Comparative efficacy of drugs for treating giardiasis: a systematic update of the literature and network meta-analysis of randomized clinical trials

Ultrastructural Alterations of the Human Pathogen Giardia intestinalis after Drug Treatment

This review presents the main cell characteristics altered after in vitro incubation of the parasite with commercial drugs used to treat the disease caused by Giardia intestinalis. This important intestinal parasite primarily causes diarrhea in children. Metronidazole and albendazole are the primary compounds used in therapy against Giardia intestinalis. However, they provoke significant side effects, and some strains have developed resistance to metronidazole. Benzimidazole carbamates, such as albendazole and mebendazole, have shown the best activity against Giardia. Despite their in vitro efficacy, clinical treatment with benzimidazoles has yielded conflicting results, demonstrating lower cure rates. Recently, nitazoxanide has been suggested as an alternative to these drugs. Therefore, to enhance the quality of chemotherapy against this parasite, it is important to invest in developing other compounds that can interfere with key steps of metabolic pathways or cell structures and organelles. For example, Giardia exhibits a unique cell structure called the ventral disc, which is crucial for host adhesion and pathogenicity. Thus, drugs that can disrupt the adhesion process hold promise for future therapy against Giardia. Additionally, this review discusses new drugs and strategies that can be employed, as well as suggestions for developing novel drugs to control the infection caused by this parasite.

Incidence, Management Experience and Characteristics of Patients with Giardiasis and Common Variable Immunodeficiency

Common variable immunodeficiency (CVID) is an antibody immunodeficiency with a wide variety of clinical and immunological manifestations, and whose genetic cause is found in about 25% of diagnosed cases. Giardia lamblia is one of the main causes of gastrointestinal infections in CVID. 5-Nitroimidazoles are the most used first-line treatment, but nitroimidazole-refractory giardiasis is increasing. Nevertheless, only a few cases of refractory giardiasis in CVID have been reported. This study aimed to determine the incidence of Giardia infection in our CVID cohort, shows our management experience and describes patients' phenotypic features. Clinical data collection, immunological, immunogenetics and microbiology assays were performed, and previous cases of giardiasis in CVID were reviewed. The incidence of symptomatic giardiasis was 12.9%. The main immunological features were undetectable or decreased IgA levels and reduced switched memory B cells. A probable PTEN pathogenic variant was detected in one. Three patients responded to metronidazole but suffered reinfections, and one was a refractory giardiasis eradicated with innovative quinacrine plus paromomycin combination. This work could contribute to the decision-making and therapeutic management of future patients with CVID and giardiasis, highlighting the importance of the early detection and treatment of infections in patients with CVID to ensure a good quality of life.

Pre-and post-treatment evaluation of intestinal inflammation in Giardia and Blastocystis infected children: a community-based study

Giardia intestinalis and Blastocystis hominis cause frequent infections in children in developing countries. However, the role of intestinal inflammation in their pathogenesis is still poorly understood. Faecal calprotectin (FC) level is used as an indicator of intestinal inflammation and neutrophil migration in the intestinal tract. The present study aimed to evaluate intestinal inflammation by measuring FC level among children infected with either G. intestinalis or B. hominis before and after treatment. Stool samples were collected from 282 children inhabiting a rural area in Egypt and examined microscopically for intestinal parasites. FC level was estimated in a group of children infected with G. intestinalis (n = 12) or B. hominis (n = 12) before and 3 weeks after receiving nitazoxanide (200 mg twice daily for 3 days) and compared to a control group (n = 18) of parasite-free children. Cases of mixed infection were excluded. Nitazoxanide cure rate was 83% in both infections with a remarkable reduction of infection intensity in uncured children. The difference in FC levels between infected children and controls was not statistically significant. Also, the difference between the pre- and post-treatment estimations was not statistically significant. Elevated levels were observed before treatment in three children (two infected with G. intestinalis and one with B. hominis) who displayed normal post-treatment levels. Although G. intestinalis and B. hominis infections appear to cause no remarkable intestinal inflammation, they may induce abnormally elevated FC levels in a subset of children.

Giardia duodenalis: Biology and Pathogenesis

Giardia duodenalis captured the attention of Leeuwenhoek in 1681 while he was examining his own diarrheal stool, but, ironically, it did not really gain attention as a human pathogen until the 1960s, when outbreaks were reported. Key technological advances, including in vitro cultivation, genomic and proteomic databases, and advances in microscopic and molecular approaches, have led to an understanding that this is a eukaryotic organism with a reduced genome rather than a truly premitochondriate eukaryote. This has included the discovery of mitosomes (vestiges of mitochondria), a transport system with many of the features of the Golgi apparatus, and even evidence for a sexual or parasexual cycle. Cell biology approaches have led to a better understanding of how Giardia survives with two nuclei and how it goes through its life cycle as a noninvasive organism in the hostile environment of the lumen of the host intestine. Studies of its immunology and pathogenesis have moved past the general understanding of the importance of the antibody response in controlling infection to determining the key role of the Th17 response. This work has led to understanding of the requirement for a balanced host immune response that avoids the extremes of an excessive response with collateral damage or one that is unable to clear the organism. This understanding is especially important in view of the remarkable ranges of early manifestations, which range from asymptomatic to persistent diarrhea and weight loss, and longer-term sequelae that include growth stunting in children who had no obvious symptoms and a high frequency of postinfectious irritable bowel syndrome (IBS).

Effects of Tinidazole on Food Intake in Chinchillas (Chinchilla lanigera)

Tinidazole is a second-generation nitroimidazole compound that is used as an antimicrobial to treat anaerobic bacterialand protozoal infections in humans and, less frequently, in veterinary medicine. However, metronidazole, another secondgeneration nitroimidazole, is more commonly used. Nonetheless, tinidazole has proven to be a superior therapy for parasitic infections in humans, particularly in the treatment of giardiasis. Furthermore, in chinchillas, metronidazole has been shown to cause a clinically relevant reduction in food intake after oral administration at published dosages. This study's objective was to evaluate the effect of orally administered tinidazole on food intake in healthy chinchillas. In 2 randomized, placebocontrolled,blinded, crossover studies, tinidazole was evaluated at 2 single high doses (100 mg/kg and 200 mg/kg PO, n =9) and a repeated dosing schedule at a lower dose (20 mg/kg PO q12h for 10 doses, n = 12). Food intake was measured over24-h periods before and after drug administration. The single-dose treatment groups both displayed significantly reducedfood intake (200 mg/kg: -26 ± 21%; 100 mg/kg: -9 ± 21%, P < 0.01) as compared with the control group during the first 24 hafter drug administration. Food intake returned to pretreatment values within 4-5 d. Repeated administration at 20 mg/kg q12h was not associated with any significant changes in food intake. No other adverse effects were noted during this study. Tinidazole administration at single higher doses resulted in an acute self-limiting reduction in food intake. In comparison, repeated administration of lower doses (20 mg/kg PO q12h) had no significant effects on food intake in healthy chinchillas. Therefore, tinidazole may be a more suitable drug for treating Giardia and anaerobic bacterial infections in this species than the more commonly used metronidazole.

Risk factors for and management of metronidazole-refractory giardiasis in international travellers: A retrospective analysis

BACKGROUND

Giardia lamblia is a common cause of diarrhoea in returning travellers. Failure of the recommended first-line treatment, metronidazole, has frequently been observed. Recommendations for treatment of metronidazole-refractory giardiasis lack clarity and evidence.

METHODS

We conducted a retrospective data analysis of returned travellers with confirmed giardiasis at the Bernhard-Nocht-Clinic in Hamburg, Germany, between 2007 and 2016.

RESULTS

We identified 339 cases of giardiasis, mostly acquired in South Asia (n = 157). 308 patients received metronidazole as first-line treatment, leading to treatment failure in 93 cases. Statistical analysis suggested by far the highest risk of metronidazole treatment failure for travellers returning from South Asia (Odds Ratio 8.73). Second-line therapy consisted of various different therapy regimens. Combination therapy as second-line treatment seemed to be more effective than monotherapy. A repeat course of metronidazole proved to be futile.

CONCLUSION

This study reveals a strikingly low effectiveness of metronidazole, especially in patients returning from South Asia. Second-line treatment showed inconsistency of regimens and yielded unsatisfactory results. These findings require reconsideration of treatment strategies for giardiasis. Large prospective trials are urgently needed to assess new first-line treatment options and to help implement advice for effective, agreed second-line treatment strategies. Translational projects should be created to link the understanding of resistance mechanisms with epidemiological data and clinical outcome.

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.

Clinical Management of Infectious Diarrhea

BACKGROUND

Infectious diarrhea is the most common cause of diarrhea worldwide and is responsible for more deaths than other gastrointestinal tract diseases such as gastrointestinal cancers, peptic ulcer disease or inflammatory bowel disease. Diarrheal disease still represents the 8th leading cause of death worldwide, with more than 1,6 million attributed fatalities in 2016 alone. The majority of cases can be divided into three principal clinical presentations: acute watery diarrhea lasting 5-10 days and normally self-limiting, bloody diarrhea (dysentery), and persistent diarrhea with or without intestinal malabsorption.

METHODS

We performed an electronic search on PUBMED of the scientific literature concerning infectious diarrhea and its clinical management.

AIM

In this review article, we analyze the most important causes of infectious diarrhea and their constellation of signs and symptoms, providing an update on the diagnostic tools available in today's practice and on the different treatment options.

CONCLUSION

Even though the majority of intestinal infections are self-limiting in immunocompetent individuals, specific diagnosis and identification of the causative agent remain crucial from public health and epidemiological perspectives. Specific diagnostic investigation can be reserved for patients with severe dehydration, more severe illness, persistent fever, bloody stools, immunosuppression, and for cases of suspected nosocomial infection or outbreak and it includes complete blood count, creatinine and electrolytes evaluation, determination of leukocytes and lactoferrin presence in the stools, stool culture, together with C. difficile testing, PCR, ova and parasites' search, endoscopy and abdominal imaging. Since acute diarrhea is most often self-limited and caused by viruses, routine antibiotic use is not recommended for most adults with mild, watery diarrhea. However, when used appropriately, antibiotics are effective against shigellosis, campylobacteriosis, C. difficile colitis, traveler's diarrhea, and protozoal infections. Furthermore, antibiotics use should be considered in patients who are older than 65 years, immunocompromised, severely ill, or septic.

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.

Treatment-refractory giardiasis: challenges and solutions

Giardia is the commonest parasitic diarrheal pathogen affecting humans and a frequent cause of waterborne/foodborne parasitic diseases worldwide. Prevalence of giardiasis is higher in children, living in poor, low hygiene settings in developing countries, and in travelers returning from highly endemic areas. The clinical picture of giardiasis is heterogeneous, with high variability in severity of clinical disease. It can become chronic or be followed by post-infectious sequelae. An alarming increase in cases refractory to the conventional treatment with nitroimidazoles (ie, metronidazole) has been reported in low prevalence settings, such as European Union countries, especially in patients returning from Asia. In view of its relevance, we aim in this review to recapitulate present clinical knowledge about Giardia, with a special focus on the challenge of treatment-refractory giardiasis. We propose a working definition of clinically drug-resistant giardiasis, summarize knowledge regarding resistance mechanisms, and discuss its clinical management according to research-based evidence and medical practice. Advances in development and identification of novel drugs and potential non-pharmacological alternatives are also reviewed with the overall aim to define knowledge gaps and suggest future directions for research.