Evaluation of mechanical transmission of Anaplasma marginale by Stomoxys calcitrans

The objective of this study was to investigate the mechanical transmission of Anaplasma marginale to cattle by Stomoxys calcitrans. The S. calcitrans were obtained in field condition and their offspring (first generation) were used in this study originating in the laboratory. In method 1 (flies released freely in cattle pens), from D0 to D + 10, approximately 3300 flies fasted for 24 h were released daily per pen with infected and healthy calves. In the second method (feeding chambers for artificial interruption of blood meals), for each negative calf, three chambers were used, each containing four flies fasted for 24 h, totaling 12 flies per calf. Blood smears, PCR and ELISA were performed to detect A. marginale in the animals. Furthermore, the animals' head tossing and hoof stomping and the number of flies near the pens' inner walls were recorded. In the presence of the flies, the calves exhibited defensive movements compared to those without flies. None of the negative calves demonstrated the presence of A. marginale (blood smear, PCR, and ELISA). In conclusion, although A. marginale was found on the abdomen of S. calcitrans, this fly failed to transmit this rickettsia to cattle in either transmission method employed.