EHRLICHIOSIS (COWDRIOSIS, HEARTWATER)

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Causative Agent(s)

The causative organism is an obligate intracellular parasite, previously known as Cowdria ruminantium. Molecular evidence led to reclassification of several organisms in the order Rickettsiales, and it is now classified as Ehrlichia ruminantium. Under natural conditions, E ruminantium is transmitted by Amblyomma ticks.

Clinical Presentation and Epidemiology

A per acute, acute, sub-acute or chronic disease may occur.

Per acute syndrome is characterised by sudden death without premonitory signs. Sometimes animals may exhibit high fever, exaggerated respiratory distress, lacrimation, prostration, and terminal convulsions.

Acute disease is characterised by pyrexia, dullness, anorexia, congested and friable mucous membranes. Respiratory distress slowly develops along with nervous signs which include hyperaesthesia, unsteady or high-stepping gait, ataxia, circling or galloping movements, chewing movements, exaggerated blinking of eyes and aggression. Terminally, convulsions and prostration with bouts of opisthotonos, “pedalling”, “thrashing” or stiffening of the limbs are observed. Diarrhoea is seen occasionally.

Sub-acute heartwater clinical signs are less pronounced. Signs include listlessness, loss of weight and hair/wool, fall in temperature and ruminal atony. CNS involvement is inconsistent.

The chronic disease which is common in indigenous breeds of goats and sheep may be characterised by transient fever. Natural recovery and subsequent re-infection may be observed.

Diagnostic Considerations

Microscopic demonstration of the colonies of C. ruminatium in the cytoplasm of the endothelial cells of blood vessels and the brain, obtained by biopsy is necessary for definitive diagnosis. In dead animals, the organism can be demonstrated in brain crush smears prepared from the hippocampus or cerebral cortex.

Other method is by inoculation of blood from suspected animals in susceptible animals in which reproduction of clinical disease is a positive diagnosis.

Management and Treatment
  • Oxytetracycline long acting 20 mg/kg IM, repeated in 3-4

Doxycycline 5–10 mg/kg PO or IV for 10–21 days (drug of choice)

  • Tetracycline: 22 mg/kg, PO, three times a day for 10-21 days
  • Imidocarb dipropionate: 2 doses, 5–7 mg/kg, IM, 2 weeks apart
  • Supportive treatment: NSAIDs and appropriate fluid therapy