Refractory giardiasis: a molecular appraisal from a tertiary care centre in India

Refractory giardiasis in a child with steroid-resistant nephrotic syndrome

Giardiasis is an infection of the small intestine caused by the protozoan parasite Giardia intestinalis and one of the most common parasitic intestinal diseases in humans worldwide. It mainly manifests as a self-limited illness in the case of immunocompetent patients and usually does not require treatment. However, immunodeficiency is a risk factor for the onset of severe Giardia infection. In this report, a case of recurrent giardiasis refractory to nitroimidazole therapy is presented. A 7-year-old male patient with steroid-resistant nephrotic syndrome came to our hospital because of chronic diarrhoea. The patient was on long-term immunosuppressive therapy. Microscopic examination of stool showed a significant number of trophozoites and cysts of G. intestinalis. Treatment with metronidazole for longer duration than recommended has failed to clear the parasite in the present case.

Application of Proteomics to the Study of the Therapeutics and Pathogenicity of Giardia duodenalis

Giardia duodenalis remains a neglected tropical disease. A key feature of the sustained transmission of Giardia is the ability to form environmentally resistant cysts. For the last 38 years, proteomics has been utilised to study various aspects of the parasite across different life cycle stages. Thirty-one articles have been published in PubMed from 2012 to 2022 related to the proteomics of G. duodenalis. Currently, mass spectrometry with LC-MS/MS and MALDI-TOF/TOF has been commonly utilised in proteomic analyses of Giardia, which enables researchers to determine potential candidates for diagnostic biomarkers as well as vaccine and drug targets, in addition to allowing them to investigate the virulence of giardiasis, the pathogenicity mechanisms of G. duodenalis, and the post-translational modifications of Giardia proteins throughout encystation. Over the last decade, valuable information from proteomics analyses of G. duodenalis has been discovered in terms of the pathogenesis and virulence of Giardia, which may provide guidance for the development of better means with which to prevent and reduce the impacts of giardiasis. Nonetheless, there is room for improving proteomics analyses of G. duodenalis, since genomic sequences for additional assemblages of Giardia have uncovered previously unknown proteins associated with the Giardia proteome. Therefore, this paper aims to review the applications of proteomics for the characterisation of G. duodenalis pathogenicity and the discovery of novel vaccine as well as drug targets, in addition to proposing some general directions for future Giardia proteomic research.

Treatment strategies for nitroimidazole-refractory giardiasis: a systematic review

RATIONALE FOR REVIEW

Giardiasis is one of the most common human protozoal infections worldwide. First-line therapy of giardiasis includes nitroimidazole antibiotics. However, treatment failure with nitroimidazoles is increasingly reported, with up to 45% of patients not responding to initial treatment. There is no clear consensus on the approach to the management of nitroimidazole-refractory giardiasis. This systematic review aims to summarize the literature on pharmacotherapy for nitroimidazole-refractory giardiasis.

METHODS

We conducted a systematic review of the literature to determine the optimal management strategies for nitroimidazole-refractory giardiasis. We searched Pubmed/MEDLINE, Embase and Cochrane library using the following search terms 'Giardia' AND 'treatment failure' OR 'refractory giardia' OR 'resistant giardia' with date limits of 1 January 1970 to 30 June 2021. We included all reports on humans, which described clinical outcomes of individuals with treatment refractory giardiasis, including case series and case reports. A descriptive synthesis of the data was conducted with pooling of data for interventions.

KEY FINDINGS

Included in this review were five prospective studies, three retrospective studies, seven case series and nine case reports. Across these reports, a wide heterogeneity of treatment regimens was employed, including retreatment with an alternative nitroimidazole, combination therapy with a nitroimidazole and another agent and monotherapy with non-nitroimidazole regimens, including quinacrine, paromomycin and nitazoxanide. Retreatment with a nitroimidazole was not an effective therapy for refractory giardiasis. However, treatment with a nitroimidazole in combination with albendazole had a cure rate of 66.9%. In the included studies, quinacrine monotherapy was administered to a total of 179 patients, with a clinical cure rate of 88.8%. Overall, quinacrine was fairly well tolerated.

CONCLUSIONS

Reports on the treatment of nitroimidazole-refractory giardiasis demonstrate a heterogeneous approach to treatment. Of these, quinacrine appeared to be highly effective, though more data on its safety are needed.

Quinacrine treatment of nitroimidazole-refractory giardiasis

Background

Limited evidence exists on efficacy and tolerability of quinacrine for nitroimidazole-refractory giardiasis.

Methods

Nitroimidazole-refractory giardiasis cases, defined as microbiologically (microscopy and/or PCR) confirmed treatment failure after 2 courses, during 2008–2020, were retrospectively identified.

Results

Of 87 patients, 54 (62%) had visited India. Quinacrine was used in 54 (62%); 51 received monotherapy and 3 combined with metronidazole. Only 3 had positive stool samples with persisting symptoms after quinacrine treatment (94% parasitological efficacy) and all were cured after a second treatment. One (1.9%) had mild adverse effects recorded.

Conclusions

Quinacrine is an effective treatment for nitroimidazole-refractory giardiasis with good tolerability.

Anti-Giardia Drug Discovery: Current Status and Gut Feelings

Giardia parasites are ubiquitous protozoans of global importance that impact a wide range of animals including humans. They are the most common enteric pathogen of cats and dogs in developed countries and infect ∼1 billion people worldwide. While Giardia infections can be asymptomatic, they often result in severe and chronic diseases. There is also mounting evidence that they are linked to postinfection disorders. Despite growing evidence of the widespread morbidity associated with Giardia infections, current treatment options are limited to compound classes with broad antimicrobial activity. Frontline anti-Giardia drugs are also associated with increasing drug resistance and treatment failures. To improve the health and well-being of millions, new selective anti-Giardia drugs are needed alongside improved health education initiatives. Here we discuss current treatment options together with recent advances and gaps in drug discovery. We also propose criteria to guide the discovery of new anti-Giardia compounds.

Drug resistance in Giardia: Mechanisms and alternative treatments for Giardiasis

The use of chemotherapeutic drugs is the main resource against clinical giardiasis due to the lack of approved vaccines. Resistance of G. duodenalis to the most used drugs to treat giardiasis, metronidazole and albendazole, is a clinical issue of growing concern and yet unknown impact, respectively. In the search of new drugs, the completion of the Giardia genome project and the use of biochemical, molecular and bioinformatics tools allowed the identification of ligands/inhibitors for about one tenth of ≈150 potential drug targets in this parasite. Further, the synthesis of second generation nitroimidazoles and benzimidazoles along with high-throughput technologies have allowed not only to define overall mechanisms of resistance to metronidazole but to screen libraries of repurposed drugs and new pharmacophores, thereby increasing the known arsenal of anti-giardial compounds to some hundreds, with most demonstrating activity against metronidazole or albendazole-resistant Giardia. In particular, cysteine-modifying agents which include omeprazole, disulfiram, allicin and auranofin outstand due to their pleiotropic activity based on the extensive repertoire of thiol-containing proteins and the microaerophilic metabolism of this parasite. Other promising agents derived from higher organisms including phytochemicals, lactoferrin and propolis as well as probiotic bacteria/fungi have also demonstrated significant potential for therapeutic and prophylactic purposes in giardiasis. In this context the present chapter offers a comprehensive review of the current knowledge, including commonly prescribed drugs, causes of therapeutic failures, drug resistance mechanisms, strategies for the discovery of new agents and alternative drug therapies.

5-Nitroimidazole refractory giardiasis is common in Matanzas, Cuba and effectively treated by secnidazole plus high-dose mebendazole or quinacrine: a prospective observational cohort study

OBJECTIVE

To evaluate the effectiveness and tolerability of secnidazole combined with high-dose mebendazole for treatment of 5-nitroimidazole-resistant giardiasis.

METHOD

Adults with microscopically verified Giardia intestinalis monoinfection attending a secondary level hospital in Matanzas City, Cuba were prospectively included in a cohort. A recently introduced treatment ladder consisting of metronidazole as first-line treatment, followed by secnidazole, tinidazole, secnidazole plus mebendazole and quinacrine as second-to fifth-line treatments, respectively, was used. Adverse events and treatment success were determined by questioning and microscopy on concentrated stool samples, respectively on days 3, 5 and 7 after the end of treatment. If G. intestinalis was detected on day 3, 5 or 7, then the infection was classified as refractory and no further microscopy was performed.

RESULTS

A total of 456 individuals were included. Metronidazole, 500 mg three times daily for 5 days, cured 248/456 (54%) patients. A single 2-g secnidazole dose as second-line treatment cured 50/208 (24%) patients. A single 2-g tinidazole dose as third-line treatment cured 43/158 (27%) patients. Three rounds of 5-nitroimidazole therapy therefore cured 341/456 (75%) patients. Secnidazole plus mebendazole (200 mg every 8 hours for 3 days) cured 100/115 (87%) of nitroimidazole refractory infections. Quinacrine cured the remaining 15 patients. All treatments were well tolerated.

CONCLUSIONS

5-Nitroimidazole refractory giardiasis was common, indicating that an alternative first-line treatment may be needed. Retreatment of metronidazole refractory giardiasis with an alternative 5-nitroimidazole was suboptimal, indicating cross-resistance. Mebendazole plus secnidazole were well tolerated and effective for the treatment of 5-nitroimidazole refractory G. intestinalis infection in this setting.

Epidemiological distribution of genotypes of Giardia duodenalis in humans in Spain

BACKGROUND

Although the distribution of Giardia duodenalis genotypes in humans has been increasingly reported in recent years, data on possible differences in pathogen transmission between age groups and virulence between genotypes are scarce. The purpose of this study is to investigate the genetic diversity of G. duodenalis in humans in Spain and compare the distribution of G. duodenalis assemblages A and B between children and adults and clinical presentations between the two genotypes.

METHODS

In the present study, 125 microscopy-positive fecal samples were collected from humans in Spain over a 7-year period. PCR and sequence analyses of the triosephosphate isomerase, β-giardin and glutamate dehydrogenase genes were used to identify the multilocus genotypes of G. duodenalis.

RESULTS

Sequence analysis of three genetic loci identified both G. duodenalis assemblages A (29) and B (66), with co-infections of the two in two patients. Among the sequences obtained in this study, four multilocus genotypes (MLGs) of the sub-assemblage AII were observed within assemblage A. In contrast, 19 MLGs were detected within assemblage B due to the high sequence diversity at each locus. One MLG, however, was found in 51.9% (27/52) of assemblage B samples. Children were more commonly infected by assemblage B (44/53 or 83%) than adults (22/42 or 52.4%; χ2 = 10.371, df = 1, P = 0.001). Asymptomatic infection was more common in patients with assemblage A (4/29 or 13.8%) than in those with assemblage B (1/66 or 1.5%; χ2 = 6.091, df = 1, P = 0.029), and the frequency of abdominal pain occurrence was higher in assemblage B patients (65/66 or 98.5%) than assemblage A patients (25/29 or 86.2%; χ2 = 6.091, df = 1, P = 0.029).

CONCLUSIONS

These results illustrate the existence of differences in genotype distribution between children and adults and clinical presentations between G. duodenalis genotypes. They are useful in understanding the transmission of G. duodenalis in humans in Spain.

The first multilocus genotype analysis of Giardia intestinalis in humans in the Czech Republic

To date, genotyping data on giardiasis have not been available in the Czech Republic. In this study, we characterized 47 human isolates of Giardia intestinalis from symptomatic as well as asymptomatic giardiasis cases. Genomic DNA from trophozoites was tested by PCR-sequence analysis at three loci (β-giardin, glutamate dehydrogenase and triose phosphate isomerase). Sequence analysis showed assemblages A and B in 41 (87.2%) and six (12.8%) isolates, respectively. Two of the 41 assemblage A samples were genotyped as sub-assemblage AI, and 39 were genotyped as sub-assemblage AII. Four previously identified multilocus genotypes (MLGs: AI-1, AII-1, AII-4 and AII-9) and six likely novel variations of MLGs were found. In agreement with previous studies, sequences from assemblage B isolates were characterized by a large genetic variability and by the presence of heterogeneous positions, which prevent the definition of MLGs. This study also investigated whether there was a relationship between the assemblage and clinical data (including drug resistance). However, due to the large number of genotypes and the relatively small number of samples, no significant associations with the clinical data were found.

The Use of Quinacrine in Nitroimidazole-resistant Giardia Duodenalis: An Old Drug for an Emerging Problem

Background

There is little evidence regarding the management of refractory giardiasis after treatment with nitroimidazoles. This study estimates the proportion of persistent giardiasis in 3 hospitals in Barcelona, describes associated risk factors and genotype, and evaluates the efficacy rate of quinacrine in those with persistent giardiasis.

Methods

A clinical, prospective, observational study was conducted in patients with giardiasis treated with nitroimidazoles. Those with persistent giardiasis were provided quinacrine. Molecular characterization of Giardia isolates was performed by polymerase chain reaction amplification of a fragment of tpi and bg genes.

Results

Seventy-seven patients were recruited and treated with nitroimidazoles, and in 14 of 71 (20%) of patients followed up, Giardia persisted. Refractory giardiasis was associated with malaise (P = .007) and anorexia (P = .02), with previous giardiasis (P = .03), and with previous antibiotic (P = .02) or antiparasitic(P = .04) use. Quinacrine had an effectiveness rate of 100% in refractory giardiasis (n = 13; 95% confidence interval = 75-100). Molecular characterization showed that 17 (25%) Giardia isolates belonged to assemblage A, and 31 (43%) belonged to assemblage B. In refractory giardiasis, assemblage A and B were found responsible in 4 and 6 cases, respectively.

Conclusions

Almost 20% of patients presented persistent giardiasis, belonging to both assemblages A and B, after nitroimidazole. Short course of quinacrine was effective in treating refractory cases. Further controlled studies should evaluate its efficacy and safety.

Nitroimidazole-refractory giardiasis: a growing problem requiring rational solutions

BACKGROUND

Giardia intestinalis is microaerophilic diarrhoea-causing protozoan common in countries with suboptimal sanitation. Standard treatment is with nitroimidazoles, but a growing number of refractory cases is being reported. Treatment failure has become increasingly prevalent in travellers who contract giardiasis in Asia. Clinicians are increasingly falling back on second-line and less well-known drugs to treat giardiasis.

AIMS

To review nitroimidazole-refractory G. intestinalis infection, examine the current efficacy of standard therapeutic agents, consider potential resistance mechanisms which could cause treatment failure and describe the practical aspects of managing this emerging clinical problem.

SOURCES

A PubMed search was conducted using combinations of the following terms: refractory, Giardia, giardiasis, resistance and treatment. Articles on the pharmacotherapy, drug resistance mechanisms and use of alternative agents in nitroimidazole-refractory giardiasis were reviewed.

CONTENT

We review the standard drugs for giardiasis, including their efficacy in initial treatment, mode of action and documented in vitro and in vivo drug resistance. We assess the efficacy of alternative drugs in nitroimidazole-refractory disease. Existing data suggest a potential advantage of combination treatment.

IMPLICATIONS

An optimal treatment strategy for refractory giardiasis has still to be determined, so there is no standard treatment regimen for nitroimidazole-refractory giardiasis. Further work on drug resistance mechanisms and the use of drug combinations in this condition is a priority.

Proteomic and functional analyses reveal pleiotropic action of the anti-tumoral compound NBDHEX in Giardia duodenalis

Giardiasis, a parasitic diarrheal disease caused by Giardia duodenalis, affects one billion people worldwide. Treatment relies only on a restricted armamentarium of drugs. The disease burden and the increase in treatment failure highlight the need for novel, safe and well characterized drug options. The antitumoral compound NBDHEX is effective in vitro against Giardia trophozoites and inhibits glycerol-3-phosphate dehydrogenase. Aim of this work was to search for additional NBDHEX protein targets. The intrinsic NBDHEX fluorescence was exploited in a proteomic analysis to select and detect modified proteins in drug treated Giardia. In silico structural analysis, intracellular localization and functional assays were further performed to evaluate drug effects on the identified targets. A small subset of Giardia proteins was covalently bound to the drug at specific cysteine residues. These proteins include metabolic enzymes, e.g. thioredoxin reductase (gTrxR), as well as elongation factor 1B-γ (gEF1Bγ), and structural proteins, e.g. α-tubulin. We showed that NBDHEX in vitro binds to recombinant gEF1Bγ and gTrxR, but only the last one could nitroreduce NBDHEX leading to drug modification of gTrxR catalytic cysteines, with concomitant disulphide reductase activity inhibition and NADPH oxidase activity upsurge. Our results indicate that NBDHEX reacts with multiple targets whose roles and/or functions are specifically hampered. In addition, NBDHEX is in turn converted to reactive intermediates extending its toxicity. The described NBDHEX pleiotropic action accounts for its antigiardial activity and encourages the use of this drug as a promising alternative for the future treatment of giardiasis.

Combination therapy in the management of giardiasis: What laboratory and clinical studies tell us, so far

Treatment failures in patients suffering from giardiasis are not uncommon feature. The most frequent approach in these cases is to treat these patients with longer repeated courses and/or higher doses of the primary therapy, or using drugs from a different class to avoid potential cross-resistance. However, a higher rate of adverse events may limit this strategy. In this context, combination therapy (CT) is emerging as a valuable option against refractory giardiasis. In the attempt to evaluate the benefits of CT, a number of experimental studies, clinical series, and randomized clinical trials (RCTs), as well as several veterinary studies have been performed, with varying results. Here, we present a critical analysis of the available information regarding CT for the treatment of Giardia infection, as well as the authors' opinion with respect to its use. RCTs of combination therapy are limited and the optimal combinations and administration strategies need yet to be clarified. Analyses of the cost-effectiveness and RCTs of CTs for Giardia infection are required to assess the role of these drugs for the control of giardiasis, mainly in the case of treatment failures linked to suspected drug tolerance are the case.

Frequency, diagnostic performance of coproantigen detection and genotyping of the Giardia among patients referred to a multi-level teaching hospital in northern India

Giardiasis, a common gastrointestinal parasitic infection in tropics, is diagnosed on stool microscopy (gold standard); however, its sensitivity is low due to intermittent fecal shedding. Coproantigen detection (ELISA) is useful but requires further evaluation. We aimed to study: (a) detection of Giardia by stool microscopy and/or coproantigen, (b) diagnostic performance of fecal antigen detection and microscopy, and c) genotypic characterization of G. lamblia using PCR specific for triose phosphate isomerase (tpi) gene. Stool samples from 2992 patients were examined by microscopy from March 2013 to March 2015 in a multi level teaching hospital in northern India. Giardia coproantigen detection was performed by ELISA in a subset of patients. Genetic characterization of G. lamblia was performed by PCR targeting tpi gene in a subset of microscopy positive stool samples. Of 2992 patients, 132 (4.4%) had Giardia by microscopy (cyst/trophozoite) and/or ELISA. ELISA was performed in 264 patients; of them, 127 were positive by microscopy. Sensitivity, specificity, positive and negative predictive values of ELISA were 91, 91, 94, and 91%, respectively, using microscopy as a gold standard. PCR was performed in 116 randomly selected samples having Giardia using tpi gene. Assemblages A and B were found among 44 (38%) and 72 (62%) patients, respectively. Assemblage B was more often associated with malnutrition and loss of appetite than A (48/72 [67%] vs. 21/44 [48%], P = 0.044 and 17/72 [24%] vs. 14/44 [32%], P = 0.019). We conclude that 4.4% of studied population had giardiasis. Fecal antigen is a useful method for diagnosis and assemblage B is the most common genotype.

Predominance of Giardia duodenalis Assemblage AII in Fresh Leafy Vegetables from a Market in Southern Brazil

We investigated the presence of Giardia duodenalis cysts and its genotypes in raw leafy vegetables sold in a Brazilian market. These products are different from those sold in most street markets because the producers themselves display and sell their products and rely on specialized technical and sanitary assistance. Vegetable and water samples were collected from 14 (80%) producers who cultivated vegetables that are typically consumed raw for sale at the market, obtained at the market and farms, respectively. A total of 128 samples of leafy greens (chives, parsley, cabbage, arugula, watercress, and chicory) and 14 water samples were analyzed by direct immunofluorescence and PCR techniques. The positive samples were genotyped (GHD gene) using PCR and restriction fragment length polymorphism. The analyses indicated that 16 (12.5%) of 128 samples were positive by PCR, while 1 (0.8%) of 128 samples were positive by immunofluorescence. Giardia cysts were not detected in the water samples obtained at the farms. The molecular technique revealed a genotype with zoonotic potential, which underscores the challenge in the control of giardiasis dissemination via the consumption of raw vegetables.

Travelers lowering their guard: a bacterial, viral and protozoan co-infection after a five-day journey in India

We present a case of concurrent infections by Campylobacter jejuni, Giardia intestinalis and Hepatitis E virus acquired during a 5-days travel to India by an Italian traveller : Professionals responsible for pre- and post-travel care should underline food and water precautions and prescribe an adequate diagnostic work-up in symptomatic patients.

Giardia duodenalis in Damascus, Syria: Identification of Giardia genotypes in a sample of human fecal isolates using polymerase chain reaction and restriction fragment length polymorphism analyzing method

Giardia duodenalis is a common gastrointestinal parasite that infects humans and many other mammals. It is most prevalent in many developing and industrialized countries. G. duodenalis is considered to be a complex species. While no morphological distinction among different assemblages exist, it can be genetically differentiated into eight major assemblages: A to H. The aim of this study was to determine the genetic heterogeneity of G. duodenalis in human isolates (a study conducted for the first time in Syria). 40 fecal samples were collected from three different hospitals during the hot summer season of 2014. Extraction of genomic DNA from all Giardia positive samples (based on a microscopic examination) was performed using QIAamp DNA Stool Mini Kit. β-giardin gene was used to differentiate between different Giardia assemblages. The 514 bp fragment was amplified using the Polymerase Chain Reaction method, followed by digestion in HaeIII restriction enzyme. Our result showed that genotype A was more frequent than genotype B, 27/40 (67.5%); 4/40 (10%) respectively. A mixed genotype of A+B was only detected in 9 isolates (22.5%). This is the first molecular study performed on G. duodenalis isolates in Syria in order to discriminate among the different genotypes. Further expanded studies using more genes are needed to detect and identify the Giardia parasite at the level of assemblage and sub-assemblage.

Molecular Genotyping of Giardia duodenalis Isolates from Symptomatic Individuals Attending Two Major Public Hospitals in Madrid, Spain

BACKGROUND

The flagellate protozoan Giardia duodenalis is an enteric parasite causing human giardiasis, a major gastrointestinal disease of global distribution affecting both developing and industrialised countries. In Spain, sporadic cases of giardiasis have been regularly identified, particularly in pediatric and immigrant populations. However, there is limited information on the genetic variability of circulating G. duodenalis isolates in the country.

METHODS

In this longitudinal molecular epidemiological study we report the diversity and frequency of the G. duodenalis assemblages and sub-assemblages identified in 199 stool samples collected from 184 individual with symptoms compatible with giardiasis presenting to two major public hospitals in Madrid for the period December 2013-January 2015. G. duodenalis cysts were initially detected by conventional microscopy and/or immunochomatography on stool samples. Confirmation of the infection was performed by direct immunofluorescence and real-time PCR methods. G. duodenalis assemblages and sub-assemblages were determined by multi-locus genotyping of the glutamate dehydrogenase (GDH) and β-giardin (BG) genes of the parasite. Sociodemographic and clinical features of patients infected with G. duodenalis were also analysed.

PRINCIPAL FINDINGS

Of 188 confirmed positive samples from 178 giardiasis cases a total of 124 G. duodenalis isolates were successfully typed at the GDH and/or the BG loci, revealing the presence of sub-assemblages BIV (62.1%), AII (15.3%), BIII (4.0%), AI (0.8%), and AIII (0.8%). Additionally, 6.5% of the isolates were only characterised at the assemblage level, being all of them assigned to assemblage B. Discordant genotype results AII/AIII or BIII/BIV were also observed in 10.5% of DNA isolates. A large number of multi-locus genotypes were identified in G. duodenalis assemblage B, but not assemblage A, isolates at both the GDH and BG loci, confirming the high degree of genetic variability observed in other molecular surveys. BIV was the most prevalent genetic variant of G. duodenalis found in individuals with symptomatic giardiasis in the population under study.

CONCLUSIONS

Human giardiasis is an ongoing public health problem in Spain affecting primarily young children under four years of age but also individuals of all age groups. Our typing and sub-typing results demonstrate that assemblage B is the most prevalent G. duodenalis assemblage circulating in patients with clinical giardiasis in Central Spain. Our analyses also revealed a large genetic variability in assemblage B (but not assemblage A) isolates of the parasite, corroborating the information obtained in similar studies in other geographical regions. We believe that molecular data presented here provide epidemiological evidence at the population level in support of the existence of genetic exchange within assemblages of G. duodenalis.