Nervous System

March 2017



Signalment (JPC #CG-4):  A duckling


HISTORY:  This is one of a flock of ducklings that became suddenly ill with signs of listlessness, anorexia, rapid breathing, and in some, nervous derangement prior to death.


HISTOPATHOLOGIC DESCRIPTION:  Cerebrum:  Multifocally expanding host endothelial cells and often occluding vascular lumina are moderate numbers of protozoal megaloschizonts. Meglaoschizonts are round, measure up to 60-100 µm in diameter, and contain multiple membrane bound basophilic cytomeres, each containing numerous 1 x 2 µm merozoites, which are separated by a homogenous purple proteinaceous material. In some megaloschizonts, a markedly hypertrophied endothelial cell nucleus is present. Degenerating megaloschozonts are surrounded by low numbers of lymphocytes, fewer heterophils and macrophages, necrotic debris and mild hemorrhage. There is mild gliosis of the surrounding neuropil as well and vessels in this area are cuffed by low numbers of lymphocytes. Multifocally within blood vessels, erythrocytes contain one or more 1-3 µm oval clear gametocytes that displace the nuclei peripherally. 


MORPHOLOGIC DIAGNOSIS:  Cerebrum, vessels: Intraendothelial megaloschizonts with variable vascular occlusion, multifocal, with intraerythrocytic gametocytes, and mild lymphohistiocytic encephalitis, duck, avian.


ETIOLOGIC DIAGNOSIS:  Cerebral leucocytozoonosis


CAUSE:  Leucocytozoon simondi



·         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.

·         Often affects young ducks and geese and can result in sudden detach

·         Highest incidence in the spring with a carrier state

·         Vectors are culicoid midges and simuliid flies (black flies)



·         Transmitted by black flies (Simulium spp.) and biting midges (Culicoides spp.)

·         Schizogony in the liver, lung and vascular system

·         Anemia due to destruction of parasitized erythrocytes and parasitic production of anti-erythrocytic (AE) factor



·         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 > 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 brain, liver, heart, kidney or other organs



·         Course of disease is short; animals die or recover within a few days

·         Infections may or may not be clinically apparent

·         Sudden onset of depression, anorexia, weakness, loss of equilibrium, labored breathing or sudden death

·         Clinical pathology: Intravascular hemolysis and anemia



·         Hepatomegaly, splenomegaly, and hemorrhage in the liver, lung and kidney

·         Megaloschizonts are grossly visible as multiple, gray nodules in the brain, epicardium, liver, lung, kidney, intestine and lymphoid tissue



·         Usually, minimal host response

·         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



·         Schizonts are composed of electron-dense cytomeres within membrane-bound vacuoles (parasitophorous vacuole)

·         Merozoites contains a large nucleus, a mitochondrion and well-developed apical complex consisting of three apical rings, paired rhoptries and numerous micronemes



·         Cytology: Gamonts markedly distort erythrocyte or leukocyte

·         Binucleate illusion – host cell nucleus at one end and the parasite nucleus at the other

·         Affected blood cells may be markedly elongated or spindle-shaped



Intraerythrocytic gametocytes:

·         Haemoproteus sp.:  Primarily in birds (also found in turtles and lizards); 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

·         Plasmodium sp.:  Avian malaria; mosquito vector; contain birefringent pigment granules (malaria pigment); schizogony in peripheral blood; gametocytes in mature erythrocytes



·         L. simondi: Ducks and geese

·         Anemia, leukocytosis, splenomegaly, liver degeneration and hypotrophy

·         L. caulleryi: Chickens

·         Subcutaneous hemorrhages in the wings and legs, pectoral and thigh muscles, thymus, epicardium, pancreas and kidneys

·         L. smithi: Turkeys

·         Rapid course of disease; high mortality in young turkeys

·         L. grusi: Gruiformes (cranes)

·         L. tossi: Falconiformes (raptors)

·         L. marchouxi: Columbiformes (pigeons)

·         L. naevel: Guinea fowl

·         L. centropi: Cuculiformes (cuckoos, roadrunners)



1.     Abdul-Aziz T, et al. Avian Histopathology. 4th ed. Jacksonville, FL: American Association of Avian Pathologists; 2016: 479,523,537.

2.     Bowman DD. Georgis’ Parasitology for Veterinarians. 10th ed. St. louis, MO: Elsevier Saunders; 2014: 114.

3.     Campbell TW. Exotic Animal Hematology and Cytology. 4th ed. Ames, IA: Wiley-Blackwell; 2015: 115-120.

4.     Fitz-Coy SH. Parasitic diseases. In: Boulianne M, ed. Avian Disease Manual. 7th ed. Jacksonville, FL: American Association of Avian Pathologists; 2013:159,163.

5.     Gardiner CH, et al. Apicomplexa. In: Gardiner CH, et al. eds. An Atlas of Protozoan Parasites in Animal Tissues. 2nd ed. Washington, DC: Armed Forces Institute of Pathology; 1998:65-68, 73-76.

6.     McDougald LR, et al. Protozoal Infections. In: Swayne DE, et al. eds. Diseases of Poultry. 13th ed. Ames, IA: Wiley-Blackwell; 2013: 1185-1188.

7.     Miller RE, et al. Fowler’s Zoo and Wild Animal Medicine. Vol 8. St. Louis, MO: Elsevier Saunders; 2015: 138, 151, 167, 202, 216.



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