SYMPTOMS and 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.
CAUSES and RELEVANCE to FLORIDA
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 is present on several islands in the West Indies. With increased trade and movement of animals in today’s global market, heartwater presents a significant threat to wildlife and the domestic livestock industry in the United States.
The U.S. Department of Agriculture estimates that a heartwater outbreak in the United States might cost the livestock industry $762 million in losses annually. The species of ticks that transmit Heartwater in the Caribbean islands can be carried to Florida with migratory birds. Florida is also a state that imports many exotic species of reptiles from Africa. While this trade is now regulated, history has shown that potentially infected ticks have been inadvertently imported by this route – fortunately without heartwater ensuing.
There are no commercially available vaccines for heartwater. Florida ranchers can minimize the risk of any infected ticks becoming established in Florida by regularly treating their cattle for ticks with acaricides.
The prevention of heartwater occurring in the U.S. relies upon keeping both potentially infected animals and ticks from entering the country. Strict import controls have been in place for several years for livestock originating from infected countries. More recently, import bans have been placed on certain tortoise species exported from Africa because they commonly carry potentially infected ticks. Florida’s subtropical climate accomodates these ticks in becoming established.