THE INACTIVATED COWDRIA-RUMINANTIUM VACCINE FOR HEARTWATER PROTECTS AGAINST HETEROLOGOUS STRAINS AND AGAINST LABORATORY AND FIELD TICK CHALLENGE

We previously described that art inactivated vaccine against hear?wafe r prepared fi-om Cowdria ruminantium (Crystal Springs strain) organism s and administered in complete Freund's adjuvant (cFA) protected sheep against homologous needle challenge. Further studies, described herei n, demonstrated that this vaccine protected 100% of sheep against deat h on challenge with laboratory-infected ricks and with field ticks in a heartwater endemic farm, whereas a mortality rate of 44% and 62%, re spectively, was recorded in the control sheep, Subsequently, the Mbizi strain of C, ruminantium was incorporated into the vaccine because of its wider cross-protective capacity and trial data suggested that pro tection may be achieved against challenge with diverse geographical st rains using this strain. The efficacy of five adjuvants with acceptabl e safety was compared with that of cFA, Against a homologous intraveno us challenge highest survival rates were observed in sheep vaccinated with inactivated C. ruminantium in either cFA, Montanide ISA 50 or Qui l A, The vaccine prepared in Montanide ISA 50 protected six of seven s heep against natural challenge from field ricks on a farm in Zimbabwe where heartwater is endemic whereas six of seven control sheep died (P = 0.029). These data support optimization of the vaccine prepared in Montanide ISA 50, followed by evaluation of its efficacy in all target domestic ruminant species and in other geographical regions where hea rtwater constrains livestock production. (C) 1998 Elsevier Science Ltd . All rights reserved.