Molecular characterization of Cystoisospora belli and unizoite tissue cyst in patients with Acquired Immunodeficiency Syndrome

Diagnostic Features of Blastocystis Life Cycle Forms in the Small Intestine in an HIV-Infected Patient

PURPOSE

Blastocystis spp. are parasites of the intestinal tract found in many hosts including humans. This pathogen is commonly found in immunocompetent in asymptomatic individuals and in patients with gastrointestinal and extra-intestinal symptoms. Recently, it has been implicated as an important cause of diarrheal illness in immunocompromised individuals, including HIV-infected patients. At least six life cycle stages have been described in faeces and cultures, namely vacuolar, granular, multi-vacuolar, avacuolar, ameboid and cyst forms. The aim of the present study was to describe the histological findings of Blastocystis infection in an adult HIV-infected patient with gastrointestinal symptoms.

METHODS

Parasitological techniques and PCR were applied to stool samples. Histological analysis was performed on duodenal biopsy specimens.

RESULTS

Standard parasitological methods revealed vacuolar, granular, cyst and multi-vacuolar forms of Blastocystis in faecal samples with the presence of Blastocystis DNA being confirmed by PCR. DNA sequencing revealed Blastocystis subtype ST1. Histological findings in duodenal samples showed an inflammatory infiltrate with plasma cells and lymphocytes. We identified cyst, granular, ameboid and multi-vacuolar forms in the lumen.

CONCLUSION

To our knowledge, there are no previous peer review reports describing these four different forms of Blastocystis in histological sections from the lumen and the brush border of the enterocytes.

Cystoisospora belli, liver disease and hypothesis on the life cycle

Cystoisospora belli causes chronic diarrhoea, acalculous cholecystitis, cholangiopathy and disseminated cystoisosporosis in patients with AIDS. Clinical manifestations and histological stages during C. belli infection in a patient with AIDS and liver disease were described. It was possible to identify sporozoite-like structures in the villus epithelium of the duodenum, close to the vascularization that underlies the basal membrane and unizoite tissue cysts near to the vascularization in the lamina propria. Unizoite tissue cysts were found inside of sinusoids in the liver communicating with the central vein and with a bile canaliculus and portal spaces. Based on these findings a hypothesis on C. belli life cycle could consider that the route of migration of unizoite tissue cysts up the liver is via the portal blood. The unizoite tissue cysts located in hepatic portal vein could migrated via sinusoid to central vein and general circulation through the venous system. The unizoite tissue cysts could also return via bile canaliculus to bile duct to portal triad. This hypothesis allows to understand the presence of unizoite stages in blood, the pathway by which the bile ducts become infected and unizoites in the liver being able to behave like hypnozoites that favour relapses and treatment failures.

Molecular detection of Cystoisospora belli by single-run polymerase chain reaction in stool samples

INTRODUCTION

Cystoisospora belli (C. belli) is the only pathogenic species of the Cystoisospora genus responsible for severe diarrhea in immunocompromised patients. Most common microscopic method of diagnosis is less sensitive due to intermittent shedding of oocysts. We developed a new single-run polymerase chain reaction (PCR)-based diagnostic assay for C. belli.

METHODS

A new single-run PCR-based diagnostic assay was standardized for the detection of C. belli. Diagnostic reproducibility and repeatability of the PCR assay were evaluated. A cross-sectional analytical study was done on a total of 354 stool samples collected from 331 immunocompromised patients with diarrhea. All the stool samples were tested for the presence of oocysts of C. belli and were also tested by our new PCR assay for C. belli. Three of the representative PCR products were confirmed by sequencing. Fisher's exact test was used to compare the two proportions.

RESULTS

Microscopy detected C. belli in 11/354 (3.1%) of stool samples, and the new PCR-based assay detected C. belli in 16/354 (4.5%). The new single-run PCR-based assay detected C. belli in all the stool samples which were tested positive by microscopy and additionally detected C. belli in five stool samples. The developed PCR assay detected statistically significant proportion of C. belli (p < 0.001) as compared to microscopy. The 795 base pair PCR product from one microscopy positive stool sample and two microscopy negative stool samples were confirmed by sequencing.

CONCLUSION

Our newly developed single-run PCR-based detection assay for C. belli is robust and reproducible. It may be used for molecular diagnosis of cystoisosporiasis especially in transplant, pediatrics, and human immunodeficiency virus (HIV) positive patients.

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.

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.

First detection of Cryptosporidium DNA in blood and cerebrospinal fluid of HIV-infected patients

Human cryptosporidiosis is an intestinal infection caused by different species belonging to the genus Cryptosporidium in both immunocompetent and immunocompromised individuals. The life cycle of Cryptosporidium sp. when affecting the digestive system is well known but the infection of other organs is less studied. Molecular methods are necessary for species and subtypes identification. The goal of this work is to propose a new approach that contributes to the diagnosis of the extra-intestinal dissemination process of Cryptosporidium infection. Cryptosporidium sp. was detected in stool and biopsy samples of two HIV-infected patients. DNA was extracted from feces, biopsy specimens, blood, and cerebrospinal fluid (CSF). All samples were analyzed by nested PCR-RFLP of the 18S rDNA, real-time PCR, and gp60 subtyping. Cryptosporidium DNA was detected in stool and tissue samples and it was also present in blood and CSF samples. Both cases were characterized as Cryptosporidium hominis subtype IeA11G3T3. This is the first report that demonstrates the presence of Cryptosporidium DNA in blood and CSF of HIV-infected patients.

Molecular testing for clinical diagnosis and epidemiological investigations of intestinal parasitic infections

Over the past few decades, nucleic acid-based methods have been developed for the diagnosis of intestinal parasitic infections. Advantages of nucleic acid-based methods are numerous; typically, these include increased sensitivity and specificity and simpler standardization of diagnostic procedures. DNA samples can also be stored and used for genetic characterization and molecular typing, providing a valuable tool for surveys and surveillance studies. A variety of technologies have been applied, and some specific and general pitfalls and limitations have been identified. This review provides an overview of the multitude of methods that have been reported for the detection of intestinal parasites and offers some guidance in applying these methods in the clinical laboratory and in epidemiological studies.

First report of Cystoisospora belli parasitemia in a patient with acquired immunodeficiency syndrome

Cystoisospora belli in patients with the acquired immunodeficiency syndrome (AIDS) has been described as cause of chronic diarrhea and disseminated cystoisosporosis. Diagnosis of intestinal cystoisosporosis can be achieved at the tissue level in the villus epithelium of the small bowel. Disseminated cystoisosporosis is diagnosed by microscopy identification of unizoite tissue cysts in the lamina propria of the intestine. We report a case of disseminated cystoisosporosis in a human immunodeficiency virus (HIV)-infected patient with detection of parasitemia. We studied a 39-year old patient with AIDS and chronic diarrhea by analysis of stool and duodenal biopsy samples. Blood samples were also collected and examined by light microscopy and molecular techniques for C. belli DNA detection. The unizoite tissue cyst stages were present in the lamina propria, with unsporulated oocysts in feces. Zoites were present in blood smears and DNA of C. belli was detected in blood samples. Our study identified a new stage in the life cycle of C. belli. Detection of parasitemia is a novel and noninvasive tool for diagnosis of disseminated cystoisosporosis.

Molecular diagnosis of natural fasciolosis by DNA detection in sheep faeces

Fasciolosis is an important parasitic zoonosis considered the most important helminth infection of ruminants in tropical countries. The aim of this study was to develop a PCR assay for the sensitive and specific detection of F. hepatica in formalin preserved sheep faeces. A 405-bp fragment of the cytochrome c oxidase subunit 1 gene of F. hepatica was amplified from stool samples of infected sheep. The PCR assay showed a detection limit of 20 pg of F. hepatica DNA. No cross-reactions were observed with samples containing coccidian oocysts or gastrointestinal nematodes eggs. Our PCR technique showed to be effective for specific detection of F. hepatica infections in sheep.

Cystoisospora and cyclospora

PURPOSE OF REVIEW

The present review focuses on recent epidemiological and diagnostic advances in cystoisosporiasis and cyclosporiasis.

RECENT FINDINGS

Continuous outbreaks of these parasites occur worldwide. Sporadic cases in the United States are travel acquired, but also domestically acquired. New molecular diagnostic methods allow for accurate early diagnosis in humans, and might potentially decrease the burden of disease by detecting these parasites in vehicles of transmission.

SUMMARY

Better understanding of the epidemiology of Cyclospora cayetanensis and to a less extent to Cystoisospora belli has been gained recently. However, several gaps still remain in knowledge on the transmission and on mechanisms of persistent infection in immunosuppressed patients and prevention. New molecular methods might help in filling these gaps and in controlling transmission.

Cystoisospora canis (Apicomplexa: Sarcocystidae): development of monozoic tissue cysts in human cells, demonstration of egress of zoites from tissue cysts, and demonstration of repeat monozoic tissue cyst formation by zoites

Sporozoites of Cystoisospora canis penetrated and developed to monozoic tissue cysts in 4 human, 1 monkey, 1 bovine and 2 canine cell lines. No asexual division was documented although multiple infection of a single cell was observed. Examination of cultures using transmission electron microscopy demonstrated that they were monozoic tissue cysts and contained a single sporozoite. The appearance of monozoic tissue cysts in all cell lines was similar but the parasitophorous vacuole surrounding some sporozoites in DH82 dog macrophages was swollen. Monozoic tissue cysts were observed for up to 127 days in human pigmented retinal epithelial cells. Treatment of cell cultures containing monozoic tissue cysts with 0.75 sodium taurocholic acid and 0.25% trypsin stimulated egress of zoites (former sporozoites) from tissue cysts. Zoites collected from monozoic tissue cysts were able to penetrate and develop to monozoic tissue cysts in new host cells. Monozoic tissue cysts survived exposure to acid pepsin solution indicating that they would be orally infectious. The tissue cyst wall surrounding zoites did not autofluoresce as did oocyst and sporocyst walls exposed to UV light. We believe that C. canis can be used as a model system to study extra-intestinal monozoic tissue cysts stages of Cystoisospora belli of humans.

Enteric protozoa in the developed world: a public health perspective

Several enteric protozoa cause severe morbidity and mortality in both humans and animals worldwide. In developed settings, enteric protozoa are often ignored as a cause of diarrheal illness due to better hygiene conditions, and as such, very little effort is used toward laboratory diagnosis. Although these protozoa contribute to the high burden of infectious diseases, estimates of their true prevalence are sometimes affected by the lack of sensitive diagnostic techniques to detect them in clinical and environmental specimens. Despite recent advances in the epidemiology, molecular biology, and treatment of protozoan illnesses, gaps in knowledge still exist, requiring further research. There is evidence that climate-related changes will contribute to their burden due to displacement of ecosystems and human and animal populations, increases in atmospheric temperature, flooding and other environmental conditions suitable for transmission, and the need for the reuse of alternative water sources to meet growing population needs. This review discusses the common enteric protozoa from a public health perspective, highlighting their epidemiology, modes of transmission, prevention, and control. It also discusses the potential impact of climate changes on their epidemiology and the issues surrounding waterborne transmission and suggests a multidisciplinary approach to their prevention and control.