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  Anaplasmosis is a hemoparasitic, infectious, and transmissible disease characterized by progressive anemia with intraerythrocyticAnaplasma bodies.  Anaplasmamarginale infects cattle, while Anaplasmaovis infects sheep and goats.

  The disease can be divided into four stages.  The first stage, or incubation stage, ranges from the time of introduction of the organism into the susceptible animal until the time that 1% of the erythrocytes are infected.  The first stage typically varies from one to three months in length.  No clinical signs are seen during this time.  The second stage, or developmental stage, is the stage during which anemia develops and lasts until reticulocytes appear in the peripheral circulation.  The second stage typically varies from four to nine days in length.  Most of the clinical signs characteristic of anaplasmosis appear during this stage.  The third stage, or convalescent stage, marks the resolution of the anemia.  The duration of this stage varies greatly.  During the fourth stage, or carrier stage, the animal remains infected, but Anaplasma bodies cannot be detected in the peripheral blood.  The fourth stage can last indefinitely.


  Anaplasmosis is typically transmitted by ticks or biting flies.  Iatrogenic transmission can occur when instruments are re-used without proper sanitation, including instruments used for dehorning, ear tagging, castrating, and vaccinating.  In utero transmission has been reported.

Clinical Signs

  Clinical signs increase in severity as the animal ages.  The first clinical sign is typically fever, ranging from 103o F to 106o F and lasting 12-24 hours.  Most other clinical signs are manifestations of acute anemia, including mucosal pallor, muscle weakness, tachycardia, tachypnea, exercise intolerance, and behavioral changes.  Additional signs that may be present include depression, anorexia, ptyalism, dehydration, constipation, and frequent urination with dark yellow urine.  Hemoglobinuria does not occur because the anemia results from the destruction of parasitized erythrocytes in the spleen, not from intravascular hemolysis.  Jaundice and weight loss may occur later in the disease.  Milk production declines rapidly in dairy cows. A. ovis infection in sheep and goats is typically asymptomatic.


  There are no pathognomonic gross lesions for anaplasmosis, but lesions can be suggestive of the disease.  In acute cases, the blood is thin and watery and fails to readily clot.  Gross postmortem findings typically include severe anemia with pallor of tissues and occasionally icterus.  The spleen is generally enlarged with reddish-brown pulp and enlarged splenic follicles.  The liver may be enlarged with rounded edges, and may be yellow in cases of icterus.  The gall bladder is typically distended with bile.  Histologic findings include bone marrow hyperplasia and extramedullaryhematopoiesis in the spleen and other organs.  Anaplasma organisms may be found in erythrocytes with smears of the peripheral blood.


  Tetracyclines have been shown to reduce the severity of the disease, and blood transfusions have been used as supportive therapy.  After recovery, additional treatment with tetracyclines is necessary to prevent animals from becoming asymptomatic carriers.

-by Julie Tucker, Class of 2001
-edited by Dr. Matt Renninger, ADDL
   Graduate Student

Anaplasmosis References

1.  Carlton,  William M., Donald
     Mc Gavin. Thomson’s Special Veterinary
     Pathology.  1995. Pp 293-294.

2.  Fraser, Clarence, Jan Gergeron, Asa
     Mays, Susan Aiello.  The Merck
     Veterinary Manual.  1991. Pp 68-69.

3.  Howard, Jimmy, Robert Smith.
     Current Veterinary Therapy 4:  Food
     Animal Practice.  Pp 403-410.

4.  Jones, Thomas, Ronald Hunt, Norval
     King.  Veterinary Pathology.  1997.
     Pp 395-397.

5.  Smith, Bradford P.  Large Animal
     Internal Medicine.  1996.  Pp 1214-1217.


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