Cowdriosis

Cowdria ruminantium
Kingdom	Bacteria
Phylum	Proteobacteria
Class	Alphaproteobacteria
Order	Rickettsiales
Family	Ehrlichiaceae
Genus	Cowdria
Species	C. ruminantium

Also Known As: Heartwater — Ehrlichiosis — Nintas (South Africa)

Caused by: Cowdria ruminantium Also known as: Rickettsia ruminantium

Introduction

C. ruminantium is a bacterial gram negative coccal pathogen causing the tickborne disease “Heartwater” in ruminants in Subsaharan Africa. Animals often acquire the disease when moved on to heartwater infected grazing.

It is an intracellular bacteria, residing in endothelial cells and affecting the cardiovascular, respiratory and neurological systems.

Cowdriosis has a huge economic impact in Africa, both in direct losses and as an obstruction to the improvement of breeding stock due to the susceptibility of introduced high producing breeds.

Cowdriosis is notifiable to the World Organisation for Animal Health (OIE).

Distribution

Cowdriosis occurs across the African continent, particularly in South Africa.

Cowdriosis is transmitted by bont ticks, mainly of the Amblyomma genus (A. variegatum and A. hebraeum) but also Rhipicephalus, Hyalomma, and Glossina species and the Sarcoptes scabei mite. Both adults and nymphs of tick species can transmit disease.

Heartwater is therefore also a risk for countries where the Amblyomma tick is present, such as mainland America, Asia and the Caribbean, although disease may cutrently not be.

C. ruminantium develops and replicates within both its mammalian and invertebrate hosts.

Although speculated to be potentially zoonotic, there is no evidence of cowdriosis affecting humans.

Signalment

Cowdriosis affects a wide range of domestic and wild ruminants, although not all develop clinical disease. Clinical disease is most common in young animals.

Bos indicus (zebu) cattle appear more resistant than European breeds

Clinical Signs

Clinical signs are attributable to increased vascular permeability due to vascular endothelial cell invasion and consequent oedema and hypovolaemia:

Tachycardia, petechiae on mucous membranes\conjunctiva, weak pulses, muffled heart sounds.

Dull areas on percussion of the thorax, cough, purulent nasal discharge, abnormal respiratory noises, tachypnoea.

Head tilt, tremors, coma, circling, abnormal reflexes, hyperaesthesia, aggression, head pressing, depression, nystagmus, mydriasis and blindness.

Animals display a high fever which my progress to hypothermia. They gradually stop feeding and their behaviour changes.

Cowdriosis can also cause reproductive and gastrointestinal disease.

Various factors such as species, breed, age, natural resistance, vector efficiency and immune status dictate whether clinical disease develops and its severity.

Diagnosis

On post-mortem examination, a light yellow transudate that coagulates on exposure to air is often found within the thorax, pericardium and abdomen. Volume may vary but may be several litres in cattle. Most fatal cases will display the hydropericardium that gives the disease its common name, although this is seen more commonly in sheep and goats than cattle.

Pulmonary oedema and mucosal congestion are regularly seen along with frothy fluid in the airways and cut surfaces of the lungs.

The spleen may be enlarged and pulpy in consistency.

Although neurological signs are often attributed to cerebral oedema, this is not always obvious macroscopically although in some cases the brain and gyri may be strikingly swollen and/or petechiated.

The organism may be visible in smears of peripheral blood or the buffy coat.

In all suspect cases, presence of C. ruminantium must be demonstrated in preparations of the hippocampus under Giemsa staining or histopathology of brain or kidney.

Treatment

During the early febrile stages, sulphonamides and tetracyclines appear effective.

In advanced disease, prognosis is poor due to the intensive support therapy required and degree of cell death.

Control

Tetracyclines can be used prophylactically when animals are introduced into an area endemic with cowdriosis.

There is also a blood vaccine available for protection from heartwater in calves, lambs and kids in South Africa. As it contains live C. ruminantium organisms, treatment may be required in some animals post vaccination.

Control of exposure to bont ticks, whether total or strategic allowing a level of immunity to develop, is also vital but often difficult. It can be achieved through dipping with ectoparasiticides.

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References

This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project. The datasheet was accessed on 06 June 2011.