B055 - HEARTWATER

Nature of the disease

Heartwater or Cowdriosis is a ricketsial disease of Ruminants caused by Cowdria ruminantium and transmitted by ticks of the genus Ambylomma. It is characterrised by fever, oedema and diarrhea and has often a fatal issue.

Classification

OIE List B disease

Susceptible species

Domestic and wild ruminants species, including: cattle, buffaloes, goats, sheep, cervidae, antilope.

Distribution

Heartwater distribution was primarly limited to the African continent but it has recently extended to several Carribbean islands.

Clinical signs

Symptoms appear one to three weeks after the transmission, the disease is usually acute to peracute in naive animals, a mild form has been described where the disease is endemic.

The peracute form is characterised by a sudden offset of fever, prostration and death within one or two days.

The acute form includes the following signs:

Sudden high fever,
Loss of apetite and depression,
Resiparotry problem with dyspnea, tachypnea and respiratory distress,
Nervous signs such as ataxia, chewing movements, circling, aggression, blindness, recumbency and convulsions,
Fetid diarrhea,
Mortality ranges from 50 to 90 %, death occuring within the first two weeks

Post-mortem findings

Typical lesions observed at necropsy include:

Oedema in natural cavities including, hydrothorax, hydropericardum, ascites, pulmonary foecal,
Swollen lymph nodes,
Enlarged spleen

Differential diagnosis

Differential diagnosis includes:

Nervous conditions caused by tetanus or rabies
Poioning by strychnine, lead, arsenic, organophosphate or some plants
Babesiosis
Theileriosis,
Listeriosis

Specimens required for diagnosis

On the live animal serologic diagnostic can be realised by ELISA from serum samples. Identification of the agent can be attempted from blood on anticoagulant.

At postmortem identification of the agent can be done from smears from the cerebral cortex and cerebellum, intima of large blood vessels and spleen. Techniques include culture and PCR.

Transmission

Heartwater is transmitted by ticks of the genus Ambylomma. In ticks the tansmission is trans-stadial or trans-ovarian. Infected animals that recoered can be become chronic carriers for up to 8 months. The disease is not contagious.

Risk of introduction

The risk of introducing heartwater is mainly through the importation of infected animals or infectious ticks. The establishment of the disease depends on the existence of comptetent vector.

Control / vaccines

Medical treatment can be attempted using Tetracyclines and Sulfonamides.

Control of the disease depends mainly on the control of ticks. There is currently no vaccine available although experimental studies showed protection from inactivated vaccines.

References

Heartwater, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 531-532
Heartwater in Exotic Diseases of Animals, Aust Gov Publishing Service, Canberra, 1995, p. 349-353
Heatwater, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 1153-1155
Office International des Epizooties, 2002

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