Molecular detection of Anaplasma marginale infections in swamp buffaloes (Bubalus bubalis) in northeast, Thailand.

Bovine anaplasmosis caused by Anaplasma spp. is normally found in tropical and subtropical regions. Anaplasmosis pose important problems for animal health in Thailand since the disease is a tick-borne disease distributed via ticks that are prevalent in the cattle of the Northeastern, Thailand. However, there is few information of this disease in water buffaloes. The objective of this study was to determine the prevalence of A. marginale infections of water buffaloes in Northeast, Thailand by polymerase chain reaction (PCR). The molecular assay employs one set of primers for specific amplification and sequence analysis of the major surface protein 4 (MSP4). A total of 625 blood samples of water buffaloes collected from 6 provinces including Ubon Ratchathani, Roi Et, Buriram, Sakon Nakhon, Surin and Sisaket were investigated. The factors associated with Anaplasma spp. infections was compared on the basis of ages, genders, geographical regions, and herd. The overall infection was 8% (50/625) and all PCR positive was confirmed for A. marginale by sequencing. Herd prevalence was 13.6% (39/287) with statistically significant differences (P<0.05). The prevalence of water buffaloes with less than 1 year and between 1-5 years were 8.1% (3/37) and 8.1% (27/334) respectively, compared to 7.9% (20/254) in animals over 5 years. Males had the higher infection (10%, 9/90) than of females (7.7%, 41/535), and Ubon Ratchathani had the highest prevalence at 11.6% (16/138). INTRODUCTION Anaplasmosis is one of the major tick-borne diseases of cattle and other ruminants caused by species of the genus Anaplasma (Rickettsiales: Anaplasmataceae) (Dumler et al, 2001).The genus of Anaplasma spp. includes three species that infect ruminants such as A. marginale, A. central, A. bovis and A. phagocytophilum. Bovine Anaplasmosisis was characterized by haemolytic anemia associated with fever, weight loss, abortion, decreased milk production, and death (Wanduragala and Ristic, 1993). Transmission of A. marginale in cattle was occured by ticks, biting flies, and blood contaminated fomites (Kocan et al., 2003). Excluding cattle, A. marginale was found in water buffalo (Bubalus bubalis), American bison (Bison bison), white-tailed deer (Odecoileusvirginianus), mule deer (Odocoileus hemionus), black tailed deer (Odercoileus hemionus columbianus) and Rocky Mountain elk (Cervus elaphus nelsoni) (Zaugg et al., 1996). The conventional method for the diagnosis of Anaplasma infection is by the microscopic examination of stained blood smears. However, due to the low parasitemia in animals, this method is not recommended for the detection of subclinical animals or carriers (Carelli et al., 2007). Therefore, serological tests such as enzyme linked immunosorbent assay (ELISA) and immunofluorescent antibody test (IFAT) are required for their higher sensitivity tests. To consider the specificity of a test, polymerase chain reaction (PCR) is one of the alternative diagnosis that provides a powerful tool for epidemiological investigations with the high accuracy of Anaplasma spp. infection (de la Fuente et al., 2002). This molecular tool allows theoretically one molecule of DNA from the parasite to amplify up to million folds with high sensitivity and specificity. This technique has considerably decreased the number of false negative animals that are capable of revealing carriers. Thailand is an agricultural country located in Southeast Asia, where the livestock industry has been hampered by the severe tick-borne haemoparasites (Jittapalapong and Lieowijak, 1988). Water buffaloes are predominant animals in the Northeast, Thailand and provide an important source of meat, horns, hides, milk products, leather, land plowing, and transportation of people and crops (Somparn et al., 2004). Buffaloes are also susceptible to cattle diseases and parasites with less damages due to their breed resistance (Rajput et al., 2005). However, there are less update information of Anaplasma spp. infection in buffaloes. The objective of this study was to determine the prevalence of A. marginale infections of water buffaloes in Northeast, Thailand using Polymerase Chain