JPC SYSTEMIC PATHOLOGY
SIGNALMENT: A dog
HISTORY: Blood smear from a dog. Differential white cell count: Segs - 85% (35-75), Bands 5%, Monos - 8% (1-4), Lymphs - 2% (20-55), nRBC - 18/100 WBC.
HISTOPATHOLOGIC DESCRIPTION: Peripheral blood: In this highly cellular, good quality blood smear erythrocytes are decreased in density and widely separated within the monolayer (anemia), with a mild increase in white blood cells (leukocytosis), and a paucity of platelets (thrombocytopenia). The majority of white blood cells are segmented neutrophils with fewer scattered bands neutrophils. There are increased numbers of monocytes (monocytosis) with rare lymphocytes (lymphopenia). There are numerous nucleated red blood cells and a moderate degree of anisocytosis and polychromasia (regenerative anemia). There are numerous 1-µm diameter, basophilic, coccobacillary bacteria on the surface of over 90% of the erythrocytes in this smear. They occur singularly, in pairs and in short chains. There are numerous background crystalline structures (artifact).
MORPHOLOGIC DIAGNOSIS: Peripheral blood smear: Regenerative anemia with neutrophilia, left shift, monocytosis, lymphopenia and epicellular erythrocytic bacteria, morphology consistent with Mycoplasma haemocanis, breed unspecified, canine.
ETIOLOGIC DIAGNOSIS: Hemotropic mycoplasmas; Erythrocytic mycoplasmosis; Hemoplasmosis
CAUSE: Mycoplasma haemocanis
SYNONYMS: Hemobartonella canis; Eperythrozoon spp.
- Reclassified as a mycoplasma
- Gram negative, non-acid fast, epicellular parasites of erythrocytes that cause severe hemolytic anemia in splenectomized or immunosuppressed dogs
- Contain both DNA and RNA and replicate by binary fission
- Part of normal flora in the upper respiratory tract of canines
- Reported worldwide distribution in dogs
- South American camleids are uniquely susceptible to mycoplasmosis (Mycoplasma hemolamae)
- Transmission: Blood sucking arthropods; fleas or Rhipicephalus sanguineus ticks
- Predominantly non-pathogenic in dogs except with splenectomy, concurrent Ehrlichia , Babesia sp., bacterial or viral infection, or immunosuppressive therapy
- Mycoplasma haemofelis (H. felis) is the causative agent of feline infectious anemia (FIA)
- haemofelis can cause acute hemolytic anemia in immunocompetent cats
- Extravascular hemolytic anemia
- Binding of haemofelis (H. felis) to the RBC surface exposes hidden antigens on the RBC surface or alters membrane antigens; this results in antibody production against red blood cell antigens
- Antibodies are made against adsorbed mycoplasma antigen with complement fixation; the erythrocyte is damaged as an "innocent bystander" effect
- Structural damage caused by association of the organism with the erythrocyte membrane may cause increased fragility and early clearance
- Four stages of disease:
- Preparasitemic: 1 - 3 weeks from initial infection to detectable parasitemia
- Acute: From between the first and last major parasitemia; parasitemia is cyclic in nature; organism is thought to be sequestered in the spleen during non-parasitemic periods; this phase lasts several months
- Recovery: Period from last major parasitemia until PCV normalizes
- Carrier: Clinically normal chronically infected cat
TYPICAL CLINICAL FINDINGS:
- Tends to be non-pathogenic in dogs but can cause hemolytic anemia, lethargy, weight loss, fever and anorexia
- Depression, weakness, emaciation (75%), pale mucous membranes, splenomegaly (50%)
- Anemia varies from mild and subclinical to severe and life threatening
- Coomb’s positive regenerative anemia
- Erythrophagocytosis by monocytes
- 50% are FeLV positive
TYPICAL GROSS FINDINGS:
- Extravascular hemolysis, icterus, splenomegaly, distended gallbladder
- Animal often splenectomized and anemic (pale mucous membranes, etc)
- Cattle can have hind limb edema and swelling of the teats
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Romanowsky stained blood smear
- Reticulocytosis, polychromasia, anisocytosis, nucleated erythrocytes, Howell Jolly bodies
- Blue cocci or rods (0.5 - 1.0 µm), in chains, or in rings on surface of erythrocytes
- Erythrophagocytosis by macrophages in spleen, liver and bone marrow
- Bone marrow evaluation can help predict duration of disease
- Acute: Myeloid and erythroid hyperplasia, decreased M:E ratio
- Chronic: Bone marrow depletion
- Partially buried in the surface membrane of RBC with intermittent contact points
- Organism (0.5 µm diameter) surrounded by a single membrane; cytoplasm with granules of varying size and density; no identifiable organelles
ADDITIONAL DIAGNOSTIC TESTS:
- Demonstration of organisms on a blood smear
- Hemotropic mycoplasmas can induce cold agglutinins
- Romanowsky stained smears should be examined BEFORE treatment; reticulocyte stains (new methylene blue) should not be used because these organisms cannot be differentiated from punctate reticulocytes in cats
- Acridine orange / direct FA more sensitive but requires a flourescent microscope
- Culture still remains a commonly used method for detection in canines
- The demonstration of organisms in the blood does not prove causality
- Pathogens that target red blood cells usually produce splenic lesions
- Mycoplasm spp; Babesia spp; Plasmodium spp; Anaplasma spp; Theileria spp; Eperythrozoon spp.
- Coomb’s positive, regenerative anemia with erythrophagocytosis by blood monocytes in a cat is suggestive of FIA; differential diagnosis includes primary immune-mediated hemolytic anemia and FeLV-induced hemolytic anemia
COMPARATIVE PATHOLOGY: Hemotropic mycoplasmas, or called hemoplasmas
M. haemofelis, M. turicensis, M. haemominutum
M. haemocanis (H canis; Bartonella canis)- anemia
M. cynos - respiratory disease
M. canis - urogenital tract infections
Anaplasma marginale / centrale
Paranaplasma caudatum / discoides
M. wenyonii - anemia, edema, lymphadenopathy, and fever
M. hemobos - pathogenicity is unclear
M. ovis - only rarely causes hemolytic anemia
M. haemolamae - acute anemia, in crias and stressed adults
M. haemosuis - piglets fever, hemolytic anemia, and hypoglycemia
Mycoplasma spp.- abortions
Hemobartonella-like noted in Cynomolgus macaques
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