September 2018



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




HISTOPATHOLOGIC DESCRIPTION: D-P01a Cecum: Circumferentially expanding the lamina propria and infiltrating the mucosal/crypt epithelium are myriad developing coccidial life stages including numerous intracellular macrogamonts and microgamonts, and both intra and extracellular schizonts; and many developing oocysts which comprise the majority of the developing stages. Macrogamonts are approximately 30 um in diameter with a single, central nucleus and a peripheral ring of 2 um diameter eosinophilic granules; microgamonts are round to oval, approximately 15-20 um in diameter with multiple small 1um basophilic nuclei; schizonts are 40-60 um in diameter with numerous basophilic 4x2um crescentic merozoites. Oocysts within the cecal crypt lumina and within crypt epithelium are 15-20um diameter, thick walled, oval to irregular, and filled with eosinophilic pale granular material and/or a single eosinophilic central nucleus and are admixed with a small amount of necrotic debris. Multifocally, the mucosa is eroded with loss of enterocytes and replacement by hemorrhage, fibrin, eosinophilic cellular and karyorrhectic debris, and inflammatory cells (lymphocytes, few heterophils). Expanding the lamina propria and submucosa and multifocally extending into the muscularis and serosa is a moderate cellular infiltrate composed of lymphocytes, plasma cells, macrophages and few heterophils admixed with hemorrhage, fibrin, edema, and scattered colonies of cocci. The cecum lumen is distended with numerous previously described coccidial life stages, necrotic debris, fibrin, hemorrhage, degenerate inflammatory cells, sloughed enterocytes, and few clusters of cocci and bacilli.


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


Signalment (JPC #3107701): Multiple 4 week old broiler chickens.


HISTORY: Six 4-week-old broilers were submitted for necropsy from a flock of 12,000 birds. There had been a prominent spike in mortality in one of four barns and approximately 250 birds had been lost.


HISTOPATHOLOGIC DESCRIPTION: D-P01b Cecum: Diffusely and circumferentially, the mucosa is eroded or ulcerated and the mucosal epithelium is lost and replaced by eosinophilic cellular and karyorrhectic debris (lytic necrosis), few lymphocytes, viable and degenerate heterophils, macrophages, fibrin, edema, and previously described schizonts and free merozoites, which are present in abundance. Remaining crypts are often dilated and contain numerous oocysts, necrotic debris, and fibrin (crypt abscesses), and the crypt epithelium is frequently expanded by previously described intracellular gamonts. Multifocally, schizonts are present in the muscularis mucosa, admixed with fibrin, hemorrhage, edema, and previously described inflammatory cells that diffusely extends into and expands the submucosa. The cecal lumen contains abundant hemorrhage, fibrin and necrotic debris admixed with few oocysts, schizonts, merozoites, numerous 1x4 bacilli, sloughed epithelial cells, few heterophils, and lymphocytes. Numerous bacterial colonies containing both rods are cocci and present within vessels in the muscularis and submucosa.


MORPHOLOGIC DIAGNOSIS: Cecum: Typhlitis, necrohemorrhagic, subacute, diffuse, severe, with numerous intra- and extracellular schizonts, merozoites, gamonts, and oocysts.


ETIOLOGIC DIAGNOSIS: Cecal coccidiosis (Eimeriosis)


CAUSE: Eimeria tenella



·      Important worldwide poultry disease; causes enteritis and/or typhlitis

·      Coccidiosis typically affects intensively managed animals; usually mild disease, severe outbreaks may have high mortality

·      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

·      Eimeriosis is a disease of young animals, occurring in chicks 3 to 6 weeks of age (E. necatrix infects chicks at 8 to 18 weeks)

·      Immunity is species specific; experimentally, resistance to coccidial infection is largely from T-cell promoted intracellular killing, directed primarily at asexual stages



·      Oral ingestion > enterocytes are damaged when mature schizonts rupture and release merozoites

·      Malabsorption due to villus atrophy

·      Exudative enteritis and typhlitis due to epithelial erosion and ulceration

·      Heat-labile neurotoxin associated with development of nervous disorders in cattle with coccidiosis



·      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



·      Bloody diarrhea

·      Bleeding, weight loss, loss of skin pigment



·      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



·      Organisms in various stages of development randomly scattered within enterocytes or free in the lamina propria

·      Asexual replication: Schizogony or merogony

·      Schizonts: Asexual replication/schizogony or merogony; encapsulated cyst containing crescentic 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)

·      Hemorrhage and necrosis near blood vessels of the inner circular layer of the tunica muscularis (early)

·      Lamina propria, submucosa: Lymphocytic, heterophilic and eosinophilic infiltrates

·      Destruction of the mucosa and tunica muscularis; disrupted cecal glands

·      Sloughed parasitized enterocytes, blood, and necrotic debris within the intestinal lumen, glands and crypts



·      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



·      Fecal flotation; histopathology; gross pathology; IFA, PCR



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)


·      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)






Organ affected/Clinical signs











Geese & ducks






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









Watery intestinal contents, catarrhal inflammation

Middle 1/3, +/- duodenum, cecum

Cecum, ileum

SI (anterior 2/3)

Ileum, LI




Kidney/anorexia, depression













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



Abomasal glands


Common; diarrhea progresses to dysentery; hemorrhagic or fibrinohemorrhagic typhlocolitis; +/- mucosal ulceration


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


Universal; young animals; E. bakuensis and E. ahsata can cause nodular polypoid structures NOT assoc. w/ clinical disease


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












E. leuckarti

Klossiella equi

SI (mainly foals)



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


Cystisospora canis

C. ohioensis

C. burrowsi

C. neorivolta

Distal SI; occas. LI

SI, esp. ileum; LI


SI; rarely cecum, colon



Cystoisospora felis

C. rivolta

SI; occas. LI

SI and LI



E. falciformis

E. vermiformis

E. papillata

E. ferrisi

Klossiella muris






Typhlocolitis in pet and wild mice


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 accomp. by overgrowth of E. coli and presence of rotavirus


E. furonis



Przewalski’s Gazelle

E. jiangi

E. cagandzeeri



HP = highly pathogenic; NP = non-pathogenic




1.    Abdul-Aziz T, Barnes HJ. Avian Histopathology Text and Atlas. Jacksonville, FL: American Association of Avian Pathologists; 2018: 154-158.

2.    Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 82, 297.

3.    Boulianne M, et al. Avian Disease Manual. 7th ed. Jacksonville, FL: AAAP; 2013:164-167, 248-250.

4.    Cebra CK, Valentine BA, Schlipf JW, et al. Eimeria macusaniensis infection in 15 llamas and 34 alpacas. J Am Vet Med Assoc. 2007; 230(1): 94-100.

5.    Hensel M, Bertram M, Rech R, Hamer G, Hamer S. Survey of gross and histopathologic findings in two wintering subpopulations of Sandhill cranes (Antigone canadensis). J Wildl Dis. 2018; 54(1): 156-160.

6.    Kwon YK, Jeon WJ, Kang MI, Kim JH, Olsen GH. Disseminated visceral coccidiosis in a wild white-naped crane (Grus vipio). J Wildl Dis. 2006; 42(3): 712-714.

7.    McDougald LR. Protozoal infections. In: Swayne DE, ed. Diseases of Poultry. 13th ed. Ames, IA: John Wiley & Sons, Inc.; 2013: 1148-1166.

8.    Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2nd ed. Philadelphia, PA: John Wiley & Sons, Inc.; 2015: 82.

9.    Sledge DG, Bolin SR, Lim A, Kaloustian LL, Heller RL, Carmona FM, Kiupel M. Outbreaks of severe enteric disease associated with Eimeria furonis infection in ferrets (Mustela putorius furo) of 3 densely populated groups. J Am Vet Med Assoc. 2011; 239(12): 1584-1588.

10. 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.

11. Wang Y, Du S, Yang Y, et al. Intestinal parasites in the critically endangered Przewalski’s gazelle (Procapra przewalskii) in China, with the description of a new species of Eimeria (Apicomplexa: Eimeriidae). J Wildl Dis. 2016; 52(4): 945-948.







·      Sporocyte (A) ingested à enzymatic degradation à free sporozoites invade enterocyte (1) à within parasitophorous vacuole develops into schizont (syn meront) (2/3) à merozoites form within meront à cell lysis and reinvasion (4/5) à 2nd and 3rd generation merozoites (6) à formation of gametes (7. male - microgamont, 8. female - macrogamont) à fertilization (9/10) à zygote à oocyst à discharged in feces (11) à sporulation in wet, warm soil (12) à sporocysts ingested (1)



Dipl. Biol. Andreas Weck-Heimann: Life cycle eimeria,

Click the slide to view.

Click on image for diagnostic series.

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