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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY AND CONTROL OF TICKS OF VETERINARY AND HUMAN IMPORTANCE

Location: Tick and Biting Fly Research

Title: Spatial and Temporal Distribution of Lyme Disease Infected Ticks in the Texas-Mexico Border Region

Authors
item Feria, Teresa -
item Gordillo-Perez, Guadalupe -
item Cavazos, Ana -
item Vargas-Sandoval, Margarita -
item Brown, Alexandra -
item Grover, Abha -
item Torres, Javier -
item Medina, Raul -
item Castro-Arellano, Ivan -
item PEREZ DE LEON, ADALBERTO
item Esteve-Gassent, Maria -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 14, 2013
Publication Date: N/A

Interpretive Summary: In some parts of the world tick-borne illnesses are among the most widespread and medically important vector-borne infectious diseases. Several tick-borne infectious agents affect livestock only, whereas others can be transmitted from animals upon tick feeding and cause disease in humans. Zoonotic is the term used to describe disease-causing agents transmitted from animals to humans. Climate variability is an aspect of global change that may influence the distribution and number of tick-borne disease cases in animal and human populations. Lyme disease (LD) is the most commonly reported vector-borne disease affecting humans in the U.S. There were 33,097 cases of LD reported to the Centers for Disease Control and Prevention in 2011. In the U.S., LD is caused by Borrelia burgdorferi, which is a micro-organism that can be transmitted to susceptible hosts by infected ticks of various species belonging to the genus Ixodes. There is a need to understand the current and future distribution of ticks transmitting the agent causing LD. In this regard, studies focusing on the Southern U.S., and in particular the U.S.-Mexico border, are lacking. We correlated geographic data with climatic variables using a tool that provides a range of probabilities in terms of habitat suitability for I. scapularis in the study area ranging from least suitable to most suitable habitat. This was done to forecast the present and future distribution of infected I. scapularis ticks in the U.S.-Mexico border region comprising south Texas and the northeastern Mexican states of Coahuila, Nuevo Leon, and Tamaulipas. One-hundred models were developed and evaluated using several climate change scenarios that predict a more heterogeneous world by 2050. The final model produced was the average of the 100 models analyzed. Maps were created to assess stable habitat for I. scapularis in the future. These findings showed suitable habitat now and in the future on the east and central parts of Texas and northern Mexico. These areas should be monitored to control I. scapularis populations and to assess the risk for humans to acquire LD. Other studies are underway in south Texas to evaluate several animal species as reservoirs for the LD causing agent in the transboundary region between the U.S. and Mexico.

Technical Abstract: Lyme disease (LD) is the most prevalent arthropod-borne infection in the United States, with 33,097 cases of LD reported to the Centers for Disease Control and Prevention (CDC) in 2011. The disease is transmitted to a mammalian host by Ixodes ticks infected with Borrelia burgdorferi. Efforts to understand the current and future distribution of Ixodes ticks are limited. Studies targeting the Southern U.S., and in particular the U.S.-Mexico border are lacking. Here, a systematic approach was applied to forecast the present and future distribution of infected Ixodes scapularis ticks in the U.S.-Mexico border region comprising south Texas and the northeastern Mexican states of Coahuila, Nuevo Leon, and Tamaulipas. Geographic data was correlated with climatic variables using a maximum entropy approach. Three different general circulatory models (CCCMA, CSIRO, and HANDLEY), and two IPCC scenarios (A2 and B2) were used. One hundred models were developed and evaluated via cross validation by dividing the data into 60% and 40% using the Area under the Curve (AUC) in a Receiver Operating Characteristics plot. The final model and AUC are the average of the 100 models. Binary maps were created to assess stable habitat for I. scapularis in the future. The final models had AUC >0.80, which indicates that the models were robust. These findings show suitable habitat now and in the future on the east and central parts of Texas and northern Mexico. These areas should be monitored to control I. scapularis tick populations and to assess the risk for humans to become infected with B. burgdorferi. Other studies are underway in south Texas to evaluate several animal species as reservoirs for the LD causing agent in the transboundary region between the U.S. and Mexico.

Last Modified: 7/25/2014
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