Giardiasis: An Overview

BACKGROUND

Giardiasis is an important cause of waterborne and foodborne diarrhea, daycare center outbreaks, and traveler's diarrhea.

OBJECTIVE

The study aimed to provide an update on the evaluation, diagnosis, and treatment of giardiasis.

METHODS

A PubMed search was completed in Clinical Queries using the key terms "giardiasis", "Giardia lamblia", "Giardia duodenalis" and "Giardia intestinalis". The search strategy included metaanalyses, randomized controlled trials, clinical trials, observational studies, and reviews. The search was restricted to the English literature. Patents were searched using the key term "giardiasis" from www.freepatentsonline.com.

RESULTS

Giardiasis is caused by the protozoan parasite Giardia lamblia. The parasite is transmitted by the fecal-oral route, frequently through ingestion of contaminated water and food or person-to person transmission. Risk factors for infection include children in day-care settings, child-care workers, institutionalized individuals, travelers in endemic areas, ingestion of contaminated or recreational water, immunodeficiency, cystic fibrosis, and oral-anal sex. Approximately 50 to 75% of infected children are asymptomatic. Other children present acute or chronic diarrhea. Direct fluorescent antibody tests that detect intact organisms, enzyme immunoassays that detect soluble antigens, and multiplex real-time polymerase chain reaction assays that detect specific genes of the parasite in stool samples have improved sensitivity and specificity compared with microscopic examination of stool specimens for the detection of Giardia trophozoites or cysts. Drugs used in the treatment of symptomatic giardiasis are reviewed in this study. Moreover, recent patents related to the management of giardiasis are also discussed.

CONCLUSION

Metronidazole, tinidazole, and nitazoxanide are drugs of choice. Resistance to common antigiardial drugs has increased in recent years, therefore, the search for new molecular targets for antigiardial drugs is urgently needed. In general, treatment of asymptomatic carriers is not recommended. Purification of water supply is an important preventive measure.

Efficacy of mebendazole in paediatric patients with giardiasis: A systematic review and meta-analysis

Mebendazole (MBZ), a benzimidazole compound, has received attention in treating patients with giardiasis because it has shown beneficial effects both in vitro and in vivo. The aim of this study was to assess with a systematic review and meta-analysis of randomized controlled trials (RCTs) the efficacy of MBZ compared to other antigiardial agents in children. We searched RCTs of MBZ for the treatment of Giardia infections published in PubMed and EBSCOhost. Application of inclusion and exclusion criteria, data extraction, and assessment of methodological quality were independently performed in duplicate. The primary outcome was the parasitological cure. We included 7 RCTs in the systematic review (639 patients). There was no clinical difference in the parasitological cure between MBZ and metronidazole (MTZ). The relative risk (RR) was 0.81 [95% Confidence Interval 0.61-1.09], with high heterogeneity (4 trials, I² = 81%). The prediction interval expected to cover the results of a new trial was wide enough (0.22-2.96) to support both a clinically relevant difference favouring either MBZ or MTZ. The decision to support any treatment should be based not only on efficacy but also safety and cost. Although our results suggest that MBZ may be an effective treatment option for children with Giardia infection, they should also be interpreted and translated into clinical practice with caution, as the evidence is based on a limited number of RCTs presenting high heterogeneity.

Evaluation of Giardia lamblia thioredoxin reductase as drug activating enzyme and as drug target

The antioxidative enzyme thioredoxin reductase (TrxR) has been suggested to be a drug target in several pathogens, including the protist parasite Giardia lamblia. TrxR is also believed to catalyse the reduction of nitro drugs, e.g. metronidazole and furazolidone, a reaction required to render these compounds toxic to G. lamblia and other microaerophiles/anaerobes. It was the objective of this study to assess the potential of TrxR as a drug target in G. lamblia and to find direct evidence for the role of this enzyme in the activation of metronidazole and other nitro drugs. TrxR was overexpressed approximately 10-fold in G. lamblia WB C6 cells by placing the trxR gene behind the arginine deiminase (ADI) promoter on a plasmid. Likewise, a mutant TrxR with a defective disulphide reductase catalytic site was strongly expressed in another G. lamblia WB C6 cell line. Susceptibilities to five antigiardial drugs, i.e. metronidazole, furazolidone, nitazoxanide, albendazole and auranofin were determined in both transfectant cell lines and compared to wildtype. Further, the impact of all five drugs on TrxR activity in vivo was measured. Overexpression of TrxR rendered G. lamblia WB C6 more susceptible to metronidazole and furazolidone but not to nitazoxanide, albendazole, and auranofin. Of all five drugs tested, only auranofin had an appreciably negative effect on TrxR activity in vivo, albeit to a much smaller extent than expected. Overexpression of TrxR and mutant TrxR had hardly any impact on growth of G. lamblia WB C6, although the enzyme also exerts a strong NADPH oxidase activity which is a source of oxidative stress. Our results constitute first direct evidence for the notion that TrxR is an activator of metronidazole and furazolidone but rather question that it is a relevant drug target of presently used antigiardial drugs.