John Kirk and Heidi Hamlen

January 14, 2000

From Veterinary Medicine Extension, School of Veterinary Medicine, University of California Davis, Tulare (Kirk) and Animal Health Branch, Division of Animal Industry, California Department of Food and Agricultural (Hamlen).

Heartwater is a rickettsial disease of ruminants that occurs mostly in Africa and a few Caribbean Islands so why should dairymen in western United States even be remotely concerned about it? Heartwater is caused by the rickettsia Cowdria ruminantiu m and is a tick-borne disease. This means that the rickettsia is carried or transferred by ticks. The carrier ticks are in the family or genus, Amblyoma. Amblyoma ticks such as A. americanum, the Lone Star Tick and A. maculatum, the Gulf Coast Tick, are common in the US. These common ticks do not carry the Heartwater rickettsia, however, these ticks are similar to A. variegatum, the Bont Tick (Picture 1) that does carry the rickettsial agent of Heartwater. The carrier tic ks transmit the disease from one cow to another as they bite the cow and suck a blood meal (Picture 2).

The reason for concern is that the Bont Ticks having been showing up in the US. The ticks have been found in Florida on imported tortoises. Often pet owners become disenchanted with their exotic pets and release them into the wild. Released turtles wi th tick could easily transfer the ticks to other wild hosts. The ticks would certainly seek out other hosts, as they require three hosts to complete their life cycle. There is also the potential for infected ticks to arrive on Cattle Egrets (Picture 3) f lying in on hurricane winds from the Caribbean Islands. Each hurricane season brings new egrets to the US. These birds are seen commonly in California as they search for food in fields being irrigated.

Our cattle and wild ruminants are completely susceptible to Heartwater as it is a foreign animal disease that currently does not occur in the US. It has been estimated that we could expect between a 40% and 100% death rate if Heartwater entered the US . Clinical signs of Heartwater can be seen within 14 to 28 days after an infected tick feeds on a ruminant host. The death rate could be reduced by early treatment with tetracyclines if the disease is rapidly detected and properly diagnosed.

Heartwater exists in four different forms across the world. Upon entry into the susceptible populations, such as the US livestock, the peracute form would probably be seen. This form is characterized by sudden death preceded by only fever and convulsi ons (Picture 4). Later on Heartwater would be seen as fever followed by decreased eating, depression, listlessness and rapid breathing. Soon after, nervous signs such as chewing movements, twitching of eyelids, protrusion of tongue and circling would app ear. Death usually occurs within a week after the onset of these signs. This clinical picture could be confused with anthrax, rabies, tetanus, strychnine, lead or organophosphate poisoning,

The disease gets is name from the accumulation of fluid that is found around the heart in dead animals (Picture 5). Excess fluids are also found in the other body cavities (Picture 6) and edema is frequently seen.

The intent here is just to increase the level of awareness of the dairy industry to this potential disease threat. Actions are now being taken to prevent the entry of potential reptile carriers of the Bont Tick. Veterinary diagnostic laboratories acro ss the southern US are on alert for the presence of the Bont Tick on cattle and wildlife. Diagnosticians are watching for dead animals with the clinical signs of Heartwater. All these actions will clearly minimize the risk of a Heartwater outbreak in the US. For more information on Heartwater and other foreign animal diseases click on the USDA Animal Plant Health Inspection Service website at http://www.aphis.usda.gov/oa/new/ah.html or talk with you r local veterinarian.

Picture 1. Various stages of Amblyoma ticks similar to those that transmit Heartwater. Each stage of the tick from the very smallest to the fully-grown adults can carry the rickettsia.

Picture 2. Heartwater ticks shown feeding on a cow. During feeding, the ticks transmit the rickettsia from one cow to another.

Picture 3. Cattle Egret are known carriers of the Heartwater ticks.

Picture 4. Convulsions are a sign of Heartwater. This picture is of a deer reminding us that wild ruminants could play an important role in a Heartwater outbreak.

Picture 5. The exposed heart is located in the center of the photo surrounded by excessive fluid in the sac that surrounds the heart.

Picture 6. In addition to the fluids around the heart, excessive fluids are also seen in other body cavities such as seen around lungs in the chest cavity.