Anaplasmosis in cattle
Guy Sheppard, DVM
Anaplasmosis is a blood cell parasite of cattle with a worldwide distribution, but the disease is most common in tropical and subtropical areas. Anaplasma marginale is the most common organism involved in cattle, and it is transmitted through the bite of Dermacentor spp. ticks or tabanid flies, as well as through the use of blood-contaminated instruments. As a result, transmission is highest during heavy tick and fly seasons. Severe outbreaks of the disease can occur when naïve animals are moved into an endemic area or carrier animals are moved into a herd in a nonendemic area. Death losses in such herds can approach 50%. Mature cattle are the most susceptible to severe clinical signs of the disease while cattle under six months of age generally show no signs.
The Anaplasma organism invades the red blood cells of infected cattle and the spleen destroys the infected cells. As a result, infected animals become anemic, weak, lethargic, go off feed, and run a fever. The mucous membranes become pale and possibly yellow from the waste products of red blood cell destruction. A characteristic of anaplasmosis, however, is that the urine will not be red or brown as with “redwater” or leptospirosis. The packed cell volume of severely infected cattle can get extremely low making these animals prone to die with minimal exertion. Acute death and abortion have also been associated with some outbreaks of anaplasmosis.
Animals showing signs from anaplasmosis should be treated with appropriate antibiotics as soon as possible. Some animals are anemic to the point that a blood transfusion may be indicated. For animals in which standard antibiotic dosage therapy is successful in curbing clinical signs of infection, a carrier state will persist. Carrier animals will be immune to further disease from anaplasmosis and may be desirable in endemic areas. More intensive antibiotic therapy is sometimes administered in an effort to eliminate the carrier state with mixed results.
In endemic areas, control of the disease can be achieved with daily low-level antibiotic therapy in the feed during the vector season. Control of ticks and flies as well as proper cleaning and disinfection of dehorning, tagging, and injection equipment and supplies is also helpful in reducing the spread of this disease. A few vaccines are available for anaplasmosis, but consideration should be made for using these vaccines in late gestation due to the possibility of neonatal isoerythrolysis in calves born to vaccinated cows.
Preliminary diagnosis of anaplasmosis can be made based on the clinical signs of anemia and fever. The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) offers multiple tests to detect Anaplasma marginale that vary from very simple (direct examination of blood) to complex (ELISA and PCR). Veterinary assistance in suspected cases of anaplasmosis is very helpful in diagnosis, treatment, and control of this disease.
For more information about testing for anaplasmosis, visit tvmdl.tamu.edu or call one of the agency’s full-service laboratories.
Capucille, Dawn J., Blackwell’s Five-Minute Veterinary Consult: Ruminant; Scott R.R. Haskell, DVM, editor. 2008 pgs. 50-51.