Heartwater, also known as Cowdriosis, is a tick-borne disease of ruminants caused by the rickettsial organism Ehrlichia cowdriatum. The organism was formerly called Cowdria ruminatum, but the results of molecular studies precipitated the name change. It is transmitted by ticks of the genus Amblyomma and occurs in parts of Africa, some islands in the Indian Ocean as well as some islands in the eastern Caribbean.
In the 1990’s there was a concerted effort to eradicate Amblyomma ticks from the Eastern Caribbean and, as a result halt the spread of Heartwater which had been introduced to the region by some unknown means. The programme involved the use of the acaricide flumethrin (Bayticol®) at specified intervals on all ruminant species. There was also research into the migratory patterns of the Cattle Egret (Bubulcus ibis) which had been shown to transport nymphal stages of the tick, an could therefore spread it between the islands. It was unsuccessful in eliminating the tick, but at this time Heartwater appears to be confined to the islands of Antigua and Guadeloupe3 where the principal transmitting species is the Tropical Bont tick A. variegatum.
Heartwater is a serious, life-threatening illness affecting domestic and wild ruminants. Among the domestics, goats are most susceptible. Clinical signs may vary in severity from peracute to sub-acute and include respiratory distress, collapse, neurological signs such as opisthotonus and paddling. Death may occur in hours to days in the peracute or acute forms, while animals with the less severe form may undergo a long recovery.
Post mortem gross lesions of note include pleural and pericardial effusion (fluid in the chest and around the heart) which clots rapidly on contact with air, pulmonary edema and intestinal congestion. Smears of brain tissue may be examined for organisms and their presence is considered diagnostic.
If caught early, treatment can be effective. Tetracyclines such as Oxytetracycline, Chlortetracycline and Doxycycline may be used along with other supportive measures.
Heartwater has not been diagnosed in Jamaica, but as usual, the veterinary community must maintain vigilance as ticks are very capable of stowing away on the bodies of migrating birds. A recently published paper documents the discovery of Amblyomma dissimile ticks – normally resident in Central and South America and the Caribbean - on a migratory songbird in Canada4.
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