Experimental use of the attenuated Ehrlichia ruminantium (Welgevonden) vaccine in Merino sheep and Angora goats

The attenuated Ehrlichia ruminantium (Welgevonden) stock provides protection against a virulent homologous needle challenge in Merino sheep and Boer goats against heartwater. In this study, cryopreserved stabilates were tested for their suitability as a vaccine in Merino sheep. Vaccination did not produce disease and upon challenge with the virulent homologous stock all animals were fully protected. The vaccination protected all except one animal out of 5 challenged 12 months after immunization. The intramuscular route gave better protection than the subcutaneously applied vaccine. The attenuated vaccine was further evaluated in highly susceptible Angora goats. Although the attenuated vaccine showed an unexpectedly high degree of virulence, animals were fully protected against a lethal needle challenge.