Demonstration of Anaplasma marginale Theiler in ticks by tick transmission, animal inoculation, and fluorescent antibody studies.

Cattle were inoculated with a Virginia isolate of Anaplasma marginale Theiler and served as an infective source for laboratory-reared Dermacentor andersoni Stiles and D variabilis (Say) nymphs. Transstadial transmission of A marginale was demonstrated by feeding the newly molted adult ticks of both species on susceptible cattle and by inoculation of gut and salivary gland homogenates collected from adult ticks at postattachment days 5 and 7. Oral secretions collected from the same group of ticks and inoculated into a susceptible cow did not cause infection. Fluorescent antibody studies of infected tick gut and salivary glands were positive, although smears of tick oral secretions were negative for fluorescence.