History
A 3-week-old 31.0-kg (68.2-lb) male mixed-breed calf with a 3-day history of anorexia and severe hemorrhagic diarrhea was submitted for necropsy. The calf was part of a small beef herd and was the only bovid that had clinical signs.
Clinical and Gross Findings
A complete physical examination conducted by the referring veterinarian revealed dehydration, lethargy, and hemorrhagic diarrhea. The calf was initially treated IV with fluids and dextrose, but the hemorrhagic diarrhea worsened; given the poor prognosis, the owner elected euthanasia by means of IV barbiturate solution overdose. External examination during necropsy revealed poor body condition (body condition score, 2/5), oral and ocular mucosal pallor, and sunken eyes. The ascending, spiral, and descending colons were diffusely and markedly distended by abundant, dark red, fibrillar casts (Figure 1). The small intestines were mildly dilated and contained moderate amounts of dark brown to green fluid material. The liver was slightly swollen and diffusely pale and had multifocal, 1- to 3-mm-diameter, well-demarcated, dark yellow areas. The thoracic cavity contained 15 mL of straw-colored fluid admixed with yellow fibrin strands. The lungs did not collapse when the thoracic cavity was opened and were diffusely red, wet, and heavy, with prominent interlobular septa and excessive blood on the cut surface. The pericardium contained 7 mL of straw-colored fluid with yellow fibrin strands.
Photograph of the colon of a 3-week-old calf that was euthanized because of anorexia and severe hemorrhagic diarrhea and submitted for necropsy. Notice that the colon is diffusely expanded by dark red casts composed of hemorrhagic debris and yellow strands of fibrin.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photograph of the colon of a 3-week-old calf that was euthanized because of anorexia and severe hemorrhagic diarrhea and submitted for necropsy. Notice that the colon is diffusely expanded by dark red casts composed of hemorrhagic debris and yellow strands of fibrin.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photograph of the colon of a 3-week-old calf that was euthanized because of anorexia and severe hemorrhagic diarrhea and submitted for necropsy. Notice that the colon is diffusely expanded by dark red casts composed of hemorrhagic debris and yellow strands of fibrin.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Histopathologic and Microbiological Findings
Several formalin-fixed tissue samples were collected for histologic examination. In the colon, the mucosa was diffusely collapsed as a result of severe necrosis and inflammation (Figure 2). Multifocal areas with loss of colonic crypts and extensive mucosal erosion and ulceration were evident. Approximately 70% of the remaining enterocytes were expanded by cytoplasmic coccidial organisms (Figure 3). Most of these organisms were 15- to 20-µm-diameter schizonts containing multiple basophilic crescent-shaped merozoites. In addition, there were multiple 20-μm-diameter microgametes and macrogametes (the latter containing multiple eosinophilic globules) and 25-μm-diameter, thick-walled oocysts with a central eosinophilic nucleus. There was multifocal colonic crypt necrosis with free merozoites within the crypt lumens. The remaining crypts had multifocal evidence of regeneration characterized by enlarged epithelial cells with large nuclei and high mitotic activity or were dilated by luminal accumulations of eosinophilic necrotic cell debris and lined by attenuated epithelium. The lamina propria was edematous and had diffuse accumulations of moderate numbers of lymphocytes and plasma cells with fewer neutrophils and eosinophils. Inflammatory cells extended into the underlying submucosa and muscle layers. Within the lumen of the colon, oocysts were also observed admixed with necrotic cell debris, fibrin, hemorrhage, and bacilli. Sections of jejunum and ileum had moderate numbers of lymphocytes and plasma cells with fewer neutrophils and eosinophils throughout the edematous lamina propria, but no coccidial organisms were observed in these areas. No lesions were observed in sections of cecum. Sections of mesenteric lymph nodes had large numbers of macrophages and areas of hemorrhage within the medullary sinuses. Scattered throughout the hepatic parenchyma were multifocal, random foci of hepatocellular necrosis admixed with cell debris, fibrin, neutrophils, macrophages, and rare eosinophils. Throughout the sinusoids there were small numbers of neutrophils. No bacteria were observed within these necrotic foci in sections stained with Lillie Twort Gram stain. In the lungs, there was abundant alveolar, perivascular, and interlobular edema.
Photomicrograph of a section of the colon from the calf in Figure 1. Extensive areas of the mucosa are collapsed because of necrosis. Colonic crypts contain cell debris (asterisk), and a mixed inflammatory infiltrate is present throughout the edematous lamina propria (thin arrow). Remaining enterocytes contain cytoplasmic coccidial organisms (arrowheads) and there is evidence of epithelial cell regeneration (thick arrow) characterized by enlarged cells with prominent nuclei. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photomicrograph of a section of the colon from the calf in Figure 1. Extensive areas of the mucosa are collapsed because of necrosis. Colonic crypts contain cell debris (asterisk), and a mixed inflammatory infiltrate is present throughout the edematous lamina propria (thin arrow). Remaining enterocytes contain cytoplasmic coccidial organisms (arrowheads) and there is evidence of epithelial cell regeneration (thick arrow) characterized by enlarged cells with prominent nuclei. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photomicrograph of a section of the colon from the calf in Figure 1. Extensive areas of the mucosa are collapsed because of necrosis. Colonic crypts contain cell debris (asterisk), and a mixed inflammatory infiltrate is present throughout the edematous lamina propria (thin arrow). Remaining enterocytes contain cytoplasmic coccidial organisms (arrowheads) and there is evidence of epithelial cell regeneration (thick arrow) characterized by enlarged cells with prominent nuclei. H&E stain; bar = 100 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photomicrographs of sections of the colon from the calf in Figure 1 with protozoal organisms (arrowheads) at different stages of development. The cytoplasm of enterocytes contains coccidial schizonts with crescent-shaped merozoites (A), microgametes (B), macrogametes (C), and oocysts (D). H&E stain; bar = 25 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photomicrographs of sections of the colon from the calf in Figure 1 with protozoal organisms (arrowheads) at different stages of development. The cytoplasm of enterocytes contains coccidial schizonts with crescent-shaped merozoites (A), microgametes (B), macrogametes (C), and oocysts (D). H&E stain; bar = 25 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
Photomicrographs of sections of the colon from the calf in Figure 1 with protozoal organisms (arrowheads) at different stages of development. The cytoplasm of enterocytes contains coccidial schizonts with crescent-shaped merozoites (A), microgametes (B), macrogametes (C), and oocysts (D). H&E stain; bar = 25 μm.
Citation: Journal of the American Veterinary Medical Association 249, 8; 10.2460/javma.249.8.905
High numbers of Eimeria oocysts were detected by fecal flotation. Bacteriologic culture of samples of large intestinal contents yielded no growth of Salmonella spp. Results of fluorescent antibody testing of fresh intestinal tissue samples were negative for the presence of Escherichia coli K99 and F41 antigens, bovine rotavirus, bovine coronavirus, and bovine viral diarrhea virus.
Morphologic Diagnosis and Case Summary
Morphologic diagnosis: severe, subacute, diffuse necrotizing colitis with crypt epithelial cell regeneration and intraepithelial coccidial organisms (morphologically consistent with Eimeria spp) and moderate, acute, multifocal necrotizing hepatitis.
Case summary: colonic coccidiosis with secondary necrotizing hepatitis in a calf.
Comments
Gross and histologic findings in the case described in the present report were highly consistent with colonic coccidiosis caused by Eimeria spp, and the diagnosis was confirmed by the presence of high numbers of Eimeria oocysts in feces from the calf. Eimeria spp are intracellular protozoan organisms that develop within enterocytes and endothelial cells.1–5 More than a dozen species of Eimeria are known to infect cattle, but only a few cause severe clinical disease.2,3 Eimeria bovis and Eimeria zuernii are the main pathogenic species associated with potentially fatal intestinal coccidiosis in cattle. Young calves are generally more susceptible to Eimeria spp infection, whereas adult cattle usually have an effective immune response subsequent to earlier exposure, which prevents development of severe clinical disease but allows further shedding of oocysts into the environment.2 Therefore, environmental contamination by infective oocysts can occur in the soil, vegetation, and water on farms with infected cattle.1 Following ingestion of sporulated oocysts, organisms undergo 1 or more asexual reproductive cycles (schizogony) within the cytoplasm of enterocytes or lacteal endothelial cells. Merozoites released from schizonts differentiate into microgametes and macrogametes within newly infected cells, where fertilization occurs (sexual cycle). The resulting zygotes further develop into unsporulated oocysts, which are shed in the feces. Although the second generation of schizonts and gamonts of both species of Eimeria typically replicate within the colonic and cecal crypts, leading to severe hemorrhagic diarrhea, major differences exist regarding their primary site of replication after infection.3 Whereas first generations of E bovis replicate in lacteal endothelial cells in the lower small intestine, E zuernii primarily replicates within the deep lamina propria in the terminal portion of the ileum. Therefore, given the lack of organisms detected in sections of small intestine from the calf of the present report, it is likely that the colonic lesions were caused by second generations of coccidial organisms.3 Enterocyte disruption occurs in all stages of the protozoal life cycle, and the diminished epithelial turnover in young animals explains their high susceptibility to Eimeria–related clinical disease.4
Infections with Eimeria spp more typically result in subclinical disease in cattle and decreased production because of reduced rates of weight gain, feed conversion, and growth performance and increased susceptibility to other diseases in cattle herds.6 Compared with the effects of clinical bovine coccidiosis, subclinical disease is generally associated with higher economic losses, with annual costs that can exceed $400 million for cattle ranchers.7 The survival of oocysts in the environment is enhanced by mild temperatures and moist environmental conditions, whereas dry or extremely cold conditions shorten their infective capacity.1 Once individual animals are infected, the degree of intestinal damage is directly dependent on multiple parasite- and host-related factors. Therefore, clinical disease is highly dependent on the pathogenicity of the infective species and on the parasite load.1 In addition, important host-related factors considered as major facilitators for the development of clinical coccidiosis in cattle include young age, lack of specific immunity, concurrent disease, and stressful situations, such as shipping, crowding, food changes, and unfavorable weather conditions (especially blizzards or hot ambient temperatures).1,3 These host-related factors may also cause reactivation of latent schizonts and consequent clinical disease.3 The prepatent period of Eimeria spp is generally 2 weeks, and oocyst release has been observed in calves as young as 3 weeks old. Therefore, infection can occur immediately after birth.5 The extensive damage to the colonic mucosa in cattle with coccidiosis usually leads to blood loss and subsequent anemia, hypoproteinemia, dehydration, and intestinal malabsorption.1,3,4 The hydrothorax and hydropericardium in the calf of the present report could have been consequences of hypoproteinemia, but the presence of random hepatocellular necrosis suggested that septicemia or endotoxemia (secondary to extensive mucosal damage in the colon) could have acted as a complicating factor, which led to an increase in vascular permeability and leakage of plasma components.8
Differential diagnoses in the case described in the present report included salmonellosis, colibacillosis, bovine coronaviral infection, bovine adenoviral infection, bovine viral diarrhea virus infection, malignant catarrhal fever, and cryptosporidiosis.3 Salmonella spp infection typically causes fibrinonecrotic enterocolitis with vascular thrombosis. Several strains of E coli can affect young calves and cause enterocolitis of variable severity that may culminate in septicemia. Coronaviral infection is typically characterized by atrophic enteritis. The virus replicates in the small and large intestines and can lead to a severe necrotizing enterocolitis.3,9 All these infectious agents were ruled out by the absence of the characteristic pathological changes and negative results of fluorescent antibody testing of fresh samples of intestinal tissue. Bovine adenoviral infection may cause necrotizing enteritis with vasculitis, thrombosis, and prominent viral inclusions within endothelial cells. Bovids with bovine viral diarrhea and malignant catarrhal fever typically have erosions and ulcerations throughout the gastrointestinal tract. Furthermore, histologic features of malignant catarrhal fever include perivascular mononuclear inflammation and fibrinoid necrotizing vasculitis in multiple organs. Cryptosporidium spp are readily visible on the apical surface of enterocytes in sections of intestine of infected calves.3 None of these findings were observed in the calf of this report.
Effective strategies for coccidiosis control include minimizing possible stress-inducing conditions, minimizing the exposure of susceptible young calves to infective oocysts, and administration of prophylactic coccidiostatic drugs to infected animals. Amprolium, lincomycin, monensin, and salinomycin are commonly used in calves and inhibit the early stages of coccidial development.1 Sulphonamides primarily act on the asexual phase of coccidial development and are also effective against bacterial agents that may cause secondary infections such as pneumonia and necrotizing hepatitis,10 as observed in the calf of the present report.
Acknowledgments
Dr. Brito was a visiting student at the Department of Pathology, College of Veterinary Medicine, The University of Georgia, Athens, GA 30602 at the time of the case.
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