Epithelial Inclusions in Gallbladder Specimens Mimic Parasite Infection: Histologic and Molecular Examination of Reported Cystoisospora belli Infection in Gallbladders of Immunocompetent Patients

Where Have All the Diagnostic Morphological Parasitologists Gone?

Advances in laboratory techniques have revolutionized parasitology diagnostics over the past several decades. Widespread implementation of rapid antigen detection tests has greatly expanded access to tests for global parasitic threats such as malaria, while next-generation amplification and sequencing methods allow for sensitive and specific detection of human and animal parasites in complex specimen matrices.

Comparison of Two Real-Time PCR Assays Targeting Ribosomal Sequences for the Identification of Cystoisospora belli in Human Stool Samples

Cystoisospora (C.) belli is a coccidian parasite associated with acute or chronic gastroenteritis in immunocompromised patients. Dissatisfactory sensitivity of microscopy as the diagnostic standard approach has been described. Here, we comparatively evaluated two real-time PCRs targeting ribosomal RNA gene sequences of C. belli in stool in a test comparison without a reference standard applying latent class analysis. Therefore, 1000 stool samples from Ghanaian HIV (human immunodeficiency virus) patients (n = 905) as well as military returnees from the tropics (n = 95) were assessed by both assays in parallel. After the exclusion of 33 samples showing PCR inhibition, 29 and 33 positive results were recorded with the 5.8S rRNA gene/ITS-2 sequence PCR and the ITS-2 sequence PCR, respectively, resulting in an accuracy-adjusted prevalence of 3.2%. Nearly perfect agreement between both assays was indicated by Fleiss’ kappa of 0.933 with sensitivity and specificity of 92.8% and 100% as well as 100% and 99.8% for the 5.8S rRNA gene/ITS-2 sequence PCR and the ITS-2 sequence PCR, respectively. Both assays proved to be suitable for the diagnosis of C. belli in human stool samples with slightly better sensitivity of the ITS-2 sequence assay, while the 5.8S rRNA gene/ITS-2 sequence PCR may be considered for confirmatory testing.

Pitfalls in Morphologic Diagnosis of Pathogens: Lessons Learned From the Pseudo-Cystoisospora Epidemic

Multiple groups have recently reported involvement of the gallbladder mucosa of immunocompetent patients by cystoisospora organisms. However, this has recently been disproved with the support of molecular and ultrastructural studies. Here we present a summary of these events, recounting how this pseudo-Cystoisospora epidemic began and ended. This review also highlights the important role played by ancillary techniques in supplementing the morphologic diagnosis of pathogens.

Ultrastructural Characteristics of Gallbladder Epithelial Inclusions Mimicking Cystoisospora

OBJECTIVES

There is recently reported increased prevalence of Isospora organisms in cholecystectomy specimens from immunocompetent patients, especially in acalculous cholecystectomies. We performed an ultrastructural and molecular evaluation of these specimens.

METHODS

From 28 gallbladders with intraepithelial inclusions, two specimens with diffuse involvement of the gallbladder epithelium were analyzed by electron microscopy. Polymerase chain reaction was performed on five samples for the ITS2 region of C belli and eukaryotic 18S region. The 18S products were sequenced by next-generation sequencing.

RESULTS

Electron microscopic analysis showed cytoplasmic condensations leading to vacuole formation. In contrast with true C belli, there were no identifiable organelles or organization. None of these cases showed amplified products other than human on molecular analysis.

CONCLUSIONS

Electron microscopic analysis demonstrates that the inclusions are condensed cytoplasmic material and not true organisms.

Cystoisospora belli infections in humans: the past 100 years

Cystoisospora belli is a coccidian parasite of humans, with a direct fecal-oral transmission cycle. It is globally distributed, but mainly found in tropical and subtropical areas. Many cases of C. belli infections have been reported in patients with HIV, and in patients undergoing immunosuppressive therapy for organ transplants or those treated for tumours worldwide. Unsporulated or partially sporulated oocysts of C. belli are excreted in feces. When sporulated oocysts in contaminated water or food are ingested, asexual and sexual stages of C. belli are confined to the epithelium of intestines, bile ducts and gallbladder. Monozoic tissue cysts are present in extra-intestinal organs (lamina propria of the small and large intestine, lymph nodes, spleen, and liver) of immunosuppressed humans. However, a paratenic host has not been demonstrated. Cystoisospora belli infections can be persistent, lasting for months, and relapses are common; the mechanism of relapse is unknown. Recently, the endogenous stages of C. belli were re-examined and attention was drawn to cases of misidentification of non-protozoal structures in the gallbladder of patients as C. belli. Here, we review all aspects of the biology of C. belli, including morphology, endogenous stages, prevalence, epidemiology, symptoms, diagnosis and control.

Cytoplasmic Fibrillar Aggregates in Gallbladder Epithelium Are a Frequent Mimic of Cystoisospora in Pediatric Cholecystectomy Specimens

Context.—

Cystoisospora belli is an intracellular parasite associated with gastrointestinal disease in immunocompromised hosts. Although infection has been classically associated with intestinal disease, studies have identified Cystoisospora in the gallbladder of immunocompetent patients based on hematoxylin-eosin morphology. Recently, the identity of this histologic finding as Cystoisospora has been questioned based on negative results of nucleic acid studies.

Objective.—

To determine the prevalence of this histologic feature in pediatric patients, we retrospectively reviewed all cholecystectomy specimens from a pediatric hospital during a 24-month period.

Design.—

In 180 cholecystectomy specimens, we identified 11 cases (6.1%) with classical histologic features previously described to represent Cystoisospora organisms. To further investigate these structures, we retrieved tissue from paraffin-embedded blocks and performed electron microscopy.

Results.—

Ultrastructural examination identified ovoid perinuclear cytoplasmic structures composed of dense fibrillar aggregates rather than organisms. Patients with positive cases were similar in age to controls (positive cases: mean patient age 13.4 years [range, 2–23 years]; negative cases: mean patient age 14.7 years [range, 12 weeks–31 years]; P = .35). There was no significant association of this finding with cholelithiasis (54.5% versus 65.1%, P = .52), cholesterolosis (0% versus 22.5%, P = .12), acute cholecystitis (9.1% versus 10.1%, P > .99), or chronic cholecystitis (45.5% versus 66.3%, P = .20).

Conclusions.—

To our knowledge, this is the first positive identification of these structures as cytoplasmic fibrillar aggregates rather than parasitic inclusions by ultrastructural examination, and the first study of this histologic finding in pediatric cholecystectomies.

Endogenous development of Cystoisospora belli in intestinal and biliary epithelium of humans

Cystoisospora(Isospora)belliis a coccidian parasite of humans. It can cause serious digestive disorders involving infection of intestines, biliary tract and gallbladder, especially in those with depressed immunity. It has a direct fecal–oral transmission cycle. After ingestion of sporulated oocysts, the parasite multiplies asexually and sexually within host epithelial cells, resulting in unsporulated oocysts that are excreted in feces. The details of asexual and sexual stages are not known and certain inclusions in epithelial cells in biopsy samples have been erroneously identified recently asC. belli. Here, we provide details of developmental stages ofC. belliin two patients, in duodenal biopsy of one and biliary epithelium of the other. Immature and mature asexual stages (schizonts/meronts) were seen in epithelial cells. The merozoites were seen singly, in pairs and in groups in single parasitophorous vacuole (pv) in host cytoplasm. Immature and mature meronts were seen together in the same pv; up to eight nuclei were seen in meronts that retained elongated crescent shape; round multinucleated schizonts, seen in other coccidians, were not found. Meronts were up to 25µm long and contained up to ten merozoites that were 8–11µm long. The merozoites and meronts contained PAS-positive granules. Microgamonts (male) contained up to 30 nuclei that were arranged at the periphery and had condensed chromatin; 1–3 PAS-positive, eosinophilic, residual bodies were left when microgametes were formed. The microgametes were 4µm long and PAS-negative. All stages of macrogamonts, including oocysts were PAS-positive. The detailed description of the life cycle stages ofC. bellireported here should facilitate in histopathologic diagnosis of this parasite.