Risk of Leishmaniasis in North America

Range shifts of vector and reservoir species are a probable effect of climate change that would influence the spread of infectious diseases throughout the world. Leishmaniasis, a vector-borne parasitic disease endemic in most tropical regions of the world, depends on the female blood-feeding sand fly vectors from the genus Lutzomyia as well as several mammal reservoir species for transmission. A study by González et al. (2010) used ecological niche models (ENMs) to determine the distribution on two sand fly vector species (Lutzomyia anthophora and L. diabolica), three confirmed rodent reservoir species (Neotoma albigula, N. floridana, and N. micropus), and one potential rodent reservoir species (N. Mexicana) in northern México and the United States. The researchers found high potential for the spread of leishmaniasis in North America due to climate change-induced range shifts for N. floridada and L. diabolica in the east and N. micropus and L. anthopara in the west. Carolyn Campbell
González, C., Wang, O., Strutz, S.E., González-Salazar, C., Sánchez-Cordero, V., Sarkar, S., 2010. Climate change and the risk of leishmaniasis in North America: Predictions from ecological niche models of vector and reservoir species. Public Library of Science 4, 1–16.

In the United States and tropical America, leishmaniasis transmission depends on sand fly vectors and mammalian parasite hosts. The dynamics of the disease are correlated with population changes in reservoir and vector species, environmental changes, and climatic factors. In order to test the potential future distributions of vector and reservoir species, González et al. utilized an ENM for these species based on point occurrence data, digitized environmental layers, and machine learning algorithms. Disease risk was evaluated using two risk components: (i) the potential for the presence of vector and reservoir species based on quality of available habitat and dispersal ability and (ii) projected “cost” measured by the number of people potentially exposed to the disease. Models were projected for future climate scenarios in 2020, 2050, and 2080, using A2 (most extreme) and B2 (conservative) climate scenarios based on the 2003 Third Intergovernmental Panel on Climate Change Assessment Report. The study used two species dispersal models: (i) the universal dispersal model assumed that each species occupies all of its suitable habitat; and (ii) the contiguous dispersal model assumed that species occupy a suitable cell only if it is connected to the range of the species at the last temporal state through a pathway of suitable cells. The study area for the model consisted of all terrestrial regions of Canada, the United States, and México delimited by the 14.13 °N line of latitude to the south. °
            Predicted range expansions were found for all reservoir species, except N. Mexicana, for both climate change scenarios. In many cases, there was an initial decrease in 2020, followed by rapid increase in 2050 and 2080. The number of individuals affected by leishmaniasis, even under the contiguous dispersal model, is expected to increase to more than twice the current value. The main reasons for this probably spread of leishmaniasis are the range shifts for N. floridana and L. diabolica in the east and for N. micropus and L. anthophora in the west. However, factors not taken into consideration when developing the model, such as precipitation, water availability, vegetation composition, and soil type, may prevent sufficiently high densities of vector and reservoir species for disease transmission. Additionally, leishmaniasis typically affects only rural populations yet much of the future population is expected to live in unban environments.
While this model predicts increased exposure to leishmaniasis, increased disease cases may be avoided. Preventative measures, such as expanded surveillance and control programs and improved efforts at vector and reservoir control, would help to limit the impact of climate change on leishmaniasis exposure and transmission. 

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