Immunohistochemical identification of Cowdria ruminantium in formalin-fixed tissue sections from mice, sheep, cattle and goats.

An immunohistochemical staining technique in which a monospecific serum was used against the major antigenic protein -1 (MAP-1) of Cowdria ruminantium, was evaluated for the detection of C. ruminantium in formalin-fixed tissues of experimentally infected mice and field cases of heartwater in sheep, cattle and goats. Mice were infected with the mouse-pathogenic stocks: Mara, Kwanyanga, Welgevonden, Nonile, Vosloo, Kümm, Mali and Omatjenne. In all these cases and in the naturally infected cattle, sheep and goats, Cowdria colonies were identified as clearly-defined, brown-staining rickettsial colonies within the cytoplasm of endothelial cells. No positive staining was observed in the control group. This technique was shown to be reliable for detecting infection with C. ruminantium in the formalin-fixed tissues of mice and domestic ruminants.