Genetic diversity of Anaplasma marginale strains from an outbreak of bovine anaplasmosis in an endemic area Consuelo Alamza ´n a , Citlaly Medrano a , Martı ´n Ortiz b , Jose ´ de la Fuente c,d, * a Facultad de Medicina Veterinaria y Zootecnia, Universidad Auto ´noma de Tamaulipas, Km. 5 carretera Victoria-Mante, CP 87000 Victoria, Tamaulipas, Mexico b Novartis Salud Animal, SA de CV, Mexico c Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA d Instituto de Investigacio ´n en Recursos Cinege ´ticos IREC (CSIC-UCLM-JCCM), Ronda de Toledo s/n, 13005 Ciudad Real, Spain Received 13 August 2008; received in revised form 27 August 2008; accepted 27 August 2008 Abstract Anaplasma marginale is a tick-borne pathogen of cattle that causes the disease bovine anaplasmosis worldwide. Major surface proteins (MSPs) are involved in host–pathogen and tick–pathogen interactions and have been used as markers for the genetic characterization of A. marginale strains. A. marginale genotypes are highly variable in endemic areas worldwide. The genetic composition of A. marginale strains during anaplasmosis outbreaks has been characterized in one study only which reported a single msp1a genotype in infected cattle. However, more information is required to characterize whether a single genotype is responsible for an anaplasmosis outbreak or whether multiple genotypes can cause disease in naı ¨ve cattle within a single herd in endemic areas. The aim of this study was to characterize the genetic diversity of A. marginale strains from an outbreak of bovine anaplasmosis in the State of Tamaulipas, Mexico. A. marginale genotypes were characterized at the molecular level using msp4 and msp1a gene sequences. The results revealed that several A. marginale genotypes are present in cattle during acute anaplasmosis outbreaks, thus suggesting that mechanical transmission or stochastic biological transmission through equally efficient independent transmission events may explain A. marginale genotype frequency in a cattle herd during acute bovine anaplasmosis outbreaks in endemic areas. The results reported herein corroborated the genetic heterogeneity of A. marginale strains in endemic regions worldwide. The development and implementation of anaplasmosis control measures is dependent upon understanding the epidemiology of A. marginale in endemic regions, including the characterization of the genetic diversity of strains that produce outbreaks of bovine anaplasmosis. # 2008 Elsevier B.V. All rights reserved. Keywords: Anaplasmosis; Major surface protein; Evolution; Tick; Genetics; Mexico; Boophilus microplus 1. Introduction Bovine anaplasmosis is caused by Anaplasma marginale, the type species of the genus Anaplasma (Rickettsiales: Anaplasmataceae). Ticks are biological vectors of A. marginale but the pathogen is often transmitted mechanically to susceptible cattle by blood- contaminated mouthparts of biting flies or fomites (Kocan et al., 2004). These obligate intracellular www.elsevier.com/locate/vetpar Available online at www.sciencedirect.com Veterinary Parasitology 158 (2008) 103–109 * Corresponding author at: Instituto de Investigacio ´n en Recursos Cinege ´ticos IREC (CSIC-UCLM-JCCM), Ronda de Toledo s/n, 13071 Ciudad Real, Spain. Tel.: +34 926 295450; fax: +34 926 295451. E-mail addresses: jose_delafuente@yahoo.com, josedejesus.fuente@uclm.es (J. de la Fuente). 0304-4017/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2008.08.015