Implications of climate change on the distribution of the tick vector Ixodes scapularis and risk for Lyme disease in the Texas-Mexico transboundary region

Authors: FERIA-ARROYO, TERESA - University Of Texas; CASTRO-ARELLANO, IVAN - Texas State University; GORDILLO-PEREZ, GUADALUPE - Unidad De Investigacion En Enfermedades Infecciosas, Centro Medico Nacional Sxxi, Imss; CAVAZOS, ANA - University Of Texas; VARGAS-SANDOVAL, MARGARITA - Universidad Michoacana De San Nicolas De Hidalgo; GROVER, ABHA - Texas A&M University; TORRES, JAVIER - Unidad De Investigacion En Enfermedades Infecciosas, Centro Medico Nacional Sxxi, Imss; MEDINA, RAUL - Texas A&M University; Perez De Leon, Adalberto - Beto; ESTEVE-GASSENT, MARIA - Texas A&M University

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2014
Publication Date: 4/25/2014
Citation: Feria-Arroyo, T.P., Castro-Arellano, I., Gordillo-Perez, G., Cavazos, A.L., Vargas-Sandoval, M., Grover, A., Torres, J., Medina, R.F., Perez de Leon, A.A., Esteve-Gassent, M.D. 2014. Implications of climate change on the distribution of the tick vector Ixodes scapularis and risk for Lyme disease in the Texas-Mexico transboundary region. Parasites & Vectors. 7:199.

Interpretive Summary: Lyme disease (LD) affects many people and domestic animals, including livestock, in the US and Europe and is caused by the microbe Borrelia burgdorferi, which is transmitted by some species of ticks in the genus Ixodes. Blacklegged ticks (I. scapularis) infected with B. burgdorferi can transmit this microbe to susceptible humans and animals through their bite. The blacklegged tick is present in the northeastern, upper midwestern, and southern US. However, LD is not transmitted everywhere the blacklegged tick lives. Knowing where infected blacklegged ticks exist is important to understand the risk for exposure to LD. Additionally, investigating how climate change may affect the suitability of habitats for the blacklegged tick will improve the accuracy of maps depicting the risk for LD transmission to humans and domestic animals. In this regard, LD risk maps in the transboundary region between the U.S. and Mexico are lacking and none of the published studies that evaluated the effect of climate change in the spatial and temporal distribution of the blacklegged tick have focused on this region. The area of study included Texas and a portion of northeast Mexico. This area is referred herein as the Texas-Mexico transboundary region. Tick samples were obtained from various animal species in this region. Ticks identified as I. scapularis were processed to determine by molecular techniques if they were infected with B. burgdorferi. A modeling approach called maximum entropy was used to forecast the present and future, up to the year 2050, distribution of blacklegged ticks in the Texas-Mexico transboundary region by correlating geographic data with climatic variables. The model generated through this study shows that the blacklegged tick can potentially be widely occurring in Eastern Texas and Northern parts of Mexico along the Gulf Coast as a continuous region. Extreme climate change conditions predict the maintenance of suitable areas for the blacklegged tick similar to those currently observed and potentially expanding towards central Texas. However, the ecology of LD remains to be fully understood in the Texas-Mexico transboundary region. Under these conditions, it will be necessary to continue the study of the distribution of this tick vector at the western and southern edges of its known range. Research on the range of animals the immature stages of the blacklegged tick can parasitize is required to enhance our understanding of the risk for LD transmission in the southern US and Mexico. The cycle of B. burgdorferi in wildlife from this region remains to be fully understood. A binational and collaborative approach to such scientific efforts is recommended to develop and adapt control and prevention strategies that will help manage the risk, and reduce the burden of LD in human populations living along the US-Mexico border.

Technical Abstract: Disease risk maps are important tools that help ascertain the likelihood of exposure to specific infectious agents. Understanding how climate change may affect the suitability of habitats for ticks will improve the accuracy of risk maps of tick-borne pathogen transmission in humans and domestic animal populations. Lyme disease (LD) is the most prevalent arthropod borne disease in the US and Europe. The bacterium Borrelia burgdorferi causes LD and it is transmitted to humans and other mammalian hosts through the bite of infected Ixodes ticks. LD risk maps in the transboundary region between the U.S. and Mexico are lacking. Moreover, none of the published studies that evaluated the effect of climate change in the spatial and temporal distribution of I. scapularis have focused on this region. The area of study included Texas and a portion of northeast Mexico. This area is referred herein as the Texas-Mexico transboundary region. Tick samples were obtained from various vertebrate hosts in the region under study. Ticks identified as I. scapularis were processed to obtain DNA and to determine if they were infected with B. burgdorferi using PCR. A maximum entropy approach (MAXENT) was used to forecast the present and future (2050) distribution of B. burgdorferi-infected I. scapularis in the Texas-Mexico transboundary region by correlating geographic data with climatic variables. Of the 1235 tick samples collected, 109 were identified as I. scapularis. Infection with B. burgdorferi was detected in 45% of the I. scapularis ticks collected. The model presented here indicates a wide distribution for I. scapularis, with higher probability of occurrence along the Gulf of Mexico coast. Results of the modeling approach applied predict that habitat suitable for the distribution of I. scapularis in the Texas-Mexico transboundary region will remain relatively stable until 2050. The Texas-Mexico transboundary region appears to be part of a continuum in the pathogenic landscape of LD. Forecasting based on climate trends provides a tool to adapt strategies in the near future to mitigate the impact of LD related to its distribution and risk for transmission to human populations in the Mexico-US transboundary region.