DEMONSTRATION OF VERTICAL TRANSMISSION OF COWDRIA-RUMINANTIUM, THE CAUSATIVE AGENT OF HEARTWATER, FROM COWS TO THEIR CALVES

One of the most important questions about the epidemiology of heartwat er in the field is how Cowdria ruminantium is transmitted within verte brate host populations. In this study vertical transmission of C. rumi nantium from cows to their calves was demonstrated. Twelve mixed-breed calves, born to dams living in a heartwater-endemic area of Zimbabwe, were tested post-natally for the presence of C. ruminantium. Vertical transmission was demonstrated to occur under natural field conditions using tests in which uninfected laboratory-reared Amblyomma ticks wer e fed on neonatal calves and subsequently either fed on, or inoculated into, susceptible small ruminants or tested by a polymerase chain rea ction (PCR) assay. Prior to natural Amblyomma tick infestation, C. rum inantium infection in 5 of the 12 calves was confirmed by tick transmi ssion to small ruminants and 11 of the 12 calves tested positive based on PCR analysis of ticks fed on them. The role of colostral cells, as one mode of infection, was demonstrated by the transmission of C. rum inantium to three out of five goats inoculated intravenously with viab le colostral cells collected from dams living in a heartwater-endemic area. The significance of vertical transmission is presented in relati on to the epidemiology and control of heartwater.