Lutzomyia spp. Credit: Dr Ray Wilson  Molecular & Biochemical Parasitology Liverpool School of Tropical Medicine  Pembroke Place  Liverpool

The New World sand fly, Lutzomyia spp, the disease vector of Leishmaniasis. Image credit: Dr Ray Wilson  Molecular & Biochemical Parasitology Liverpool School of Tropical Medicine  Pembroke Place  Liverpool

Researchers from the Centre for Ecology & Hydrology (CEH) have led an international team of scientists who are among the first to analyse and project impacts of urbanisation, deforestation and agricultural intensification as well as climate change on occurrences of leishmaniasis diseases in the Americas.

The scientists, in a study published in the journal PLOS ONE, linked future socio-economic and climate change pathways to dynamic land use models to understand past and future outbreaks of cutaneous and visceral leishmaniasis in southern American countries including Brazil, Mexico, Bolivia and Guyana.

Through data obtained from sources including the HealthMap database, GenBank, the Brazilian Ministry of Health and the Centre National de Référence des Leishmanioses (CNR-L) in Montpellier, France, the researchers found climatic factors explained 80% and land use factors only 20% of the variance in past disease patterns of leishmaniasis.

Both diseases, especially cutaneous leishmaniasis, are associated with low seasonality in temperature and precipitation. The team suggest that since such seasonality increases under future climatic change both diseases are predicted to contract in geographical extent over the next three decades to 2050 – with cutaneous leishmaniasis reducing by between 35% and 50% in extent across the region. However, our finding that climate largely constrains where Leishmaniases can occur now and in the future is a function of the continental scale of our study. We expect the influence of ecosystem and socio-economic changes on disease patterns to be stronger and easier to detect when disease patterns are studied within countries or regions.

Leishmaniasis is a parasite disease spread through bites from the phlebotomine sand-fly and affects about 12 million people globally – mostly in South or Central America, Africa and the Middle East.

Cutaneous leishmaniasis – also known as tropical sore – causes skin infections that result in mutilation and disability and impacts on livelihoods if untreated. The most dangerous visceral leishmaniasis – also known as Kala azar – spreads into the spleen, bone marrow and liver, attacks the immune system and leads to death in around 10% of cases.

Lead author of the study Dr Beth Purse, who heads CEH’s Disease Ecology Group, said, “This challenges the paradigm that all vector-borne diseases will increase in impacts under climate change and highlights the importance of quantifying disease-environment links on a case-by-case basis, linking disease changes to the socio-ecological features of disease systems where ever possible.”

Co-author Dr Laurence Jones, an ecologist at CEH, said, “Changes in leishmaniasis are an important part of the wider picture associated with climate and land-use change. We need to understand how disease incidence as well as biodiversity, carbon storage and agricultural production will change in the future, and how government policies can help reduce any adverse effects.”

The research leading to these results has received partial funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 283093 – The Role of Biodiversity in Climate Change Mitigation (ROBIN) – and the Natural Environment Research Council (NERC). It was carried out in conjunction with scientists from the National Autonomous University of Mexico, the Instituto de Ecología in Mexico, the University of Melbourne and the University of Washington.

It makes important advances towards a framework for understanding disease disservices, their connections to ecosystem characteristics, and for their prediction under alternative climate change pathways and scenarios.

Additional information

Full paper reference: Purse B.V., Masante D., Golding N., Pigott D., Day J.C., Ibañez-Bernal S., Jones L., How will climate change pathways and mitigation options alter incidence of vector-borne diseases?, PLOS ONE, published online 11 Oct 2017. DOI: 10.1371/journal.pone.0183583

The paper is available as an open access document.

Staff page of Dr Bethan Purse, Centre for Ecology & Hydrology

Staff page of Laurence Jones, Centre for Ecology & Hydrology

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