As shown in Table 1, the prevalence of T. equi among stable horses was higher than that among grazing horses (25.81% vs. 15.02%, p b 0.0001). Different environmental conditions have a substantial effect on disease spread. This observed difference in T. equi prevalence may be related to a lower tick population among grazing horses as well as higher exposure to iatrogenic infection among stabled animals , the latter which is a documented malpractice seen in illegal horse racing in Mexico .