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. 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. 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. 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.

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

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.

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Urban lymphatic filariasis

Since the World Health Assembly’s (Resolution WHA 50.29, 1997) call for the elimination of lymphatic filariasis by the year 2020, most of the endemic countries identified have established programmes to meet this objective. In 1997, a National Lymphatic Filariasis Elimination Plan was drawn up by the Ministry of Health of Brazil, creating local programs for the elimination of Bancroftian filariasis in areas with active transmission. Based on a comprehensive bibliographic search for available studies and reports of filariasis epidemiology in Brazil, current status of this parasitic infection and the outlook for its elimination in the country were analysed. From 1951 to 1958 a nationwide epidemiological study conducted in Brazil confirmed autochthonous transmission of Bancroftian filariasis in 11 cities of the country. Control measures led to a decline in parasite rates, and in the 1980s only the cities of Belem in the Amazonian region (Northern region) and Recife (Northeastern region) were considered to be endemic. In the 1990s, foci of active transmission of LF were also described in the cities of Maceio, Olinda, Jaboatao dos Guararapes, and Paulista, all in the Northeastern coast of Brazil. Data provide evidence for the absence of microfilaremic subjects and infected mosquitoes in Belem, Salvador and Maceio in the past few years, attesting to the effectiveness of the measures adopted in these cities. Currently, lymphatic filariasis is a public health problem in Brazil only in four cities of the metropolitan Recife region (Northeastern coast). Efforts are being concentrated in these areas, with a view to eliminating the disease in the country.

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Lymphatic filariasis in Brazil: epidemiological situation and outlook for elimination

Summary


Objective To describe the spatial distribution of lymphatic filariasis and its relationship with the socioenvironmental risk indicator, thus identifying priority localities for interventions in endemic urban areas.



Methods  The study area was the municipality of Jaboatao dos Guararapes, State of Pernambuco, Brazil. The data sources were a parasitological survey and the 2000 demographic census. From these data, a socioenvironmental composite risk indicator was constructed using the 484 census tracts (CT) as the analysis units, based on the score-formation technique. Census tracts with higher indicator values presented higher risk of occurrences of filariasis.



Results  Six thousand five hundred and seven households were surveyed and 23 673 individuals were examined, among whom 323 cases of microfilaremia were identified. The mean prevalence rate for the municipality was 1.4%. The indicator showed that 73% (237/323) of the cases of microfilaremia were in high-risk areas (third and fourth quartiles) with worse socioenvironmental conditions (RR = 4.86, CI = 3.09–7.73, P < 0.05).



Conclusions  The socioenvironmental composite risk indicator demonstrated sensitivity, since it was able to identify the localities with greater occurrence of infection. Because it can stratify spaces by using official and available data, it constitutes an important tool for use in the worldwide program for eliminating lymphatic filariasis.



Un indice composite socioenvironnemental comme un outil pour identifier les zones a risque de la filariose lymphatique



Objectif:  Decrire la distribution spatiale de la filariose lymphatique et sa relation avec l’indicateur de risque social et environnemental, en identifiant les aires prioritaires d’intervention dans les zones d’endemie urban.



Methodes:  L’aire d’etude a ete la ville de Jaboatao dos Guararapes, localisee dans l’etat de Pernambuco, Bresil. Les donnees ont comme source l’enquete parasitologique et des donnees des secteurs (SC) du Recensement Demographique de 2000. Avec ces donnees il a ete construit un indicateur de risque social et environnemental (IRS), dont l’unite d’analyse ont ete les 484 SC, base sur la technique de formation des scores. Les valeurs les plus elevees de l’IRS indiquent que le SC presente un plus grand risque d’occurence de la filariose.



Resultats:  6.507 domiciles ont fait partie de l’etude, ayant 23.673 personnes examinees, ou 323 portaient des microfilaires dans le sang, avec taux moyen de prevalence dans la ville de 1,4%. L’IRS a identifie que 73% (237/323) des cas de microfilaremiques sont localises dans les SC de la zone a haut risque (3e et 4e quartile), avec la plus mauvaise condition sociale et environnementale, ayant un risque 4,86 fois plus grand d’avoir des cas de filariose que dans la zone a bas risque (IC = 3.09 - 7.73, p < 0,05).



Conclusions:  L’indicateur synthetique de risque pour la filariose IRS a montre une bonne sensibilite, parce qu’il a ete en mesure d’identifier geographiquement les lieux les plus importants d’occurence de l’endemie. Cet indicateur se configure comme un outil important pouvant etre utilise dans les programmes pour le controle de la filariose lymphatique, puisqu’il stratifie l’espace en travaillant avec des petites zones geographiques



Un socio indice compuesto como una herramienta para identificar zonas de riesgo urbana de la filariasis linfatica



Objetivo:  describir la distribucion espacial de la filariosis linfatica y su relacion con el indicador de riesgo socioambiental, identificando locales prioritarios para intervencion en area urbana.



Metodos:  el area del estudio fue el municipio de Jaboatao dos Guararapes, estado de Pernambuco, Brasil. Las fuentes de las informaciones fueron la investigacion parasitologica y los datos por sectores censitarios (SC) del Censo Demografico 2000. Con esos datos fue construido un indicador de riesgo socioambiental, cuya unidad de analisis fueron los 484 SC, en base a la tecnica de formacion de scores. Los valores mas altos del indicador muestran que el SC presenta mayor riesgo de presencia de filariosis.



Resultados:  fueron investigados 6.507 domicilios y examinados 23.673 individuos, identificandose 323 casos de microfilaremiasis, con tasa promedio de presencia patologica de 1,4% para el municipio. El indicador identifico que el 73% (237/323) de los casos de microfilaremiasis se encuentra en el area de alto riesgo (3o y 4o cuartiles), peor condicion socioambiental, con un nivel de riesgo 4,86 veces mas alto de surgimiento de casos de filariosis en comparacion con el area de bajo riesgo (IC = 3,09 – 7,73, p < 0,05).



Conclusiones:  el indicador de riesgo socioambiental mostro sensibilidad, una vez que fue capaz de identificar los locales de mayor presencia de infeccion. Puesto que aquel estratifica el espacio y trabaja sobre pequenas areas, constituye un importante instrumento a ser utilizado en el programa global de eliminacion de la filariosis linfatica.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3156.2009.02317.x

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

Summary To interrupt transmission of Wuchereria bancrofti , a parasite that causes lymphatic filariasis, mass treatment of at-risk populations with antifilarial drugs is recommended for 4–6 years, the minimum estimated adult worm lifespan. Factors associated with adult worm longevity are unknown. In Recife, Brazil, we conducted a retrospective cohort study of 57 men whose adult W. bancrofti were not sensitive to diethylcarbamazine and who were followed with semi-annual physical examinations (to detect intrascrotal nodules, indicative of adult worm death) and ultrasound examinations (to detect the ‘filaria dance sign’ (FDS), indicative of living adult worms). After 5 years, the FDS remained detectable in 10 (24.4%) of 41 adult worm nests in 25 men from areas of high filariasis transmission intensity and in 30 (90.9%) of 33 nests in 32 men from areas of low transmission ( P W. bancrofti is inversely associated with transmission intensity. These findings have implications for filariasis elimination and research.

Does longevity of adult Wuchereria bancrofti increase with decreasing intensity of parasite transmission? Insights from clinical observations

This article analyzes the results of an epidemiological survey on the occurrence and distribution of lymphatic filariasis in Cavaleiro, a district in the city of Jaboatao dos Guararapes in Greater Metropolitan Recife, Pernambuco State, Brazil. The district was divided into 12 areas, and a cross-sectional technique was used to examine 9,520 individuals, of whom 2.2% were found to be infected. There were positive cases in 11 of the areas. The prevalence rate ranged from 0% to 5.15%. The majority (64.3%) of infected individuals were males (p < 0.05). Infected individuals were identified in all age groups. The results show that lymphatic filariasis is still an important public health problem in the Cavaleiro district and that it deserves attention by municipal authorities and health planners.

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The occurrence and distribution of lymphatic filariasis in Greater Metropolitan Recife: the case of an endemic area in Jaboatão dos Guararapes, Pernambuco, Brazil

Maria José Evangelista

Papers

The occurrence and distribution of lymphatic filariasis in Greater Metropolitan Recife: the case of an endemic area in Jaboatão dos Guararapes, Pernambuco, Brazil