The influence of serial fecal sampling on the diagnosis of giardiasis in humans, dogs, and cats

Comparison of Giardia duodenalis point-of-care antigen faecal tests to reference laboratory assays in non-symptomatic dogs

Giardia duodenalis is one of the most prevalent enteric parasites of dogs. Point-of-care antigen tests (POC) are rapid and do not require additional equipment, or a specialised diagnostic laboratory. The aim of this study was to compare diagnostic tests available in veterinary practices and in a diagnostic laboratory for the detection of G. duodenalis on a cohort of group-housed dogs from New South Wales, Australia. Two different POC tests were used for the detection of G. duodenalis. Laboratory tests used were the multiplexed-tandem PCR panel (MT-PCR) that includes detection of G. duodenalis DNA, and two reference tests (an in-house TaqMan real-time PCR and a direct immunofluorescence assay, DFA). Canine faecal samples (n = 40) were tested simultaneously for the detection of G. duodenalis. Using either DFA or TaqMan real-time PCR as reference tests, 77.5% (31/40) and 82.5% (33/40) of dogs tested positive, respectively. Agreement (Kappa) between the DFA and TaqMan real-time PCR was 0.84 (95% CI 0.64 to 1.00). There was substantial G. duodenalis test outcome agreement between the two POC tests, Kappa = 0.75. Combining the two POC tests yielded 77% sensitivity and 100% specificity with DFA as reference, and for TaqMan real-time PCR it was 73% sensitivity and 100% specificity. The MT-PCR was in excellent agreement with each reference test, DFA or TaqMan real-time PCR. Due to the high specificity of both POC tests, they can be confidently used as rule-in diagnostics. Confirmatory testing that detects different biological parameters such as DNA, e.g. PCR (inc. MT-PCR), should be implemented before concluding that a dog is negative for the presence of G. duodenalis.

Prevalence of Intestinal Parasites in Dogs and Cats from the Kvarner Region in Croatia

Intestinal parasites of dogs and cats may affect their health with a significant zoonotic risk to public health. Therefore, establishing an efficient control program should pass through the determination of the diversity, prevalence, and pathogenicity of those parasites. This study aimed to determine the prevalence of intestinal parasites in dogs and cats and proceed to infection comparisons between young and adult animals. The detection of parasites in fecal samples was determined using flotation and immunofluorescent methods across 320 dogs and 64 cats from the Kvarner region in Croatia. The prevalence was calculated for each detected parasite in its host. Differences in prevalence between young animals and adults were analyzed. Parasites were detected in 32 dogs and 34.4% of cats. In total, 12 different genera were detected; Giardia spp. was the most prevalent parasite in both species, infecting 24.7% and 18.8% of investigated dogs and cats, respectively. Cryptosporidium spp. and Toxocara cati had a prevalence of (18.4%) and (6.3%), respectively. Prevalences of Giardia spp., Cryptosporidium spp., and Cystoisospora spp. were significantly (P < 0.05) higher in puppies compared to adult dogs. Pentatrichomonas hominis (P. hominis) was detected in one puppy. In addition to the first report of P. hominis, a relatively high prevalence of intestinal parasites in dogs and cats in the Kvarner region of Croatia was recorded, posing a potential zoonotic risk.

Is there added value from using three serial samples when surveying the occurrence of intestinal parasites in children?

BACKGROUND

Surveys for intestinal parasitic infections (IPIs) often involve samples from three sampling dates analysed by various microscopy techniques. However, analysis of three samples per individual is a huge burden on time and resources. We compared the value from analysing three or fewer samples.

METHODS

In this cross-sectional study, three faecal samples were collected every other day from 332 children from two locations in Guantanamo province, Cuba. Samples were analysed by wet mount with Lugol stain, Willis flotation method and Kato-Katz thick smear.

RESULTS

Most parasites were detected by wet mount, although helminth eggs not found by wet smear were detected by the Willis flotation method (in particular) and Kato-Katz smear. Blastocystis spp. was the most commonly detected parasite (about 65%), then Giardia duodenalis and then Entamoeba spp. Although analysis of two stool samples significantly increased occurrence data for Blastocystis, this was not so for the other parasites. For none of the protozoan parasites were results from analysing three samples significantly higher than results from analysing just two samples.

CONCLUSIONS

Analysing two faecal samples by wet mount and the Willis flotation method provides useful data for estimating the prevalence of IPIs in relatively high prevalence settings. Analysing further samples provides limited additional information and adds an extra burden in terms of time and resources.

Comparative analysis of routine parasitological methods for recovery of cysts, molecular detection, and genotyping of Giardia duodenalis

In order to improve the diagnosis of giardiasis, fecal samples (high/medium/low concentration of cysts) were processed by the parasitological methods used in the routine: Faust, Lutz e Ritchie modified (replacement of formaldehyde by distilled water). The cysts were quantified; the DNA was extracted and amplified by semi-nested PCR (GDH gene). Fifteen clinical samples were analyzed to validate the study by PCR-RFLP. The results showed that the parasite was only detected and genotyped correctly when samples from children with high, medium, and low parasitic load, belonging to genotype AII, were processed by the modified Ritchie method, different from what was observed for the other methods used in laboratory routine (Faust and Lutz). The modified Ritchie method proved to be more suitable, recovering a greater number of cysts from samples, regardless of parasitic load, which reduces the chance of false negative results and has epidemiological repercussions since individuals with low parasite load are usually asymptomatic and the main disseminators of this infection.

Intestinal giardiasis in children: Five years' experience in a reference unit

BACKGROUND

Giardiasis is highly prevalent in children and is often mildly symptomatic. First-line treatment is metronidazole, but treatment failure is not uncommon. We describe a paediatric series, to identify risk factors for treatment failure and to analyse the safety and effectiveness of other treatment strategies.

METHODS

Retrospective observational study, including children diagnosed with giardiasis from 2014 to 2019. Diagnosis was based on direct visualisation by microscopy after concentration using an alcohol-based fixative, antigen detection and/or DNA detection by polymerase chain reaction in stool. Treatment failure was considered when GI was detected 4 weeks after treatment.

RESULTS

A total of 120 patients were included, 71.6% internationally adopted, median age 4.2 (2.3-7.3) years. Only 50% presented with symptoms, mainly diarrhoea (35%) and abdominal pain (14.1%); co-parasitism was frequent (45%). First-line treatment failure after a standard dose of metronidazole was 20%, lowering to 8.3% when a higher dose was administered (p < 0.001). Quinacrine was administered in 10 patients, with 100% effectiveness. Children <2 years were at higher risk of treatment failure (OR 3.49; 95% CI 1.06-11.53; p = 0.040).

CONCLUSIONS

In children with giardiasis, treatment failure is frequent, especially before 2 years of age. Quinacrine can be considered as a second-line treatment. After treatment, eradication should be confirmed.

Rapid on-site diagnosis of canine giardiosis: time versus performance

BACKGROUND

Infections by protozoans of the genus Giardia are a common cause of diarrhea in dogs. Canine giardiosis constitutes a disease with a zoonotic potential; however, it is often underestimated due to its challenging diagnosis. The objective of the study was to assess the diagnostic performance of an immunochromatographic strip test (SpeedTM Giardia, Virbac, France) comparing it with microscopy (zinc sulfate flotation) by utilizing the combination of an enzyme immunoassay (ProSpecTTM Giardia EZ Microplate Assay, Oxoid Ltd., UK) and the PCR as the gold standard. A positive result in both ELISA and PCR was set as the gold standard.

METHODS

Initially, fecal samples from dogs with clinical signs compatible with giardiosis were tested with the SpeedTM Giardia test and separated into two groups of 50 samples each: group A (positive) and group B (negative). Thereafter, all samples were examined by zinc sulfate centrifugal flotation technique and assayed by the ProSpecTTM Giardia Microplate Assay and PCR. The performance of the SpeedTM Giardia and zinc sulfate centrifugal flotation tests were calculated estimating sensitivity, specificity, and positive and negative likelihood ratio; the chi-square and McNemar tests were used for the comparison of the two methods.

RESULTS

Giardia cysts were not detected by microscopy in 16 out of the 50 samples (32%) of group A and in none of group B samples. Eight out of 50 samples in group B (16%) were tested positive both with the ProSpecTTM Giardia Microplate Assay and PCR. Fecal examination with the SpeedTM Giardia test was more sensitive (86.2%) than the parasitological method (58.6%, P < 0.001) while the specificity of both methods was 100%.

CONCLUSIONS

The SpeedTM Giardia test is an easy-to-perform diagnostic method for the detection of Giardia spp., which can increase laboratory efficiency by reducing time and cost and decrease underdiagnosis of Giardia spp. infections. This immunochromatographic strip test may be routinely exploited when a rapid and reliable diagnosis is required, other diagnostic techniques are unavailable and microscopy expertise is inefficient. In negative dogs with compatible clinical signs of giardiosis, it is recommended either to repeat the exam or proceed with further ELISA and PCR testing.

Rectal Swabs as an Alternative Sample Collection Method to Bulk Stool for the Real-Time PCR Detection of Giardia duodenalis

Though bulk stool remains the gold standard specimen type for enteropathogen diagnosis, rectal swabs may offer comparable sensitivity with greater ease of collection for select pathogens. This study sought to evaluate the validity and reproducibility of rectal swabs as a sample collection method for the molecular diagnosis of Giardia duodenalis. Paired rectal swab and bulk stool samples were collected from 86 children ages 0-4 years living in southwest Niger, with duplicate samples collected among a subset of 50 children. Infection was detected using a previously validated real-time PCR diagnostic targeting the small subunit ribosomal RNA gene. Giardia duodenalis was detected in 65.5% (55/84) of bulk stool samples and 44.0% (37/84) of swab samples. The kappa evaluating test agreement was 0.81 (95% CI: 0.54-1.00) among duplicate stool samples (N = 49) and 0.75 (95% CI: 0.47-1.00) among duplicate rectal swabs (N = 48). Diagnostic sensitivity was 93% (95% CI: 84-98) by bulk stool and 63% (95% CI: 49-75) by rectal swabs. When restricting to the lowest three quartiles of bulk stool quantitation cycle values (an indication of relatively high parasite load), sensitivity by rectal swabs increased to 78.0% (95% CI: 64-89, P < 0.0001). These findings suggest that rectal swabs provide less sensitive and reproducible results than bulk stool for the real-time PCR diagnosis of G. duodenalis. However, their fair sensitivity for higher parasite loads suggests that swabs may be a useful tool for detecting higher burden infections when stool collection is excessively expensive or logistically challenging.

Apparent lack of spill-over of parasites from an invasive anuran: PCR detects Entamoeba in cane toads (Rhinella marina) but not in sympatric Australian native frogs

The recent detection of a novel amoebozoan parasite (Entamoeba sp. CT1) killing invasive cane toads (Rhinella marina) in tropical Australia raises concerns of potential spill-over into native anuran populations. Considering the vulnerability of anuran communities globally, Entamoeba sp. CT1 may pose a serious threat to anuran biodiversity. Through PCR-based detection and molecular identification, we investigated the prevalence of Entamoeba spp. in the faeces and colon tissue of cane toads (Rhinella marina) and eleven native Australian frog species from a single locality in the Northern Territory. No Entamoeba DNA was detected in samples of native frog faeces (N = 57) or colons (N = 17). Entamoeba DNA was detected in 24% of 45 cane toads (95%CI 14.08–38.82). Both E. ranarum and Entamoeba sp. CT1 were present in cane toads. The failure of faecal samples to indicate Entamoeba spp. in infected cane toads may be due to cysts in faeces being shed intermittently, degraded before analysis, or impervious to lysis prior to DNA isolation. Our results suggest that native frogs do not carry the pathogen in an area where 20–30% of cane toads are infected with Entamoeba sp. CT1. We demonstrate the importance of recognising PCR inhibition prior to molecular diagnostics, and the apparent inadequacy of faecal samples for the detection of Entamoeba spp. in anurans.

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Entamoeba spp. were detected in cane toads, but not in faeces or colons of native frogs.

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PCR inhibition of anuran faecal samples.

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Additional purification, the presence of inhibition was reduced.

Prevalence of Giardia duodenalis infection, co-morbidities and associated risk factors in dogs admitted to a veterinary teaching hospital in Israel

Giardia duodenalis causes gastro-intestinal (GI) disease and carries a zoonotic risk. The risk for infection depends on local prevalence and individual immunity, but clinical signs are inconsistent and the role of G. duodenalis in other GI diseases is unknown. The current study aims were to evaluate the prevalence of G. duodenalis in dogs presented to a university veterinary teaching hospital in Israel, investigate risk factors for infection and its associations with other diseases. Fecal samples from 163 dogs were tested for G. duodenalis by an antigen assay (FASTest® Giardia strip). Prevalence of G. duodenalis infection was 11.9 %. It was significantly associated with young age (≤1year) and canine parvoviral enteritis. Housing conditions, signs of GI disease or other systemic diseases were unassociated with infection. In conclusion, G. duodenalis infection prevalence is relatively low in the study population. Young age and diagnosis of co-infections are common, warranting screening for G. duodenalis.

Occurrence and molecular characterization of Giardia duodenalis in child population from Colombia

Giardia duodenalis is one of the most prevalent human intestinal parasite, with children living in developing countries being particularly at risk of infection. The occurrence and molecular diversity of G. duodenalis was investigated in stools specimens from 307 individuals aged one to nineteen years in Colombia. Samples were collected in three educational establishments (n: 163) and two hospital laboratories (n: 144) from urban and rural areas. Feces were concentrated using a biphasic sedimentation method and wet mounts of the sediment were examined by light microscopy. G. duodenalis assemblages and sub-assemblages were determined on positive samples by PCR of the triose phosphate isomerase (tpi), β-giardin (bg) and small-subunit (ssu) rRNA genes. G. duodenalis infection was detected by microscopy in 23 individuals (7.5%). The protozoan was more prevalent among specimens collected in educational establishments (11.6%) than in those obtained from hospital laboratories (2.8%). Infection was most common in individuals from urban areas and children aged 1-5 years. No significant association between diarrhea and infection could be demonstrated. Twenty Giardia-positive samples were successfully allocated to assemblage B (n: 11), sub-assemblage AII (n: 7), and assemblage A (n: 2). Results indicate the potential for transmission of G. duodenalis infection in children attending educational establishments and individuals from urban areas, where transmission seems to be primarily anthroponotic.

Assessment of the diagnostic performance of four methods for the detection of Giardia duodenalis in fecal samples from human, canine and feline carriers

Enteric parasitic diseases including giardiasis are of public health concern. Different methods are available for the diagnosis of this parasitic infection in fecal samples such as the identification of protozoan cysts and trophozoites by light microscopy, detection of specific antigens by ELISA, and amplification of DNA fragments by PCR. The present study aimed at assessing the performance of four laboratory tests for the detection of Giardia duodenalis in fecal specimens from three different host species with a previous diagnosis of giardiasis; canine, feline and human patients provided new stool samples to be retested for Giardia before initiating treatment with antiprotozoal drugs. For this purpose, triplicate fecal specimens from 54 humans, 24 dogs and 18 cats living in the city of Niterói, RJ, southeast Brazil, were analysed by light microscopy, ELISA, immunochromatography, and nested PCR. The centrifugal-flotation method detected Giardia cysts in 89.6% (86/96) of the fecal samples. The protozoan parasite was detected via immunochromatography in 87.5% (84/96) of these samples. Giardia was detected by ELISA in 69.8% (67/96) of the stool specimens from carriers with a previous diagnosis of Giardia infection. Giardia was detected by PCR in only 39.6% (38/96) of the fecal specimens. Based on these findings, we suggest that, among the four assays that were used in this study, the zinc sulphate flotation technique (Faust et al., 1939) is the best diagnostic assay in terms of sensitivity and specificity to detect G. duodenalis on serially collected samples from dogs, cats and humans.