Table Of Content

Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. 1 / : 7 nt Health Inspection Service Program Aid No. 1498 Heartwater: A Tick-Borne Disease of Ruminants a Heartwater A Tick-Borne Disease of Ruminants Heartwater is an infectious, noncontagious, tick-borne disease ofdomestic and wild ruminants, including cattle, sheep, goats, antelope, and buffalo. The disease is caused byan intracellular rickettsial parasite, Cowdria ruminantium, and istransmitted primarilyviathetropical bonttick (Amblyomma variegatum)orotherticks in the genus Amblyomma. Heartwateriscommonlytransmitted bythe tropical bonttick,Amblyomma variegatum. Thetickisabout 1/8-1/4inch long before feeding butcan growas largeas 1/2-3/4 inch longafterfeedingon ananimal. The livestockownershould inspectall animalson the premisesfortickinfestation and reportclinical signsthatsuggest heartwatertoaveterinarian orStateor Federal animal health official. Heartwateris usually an acute disease and is commonly fatal within aweek of onset ofclinical signs. The disease iswidespread in most ofAfrica and on several islands in the West Indies. With increased trade and movement of animals in today's global market, heartwater may present asignificantthreattothe domestic livestock industry in the United States. Livestock owners should monitortheiranimalsforsigns of heartwater. If heartwater is suspected, owners should immediately reportthese findingsto aveterinarian orto a State or Federal animal health official. History Heartwaterwas first identified in sheep in South Africa in the 1830's. By 1898, itwas shown to be atransmittable disease, and in 1900, the tropical bonttickwas identified as avector. In 1980, heartwaterwas reported forthe first time in the Western Hemisphere on the Caribbean island of Guadeloupe, although the vectortickwas probably introduced from Africa much earlier. The disease is also present on the Caribbean islands of Marie Galante and Antigua. The tropical bonttick has spread to several other islands in the Caribbean, although a definitive diagnosis of heartwater has not been madeto date on those islands. Theterminalstagesofheartwater. Priorto death, theanimal mayconvulseandfall, dischargingfrothymaterialfrom itsnostrils and mouth. Fluid inthethin, membranoussac surroundingthe heartisacommon postmortemfinding inan animal infected with heartwater. Signs The acute form of heartwater is the most commonly observed presentation ofthe disease. A sudden high fever (107 °F) is followed by loss ofappetite, depression, and respiratory problems. Animals may initially have an increased respiratory rate, followed within a few days by severe respiratory distress. Nervous disorders often followthe respiratorysigns and can include avariety of abnormal behaviors such as excessive chewing move- ments, incoordination, star-gazing, head tilt, overly rigid posture, and walking with a high-stepping gait. Some animals may undergo convulsions or be unableto rise. These nervous signs usually lastfor no more than 24to 48 hours, followed bythe animal's death. In some cases, the nervous signs may not be noticed priorto death. A mild form ofthe disease, known as "heartwaterfever," is present in some affected regions among indigenous breeds with a natural oracquired resistanceto heartwater. The only clinical sign ofthe mild form ofthe disease is a transientfever, and animals with thisform usually recover. Postmortem Lesions Heartwaterderives its namefrom a common postmortem finding ofexcessive fluid in the sac surrounding the heart. More commonly, the fluid accumulates within the lungs, thusthe lungs appear"wet" and heavy. The fluid may also accumulatewithin the chestcavity itself, outsidethe lungs. Confusion With Other Diseases The observed nervous system abnormalities suggest otherdiseases (such as rabies, tetanus, meningitis, or encephalitis) ortoxic poisoning. Adefinitive diagnosis of heartwater is made by micro- scopic examination and observation ofthe causative rickettsia in a brain tissue smear. How Spreads It Heartwater is transmitted only byticks ofthe genus Amblyomma, with thetropical bonttickthe most important vector. Thistick is widely distributed throughoutAfrica, Yemen, the Cape Verde islands, and several islands in the Caribbean. The life cycle ofAmblyommaticks maytake from 5 months to 4 years to complete. Thus, the infection may persist in the environment, insidethetick, fora long time. The immature stages ofthe tickwill feed on awidevariety of livestock, wild ungulates, groundbirds, small mammals, reptiles, and amphibians. Rapid spread ofthetropical bonttick in theWest Indies has occurred sincethe 1960's. Movement oftick-infested livestockwas incriminated in some cases, but overall, the cause ofthe spread of heartwaterhas not been deter- mined. Cattle egrets became established in the region in the 1950's and have been implicated in much ofthe recent spread of heartwater. Small numbers oftick-infested cattle egrets have been shown to move among islands in the region, butthese birds are notconsidered to be efficient disseminators ofthetick. Susceptible Species Animals susceptibleto heartwater include domesticcattle, sheep, goats, and buffalo. Some breeds ofcattle (e.g.. Jerseys and Brahmas) may be more susceptiblethan others. Exotic ruminants can also contractthe disease. In laboratorytests in the United States, thewhite-tailed deer (Odocoileus virginianus)has been shown experi- mentallyto be highlysusceptibleto heartwater. Amblyomma maculatum, anotherpotential vector, is a common parasite ofwhite-tailed deer in the Southern United States. However, there is no evidencethat heartwater is present in wildlife in thiscountry. Prevention and Control Preventive measures bythe livestock ownershould include implementation ofan effectivetick-control program, including regular inspection ofanimals and pastures forticks and elimination ofthe vectorthrough acaricides. To prevent introduction of heartwaterorany otherforeign animal disease, the U.S. Department ofAgriculture's Animal and Plant Health Inspection Service (APHIS) tests imported animals for heartwaterand otherdiseases and ensures that all animals are free ofticks orotherpotential insectvectors before entry into the United States is permitted. A"U.S. GOVERNMENT PRINTINGOFFICE 1993: 359-993 What Can the U.S. Livestock Owner Do? Livestock owners should monitortheiranimals regularly forclinical signs of heartwaterortick infestation. If heartwater is suspected, aveterinarian, State or Federal animal health official, orcounty agricultural agent should be contacted at once. The livestockowner is an essential link in the cooperative effortto protect our Nation's livestock resources from costly and deadlyforeign animal diseases. Both early recognition of disease signs and prompt notification of animal health officials are essential if prevention or eradication ofthese diseases isto be successful. Forfurther information on heartwaterdisease, you may contact: USDA-APHIS-Veterinary Services Emergency Programs P.O. Box 96464 Washington, DC 20090-6464 ortelephonethat office at (301) 436-8073. The U.S. DepartmentofAgriculture (USDA) prohibitsdiscrimina- tion in itsprogramsonthebasisofrace, color, nationalorigin, sex, religion, disability, political beliefs, and marital orfamilial status. (Notall prohibited basesapplytoall programs.) Persons with disabilitieswho requirealternative meansforcommunication ofprogram information (braille, large print, audiotape, etc.) should contactthe USDAOfficeofCommunicationsat(202) 720-5881 (voice) or(202) 720-7808 (TDD). Tofileacomplaint, writetheSecretaryofAgriculture, U.S. DepartmentofAgriculture, Washington, DC20250, orcall (202) 720-7327 (voice) or(202) 720-1127(TDD). USDAisan equal employmentopportunityemployer.