JPC SYSTEMIC PATHOLOGY

HEMOLYMPHATIC SYSTEM

February 2024

H-P06

 

SIGNALMENT (JPC #2377154): 4-week-old red-fronted parakeet (Cyanoramphus novaezelandiae)

 

HISTORY: This parakeet was one of five in a brood that died suddenly. Both parents were healthy.

 

HISTOPATHOLOGIC DESCRIPTION: Heart: Multifocally affecting 40% of the myocardium are numerous individual or aggregated intrahistiocytic protozoal megaloschizonts which measure up to 370 μm in diameter and expand the myocardium, elevate the epicardium and endocardium and separate and compress adjacent cardiac myocytes. Megaloschizonts have a pale eosinophilic, faintly anisotropic, 15 to 40 μm thick wall that is often surrounded by an amphophilic matrix; the center is filled by abundant basophilic to eosinophilic granular cytoplasm, numerous clear spaces (artifact) and many variably distinct 1 to 2 μm diameter basophilic, oval merozoites. Adjacent to the megaloschizonts, there is compression, degeneration, atrophy, and loss of cardiac myocytes. Multifocally, hemorrhage and few lymphocytes and heterophils surround the megaloschizonts.

 

MORPHOLOGIC DIAGNOSIS: Heart, myocardium: Protozoal megaloschizonts, intrahistiocytic, numerous, with minimal lymphocytic and heterophilic myocarditis, hemorrhage, and myocardial loss, red-fronted parakeet (Cyanoramphus novaezelandiae), avian.  

 

ETIOLOGIC DIAGNOSIS: Cardiac leucocytozoonosis

 

CAUSE: Leucocytozoon sp.

 

GENERAL DISCUSSION:

• Leucocytozoonosis is a parasitic protozoal disease that infects many species of domestic and wild birds in Europe, Asia and North America  
• Leucocytozoon sp. (phylum Apicomplexa, family Plasmodiidae) is closely related to Haemoproteus sp. and Plasmodium sp., based on similarities in life cycle and ultrastructure
• Vectors are culicoid midges and simuliid flies (black flies); need for the vector gives seasonality to outbreaks (and deference to marshy, wetter regions)

 

PATHOGENESIS:

·   Megaloschizonts can cause tissue damage and pathogenic Leucocytozoon sp. produce an anti-erythrocytic factor that causes intravascular hemolysis and anemia

 

LIFE CYCLE: 

• Insect bites bird > sporozoites in salivary gland of insect enter bloodstream > schizonts develop in liver > release merozoites (1 μm) > second generation develops in liver and phagocytic cells throughout body > become megaloschizonts (100-200 μm) > release merozoites (1 μm) > schizogony in liver or entry into circulating erythrocytes or leukocytes (depending on Leucocytozoon species) > development into microgamonts or macrogametes > insect feeds on bird > sexual maturation, fertilization and sporogony take place in insect
• No merogony occurs in either leukocytes or erythrocytes; merogony occurs in the parenchyma of liver, heart, kidney or other organs

 

TYPICAL CLINICAL FINDINGS: 

• Infections may or may not be clinically apparent; usually sudden onset of depression, anorexia, weakness, loss of equilibrium, labored breathing or sudden death; anemia; high mortality in young birds
• Course of disease is short; animals die or recover within a few days

 

TYPICAL GROSS FINDINGS:  

• Splenomegaly; hepatomegaly; hemorrhage in kidney, heart and lung; pericardial effusion
• Megaloschizonts appear as gray-white nodules found in the heart, liver, lung or spleen

 

TYPICAL LIGHT MICROSCOPIC FINDINGS: 

• Megaloschizonts and schizonts in various organs, including liver, brain, heart, spleen, kidney, gizzard and occasionally feather pulp
• Usually minimal host response; sometimes associated with lymphoplasmacytic infiltrates and multifocal ischemic necrosis due to occlusion of blood vessels by megaloschizonts in endothelial cells; ruptured schizonts may induce granulomatous reaction in the surrounding tissues

 

TYPICAL ULTRASTRUCTURAL FINDINGS:

 

ADDITIONAL DIAGNOSTIC TESTS:

• Identification of gamonts or gametes in blood smears (Wright or Giemsa stain)
• Serology and ELISA test for antibodies to L. caulleryi
• Tissue imprints of liver, spleen, and lung can serve as a screening method for avian hemoparasites and is more sensitive than simple histology alone

 

DIFFERENTIAL DIAGNOSIS:

Intraerythrocytic gametocytes:

     insect vectors (midges, hippoboscids, tabanids); schizonts in visceral endothelial cells; gametocytes develop in circulating erythrocytes; birefringent pigment granules in infected erythrocytes; few clinical signs reported; also associated with the pre-erythrocyte stage, characterized by large megaloschizonts, within both skeletal and smooth muscle, that have compartmentalized internal septae; inflammation is variable from absent to marked with hemorrhage and necrosis (see Wednesday Slide Conference 2016-2017, Conference 24 case 1)

• Plasmodium sp.: Avian malaria; mosquito vector; contain birefringent pigment granules (malaria pigment); schizogony in peripheral blood; gametocytes in mature erythrocytes
• “Hemoproteus Hugs the nucleus; Plasmodium (and Leucocytozoon) Peripheralizes the nucleus” when looking at microscopic features in erythrocytes

 

COMPARATIVE PATHOLOGY:

• Leucocytozoon caulleryi: Chickens in Southeast Asia; subcutaneous hemorrhages in the wings and legs, pectoral and thigh muscles, thymus, epicardium, pancreas and kidneys
• L. simondi: Ducks and geese in North America, Europe, Southeast Asia;  anemia, leukocytosis, splenomegaly, liver degeneration and hypotrophy
• L. smithi: Turkeys in North America and Europe; rapid course of disease; high mortality in young turkeys

• L. sabrezi: Chickens in Southeast Asia; anemia and paralysis of legs
• L. schoutendeni: Chickens in East Africa; little associated pathology

• L. simondi in blue-winged Teal (anas discors) in migratory corridor from Florida to Louisiana and Texas

• L. neavei: Guinea fowl
• L. andrewski: Chickens in the US; previously ID’d as L. caulleryi
• L. struthionis: Common in young ostriches in South Africa
  1. Myocarditis with megaloschizonts

 

References:

1. Abdul-Aziz T, Fletcher OJ. Hepatobiliary System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 359.
2. Abdul-Aziz T, Fletcher OJ. Respiratory System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 199, 253.
3. Abdul-Aziz T, Fletcher OJ. Urinary System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 460.
4. Barnes HJ, Fletcher OJ. Hemic System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 6.
5. Barnes HJ, Abdul-Aziz T, Fletcher OJ. Muscular System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 111
6. Fenton H, McManamon R, Howerth EK. Anseriformes, Ciconiiformes, Charadriiformes, and Gruiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 717.e6.
7. Fitz-Coy SH. Parasitic Disease. In: Boulianne M, ed. Avian Disease Manual. 7th ed. Jacksonville, FL: American Association of Avian Pathologists, Inc.; 2013:159,163.
8. Gardiner CH, Fayer R, Dubey JP. Apicomplexa. In: Gardiner CH, Poynton SL, eds. An Atlas of Protozoan Parasites in Animal Tissues. 2nd ed. Washington, DC: Armed Forces Institute of Pathology; 1998:65-68, 73-76.
9. McDougal LR. Parasitic Diseases: Protozoal Infections. In: Swayne DE, ed. Diseases of Poultry. 14^th Ed. Hoboken, NJ: Wiley, 2020: 1234-1236.
10. Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2^nd ed. Ames, IA: Wiley; 2015: 39, 109, 135, 227.
11. Shivaprasad HL. Eye and Ear. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 523, 537.
12. Stacy NI, Hollinger C. Introduction to Comparative Clinical Pathology. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 72, 109.
13. Smith DA. Palaeognathae: Apterygiformes, Casuariiformes, Rheiformes, Struthioniformes; Tinamiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 645.
14. Swayne DE, Barnes HJ, Abdul-Aziz T, Fletcher OJ. Nervous System. In: Abdul-Aziz T, Fletcher OJ, Barnes HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 479.
15. Trupkiewicz J, Garrner MM, Juan-Sallés C. Passeriformes, Caprimulgiformes, Coraciiformes, Piciformes, Bucerotiformes, and Apodiformes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Elsevier; 2018: 811-812.

 

 

 

 

 

 

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