JPC SYSTEMIC PATHOLOGY
SINGALMENT (JPC # 1727491): Common loon.
HISTORY: This common loon (Gavia immer) had been weak, unable to fly, and passed blood-tinged milky droppings two days prior to death.
HISTOPATHOLOGIC DESCRIPTION: Kidney: The ureteral epithelium is multifocally either ulcerated or hyperplastic with multiple nuclei stacked up to 15 cells layers thick with loss of cellular polarity. There are numerous coccidia in various stages of development and numerous coccidial oocysts in various stages of sporulation within the hyperplastic ureteral epithelium as well as the lamina propria and underlying interstitium, primarily at foci of ulceration. Developmental stages present include round macrogametocytes that are 15-20um diameter, thin walled, and filled with 1-4 um diameter, eosinophilic, round macrogametes; fewer microgametocytes that are 15-18um diameter with an indistinguishable cell wall and contain myriad, 1 X 2 um, crescentic, deeply basophilic microgametes; undifferentiated gamonts 4 x 10 um, ovoid, deeply basophilic and homogeneous; and ovoid to spherical oocysts characterized by 1um, undulant, nonrefractile cell that contain either clear cytoplasm or irregularly ovoid aggregates of basophilic material (presumed sporocysts). Within the ureteral lumen are numerous sloughed epithelial cells, degenerate inflammatory cells, and coccidia. The ureteral lamina propria contains moderate numbers of lymphocytes, plasma cells, fewer macrophages, and rare heterophils admixed with the previously described oocysts. Kidney tubules and collecting ducts are multifocally mildly to moderately ectatic, lined by attenuated or rarely necrotic epithelium, and often contain finely granular, pale eosinophilic flocculant material (urates – urate stasis) and variably contain intraluminal oocysts as previously described, sloughed epithelial cells, hemorrhage, and cellular and nuclear debris (cellular and granular casts). Renal tubular and collecting duct epithelium multifocally contains coccidial schizonts (meronts) with merozoites that occasionally are associated with ruptured epithelial cells, with merozoites emerging into the lumen.
- Ureter: Ureteritis, ulceroproliferative, lymphoplasmacytic, multifocal, moderate, with luminal and transmural coccidia and oocysts, common loon (Gavia immer), avian.
- Kidney: Tubular and collecting duct ectasia with intraluminal urate stasis, minimal tubular hyperplasia and necrosis, and intraepithelial and luminal coccidia and oocysts.
ETIOLOGIC DIAGNOSIS: Renal coccidiosis
ETIOLOGY: Eimeria gaviae
- Eimeria: Obligate intracellular apicomplexan protozoans of the subclass Coccidiasina; relatively host-, organ-, and tissue-specific, and primarily infect enterocytes (D-P01) of domestic and wild mammals and birds
- Phylum Apicomplexa: intracellular parasites characterized by a life cycle stage with a typical “apical complex” of organelles at the apical end of the organism
- Renal coccidiosis has been recognized in a variety of avian species as well as mice, guinea pigs, and bats
- Renal coccidiosis has caused significant mortality events in some avian species (free-ranging wild geese, eider ducklings, and double-crested cormorants), but disease is subclinical in healthy individuals of most species
- Tissue tropism of coccidians is determined by surface microneme proteins (MICs) that appear to be unique to each species of protozoan
- In renal coccidiosis, route of infection from ingestion to the kidney is unknown
- Renal tubular epithelium and ureteral epithelium are damaged upon schizont rupture with release of merozoites
- Renal outflow may be obstructed by protozoa within renal tubules and ureters
- All coccidians have a similar basic life cycle:
- Infection of a cell (often, but not always, an enterocyte) by a sporozoite released from a sporocyst in the lumen of the gut à one or more cycles of asexual division (schizogony or merogony, for our purposes schizont is equivalent to meront) à
- Merozoites infect other cells, forming another generation of meronts or transforming into sexual stages (termed gamonts) à
- Gamonts develop into female macrogametes or male microgametes à
- Macrogametes and microgametes fuse to form an oocyst, which is excreted in feces à
- Oocyst undergoes sporogony / sporulation (either within the host or more commonly in the environment after fecal passage) to form sporocysts containing infectious sporozoites;
- In renal coccidiosis, part of this life cycle occurs in the kidney
- Merogony (asexual division) may involve either:
- Endopolygeny: multiple fission or “budding” of merozoites from the periphery of the meront or from infoldings of it
- Endodyogeny: two daughter organisms develop within a mother organism which is destroyed when they are released
- The endogenous stages of coccidians are all intracellular, except temporarily the merozoite and microgamete
- Eimeria and Isospora spp. are homoxenous, with sexual and asexual development taking place in a single host; Cystoisospora (formerly Isospora spp. of carnivores), Toxoplasma, Sarcocystis, Hammondia, Besnoitia, Frenkelia, Neospora, and Caryospora are all heteroxenous, indicating that asexual stages occur in an intermediate host, exploiting natural prey-predator relationships
TYPICAL CLINICAL FINDINGS:
- Most reports of renal coccidiosis are of asymptomatic birds, or birds that show minor physiological or pathological changes due to the parasite
- Young birds and those that have been stressed by various conditions are most likely to have clinical cases of renal coccidiosis
- Infected birds may be emaciated and have a prominent keel
- Disease in domestic geese is usually acute, lasting 2-3 days, and can kill large segments of the flock
TYPICAL GROSS FINDINGS:
- In severe infections, kidneys may become enlarged and pale, containing multiple spots or foci of infection that coalesce into a mottled pattern
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Coccidian parasites within the epithelium and occasionally the lumen of collecting ducts, ureters, and/or renal tubules resulting in multifocal mild-to-moderate dilation, epithelial hyperplasia, and/or necrosis and degeneration, with or without associated granulomatous inflammation
- Organisms: intracytoplasmic coccidial microgamonts, macrogamonts, schizonts containing merozoites, and intracytoplasmic and free luminal oocysts
- Asexual replication: Schizogony or merogony
- Schizonts: asexual replication/schizogony or merogony; encapsulated cyst containing cresentic 2x5um merozoites
- Sexual replication: Gametogony
- Macrogamont: sexual replication/gametogeny; female; 40um round with a central nucleus and 2um peripheral eosinophilic granules
- Microgamont: sexual replication/gametogeny; male; 30um round with numerous basophilic nuclei (microgametes)
- Oocysts: spherical to ellipsoidal, truncated end, smooth walls, and a micropyle with a polar cap; contain a spherical sporont with nucleus and nucleolus and cytoplasmic amylopectin granules, which further contains sprozoites
- Asexual replication: Schizogony or merogony
TYPICAL ULTRASTRUCTURAL FINDINGS:
- Trophozoite, schizont, and all other intracellular stages of Eimeria are surrounded by a membrane-lined parasitophorous vacuole in the host cell cytoplasm (or, in some cases, nucleoplasm)
- Schizont: single walled, contains cisternae of the parasitic endoplasmic reticulum, free ribosomes, mitochondria, multiple merozoites
- Merozoites: crescent shaped; have an inner and outer membrane, conoid apparatus, micronemes, rhoptries, nuclei, parasitic endoplasmic reticulum and free ribosomes
ADDITIONAL DIAGNOSTIC TESTS:
- Direct impression smears reveal high numbers of oocysts +/- urates
- Sporulated oocyst examination: Eimeria have 4 sporocysts each containing 2 sporozoites; Cystoisospora spp. (enteric coccidian of carnivores) have 2 sporocysts each containing 4 sporozoites
- DNA sequence analysis
- No rule outs for this distinctive histological appearance in the kidneys and ureter
- Renal coccidiosis has been reported in many avian species, including chickens, turkeys, geese, and perhaps most birds are susceptible
- Duck: boschadi, E. somatarie
- Geese: truncata
- Swan: christianseni
- Intranuclear coccidiosis: parasites develop within host cell nuclei, typically of epithelium of multiple organs; these have been described in all classes of vertebrates but are rarely present in mammals (more frequently observed in fish, amphibians, and reptiles); typically nonpathogenic, but capable of causing death in tortoises
- Renal klosiellosis, caused by apicomplexan Klossiella , are typically nonpathogenic protozoans that inhabit renal epithelial cells of many species (U-P02), e.g. K. equi (horse) and K. muris (mouse)
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