JPC SYSTEMIC PATHOLOGY

HEMOLYMPHATICS SYSTEM

February 2024

H-P02 (NP)

 

Signalment (POLA File): Dog, age, breed and sex unspecified.

 

HISTORY: This dog was anemic.

 

HISTOPATHOLOGIC DESCRIPTION: Cytologic specimen, peripheral blood smear: Approximately 30% of the erythrocytes contain pale basophilic intracellular protozoa with a single, acidophilic, eccentric 1 µm diameter nucleus. The protozoa have varying morphology characterized by either 3-4 µm in diameter single, round, ring stages (trophozoites); 4-5 x 2-3 µm pairs of pyriform bodies (merozoites/piroplasms) and fewer tetrads of cruciform bodies. There is also mild polychromasia, poikilocytosis, anisocytosis, spherocytosis, thrombocytopenia, and multifocal agglutination of parasitized erythrocytes.

 

Differential white cell count: Segmented neutrophils – 81%, Bands – 3%, Monocytes – 2%, Lymphocytes – 14%

 

MORPHOLOGIC DIAGNOSIS: Cytologic specimen, peripheral blood smear: Regenerative anemia, mild, with thrombocytopenia and many intraerythrocytic protozoa, breed unspecified, canine.

 

CAUSE: Babesia canis

 

CONDITION: Babesiosis, piroplasmosis

 

GENERAL DISCUSSION:  

• Tick-borne disease caused by the apicomplexan protozoan genus Babesia, which infects and replicates exclusively in erythrocytes
• Over 100 species of Babesia spp. worldwide; occurs in a wide range of mammals including domestic animals and wild ruminants, birds, and man, primarily in warmer climates

• Canine babesiosis is caused by: 

• B. canis (3 subtypes): Large babesial organism in dogs

• B. canis vogeli occurs in America as well as tropical and subtropical regions of  most continents, is least pathogenic
• B. canis canis occurs in Europe and Asia; is intermediately pathogenic
• B. canis rossi occurs in South Africa; severe peracute illness with 10-20% mortality

• B. gibsoni: Small babesial organism in dogs occurs in America, Asia and Africa

• Transmitted by different ticks in different countries; Rhipicephalus sanguineus (Ixodid), the brown dog tick, is the primary vector 

• Recovery from infection confers good immunity 

 

PATHOGENESIS:  

      cells > intravascular hemolysis coupled with increased erythrophagocytosis and secondary immune-mediated damage > extra- and intra-vascular hemolysis > severe anemia > hypoxic cell damage > irreversible shock > death

•    Protozoa activate plasma vasodilatory agents (kallikrein, bradykinin) > microvascular sludging > tissue hypoxia > exuberant inflammatory reaction meditated by cytokines, nitric acid, oxygen free radicals, eicosanoids, and platelet activating factor > hypotensive shock and/or multiple-organ dysfunction
• The mechanism of penetration of red cells by the merozoites of Babesia is unclear as is the mechanism of hemolysis 

• Severity of anemia and illness is enhanced by splenectomy
• Can be persistently infected

 

LIFE CYCLE: 

 

TYPICAL CLINICAL FINDINGS:

• There are two syndrome presentations: 

•  Acute: Fever, lethargy, hemolytic anemia 
•  Peracute: Hypotensive shock and/or multiple-organ dysfunction 

• Death from severe intravascular hemolysis, anoxia and shock
• Disseminated intravascular coagulopathy in severe cases
•    Fever, listlessness, dehydration, weakness, vomiting, ascites
•    CNS disease: Mania, recumbency, paddling of limbs, coma

 

CLINICAL PATHOLOGY:

• Hemolytic anemia, thrombocytopenia, leukocytosis, hemoglobinemia, hemoglobinuria, marked erythropoiesis, elevated ALT, AST and bilirubin, increased BUN with normal serum creatinine, metabolic acidosis, bilirubinuria
• Typically no coagulation abnormalities

 

TYPICAL GROSS FINDINGS: 

• Marked splenomegaly, hepatomegaly, lymphadenopathy, jaundice, swollen reddish-brown kidneys, subepicardial and subendocardial hemorrhage, distended gallbladder filled with thick bile, ulcerative stomatitis, edema  
• Has been rarely reported to cause petechiae, ecchymoses, edema, ulceration, and necrosis of skin and pressure points.

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

•    Cytology: Erythrocytes with typically paired 2 to 4 µm long pear-shaped piroplasms; pyriform to amoeboid shapes (merozoites/piroplasms) extending across RBC, or rod or rings that are smaller (trophozoites) by may be present concomitantly; numerous, large erythrocytes primarily at the feathered edge; may see spherocytosis and, rarely, eccentrocytosis
•    Spleen: Enlarged and contains numerous parasitized cells; in peracute death, lymphocytic necrosis in the germinal centers that is also evident in the lymph nodes; chronic cases may have macrophage hyperplasia within the red pulp   
•    Capillaries: Occluded with sludged parasitized erythrocytes, microthrombi
•    Kidneys: Hemoglobinuric nephrosis, tubular degeneration, +/- membranoproliferative glomerulonephritis
•    Liver: Degeneration and loss of the periacinar hepatocytes, cholestasis
•    Bone marrow: Erythroid hyperplasia
•    Hemosiderin: Large accumulation in the kidneys, liver, spleen and bone marrow
•    Skin: Leukocytoclastic vasculitis with or without vascular necrosis

 

ADDITIONAL DIAGNOSTIC TESTS:

• Serology, indirect fluorescent antibody test, agglutination test
• Wright’s or Wright’s-Giemsa stains best demonstrate the organisms  
• A real-time fluorescence resonance energy transfer polymerase chain reaction (qFRET PCR) shown to have high sensitivity and specificity for B. canis vogeli
• Parasitized erythrocytes are best visualized on impression smears of the kidney, brain, and skeletal muscle

 

DIFFERENTIAL DIAGNOSIS:

•    B. gibsoni: 1 to 2.5 µm diameter round to oval piroplasms; hemoglobinuria rare
•    Ehrlichia canis: Leukopenia or thrombocytopenia with morulae in leukocytes
•    Mycoplasma haemocanis: Chain of coccoid or ring-shaped forms on erythrocytes
•    Plasmodium spp.: Ring form is similar to Babesia spp., but the incomplete catabolism of hemoglobin leaves a brownish pigment (hemozoin) 

 

COMPARATIVE PATHOLOGY:  

• Cattle:  

• B. bovis

• Key gross findings is congestion of gray matter throughout the brain imparting a deep pink color (cerebral flush/pink brain)

• Causes a severe febrile illness with cattle prone to weakness, fever, hemoglobinuria, and anemia
• Babesiosis results in metabolic disease more complex than just intravascular hemolysis
• In contrast to B. canis, B. bovis causes a metabolic alkalosis (rather than acidosis) leading to a syndrome of circulatory failure
• Parasitized erythrocytes may be see in vessels of all tissues, but are typically found in the kidney, grey matter of the brain, heart, and skeletal muscle
• The organisms are faint blue on routine sections and are best demonstrated in imprint preparations of fresh tissue

• B. bigemina: 

• Much less severe illness than B. bovis
• Causes erythrocyte destruction that is directly proportional to parasitemia, unlike B. bovis
• There is an absence of cerebral flushing; this is the most reliable gross feature to distinguish from B. bovis

• B. divergens, B. major

• Death results primarily from severe anemia
• Spontaneous splenic rupture reported in B. major infection 

• Horses: 

• B. equi: Severe anemia, hemoglobinuria, lacrimation, ventral and periorbital edema, and mucosal petechiae, splenomegaly
• B. caballi

• Dogs: B. canis, B. gibsoni, B. conrade, B. vogeli, B. rossi
• Sheep, goats:

• B. ovis: Cerebral congestion in sheep
• B. foliata, B. motasi 

• Cats: Infection is uncommon in cats except in Africa; B. felis, B. cati, B. herpailuri, B. pantherae
• Pigs: B. trautmanni; wild boar, warthogs and bushpigs: B. traumanni and B. perroncitoi

• Mice:  

• B. hylomysci: Severe hemoglobinuria, nephrosis
• B. rodhaini, B. microti

• Cervids: B. odocoilei
• Bovidae (desert bighorn sheep and musk oxen): B. odocoilei
• Birds (falcons): B. shortti
• Non-human primates:

• B. pitheci: confined to Africa; reported in mangabeys, guenons, macaques, baboons, and marmosets; only slightly pathogenic unless splenectomized; if splenectomized, can cause anemia and death

• Black rhinoceros: B. bicornis can cause fatal infections
• North Island kiwi birds: B. kiwiensis
• Gray kangaroo: B. Macropus
• Hyrax: B. thomasi

 

References:

1. Abee CR, Mansfield K, Tardif S, Morris T. Nonhuman Primates in Biomedical Research: Volume 2: Diseases. 2^nd ed. San Diego, CA: Elsevier; 2012:220. 
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3. Boes KM, Durham AC. Bone marrow, blood cells, and lymphatic system. In: Zachary JF ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Saunders Elsevier; 2022:832-833.
4. Duncan M. Perissodactyls. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018: 450.
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11. Smith DA. Palaeognathae: Apterygiformes, Casuariiformes, Rheiformes, Struthioniformes; Tinamiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. London, UK: Academic Press; 2018:645.
12. Stockham SL, Scott MA. Fundamentals of Veterinary Clinical Pathology. 2nd ed. Hoboken, NJ: Wiley; 2013. 
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14. Zabolotzky SM, Walker DB. Peripheral blood smears. In: Valenciano AC, Cowell RL, eds. Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier; 2020:455.

 

 

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