Molecular Detection of Anaplasma marginale in Amblyomma mixtum Infesting Cattle in the Major Livestock-Producing States of Mexico

Bovine anaplasmosis is a tick-borne disease caused by <i>Anaplasma marginale</i>, although mechanical transmission by biting flies also occurs. Infection with <i>A. marginale</i> can reach 26% mortality and morbidity is associated with reduced beef and milk production, causing economic losses for livestock producers. Between March 2022 and July 2023, 1920 ticks were collected from 52 cattle production units in major cattle-producing states in Mexico, including Chiapas, Jalisco, Michoacán, Tabasco, and Veracruz. Of all the ticks collected, 35.57% were morphologically identified as <i>Amblyomma mixtum</i>. Samples of <i>A. mixtum</i> from each state, totaling 271, were tested for <i>A. marginale</i> via polymerase chain reaction (PCR). <i>A. marginale</i> was detected molecularly in 15.3% of <i>A. mixtum</i> samples. <i>A. mixtum</i> from Chiapas had the highest prevalence of <i>A. marginale</i> (24.0%), followed by Tabasco and Veracruz (20.0% each), Jalisco (15.2%), and Michoacán (6.6%). Phylogenetic analysis supported the morphological identification of <i>A. mixtum</i> and confirmed the genetic identity of <i>A. marginale</i>. This research is the first report on the molecular detection of <i>A. marginale</i> in <i>A. mixtum</i> ticks in Mexico. Results suggest that this 3-host tick species might be a potential vector. <i>A. mixtum</i> is Mexico's second most economically significant tick feeding on cattle after <i>Rhipicephalus microplus</i>. This information about <i>A. marginale</i> prevalence in <i>A. mixtum</i> expands our understanding of bovine anaplasmosis epidemiology in Mexico. Further research is needed to assess the role of <i>A. mixtum</i> as a vector of <i>A. marginale</i>.