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

Cano J, Rebollo MP, Golding N, Pullan RL, Crellen T, Soler A, Kelly-Hope LA, Lindsay SW, Hay SI, Bockarie MJ, Brooker SJ - Parasit Vectors (2014)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom. jcano.ortega@lshtm.ac.uk.

ABSTRACT

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.

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Related in: MedlinePlus

Marginal effect curves for each covariate used in the ensemble of 120 boosted regression tree (BRT) models. Black lines represent the mean marginal effect over all 120 BRT ensembles and grey envelopes the 95% bootstrap confidence interval. The y-axis is the untransformed logit response and x-axis is the full range of covariates values. The percentage values in parenthesis show the mean relative contribution of the covariate over all 120 sub-models of the ensemble.
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Fig4: Marginal effect curves for each covariate used in the ensemble of 120 boosted regression tree (BRT) models. Black lines represent the mean marginal effect over all 120 BRT ensembles and grey envelopes the 95% bootstrap confidence interval. The y-axis is the untransformed logit response and x-axis is the full range of covariates values. The percentage values in parenthesis show the mean relative contribution of the covariate over all 120 sub-models of the ensemble.

Mentions: A subset of 6,562 surveys (4,933 occurrences and 1,629 absences) available in the assembled LF database along with the generated pseudo-absence data (5,000) were used to model the global distribution of LF. Figure 4 shows the marginal effect of each variable on the response, averaging across the effects of all other variables, and its relative contribution to the final BRT model. High suitability for LF is positively associated with precipitation in the wettest quarter (reaching a plateau at rainfall greater than 1000 mm), increased vegetation cover, population density and minimum temperature (increasing from a minimum value of 10°C), and negatively associated with increasing elevation (Figure 4).Figure 4


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

Cano J, Rebollo MP, Golding N, Pullan RL, Crellen T, Soler A, Kelly-Hope LA, Lindsay SW, Hay SI, Bockarie MJ, Brooker SJ - Parasit Vectors (2014)

Marginal effect curves for each covariate used in the ensemble of 120 boosted regression tree (BRT) models. Black lines represent the mean marginal effect over all 120 BRT ensembles and grey envelopes the 95% bootstrap confidence interval. The y-axis is the untransformed logit response and x-axis is the full range of covariates values. The percentage values in parenthesis show the mean relative contribution of the covariate over all 120 sub-models of the ensemble.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4197264&req=5

Fig4: Marginal effect curves for each covariate used in the ensemble of 120 boosted regression tree (BRT) models. Black lines represent the mean marginal effect over all 120 BRT ensembles and grey envelopes the 95% bootstrap confidence interval. The y-axis is the untransformed logit response and x-axis is the full range of covariates values. The percentage values in parenthesis show the mean relative contribution of the covariate over all 120 sub-models of the ensemble.
Mentions: A subset of 6,562 surveys (4,933 occurrences and 1,629 absences) available in the assembled LF database along with the generated pseudo-absence data (5,000) were used to model the global distribution of LF. Figure 4 shows the marginal effect of each variable on the response, averaging across the effects of all other variables, and its relative contribution to the final BRT model. High suitability for LF is positively associated with precipitation in the wettest quarter (reaching a plateau at rainfall greater than 1000 mm), increased vegetation cover, population density and minimum temperature (increasing from a minimum value of 10°C), and negatively associated with increasing elevation (Figure 4).Figure 4

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, London, United Kingdom. jcano.ortega@lshtm.ac.uk.

ABSTRACT

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.

Show MeSH
Related in: MedlinePlus