A mouse lethal dose assay for detection and titration of Cowdria ruminantium (Kwanyanga strain) in goats and ticks

A mouse lethal dose assay was used to detect a mouse pathogenic strain (Kwanyanga) of Cowdria ruminantium, the etiological agent of heartwater in goats and ticks. The titer of the rickettsial organisms in goat blood was directly related to the febrile response of the goat and the rickettsia were undetectable after the fever subsided. The maximum rickettsial titer in goat blood was 10 3 mouse LD 50 ml −1. Cowdria-infected goat blood was shown to retain infectivity when held on ice for up to 2 h, but when held at room temperature infectivity declined by > 50% in 2 h. The mouse assay detected Cowdria in feeding female Amblyomma variegatum only on the eight day of feeding and in feeding males on the second and eleventh days of feeding. Cowdria was shown to persist in the hemolymph of the soft tick Ornithodoros coriaceus for a period of at least 2 years.