| Summary: | <i>Babesia</i> and <i>Theileria</i> are apicomplexan parasites that cause established and emerging diseases in humans, domestic and wild animals. These protozoans are transmitted by Ixodid ticks causing babesiosis or theileriosis, both characterized by fever, hemolytic anemia, jaundice, and splenomegaly. In North America (NA), the most common species affecting humans is <i>B. microti</i>, which is distributed in the Northeastern and Upper Midwestern United States (US), where the tick vector <i>Ixodes scapularis</i> is established. In livestock, <i>B. bovis</i> and <i>B. bigemina</i> are the most important pathogens causing bovine babesiosis in tropical regions of Mexico. Despite efforts toward eradication of their tick vector, <i>Rhipicephalus microplus</i>, <i>B. bovis</i> and <i>B. bigemina</i> present a constant threat of being reintroduced into the southern US and represent a continuous concern for the US cattle industry. Occasional outbreaks of <i>T. equi</i>, and <i>T. orientalis</i> have occurred in horses and cattle, respectively, in the US, with significant economic implications for livestock including quarantine, production loss, and euthanasia of infected animals. In addition, a new species, <i>T. haneyi</i>, has been recently discovered in horses from the Mexico-US border. Domestic dogs are hosts to at least four species of <i>Babesia</i> in NA that may result in clinical disease that ranges from subclinical to acute, severe anemia. Herein we review the pathogenesis, diagnosis, and epidemiology of the most important diseases caused by <i>Babesia</i> and <i>Theileria</i> to humans, domestic and wild animals in Canada, the US, and Mexico.
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