Kingdom Bacteria Class Alpha proteobacteria Family Rickettsiaceae | Phylum Proteobacteria Order Rickettsiales Genus Ehrlichia | |
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Heartwater (also known as cowdriosis, nintas and ehrlichiosis) is a tick-borne rickettsial disease of domestic and wild ruminants. It is caused by Ehrlichia ruminantium (formerly Cowdria ruminantium) - an intracellular gram-negative coccal bacterium (also referred to as Rickettsia ruminantium). The disease is spread by bont ticks, which are members of the genus Amblyomma. Affected mammals include cattle, sheep, goats, antelope, and buffalo, but the disease has the biggest economic impact on cattle production in affected areas. The disease’s name is derived from the fact that fluid can collect around the heart or in the lungs of infected animals.
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The disease is common in sub-Saharan Africa and some of the West Indian islands. It was first identified in sheep in South Africa in the 1830s, and had reached the Caribbean by 1980. The ticks which carry the disease occur in Africa and the Caribbean, and feed on a wide variety of vertebrate hosts. In the Caribbean, at least, the cattle egret has been implicated in the spread of heartwater since it colonized the islands in the 1950s. Animals often acquire the disease when moved on to heartwater infected grazing.
Cowdriosis is notifiable to the World Organisation for Animal Health.
Clinical signs
Clinical disease is more common in young animals and non-native breeds. The clinical signs of disease are caused by an increased vascular permeability and consequent oedema and hypovolaemia.
The symptoms include neurological signs such as tremors and head pressing, respiratory signs such as coughing and nasal discharge, and systemic signs such as fever and loss of appetite. Physical examination may reveal petechiae of the mucous membranes, tachycardia and muffled heart sounds. Cowdriosis can also cause reproductive and gastrointestinal disease. It is frequently fatal.
Diagnosis
On post-mortem examination, a light yellow transudate that coagulates on exposure to air is often found within the thorax, pericardium and abdomen. Most fatal cases will have the hydropericardium that gives the disease its common name. Pulmonary oedema and mucosal congestion are regularly seen along with frothy fluid in the airways and cut surfaces of the lungs.
To definitively diagnose the disease, C. ruminantium must be demonstrated either in preparations of the hippocampus under Giemsa staining or by histopathology of brain or kidney.
Treatment and control
During the early stages of disease animals may be treated with sulfonamides and tetracyclines. In advanced disease, prognosis is poor.
Tetracyclines can also be used prophylactically when animals are introduced into an area endemic with cowdriosis. A live blood vaccine is available for protection of young stock, but animals may require treatment for the disease post-vaccination. Ectoparasiticides dips can be used to reduce exposure the animals exposure to bont ticks. In areas endemic for heartwater there is likely to be use of dips against other ticks of domestic animals, such as Rhipicephalus (Boophilus) and Hyalomma species and this will usually contribute to control of vectors of Ehrlichia ruminantium.