Introduction: Anaplasmosis is a disease that destroys the red blood cells of the body. It can infect any breed of cattle and is found most commonly in the tropics and subtopics of the American and African continents, and in Australia and the South Pacific. It has been diagnosed in cattle in all of the 48 contiguous United States, but is most often found in the southeast, the Intermountain West and California.
Causative Agent: Anaplasmosis is caused by an organism called Anaplasma marginale. Anaplasma marginale is technically a rickettsial organism which is smaller than a bacteria and larger than a virus. There is also a more benign species, Anaplasma centrale, which is found commonly in cattle in Africa. Some species of Anaplasma are found in deer and antelope.
Since anaplasmosis can be transmitted by ticks, it is often transmitted along with Babesiosis bovis and B. bigemina (see page F60). The combination then produces tick fever, a fatal syndrome in cattle.
Clinical Signs: Depression, lack of appetite, fever (commonly between 104-106 degrees F), decreased milk production, and jaundice (yellowness to the gums and whites of the eyes) are common signs. As the disease progresses, anemia (lack of red blood cells) develops, followed by weight loss and dehydration. Clinicians will often discover hypoxia (a lack of oxygen) to be the cause of death when affected animals are moved or handled for treatment.
The age of the affected animal often determines the severity of the disease. Calves usually suffer mild infections with little or no mortality. Yearlings suffer more, but most recover. Adult cattle have marked anemia and mortality is between 20% and 50%. Recovered animals often remain carriers for life.
Disease Transmission: The infection is easily transferred by exposure to infected blood. This can happen in situations such as mass operations of dehorning, castrating, ear-tagging, and vaccinating without proper disinfection of equipment between animals. The disease can also be spread by ticks. At least 20 tick species have been known to transmit the disease.
Diagnosis: Mature cattle with anemia, yet without hemoglobinuria (blood in the urine), and those with jaundice should be suspected to have contracted the disease. Several tests can be used to identify anaplasmosis. Some of these include Giemsa-stained RBCs in blood smears, serology, indirect FA test and a DNA probe. During a necropsy on an infected animal, the blood is usually thin and watery, and jaundice is noted throughout the carcass. The spleen will be enlarged and soft. The liver will be discolored to a mottled mahogany color. The bile is thick and brownish green and the gallbladder can be distended.
Treatment: Since even mild exertion can result in hypoxia and death, it is important that the affected animal be disturbed as little as possible. Most animals that survive the initial destruction of RBCs usually recover gradually. Administration of tetracyclines is the most effective treatment for acute anaplasmosis, especially if the drug is used early in the course of the infection. Some attempts to clear carrier infections have been successful with intramuscular (IM) administration of oxytetracycline at 20 mg/kg body weight, 4 times at 3-day intervals, or 3 times at 7-day intervals.
In some cases, transfusions may be performed. Between 4 and 12 liters of blood can be transfused and may be repeated after 48 hours. Large volumes of water administered by stomach tube and the administration of dextrose are also helpful. Although mild laxatives may be given, saline laxatives should be avoided because they can cause further dehydration of the animal. Access to plenty of feed, water and shade are important for recovery.
Prevention: Managing the presence of ticks (especially the Dermacentor tick) and large biting flies (such as horse flies) with frequent use of chemical dusts and sprays is an effective way to control the spread of anaplasmosis. A killed vaccine for anaplasmosis is available in the United States and will reduce the severity of infection in most cases. Imidocarb dipropionate is also effective against anaplasmosis when administered as a prophylactic (preventative) at 1.4 mg/lb. It will provide several weeks protection to susceptible animals moved into an endemic area.