Species distribution and circuit-based dispersal models of vector-borne disease: Is cutaneous leishmaniasis expanding due to environmental change in the southern United States

Background/Question/Methods

One major predicted but rarely documented consequence of climate change is infectious disease expansion. During the past four decades cutaneous leishmaniasis, a vector-borne disease spread by sandflies (Lutzomyia spp.) and woodrats (Neotoma spp.), traveled northeastward over 560 km in the southern United States. Climate change is expected to have a direct positive effect on parasite development and carrier range expansion of leishmaniasis. Texas has experienced wetter, warmer, and more variable climate during the past four decades compared to averages from the earlier half of the 20th century. Have these environmental changes increased the range of the parasite?

Species distribution models, SDMs, can be built to explain past ecological phenomena or to predict suitable habitat. This analysis employs the former explanatory use of SDMs to construct models of Leishmania mexicana habitat through time using variables predicted to have a direct effect on abundance and growth rate. Circuit-based dispersal modeling is also employed to discern where parasite corridors may have developed through time. 

Results/Conclusions

Explanatory species distribution and circuit-based dispersal models of L. mexicana, the causative agent of cutaneous leishmaniasis in North America, show recent changes in parasite range and habitat connectivity. Historically, L. mexicana occurred within the South Texas Plains and southern Gulf Coast region. Forecasted species distribution models predict expanded areas of habitat suitability and northward shifts. Circuit-based dispersal network models reveal corridors in central Texas which may have contributed to transmitting the pathogen to new regions.