Efficacy of different methods for detection of low Cryptosporidium parvum oocyst numbers or antigen concentrations in stool specimens

Comparison of current methods used to detect Cryptosporidium oocysts in stools

In this review all of the methods that are currently in use for the investigation of Cryptosporidium in stool material are highlighted and critically discussed. It appears that more qualifications and background knowledge in this field regarding the diagnosis of the Cryptosporidium parasite is required. Furthermore, there is no standardization for the protocols that are commonly used to either detect oocysts in faeces or to diagnose the Cryptosporidium infection. It is therefore necessary to initiate further education and research that will assist in improving the accuracy of the diagnosis of Cryptosporidium oocysts in the faecal micro-cosmos. Where ambient concentrations of oocysts are low in stool material, detection becomes a formidable task. Procedures for ring tests and the standardization of multi-laboratory testing are recommended. It is also necessary to enhance the routine surveillance capacity of cryptosporidiosis and to improve the safety against it, considering the fact that this disease is under diagnosed and under reported. This review is intended to stimulate research that could lead to future improvements and further developments in monitoring the diagnostic methodologies that will assist in harmonizing Cryptosporidium oocysts in stool diagnosis.

Differences in the detection of Cryptosporidium and Isospora (Cystoisospora) oocysts according to the fecal concentration or staining method used in a clinical laboratory

Despite the availability of many parasitological methods for detection of Cryptosporidium and Isospora (Cystoisospora) belli in fecal samples, there are uncertainties about the accuracy of these techniques in laboratory practice. In this study, 27 formalin-fixed positive stool samples for Cryptosporidium and 15 for I. belli were analyzed by 2 concentration methods, sedimentation by centrifugation (SC) and formalin-ethyl acetate (FE), and by 3 tintorial techniques, modified Ziehl-Neelsen (ZN), safranin (SF), and auramine (AR). No significant differences were observed on Cryptosporidium identification between concentration methods, while a significantly higher number of I. belli oocysts (P < 0.0001) was detected in fecal smears concentrated by the SC than by the FE method. Fecal samples processed by FE produced a median oocyst loss to the fatty ring of 34.8% for Cryptosporidium and 45.4% for I. belli. However, FE concentration provided 63% of Cryptosporidium and 100% of I. belli slides classified as superior for microscopic examination. Regarding the efficiency of staining methods, a more significant detection of Cryptosporidium oocysts was observed in fecal smears stained by ZN (P < 0.01) or AR (P < 0.05) than by the SF method. Regular to high-quality slides for microscopic examination were mostly observed in fecal smears stained with AR or ZN for Cryptosporidium and with SF or ZN for I. belli. This study suggests a great variability in oocyst power detection by routine parasitological methods, and that the most frequent intestinal coccidians in humans have specific requirements for concentration and staining.

Cryptosporidiosis: comparison of three diagnostic methods and effects of storage temperature on detectability of cryptosporidia in cattle faeces

Three diagnostic methods (a modified Ziehl-Neelsen staining technique (MZN), a negative staining with carbol fuchsine (CF) and a commercial enzyme immunoassay (EIA) kit, ProSpecT® Cryptosporidium Microplate Assay (Remel, Lenexa, KS, USA)) for detection of Cryptosporidium oocysts in cattle faeces were compared regarding sensitivity and suitability under routine laboratory conditions, with particular emphasis on sample storage. In the 103 faecal samples examined, cryptosporidia infections were detected significantly more often by EIA (p<0.05; n=76) than by MZN (n=65) if ten random fields were evaluated microscopically, but not if the whole coverslip was scanned. In contrast, sensitivities of EIA and CF (n=69) did not differ significantly. Results were obtained very rapidly by CF. However, the hands-on time of CF is comparable to EIA, while MZN is more time consuming. EIA is more expensive than CF and MZN but easy to perform and to evaluate and does not need considerably experienced staff in contrast to CF and MZN. Moreover, 45 faecal samples stored for up to 27 days at different temperatures (+6°C, +16°C, +30°C, +40°C) were examined. The sensitivity of microscopic detection of oocysts in stained smears (CF, MZN) decreased in a temperature and time-dependent manner, while EIA results were not influenced by sample storage at any temperature.

Oligonucleotide-gold nanoparticle networks for detection of Cryptosporidium parvum heat shock protein 70 mRNA

We report on a novel strategy for the detection of mRNA targets derived from Cryptosporidium parvum oocysts by the use of oligonucleotide-gold nanoparticles. Gold nanoparticles are functionalized with oligonucleotides which are complementary to unique sequences present on the heat shock protein 70 (HSP70) DNA/RNA target. The results indicate that the presence of HPS70 targets of increasing complexity causes the formation of oligonucleotide-gold nanoparticle networks which can be visually monitored via a simple colorimetric readout measured by a total internal reflection imaging setup. Furthermore, the induced expression of HSP70 mRNA in Cryptosporidium parvum oocysts via a simple heat shock process provides nonenzymatic amplification such that the HSP70 mRNA derived from as few as 5 x 10(3) purified C. parvum oocysts was successfully detected. Taken together, these results support the use of oligonucleotide-gold nanoparticles for the molecular diagnosis of cryptosporidiosis, offering new opportunities for the further development of point-of-care diagnostic assays with low-cost, robust reagents and simple colorimetric detection.

Detection of Cryptosporidium oocysts in fresh and frozen cattle faeces: comparison of three methods

AIMS

The aim of this study was to compare the performance of three commonly used screening tests for Cryptosporidium oocysts in fresh and frozen cattle faeces.

METHODS AND RESULTS

Twenty-nine freshly voided faecal samples were collected from calves from three farms in the northwest of England. Three diagnostic tests for Cryptosporidium were carried out on each sample both before and after freezing - the modified Ziehl-Neelsen (MZN) and auramine phenol (APh) stains and a commercial enzyme immunoassay (EIA) kit, the ProSpecT Cryptosporidium Microplate assay (Remel, Lenexa, KS). Twelve samples were deemed positive by the reference standard (polymerase chain reaction, PCR). There were some discrepancies between the results of the screening tests and the levels of agreement were quantified. The sensitivity and specificity of each method was determined, with PCR as the gold standard. Sensitivity and specificity of the MZN stain was optimized when samples with fewer than two oocyst-like bodies were classified as negative.

CONCLUSIONS

All three screening methods used were effective in detecting Cryptosporidium infection in both fresh and frozen calf faeces.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has highlighted the value of determining characteristics of tests used for diagnosis and epidemiological studies.

A Bayesian approach for the evaluation of six diagnostic assays and the estimation ofCryptosporidiumprevalence in dairy calves

The prevalence of Cryptosporidium in calves and the test properties of six diagnostic assays (microscopy (ME), an immunofluorescence assay (IFA), two ELISA and two PCR assays) were estimated using Bayesian analysis. In a first Bayesian approach, the test results of the four conventional techniques were used: ME, IFA and two ELISA. This four-test approach estimated that the calf prevalence was 17% (95% Probability Interval (PI): 0.1-0.28) and that the specificity estimates of the IFA and ELISA were high compared to ME. A six-test Bayesian model was developed using the test results of the 4 conventional assays and 2 PCR assays, resulting in a higher calf prevalence estimate (58% with a 95% PI: 0.5-0.66) and in a different test evaluation: the sensitivity estimates of the conventional techniques decreased in the six-test approach, due to the inclusion of two PCR assays with a higher sensitivity compared to the conventional techniques. The specificity estimates of these conventional assays were comparable in the four-test and six-test approach. These results both illustrate the potential and the pitfalls of a Bayesian analysis in estimating prevalence and test characteristics, since posterior estimates are variables depending both on the data at hand and prior information included in the analysis. The need for sensitive diagnostic assays in epidemiological studies is demonstrated, especially for the identification of subclinically infected animals since the PCR assays identify these animals with reduced oocyst excretion, which the conventional techniques fail to identify.

Clinical status and parasitic infection in a Wichí Aboriginal community in Salta, Argentina

In a study, carried out in 2000, of the clinical and parasitological status of a Wichi Aboriginal community living in the suburbs of Tartagal, northern Salta, Argentina, 154 individuals were screened for parasitic infections. Ninety-five faecal samples were also obtained from the same population. Ninety-three percent of the subjects were positive for 1 or more of the parasites investigated by direct test and 70.5% of them had parasitic superinfection. The most frequent helminths were Strongyloides stercoralis (50.5%) and hookworm (47.4%). We found low reinfection rates and a long reinfection period after treatment and provision of safe water and sanitation. Serum reactivity of these patients was analysed by enzyme-linked immunosorbent assay and indirect immunofluorescent assay and 22.1% of them had anti-Toxocara antibodies, 16.2% were positive for a complex antigen of Leishmania braziliensis, 29.9% were positive for a complex Trypanosoma cruzi antigen, and 17.5% were positive for a specific Trypanosoma cruzi antigen, Ag 163B6/cruzipain.

Comparison of direct immunofluorescence, modified acid-fast staining, and enzyme immunoassay techniques for detection of Cryptosporidium spp in naturally exposed kittens

OBJECTIVE

To evaluate a modified Ziehl-Neelsen acid-fast staining technique (mZN), a direct immunofluorescence detection procedure (DIF), and 3 commercial enzyme immunoassays (EIAs) for detection of Cryptosporidium oocysts in fecal specimens from kittens.

DESIGN

Prospective study.

SAMPLE POPULATION

416 fecal specimens collected from 104 randomly selected domestic shorthair kittens (8 to 16 weeks of age) that were naturally exposed to Cryptosporidium spp.

PROCEDURE

Fresh fecal specimens were collected once daily for 4 consecutive days and processed immediately. Sensitivities of mZN, DIF, and 3 commercial EIAs (EIA-1, EIA-2, and EIA-3) were estimated and compared.

RESULTS

EIA-2 had the highest sensitivity on day 1 (89%), followed by EIA-1 (80%), and mZN (72%). EIA-3 had the lowest sensitivity on day 1 (15%). EIA-2, EIA-1, and mZN had similar sensitivities after 2 consecutive fecal examinations (approx 90%). Determination of specificities was compromised by the small number of cats that had negative results for all tests (n = 3).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that EIA-2 and EIA-1 had the highest sensitivities when only a single fecal specimen was examined; however, mZN and EIA-1 had similar sensitivities when 2 consecutive fecal specimens were examined. The higher costs of EIA-2 and EIA-1 may be offset by the tests' high sensitivity, simplicity of use, and ease of interpretation and by savings in technician time.

Simultaneous detection of Entamoeba histolytica, Giardia lamblia, and Cryptosporidium parvum in fecal samples by using multiplex real-time PCR

Entamoeba histolytica, Giardia lamblia, and Cryptosporidium are three of the most important diarrhea-causing parasitic protozoa. For many years, microscopic examination of stool samples has been considered to be the "gold standard" for diagnosis of E. histolytica, G. lamblia, and C. parvum infections. Recently, more specific and sensitive alternative methods (PCR, enzyme-linked immunosorbent assay, and direct fluorescent-antibody assay) have been introduced for all three of these parasitic infections. However, the incorporation in a routine diagnostic laboratory of these parasite-specific methods for diagnosis of each of the respective infections is time-consuming and increases the costs of a stool examination. Therefore, a multiplex real-time PCR assay was developed for the simultaneous detection of E. histolytica, G. lamblia, and C. parvum in stool samples. The multiplex PCR also included an internal control to determine efficiency of the PCR and detect inhibition in the sample. The assay was performed on species-specific DNA controls and a range of well-defined stool samples, and it achieved 100 percent specificity and sensitivity. The use of this assay in a diagnostic laboratory would provide sensitive and specific diagnosis of the main parasitic diarrheal infections and could improve patient management and infection control.

[Comparison between the modified Ziehl-Neelsen and Acid-Fast-Trichrome methods for fecal screening of Cryptosporidium parvum and Isospora belli]

Due to the importance of Cryptosporidium parvum, Cyclospora cayetanensis and Isospora belli as opportunistic parasites, it is essential for laboratories to morphologically differentiate these coccidia. Among the recommended methods for diagnosis of C. parvum and I. belli is the Modified Ziehl-Neelsen stain (MZN) and recently a new technique, the Acid-Fast-Trichrome (AFT) was proposed. The purpose of this study was to compare the AFT and MZN techniques regarding the detection of C. parvum and I. belli oocysts in stool samples of HIV-positive patients. According to the presence (n=60) or absence of diarrhea (n=60), two groups were selected for inclusion in this study. The stool samples were collected in 10% formalin solution and the pellets, obtained without and after centrifugation-concentration (500xg; 10 min), were submitted to both stain techniques. Considering the positivity of the techniques (AFT and MZN), we observed the superiority of MZN stain (n=19; 100% positive cases) over AFT (n=8; 42.1%). The identification of the 101 truly-negative cases was possible with both techniques, but when the AFT stain was used, the oocysts showed a variable inner stain degree, which resulted in false-negatives. Enteric coccidiosis was more frequent among the patients who presented diarrhea (26.6%) compared to asymptomatic individuals (5%); C. cayetanensis was not detected in these groups. We were interested in evaluating the employment of AFT for the Cyclospora oocyst stain. Based on the sensitivity and specificity obtained in this study (100%), we concluded that the MZN technique is still the most indicated for routine use in clinical analysis laboratories, for the diagnosis of cryptosporidiosis and isosporosis, especially when it was used together with the centrifugation procedure (500xg; 10 min). Our results showed that with some improvements, AFT would be a simple and inexpensive technique appropriate for use in the diagnosis of intestinal coccidia (C. parvum, C. cayetanensis and I. belli). It can also be extended to the detection of microsporidia.

Cryptosporidiosis in Kuwaiti children: seasonality and endemicity

OBJECTIVE

To detect the incidence of cryptosporidial infection in children presenting with gastrointestinal symptoms at the local hospital in Kuwait.

METHODS

Over a period of 3 years, September 1995 to August 1997, a single fecal sample from 3549 children was analyzed by modified saframin-methylene blue (SM-B) staining and a direct immunofluorescence test for the presence of Cryptosporidium oocysts.

RESULTS

Cryptosporidium oocysts were detected in 51 (10%) children with diarrhea. Prevalence was highest (73%) in children > 2 years of age compared with children < 2 years of age. The maximum number of cases, 38 of 51 (75%), was seen during the months January to April, indicating a marked seasonal variation. Polyparasitism was common in children with diarrhea; however, 43 of the 51 (84%) children with cryptosporidiosis had cryptosporidium infection only. Blastocystis hominis and Endolimax nana were the most common parasites detected (38% and 15%, respectively). Forty-seven of the 51 (90%) children with cryptosporidiosis were Kuwaiti and gave no history of travel abroad, suggesting that the infection was acquired indigenously. Sociodemographic information on children with cryptosporidiosis suggests three possible modes of transmission of infection: drinking contaminated water stored in overhead water tanks, person to person, or contact with infected animals.

CONCLUSION

In this study, we observed water-borne transmission of cryptosporidium infection in children with diarrhea. The infection is seasonal and endemic.

Cloning and expression of a DNA sequence encoding a 41-kilodalton Cryptosporidium parvum oocyst wall protein

This study was conducted to produce a recombinant species-specific oocyst wall protein of Cryptosporidium parvum. Antigens unique to C. parvum were identified by gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of oocyst proteins from several different Cryptosporidium species. Antiserum was then prepared against a 41-kDa antigen unique to C. parvum and used to identify a recombinant DNA clone, designated rCP41. Expression of CP41 mRNA in C. parvum oocysts was confirmed by reverse transcriptase PCR (RT-PCR). Although the CP41 sequence was shown by PCR to be present in the genome of C. baileyi, CP41 mRNA was not detected in this species by RT-PCR. Immunofluorescence staining with antiserum against recombinant CP41 detected native CP41 antigen on the surface of C. parvum oocysts but failed to detect CP41 on C. baileyi oocysts. Immunoelectron microscopy demonstrated that native CP41 was distributed unevenly on the C. parvum oocyst surface and was associated with amorphous oocyst wall material. In an enzyme-linked immunosorbent assay, purified rCP41 performed as well as native C. parvum oocyst protein in measuring the serological responses of young calves and adult cows to experimental and natural C. parvum infections. These results indicate that recombinant CP41 antigen may have potential in the immunodiagnosis of cryptosporidiosis.