Heartwater Disease

Abstract

Heartwater, or cowdriosis, is one of the main causes of death in imported and improved cattle in Africa south of the Sahara. It is an acute febrile disease of ruminants, associated with nervous, intestinal and pulmonary disorders, caused by the rickettsia Cowdria ruminantium, and transmitted by several species of Ablyomma ticks.

Local cattle in endemic regions have acquired considerable resistance through long natural selection. Endemic resistance without clinical disease is not attained in susceptible breeds. Only very young calves possess a considerable degree of age-resistance to the disease. Solid or partial protective immunity, lasting for several years, follows recovery. The nature of protective immunity is unknown.

The course of the disease, the post-mortem lesions and the pathogenesis of heart-water are reviewed. Unequivocal diagnosis of heartwater is possible only by the microscopical demonstration of rickettsial colonies in endothelial cells of blood vessels, especially in the capillaries in smears of brain cortex.

Acaricidal control of the vectors must be frequent and efficient if heartwater transmission is to be prevented. Immunization of cattle by infection and treatment is possible, but the method is rather unsatisfactory, unsuitable for application on a large scale, and far from optimally safe and effective. Attempts at attenuation of strains have failed. Tetracyclines are the best available drugs for treatment, but their action is slow and chemotherapy commonly fails if delayed until typical nervous systems have developed.