Heartwater (also known as cowdriosis) is an acute, fatal, non-contagious, infectious, tick-borne rickettsial disease of ruminants caused by Ehrlichia ruminantium (formerly Cowdria ruminantium) and transmitted by Amblyomma ticks. it occurs in nearly all sub-Saharan countries of Africa, in its neighbouring islands, and also in the Caribbean, threatening the American mainland. The disease can cause high mortality (up to 90%) in susceptible domestic ruminants. Goats and sheep are more susceptible than cattle, and European breeds are generally more susceptible than indigenous African breeds. Clinically, the disease most commonly presents as an acute form characterised by a sudden high fever, depressed demeanour, nervous signs and a high mortality. Hydropericardium and hydrothorax and lung oedema are commonly associated post-mortem signs. Acute and peracute clinical forms of the disease occur: In the former, there are high death rates without many clinical manifestations and in the latter, there is a higher recovery rate. Recovered animals become carriers of infection. Certain wild animals can play a role as reservoir; Rusa deer, white tailed deer, and springbok are susceptible to this infection and can experience high mortality. Identification of the agent: The specific diagnosis of heartwater is based on the observation of colonies of E. ruminantium in capillary endothelial cells of the brain. In the absence of adequate tools, a piece of cerebellum can easily be removed with a curette through the foramen magnum after cutting off the head, while a sample of cerebral cortex can be obtained through a hole made in the skull with a hammer and a large nail. Brain smears are prepared by crushing to a paste and spreading thinly a small piece of cerebral or cerebellar cortex between two microscope slides. The capillaries are spread out in a single eel/ layer by drawing one slide across the other. The smears are air-dried, fixed with methanol and stained with Giemsa. With fast st