuchereria bancrofti infection in children and adolescents in an endemic area of Brazil

A parasitological survey was conducted among children and adolescents in the municipality of Jaboatão dos Guararapes, Brazil to describe the occurrence and spatial distribution of lymphatic filariasis. Microfilaraemia was investigated through the thick smear technique, using 50 μl of capillary blood that was collected at night. The spatial analysis used a digital base map of the municipality, divided into districts, which were classified as hypoendemic, mesoendemic or hyperendemic. 8670 children were examined and 96 cases of microfilaraemia were identified (1.1%). The prevalence rate did not differ significantly between the sexes. Occurrences of filarial infection increased with increasing age: the greatest prevalence was recorded between 15 and 18 years of age (P<0.05). There were 49 reports of clinical manifestations. The spatial distribution of microfilaraemia according to residential district showed that 13 (54.2%) of the 24 districts investigated were positive. Approximately 33% of the districts were hyperendemic. The results demonstrated that the pediatric population had intense early exposure to the parasite, thus characterizing filariasis as endemic in the municipality. The spatial analysis allowed identification of areas with greater occurrence of infection among children, and showed localities where the populations most exposed to transmission were concentrated. Epidemiological surveillance of microfilaraemia among children and spatial analysis are important local transmission indicators and form instruments for planning actions within the Global Program to Eliminate Lymphatic Filariasis, since they make it possible to identify priority areas.

First evidence of spatial clustering of lymphatic filariasis in an Aedes polynesiensis endemic area

Successful elimination of lymphatic filariasis (LF) requires accurate identification of residual foci of transmission and stringent surveillance strategies to combat potential resurgence. This is challenging in areas where the day-biting Aedes polynesiensis is endemic, such as Samoa, since in previous studies no geographical clustering of infection has been demonstrated. Another challenge for this low prevalence phase is the choice of diagnostic assay as testing for circulating filarial antigen (CFA) or microfilariae (Mf) alone may not have adequate sensitivity. This could be solved by using the commercially available filariasis Cellabs enzyme linked immunosorbent assay (CELISA) to measure antibody. In the current study five Samoan villages were chosen based on previous epidemiological assessments to represent a range of infection prevalences. CFA, Mf, and antibody levels in children ≤ 10 years had been recorded and results linked to household of residence and/or primary school of attendance. To ascertain the location of exposure, two scenarios based on potential foci of transmission around communities and schools were explored. Both scenarios revealed significant spatial clusters of households with infected individuals and a relationship to antibody positive children when they were included in the spatial analysis. Fasitoo-Tai had the highest LF prevalence and largest geographical spatial clusters for both scenarios. In Falefa, spatial clusters were detected only for the primary school scenario. In Tafua, which spanned an area of 19.5 km(2), no spatial clusters were detected. Lastly, in Siufaga, the village with the lowest LF prevalence, significant clustering of infected individuals was observed and, for the primary school scenario, this was geographically related to exposure. These promising findings are the first published evidence of spatial clustering of LF in a day-biting Ae. polynesiensis endemic area.

Effect of annual mass administration of diethylcarbamazine and albendazole on bancroftian filariasis in five villages in south India

Annual mass drug administration (MDA) is the recommended strategy for lymphatic filariasis (LF) elimination. We assessed the effect of six rounds of mass administration of diethylcarbamazine (DEC) and albendazole (ALB) on microfilaria (Mf) prevalence and intensity and vector infection and infectivity rates and circulating filarial antigenaemia (CFA) in a group of five villages in south India, endemic for Culex-transmitted bancroftian filariasis. During different rounds of MDA, 60-70% of the eligible population (>15 kg body weight) was treated. The MDA reduced the Mf prevalence from 8.10% (CI 6.18-10.01) to 1.01% (CI 0.31-1.71) (P<0.05) and geometric mean intensity of Mf from 0.31 (CI 0.22-0.40) to 0.02 (CI 0.00-0.04) (P<0.05), equivalent to a fall of 86% and 94% respectively. The vector infection and infectivity rates declined from 13.11% (CI 11.52-14.70) to 0.78% (CI 0.16-1.40) (P<0.05) and 1.04% (CI 0.56-1.52) to 0.13% (CI 0.00-0.39) (P<0.05), respectively. Four out of the five villages recorded <0.5% Mf prevalence and 0% vector infection rate. Circulating filarial antigenaemia (CFA) fell by 86% in the total population and 100% in 1-10 year old children. One of the five villages, which showed the highest baseline vector infection rate, showed >1.0% Mf rate. The results suggest that six rounds of mass administration of DEC and ALB, with 60-70% treatment coverage, is likely to achieve total interruption of transmission and elimination of LF in the majority of villages.