Heartwater

Heartwater is an infectious, noncontagious, tick-borne

disease of domestic and wild ruminants, including

cattle, sheep, goats, antelope, and buffalo. The disease is caused by an intracellular rickettsial parasite,

Cowdria ruminantium, and is transmitted by a number

of species of ticks in the genus Amblyomma.

Heartwater is usually an acute disease and is

commonly fatal within a week of onset of clinical

signs. The disease is widespread in most of Africa

and on several islands in the West Indies. With

increased trade and movement of animals in today’s

global market, heartwater may present a significant

threat to the domestic livestock industry in the United

States.

Livestock owners should monitor their animals for

exotic ticks and for clinical signs of the disease. If

heartwater is suspected, owners should immediately

report these findings to a veterinarian or to a State or

Federal animal health official.

History

Heartwater was first identified in sheep in South

Africa in the 1830s. By 1898, it was shown to be a

transmittable disease, and in 1900, the tropical bont

tick was identified as a vector. In 1980, heartwater

was reported for the first time in the Western

Hemisphere on the Caribbean island of Guadeloupe,

although the vector tick was probably introduced from

Africa much earlier. The disease is also present on

the Caribbean islands of Marie Galante and Antigua.

The tropical bont tick has spread to several other

islands in the Caribbean, although a definitive diagnosis of heartwater has not been made to date on

those islands.

Signs

The acute form of heartwater is the most commonly observed presentation of the disease. A sudden high fever (107° F) is followed by loss of appetite,

depression, and respiratory problems. Animals may

initially have an increased respiratory rate, followed

within a few days by severe respiratory distress.

Nervous disorders often follow the respiratory signs

and can include a variety of abnormal behaviors such

as excessive chewing movements, incoordination,

head tilting upward, overly rigid posture, and walking

with a high-stepping gait. Some animals may undergo convulsions or be unable to rise. These nervous

signs usually last for no more than 24 to 48 hours,

followed by the animal’s death. In some cases, the

nervous signs may not be noticed prior to death.

A mild form of the disease, known as heartwater

fever, is present in some affected regions among

indigenous breeds with a natural or acquired resistance to heartwater. The only clinical sign of the mild

form of the disease is a transient fever, and animals

with this form usually recover.

Postmortem Lesions

Heartwater derives its name from a common

postmortem finding of excessive fluid in the sac surrounding the heart. More commonly, the fluid accumulates within the lungs, thus the lungs appear “wet”

and heavy. The fluid may also accumulate within the

chest cavity itself, outside the lungs.

Confusion With Other Diseases

The observed nervous system abnormalities suggest other diseases (such as rabies, tetanus, meningitis, or encephalitis) or toxic poisoning.

A definitive diagnosis of heartwater is made by

microscopic examination and observation of the

causative rickettsia in a brain tissue smear.

How It Spreads

Heartwater is transmitted only by ticks of the

genus Amblyomma, with the tropical bont tick as one

of the most important vectors. This tick is widely distributed throughout Africa, Yemen, the Cape Verde

islands, and several islands in the Caribbean.

The life cycle of Amblyomma ticks may take from

1 to 4 years. Thus, the infection may persist, inside

the tick for a long time. In its immature stages, the

tick will feed on a wide variety of livestock, wild ungulates, groundbirds, small mammals, reptiles, and

amphibians.

Rapid spread of the tropical bont tick in the West

Indies has occurred since the 1960s. Movement of

tick-infested livestock was incriminated in some

cases, but overall, the cause of the spread of these

ticks has not been determined.

Cattle egrets became established in the region in

the 1950s and have been implicated in much of the

recent spread of heartwater. Small numbers of tickinfested cattle egrets have been shown to move

among islands in the region, but these birds are not

considered to be efficient disseminators of the tick.

Susceptible Species

Factsheet

Veterinary Services July 2002

APHIS
Animals susceptible to heartwater include cattle,

sheep, goats, and buffalo. Some breeds of cattle

(e.g., Jerseys and Brahmas) may be more susceptible

than others. Exotic ruminants can also contract the

disease.

In laboratory tests in the United States, the whitetailed deer (Odocoileus virginianus) has been shown

experimentally to be highly susceptible to heartwater.

Amblyomma maculatum, another potential vector, is a

common parasite of white-tailed deer in the Southern

United States. However, there is no evidence that

heartwater is present in wildlife in this country.

Prevention and Control

Preventive measures by livestock owners should

include implementation of an effective tick-control program, including regular inspection of animals and pastures for ticks and elimination of the vector through

the use of acaricides.

To prevent introduction of heartwater or any other

foreign animal disease, the U.S. Department of

Agriculture’s (USDA) Animal and Plant Health

Inspection Service (APHIS) tests imported animals for

heartwater and other diseases and ensures that all

animals are free of ticks or other potential insect vectors before entry into the United States is permitted.

What Can the U.S. Livestock Owner Do?

Livestock owners should monitor their animals

regularly for clinical signs of heartwater or tick infestation. If heartwater is suspected, a veterinarian, State

or Federal animal health official, or county agricultural

agent should be contacted at once.

The livestock owner is an essential link in the

cooperative effort to protect our Nation’s livestock

resources from costly and deadly foreign animal diseases. Both early recognition of disease signs and

prompt notification of animal health officials are

essential if prevention or eradication of these diseases

is to be successful.

For more information on heartwater disease, 

contact

USDA, APHIS, Veterinary Services

Emergency Programs

4700 River Road, Unit 41

Riverdale, MD 20737–1231

Telephone (301) 734–8073

Fax (301) 734–7817

You can also find information on VS programs by

visiting the Website at http://www.aphis.usda.gov/vs

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in all its programs and activities on the basis of race, color, national

origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to

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means for communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at

(202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of

Civil Rights, Room 326–W, Whitten Building, 1400 Independence

Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964

(voice and TDD). USDA is an equal opportunity provider and

employer.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture