JPC SYSTEMIC PATHOLOGY

DIGESTIVE SYSTEM

October 2024

D-P01

 

SLIDE A: Signalment (JPC #1925258): A 2-month-old chicken.

 

HISTORY: None.

 

HISTOPATHOLOGIC DESCRIPTION: Cecum: Circumferentially expanding the lamina propria and infiltrating the mucosal/crypt epithelium are abundant apicomplexan coccidian protozoa at varying developmental life stages including numerous intracellular macrogamonts and microgamonts, intra- and extracellular schizonts, and developing oocysts. Macrogamonts are 10-20 µm in diameter with a single, central nucleus and a peripheral ring of 2 µm diameter eosinophilic granules. Microgamonts are round to oval, 15-20 µm in diameter, filled with multiple µm basophilic nuclei. Schizonts are 40-60 µm in diameter filled with numerous basophilic, 4x2 µm, crescentic merozoites. Oocysts are within the crypt epithelium or crypt lumina, are 15-20 µm diameter, thick walled, oval to irregular, and filled with eosinophilic pale granular material and/or a single eosinophilic central nucleus, admixed with a small amount of necrotic debris. Multifocally, the mucosa is eroded with loss of enterocytes and replacement by hemorrhage, fibrin, edema, and eosinophilic cellular and karyorrhectic debris, few lymphocytes and heterophils. Expanding the lamina propria and submucosa and extending into the muscularis and serosa is a moderate inflammatory infiltrate composed of lymphocytes, plasma cells, macrophages, and few heterophils admixed with hemorrhage, fibrin, and edema. The cecal lumen is distended with numerous coccidian protozoa, fibrin, hemorrhage, edema, necrotic debris, degenerate inflammatory cells, sloughed enterocytes, and few clusters of cocci and bacilli.

 

MORPHOLOGIC DIAGNOSIS: Cecum: Typhlitis, erosive, lymphoplasmacytic, diffuse, subacute, marked, with abundant intra- and extracellular coccidian gamonts, schizonts, and oocysts.

 

CAUSE: Eimeria tenella

 

SLIDE B: Signalment (JPC #4017836-00): Adult female intact alpaca.

 

HISTORY: Four days after introduction into new herd, patient began having watery diarrhea, neurologic signs, drooping of lower lip, and open mouth breathing, then died. 

 

HISTOPATHOLOGIC DESCRIPTION: Small intestine: Circumferentially expanding the lamina propria and infiltrating the mucosal and crypt epithelium are abundant developing apicomplexan coccidial life stages including macrogamonts, microgamonts, schizonts, and oocysts. Macrogamonts are 80-100 µm in diameter and contain peripheralized, brightly eosinophilic granules with an occasional round, central nucleus. Microgamonts are 70-80 µm in diameter and contain multiple 1um basophilic nuclei. Schizonts are 150-200 µm in diameter and contain nuclei arranged in circular blastophores (megaloschizont). Oocysts are within the crypt epithelium or crypt lumina and are 15-20 µm in diameter, oval to irregular, and filled with eosinophilic, pale, granular material. Multifocally the villar enterocytes are lost and villi are blunted, fused, eroded, and replaced with rare hemorrhage, fibrin, cellular debris, lymphocytes, plasma cells, and macrophages. The lamina propria, submucosa, muscularis, and serosa are mildly expanded by few lymphocytes and plasma cells. 

 

MORPHOLOGIC DIAGNOSIS: Small intestine: Enteritis, lymphoplasmacytic, diffuse, subacute, moderate, with villous blunting and loss and abundant intra- and extracellular coccidian gamonts, schizonts, and oocysts.

 

CAUSE: Eimeria macusaniensis

 

ETIOLOGIC DIAGNOSIS: Cecal/enteric coccidiosis (Eimeriosis)

 

GENERAL DISCUSSION:

• Eimeria spp. are apicomplexan coccidian parasites
• Phylum Apicomplexa: Intracellular parasites characterized by a life cycle stage with a typical “apical complex” of organelles at one end of the organism
• Highly host specific, and specific to the segment of bowel they infect; direct life cycle; grow and multiply intracellularly in epithelial and subepithelial cells in the alimentary tract
• Chickens (Eimeria acervulina, necatrix, maxima, and tenella): 
  • Eimeria tenella is the most pathogenic species causing marked typhlitis
  • Coccidiosis is an important worldwide poultry disease; causes enteritis and/or typhlitis; typically affects intensively managed animals; usually mild disease, severe outbreaks may have high mortality
  • Predisposing factor for necrotic enteritis (Clostridium perfringens Type G) and ulcerative enteritis (Clostridium colinum) in quail

 

PATHOGENESIS:

• Oral ingestion of sporulated (infective) oocyst> sporozoites invade enterocytes> enterocytes are damaged during development and replication of parasite, as well as by trauma to intestinal mucosa and submucosa
• Malabsorption due to villus atrophy
• Exudative enteritis and typhlitis due to epithelial erosion and ulceration

 

LIFE CYCLE:

• Endogenous stages are all intracellular, except merozoite and microgamete
• Sporulated oocysts ingested > excystation of oocysts via enzymatic degradation in duodenum > release of sporozoites> free sporozoites invade mucosal epithelium > sporozoites become trophozoites > trophozoites divide to become schizonts (a large encapsulated structure containing many merozoites) > 2-3 generations of schizogony (asexual multiplication) > gametogony (sexual reproduction): schizonts and epithelial cells rupture and release merozoites > merozoites invade adjacent epithelial cells and form either macrogametocytes (female; unicellular; fill the parasitized cell) or microgametocytes (males; undergo multiple divisions and form flagellated microgametes) > fertilization of macrogamete by microgamete, formation of oocyst > unsporulated oocyst excreted > oocyst sporulates in environment (sporogony)
• Sporogony: Outside the host, the unsporulated oocyst undergoes meiosis to produce sporozoites; occurs in warm, moist environment
• The number of reproductive cycles is fixed (in a given species) and unidirectional; barring reinfection, coccidia are self-limiting

 

TYPICAL CLINICAL FINDINGS:

• Bloody diarrhea
• Bleeding, weight loss, loss of skin pigment

 

TYPICAL GROSS FINDINGS:

• Varies from excessive fluid in intestinal lumen to intestinal dilation and gray-yellow foci visible on the serosal surface; fibrinonecrotic enteritis in severe cases
• E. tenella (cecal coccidiosis): Ceca filled with caseous cores (dry compact white mass) mixed with blood; thickened cecal wall (edema and cellular infiltrates); petechiae visible from serosal surface, sometimes white spots; comb and visceral organs pale from blood loss; high mortality; blood in droppings
• E. necatrix: Mid-intestine (jejunum and ileum) markedly distended with yellow to orange mucus; red and white (clumps of schizonts) foci; ballooning intestinal walls; dysentery; petechiae and white spots visible from serosal surface; blood in droppings
• E. maxima: Mid-intestine (jejunum and ileum, +/- duodenum) mildly distended with excessive orange mucus or distended with fluid and thick bloody mucus covering mucosa; discrete focal hemorrhagic lesions on mucosal surface; soft mucoid salmon-pink colored feces; largest species, with a golden brown oocyst wall
• E. acervulina: Duodenum +/- upper jejunum with white irregular linear lesions (zebra striping or ladder rung) to coalescing white plaques associated with gamonts and oocysts clustered in villi; hemorrhage is NOT a feature

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Organisms in various stages of development randomly scattered within enterocytes or free in the lamina propria
• Characteristic findings: Varying degrees of congestion, edema, hemorrhage, heterophilic and lymphocytic inflammation, necrosis and loss of epithelial cells, villous atrophy
• E. tenella specific: Expansion of lumen with cecal core that often contain oocysts and bacteria
• Oocysts: 15 µm (E. tenella), thick walled, oval to irregular, filled with eosinophilic pale granular material and/or a single eosinophilic central nucleus 
• Asexual replication: Schizogony or merogony
  • Schizonts: Encapsulated cyst containing cresentic 2x5 µm merozoites
• Sexual replication: Gametogony
  • Macrogamont (pink females): Sexual replication/gametogeny; 40 µm (E. tenella), round with a central nucleus and 2 µm peripheral eosinophilic granules
  • Microgamont (blue males): Sexual replication/gametogeny; 30 µm (E. tenella) round with numerous basophilic nuclei (microgametes)

 

ULTRASTRUCTURAL FINDINGS:

• Schizont: Present within a parasitophorous vacuole; 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; may be present within the parasitophorous vacuole 

 

ADDITIONAL DIAGNOTIC TESTS:

 

DIFFERENTIAL DIAGNOSIS: 

Chickens:

Necrotizing typhlitis:

• Salmonella enteriditis: Can cause necrotizing enteritis and typhlitis; not specific to one section of the intestine
• Histomonas meleagridis (blackhead): Turkey poults, game birds, chickens, replacement pullets; cecal swollen with cecal cores; circular or oval recessed lesions in liver (pathognomonic lesions)

Enteritis:

• Clostridium perfringens: Chickens; focal or diffuse necrosis of intestinal mucosa, especially ileum; common in the presence of coccidiosis
• Clostridium colinum (quail disease): Captive game birds, turkeys, chickens; acute enteritis only; deep ulcers along intestine; enlarged spleen; focal and/or diffuse yellow areas in liver; often secondary in chickens
• Nonspecific enteritis: Poultry and other birds; enteritis accompanies many infectious diseases that have lesions of greater diagnostic value in other systems (cholera, erysipelas, vibrionic hepatitis, spirochetosis, botulism, aflatoxicosis; influenza, candidiasis, and others)

Camelids:

• Other intestinal Eimeria spp.:
  1. New World: E. lamae, E. alpacae, E. punoensis, E. peruviana; these are all typically a quarter of the size of E. macusaniensis, and none cause as severe clinical signs
  2. Old World: E. bactriani, E. cameli, E. dromedarii, and E. pellerdyi.
• Cryptosporidia: 4-5 µm diameter, basophilic, round organisms along the apical surface of enterocytes (intracellular but extracytoplasmic); most dense on the tips of small intestinal epithelium; villar atrophy is the main lesion

 

 

COMPARATIVE PATHOLOGY:

• Camelids:
  • Eimeria macusaniensis is most significant, and by far the largest Camelid coccidian
  • Primarily affects young NW camelids; causes severe necrohemorrhagic enteritis; predisposes to other infections, especially clostridial infections, due to destruction of intestinal crypts
  • M inimal to absent gross findings, and fecal flotation often negative even with heavy infection
  • May efface the jejunal and ileal parenchyma, colon and duodenum are rarely affected; villar necrosis and loss are the primary lesions; lamina propria fibrosis may occur with chronicity; coccidians are typically most dense in the deep crypts but can affect the entire villus in severe infections
  • Oocysts: Up to 100x80 µm
  • Macrogamont (pink females): >100 µm
  • Microgamont (blue males): >100 µm

 

Animal	Coccidia	Organ affected/Clinical signs
Birds   Chickens                       Turkey               Geese & ducks     Sandhill/whooping      cranes   Parrots	E. acervulina E. necatrix/maxima E. brunetti E. tenella E. mitis E. mivati E. praecox E. hagani   E. dispersa E. adenoeides E. meleagrimitis  E. gallopavonis E. meleagridis E. innocua E. subrotunda E. truncata E. anseris/nocens E. reichenowi E. gruis E. psittaculae	Duodenum/enteritis Mid-intestine/enteritis Ileum/enteritis Ceca/typhlitis NP SI/enteritis Duodenum/enteritis Watery intestinal contents, catarrhal inflammation Middle 1/3, +/- duodenum, cecum Cecum, ileum SI (anterior 2/3)  Ileum, LI NP NP NP Kidney/anorexia, depression Intestine Disseminated   Intestine
Cattle             Water buffalo calves	E. bovis E. zuernii E. ellipsoidalis E. alabamensis E. auburnensis E. bukidnonensis E. kosti E. bareillyi	Lower small intestine; HP Terminal meter of ileum; HP   SI; occas. LI Ileum   Abomasal glands	Common; diarrhea progresses to dysentery; hemorrhagic or fibrinohemorrhagic typhlocolitis; +/- mucosal ulceration; Heat-labile neurotoxin associated with development of nervous disorders in cattle with coccidiosis
Sheep	E. ahsata/christenseni E. bakuensis (ovina) E. crandallis E. ovinoidalis E. granulosa E. faurei E. parva E. intricata E. pallida E. caprovina E. punctata	Lower SI Lower SI SI; villus atrophy Typhlocolitis	Universal; young animals; E. bakuensis and E. ahsata can cause nodular polypoid structures NOT assoc. w/ clinical disease
Goats	E. christenseni E. arloingi E. hirci E. ninakohlyakimovea E. jolchijevi E. apsheronica E. alijevi E. kochrii E. weybridgenssis E. marsica E. caprina E. pallida E. caprovina E. punctata	Lower SI Lower SI; occas. LI SI Typhlocolitis         SI   Typhlocolitis
Equine	E. leuckarti Klossiella equi	SI (mainly foals)
Swine	E. debliecki Cystoisospora suis E. scabra E. spinosa	SI (in 1-3 week old piglets) SI, distal 1/3 of villi Lower SI; most pathogenic	C. suis - Porcine neonatal coccidiosis; fibrinonecrotic enteritis in distal SI; coccidiosis in older swine uncommon
Canine	Cystisospora canis C. ohioensis C. burrowsi C. neorivolta	Distal SI; occas. LI SI, esp. ileum; LI SI SI; rarely cecum, colon
Feline	Cystoisospora felis C. rivolta	SI; occas. LI SI and LI
Mice	E. falciformis E. vermiformis E. papillata E. ferrisi Klossiella muris	Colon Intestine Intestine Intestine Kidney	Typhlocolitis in pet and wild mice
Rabbit	E. stiedae E. intestinalis E. flavescens E. media E. magna E. piriformis E. irresidua E. perforans E. exigua E. coecicola (NP)	Bile ducts Ileum and cecum Ileum and cecum	Enteritis often accompanied by overgrowth of E. coli and presence of rotavirus
Ferret	E. furonis	SI
Przewalski’s Gazelle	E. jiangi E. cagandzeeri
Old world Camelids	E. cameli E. dromedarii E. bactriani E. pellerdyi		All have been associated with severe disease in OW camelids, especially the young. E. cameli is 3-4x larger than the others.
HP = highly pathogenic; NP = non-pathogenic

 

REFERENCES

1. Abdul-Aziz T, Barnes HJ. Avian Histopathology Text and Atlas. Jacksonville, FL: American Association of Avian Pathologists; 2018: 154-158.
2. Agnew D. Camelidae In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 200-201.
3. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 82, 297.
4. Boulianne M, et al. Avian Disease Manual. 8^th ed. Jacksonville, FL: AAAP; 2019:134-138.
5. Clarke LL, Breuer RM. Postmortem diagnoses in South American camelids and factors influencing diagnostic rate in the Upper Midwest USA, 2009-2019. J Vet Diagn Invest. 2022;34(4):727-732.
6. Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2^nd ed. Philadelphia, PA: John Wiley & Sons, Inc.; 2015: 82.
7. Spagnoli ST, Gelberg HB. Alimentary System and the Peritoneum, Omentum, Mesentery, and Peritoneal Cavity. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:. 
8. Uzal FA, Plattner BL, Hostetter JM. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier; 2016: 227-235.

Click the slide to view.

---