Comparison of iatrogenic transmission of Anaplasma marginale in Holstein steers via needle and needle-free injection techniques

Objective—To compare iatrogenic transmission of Anaplasma marginale during sham vaccination between needle and needle-free injection techniques. Animals—26 Holstein steers confirmed negative for anaplasmosis by use of a competitive ELISA (cELISA) and an A marginale-specific reverse transcription (RT)-PCR assay. Procedures—An isolate of A marginale was propagated to a circulating parasitemia of 2.0% in a splenectomized steer. Sham vaccination was performed in the left cervical muscles of the splenectomized parasitemic steer with a hypodermic needle fitted to a multiple-dose syringe. The same needle and syringe were used to sham vaccinate a naive steer. This 2-step procedure was repeated until 10 naive steers (group ND) were injected. Similarly, sham vaccination of the left cervical muscles of the splenectomized parasitemic steer and another group of 10 naive steers (group NF) was performed by use of a needle-free injection system. Five control steers were not injected. Disease status was evaluated twice we...