Cross-immunity studies in goats and mice using 4 isolates of Cowdria ruminantium, 2 from the Republic of South Africa (Kwanyanga and Kümm), 1 from the Republic of Mali (Mali 1), and 1 from Guadeloupe (Garde1), demonstrated antigenic variation among these isolates of heartwater. These studies suggest that the Mali isolate will protect goats against challenge with the Garde1 isolate, and that the Garde1 isolate will protect goats against challenge with the Kwanyanga isolate. The Kwanyanga isolate did not completely protect goats to challenge with the Garde1 isolate. The Garde1, Kwanyanga and Mali isolates, or combinations of these 3, did not protect goats from challenge with the Kümm, isolate. The Kwanyanga and Kümm isolates were compared with both homologous and hetrologous challenges in Swiss mice. The mice resisted homologous challenges, but heterologous challenge resulted in 100% death. The Garde1 and Mali isolates could not be passaged in or adapted to Swiss mice.
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