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.