Genetic diversity of Anaplasma marginale in Argentina.

PAULA RUYBAL; ROSALÍA MORETTA; ROMINA PETRIGH; ANDRES PEREZ; SILVINA WILKOWSKY; PABLO NUÑEZ; KATHERYN KOCAN; JOSE DE LA FUENTE; SUSANA TORIONI DE ECHAIDE; MARISA FARBER

Merida, Mexico

Congreso; 9th Biennial Conference of the Society of Tropical Veterinary Medicine; 2007

Society of Tropical Veterinary Medicine

Anaplasmosis, caused by the intraerythrocytic rickettsia Anaplasma marginale, is a worldwide major constraint in cattle production. This study reports the first characterization of A. marginale genetic diversity based on the genotype marker msp1a and its putative relationship with Boophilus microplus infestation influence within Argentinean soil. For this purpose, we analyzed whole blood bovine samples from anaplasmosis outbreaks from B. microplus infested (9 samples) and eradicated/free (14 samples) regions. Sequence analysis revealed the existence of 15 different genotypes and 31 different repeat units. Twenty of these repeat units were already reported in a recently published worldwide analysis of this marker, 8  of them being unique to Argentina. In addition, 6 new repeats are reported for the first time in this work. According to tick regions, three groups of repeat units could be defined: associated to the presence of ticks (20 repeats), to the absence of ticks (6 repeats) and randomly distributed (5 repeats). Even when sequence M was detected in genotypes from the two regions, it resulted statistically associated to tick absence and also presented a specific geographical distribution that underscore this association. This analytic approach of sequence distribution may collaborate to elucidate A. marginale flow within Argentinean livestock. It was previously suggested that A. marginale strains containing these repeats may have co-evolved with the tick vector. This support the higher variability observed in Argentinean tick infested region compared to tick free/eradicated region and might suggests an important role to tick-mediated transmission as significant factor for the generation of genetic variability of this parasite. Moreover, we also report the coexistence of 2 and 4 different genotypes in bovine samples from tick infested region. Finally, three of the 31 sequences showed a serine aminoacid as a new variation at position 20 within the repeat unit. This aminoacid position was suggested to be important in the rickettsia adhesion to erythrocytes and tick cells, therefore new adhesion experiments to test the function of this aminoacid in MSP1a peptides must be done. This work represents the first report of genetic variability of A. marginale strains in Argentina. Moreover, B. microplus infested and free regions were analyzed demonstrating a higher variability according to tick influence. Characterization of A. marginale strains diversity is fundamental to the design of epidemiological, virulence and vaccine development studies and control strategies for bovine anaplasmosis.