Development and transmission of Cowdria ruminantium by Amblyomma males transferred from infected to susceptible sheep

Abstract

Male Amblyomma sp. were tested as vectors of Cowdria ruminantium, causative agent of heartwater disease. The males were allowed to feed on sheep experimentally infected with C. ruminantium and then were transferred to susceptible sheep to test for transmission of the rickettsia. The experiments were done in two trials. In the first trial, A. hebraeum were exposed to the Palm River stock of C. ruminantium, while in the second trial the Kiswani stock of Cowdria was tested with A. variegatum. Ticks were collected daily throughout each experiment, cut in half, and processed for light and electron microscopy to study development of C. ruminantium in tick tissues. In both trials, the male ticks transmitted Cowdria to one of two susceptible sheep. When ticks were examined with microscopy, a few colonies were found in gut cells while none were seen in salivary glands. Both species of ticks were infected with Rickettsia conorii, as evidenced by the occurrence of rickettsiae in the nucleus and cytoplasm of salivary gland cells.