JPC SYSTEMIC PATHOLOGY
Signalment (JPC 4068027-00): Tissue from a cat.
HISTORY: Three year old, stray, male, domestic shorthair cat became lethargic, bradycardic and hypothermic, and then died within 48 hours of being neutered.
HISTOPATHOLOGIC DESCRIPTION: Lung: Multifocally throughout the section, septal capillaries and larger vessels contain and are frequently occluded and distended by many enlarged macrophages distended up to 40 microns by intracytoplasmic, developing schizonts containing many, 1-3 um, basophilic merozoites. Affected vessels contain mildly hypertrophic endothelial cells within the tunica intima, that have enlarged nuclei; there is multifocal, mild, expansion of the tunica media and adventitia by edema and small amounts of fibrin. There is prominent perivascular edema with small amounts of hemorrhage. There are few, partially occlusive fibrin thrombi. Peribronchiolar tissue is mildly expanded by edema. Multifocally alveolar septa contain a small increase in histiocytes and lymphocytes. There is mild sub-pleural edema.
MORPHOLOGIC DIAGNOSIS: Lung: Vessel occlusion by numerous schizont-laden macrophages(etiology consistent with Cytauxzoon felis) with, acute, multifocal, moderate with perivascular edema, few fibrin thrombi and mild interstitial pneumonia, breed unspecified, feline.
ETIOLOGIC DIAGNOSIS: Pulmonary cytauxzoonosis
CAUSE: Cytauxzoon felis
- Cytauxzoonosis is a rapidly progressive, systemic, generally fatal disease affecting domestic and some wild felids in North America (and other locations).
- Protozoal hemoparasite
- Transmitted by ixodid ticks
- Two phases: Early tissue mononuclear phagocyte phase and late erythrocytic phase
- A less pathogenic form may be emerging
- Tissue phase: Macrophages/monocytes enlarged by schizonts, accumulate in vessels or subendothelially causing vascular occlusion, often in the lung, liver, spleen, and lymph nodes (but can occur in any organ including CNS); sequelae include edema, ischemia, and petechial and ecchymotic hemorrhages
- Parasite by‑products liberated with the release of merozoites from macrophages are toxic, pyrogenic, and vasoactive causing endothelial damage
- Disseminated intravascular coagulation has been reported in natural infection
- Erythrocytic phase: Late phase, usually innocuous; may lead to intravascular and extravascular hemolysis; piroplasms present in 1-4% of blood erythrocytes
- Transmission by Ixodid ticks: (Dermacentor variabilis, Amblyomma americanum), or ingestion or inoculation of infected blood or tissu
- The bobcat is the natural reservoir and has mild disease
- A tick ingests RBCs containing merozoites/piroplasm (infected cat, bobcat) à sexual reproduction in the tick à sporozoite inoculated into cat à sporozoites infect monocytes à schizont formation and merozoite development à merozoites enter erythrocytes à develop into piroplasms
TYPICAL CLINICAL FINDINGS:
- Marked fever, pallor, icterus, depression, dark urine, occasionally dyspnea
- Non-regenerative anemia (likely “preregenerative”), and often neutropenia (inflammation) and thrombocytopenia (hemorrhage, DIC).
TYPICAL GROSS FINDINGS:
- Pulmonary congestion and edema (non-collapsing lung); splenomegaly; hepatomegaly; icterus
- Enlarged red lymph nodes
- Serosal petechiae and ecchymosis
- Pleural, pericardial, abdominal effusions
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Tissue monocyte/macrophage phase:
- Piroplasms are 1-3 um comma-shaped, elongated “safety-pin”, linear, or signet-ring forms
- Macrophages are enlarged with intracytoplasmic merozoite-containing schizonts and often partially or completely occlude vessels.
- Ischemic necrosis; lung, spleen, and liver are usually the most severely affected with numerous infected monocytes;
- CNS lesions include occlusion of leptomeningeal and parenchymal arterioles in the brain as well as small capillaries in the gray and white matter and choroid plexus, accompanied by variable numbers of lymphocytes and plasma cells surrounding vessels; variable ischemic changes such as neuronal degeneration and necrosis and swollen axons
- Interstitial pneumonia and intravascular macrophages containing schizonts
- Erythrocytic phase
ADDITIONAL DIAGNOSTIC TESTS:
- Wright's/Giemsa stain on blood smears and impression smears (do at necropsy) especially of lung, spleen, but also of liver, lymph nodes, and bone marrow
- A differential for piroplasmosis in cats is Babesia felis (mainly found in South Africa).
- Bobcat: Reservoir host; usually mild illness or clinically healthy carrier state
- Non-domestic felids: fatal disease reported
- Cytauxzoon spp infect African wild ungulates (e.g., kudu, eland, giraffe).
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- Clarke LL, Rissi DR. Neuropathology of Natural Cytauxzoon felis infection in domestic cats. Vet Pathol. 2015: 52(6): 1167-1171.
- Clarke LL, Krimer PM, Rissi DR. Glial changes and evidence for apoptosis in the brain of cats infected by Cytauxzoon felis. J Comp Path. 2017; 156: 147-151.
- Valli VEO, Kiupel M, Bienzle D, Wood RD. Hematopoetic system. In: Maxie MG, ed. Jubb, Kennedy, Palmer's Pathology of Domestic Animals. 6th ed. St. Louis, MO. Elsevier; 2016:(3):120.