Research

Clinical Case Review

Anaplasmosis

By: Dr. Matt Fruge Production Animal Consultation

Anaplasmosis is the term used to describe the disease of cattle caused by infection with the protozoan parasite genus Anaplasma with the most commonly encountered species being marginale. Often referred to as “Anaplaz,” the disease is common in the southern United States. Anaplasma organisms live within the red blood cells of infected cattle. Anaplasma is an economically important disease as it causes loss of production, decreased reproductive efficiency, and death loss.

Transmission

Transmission of Anaplasma parasites occurs through vectors (i.e., ticks) which vary based on geographical region and climate. Commonly, the Anaplasma parasite is spread by several species of tick. Once the tick bites an infected animal, the tick not only consumes the blood of the animal but also the Anaplasma parasite. Once inside the tick, the Anaplasma species multiply. When the tick consumes a blood meal on another animal, the organism is then spread to that animal. In some regions, transmission occurs mechanically through the biting of Tabanid flies (deer flies, horse flies). Another important mechanism of transmission is through production practices which exchange blood between animals, such as using the same needle between animals, dehorning, castrating, palpating, etc.

Pathogenesis

Once infection occurs, the organism colonizes red blood cells within the infected animal. Usually, the infected animal can keep the organism to a manageable level without evidence of clinical disease. The infected red blood cells are generally recognized by the immune system and then are destroyed. By this mechanism the parasite is kept at low enough levels to prevent clinical disease. Some animals become immunosuppressed which may lead to clinical signs due to concurrent disease. Generally, as animals age they lose their ability to resist clinical disease. Although calves are very susceptible to becoming infected with the parasite, infection is usually subclinical in cattle younger than one year old. Yearlings up to two years of age may suffer moderate illness from infection, and cattle older than two years become severely ill if their immune system can not keep the parasite at bay.

Clinical Disease

Severity of clinical disease is dependent on age of the animal affected. Calves under 12 months of age are very resistant to clinical disease and rarely show symptoms following natural infection. Cattle between 12 and 24 months of age are more likely to show clinical symptoms of disease, but rarely die from it. Animals over 2 years of age are much more likely to suffer severe disease and many of them die if they do not receive timely treatment. Older animals are also more likely to become chronically infected with the disease and are more likely to exhibit long term loss of production and become a source of infection for herd mates.

Clinical illness associated with acute anaplasmosis is often colloquially referred to as “jaundice,” due to the animal’s apparent yellow color. This is the result of red blood cell destruction by the immune system. Contents of red blood cells color the animal’s mucous membranes yellow. Other findings may include rapid loss of condition, inappetence, depression, abrupt reduction in milk production, brown urine, and high fever. Animals may be found wading in mud holes in an attempt to cool off due to elevated temperature. Pregnant animals often abort. Advanced disease causes very anemic animals resulting in cattle which are exercise intolerant. Occasionally, severely affected animals show an aggressive nature, so care should be taken to not allow anyone to be hurt by a belligerent animal.

Diagnosis

Generally, in endemic areas, diagnosis is made on an individual animal basis by clinical signs. For diagnosis of disease on a herd level in non-endemic areas, blood samples may be taken and serologic testing can be done to look for antibodies to the organism. Blood smears may also be taken to look for the presence of the parasite within the blood cells.

Necropsy of animals which died of acute disease will show a gross yellowing of tissues within the animal including mucous membranes, fat, and sclera of the eyes. Also, the spleen may be enlarged as it is the sight of red blood cell destruction.

Treatment and Control

Treatment is often accomplished through the use of tetracycline antibiotics, which are capable of crossing the cell membrane of red blood cells to reach the organism. An animal which is acutely ill may be treated parenterally with a long-acting oxytetracycline drug, of which many exist. In the event of an outbreak or for preventative measures, a herd may be treated orally with chlortetracycline (CTC). Currently, it is legal to feed CTC free choice for the treatment or control of anaplasmosis, but a VFD is required. There is also a vaccine for anaplasmosis which is licensed in several states, including conditional licensing in several states.

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