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 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
-by Julie Tucker, Class of 2001
-edited by Dr. Matt Renninger, ADDL
William M., Donald
Mc Gavin. Thomsons 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.
5. Smith, Bradford P. Large Animal
Internal Medicine. 1996. Pp 1214-1217.