Giardia hinders growth by disrupting nutrient metabolism independent of inflammatory enteropathy

Mucosal vaccination in a murine gnotobiotic model of Giardia lamblia infection

Giardia lamblia is an important protozoan cause of diarrheal disease worldwide, delayed development and cognitive impairment in children in low- and middle-income countries, and protracted post-infectious syndromes in developed regions. G. lamblia resides in the lumen and at the epithelial surface of the proximal small intestine but is not mucosa invasive. The protozoan parasite is genetically diverse with significant genome differences across strains and assemblages. Animal models, particularly murine models, have been instrumental in defining mechanisms of host defense against G. lamblia, but mice cannot be readily infected with most human pathogenic strains. Antibiotic pretreatment can increase susceptibility, suggesting that the normal microbiota plays a role in controlling G. lamblia infection in mice, but the broader implications on susceptibility to diverse strains are not known. Here, we have used gnotobiotic mice to demonstrate that robust intestinal infection can be achieved for a broad set of human-pathogenic strains of the genetic assemblages A and B. Furthermore, gnotobiotic mice were able to eradicate infection with a similar kinetics to conventional mice after trophozoite challenge. Germ-free mice could also be effectively immunized by the mucosal route with a protective antigen, α1-giardin, in a manner dependent on CD4 T cells. These results indicate that the gnotobiotic mouse model is powerful for investigating acquired host defenses in giardiasis, as the mice are broadly susceptible to diverse G. lamblia strains yet display no apparent defects in mucosal immunity needed for controlling and eradicating this lumen-dwelling pathogen.

Perspective: Connecting the dots between domestic livestock ownership and child linear growth in low- and middle-income countries

Child stunting due to linear growth faltering remains a pervasive issue in low- and middle-income countries. Two schools of thought have existed pertaining to the role of domestic livestock ownership (DLO) in child linear growth. On one hand, it is argued that DLO leads to greater income and financial security, resulting in better child-raising conditions, including greater animal-source food (ASF) consumption, having protective effects towards child stunting. On the other hand, researchers argue that DLO contributes to faecal contamination and transmission of zoonotic enteric infections from animals to children, thus having destructive effects on child growth. Reviews of this association have revealed ambiguous findings. In this perspective, we argue that measuring the association between exposures to domesticated animals and child stunting is difficult and the ambiguous associations revealed are a result of confounding and differences in the management of DLO. We also argue that the increasingly prominent area of research of environmental enteric dysfunction, a sub-clinical condition of the small intestine thought to be due to frequent faecal pathogen exposure and associated with stunting, will be a useful tool to measure the potential destructive effects of DLO on child growth. We present our argument and identify challenges and considerations and directions for future research.

Giardia lamblia Diagnosed During Upper Gastrointestinal Endoscopy: Clinical Manifestation, Histopathologic Findings and the Association With Celiac Disease

BACKGROUND

Giardia lamblia may be found incidentally during upper gastrointestinal (GI) endoscopy, including when biopsies are taken for celiac disease (CeD) diagnosis. We aimed to study the clinical presentation and histopathology of G. lamblia and determine its association with CeD.

METHODS

A retrospective case series of pediatric patients diagnosed with G. lamblia based on intestinal biopsies between January 1999 and January 2023. Baseline data; demographics, symptoms, celiac serology, stool testing, macroscopic and histopathologic findings. Follow-up data; treatment and repeated celiac serology.

RESULTS

Of 38 patients with G. lamblia , 15 (39.5%) were female, mean age of 6.7 (±4.8 SD) years. Clinical symptoms; GI 19/38 (50%), growth retardation and/or iron deficiency anemia 8/38 (21.1%) or a combination 11/38 (28.9%). Celiac serology was positive in 13/38 (34.2%). Duodenal endoscopic findings; normal (n = 23, 60.5%), nodularity (n = 12, 32.4%), erosions in 2 (5.4%) and scalloping in 1 (2.7%). Histopathology; normal villi 24/38 (63.2%), villous shortening with increased intraepithelial lymphocytes (IEL) 5/38 (13.2%), isolated IEL 3/38 (7.9%) and duodenitis in 6/38 (15.8%). Children with positive CeD serology were younger (4 vs. 8.1 years, P = 0.019), had fewer GI symptoms (23.1% vs. 64%, P = 0.017) and a higher rate of villous shortening with increased IEL (38.5% vs. 0, P < 0.001) versus children with negative serology. On follow-up, metronidazole treatment was recommended to all but was documented to be given in 22/38 (57.9%). Among the 13 children with positive CeD serology, serology normalized in 10 (77%).

CONCLUSIONS

G. lamblia is a rare histopathologic finding in children. It may be an incidental finding in CeD or may cause false positive celiac serology.

Giardia Antagonizes Beneficial Functions of Indigenous and Therapeutic Intestinal Bacteria during Malnutrition

Undernutrition in children commonly disrupts the structure and function of the small intestinal microbial community, leading to enteropathies, compromised metabolic health, and impaired growth and development. The mechanisms by which diet and microbes mediate the balance between commensal and pathogenic intestinal flora remain elusive. In a murine model of undernutrition, we investigated the direct interactions Giardia lamblia, a prevalent small intestinal pathogen, on indigenous microbiota and specifically on Lactobacillus strains known for their mucosal and growth homeostatic properties. Our research reveals that Giardia colonization shifts the balance of lactic acid bacteria, causing a relative decrease in Lactobacillus spp . and an increase in Bifidobacterium spp . This alteration corresponds with a decrease in multiple indicators of mucosal and nutritional homeostasis. Additionally, protein-deficient conditions coupled with Giardia infection exacerbate the rise of primary bile acids and susceptibility to bile acid-induced intestinal barrier damage. In epithelial cell monolayers, Lactobacillus spp . mitigated bile acid-induced permeability, showing strain-dependent protective effects. In vivo, L. plantarum, either alone or within a Lactobacillus spp consortium, facilitated growth in protein-deficient mice, an effect attenuated by Giardia , despite not inhibiting Lactobacillus colonization. These results highlight Giardia's potential role as a disruptor of probiotic functional activity, underscoring the imperative for further research into the complex interactions between parasites and bacteria under conditions of nutritional deficiency.

Epidemiology of giardiasis and assemblages A and B and effects on diarrhea and growth trajectories during the first 8 years of life: Analysis of a birth cohort in a rural district in tropical Ecuador

BACKGROUND

There are limited longitudinal data on the acquisition of Giardia lamblia infections in childhood using molecular assays to detect and type assemblages, and measure effects of infections on diarrhea risk and childhood growth.

METHODS

We analysed stool samples from a surveillance sample within a birth cohort in a rural district in tropical Ecuador. The cohort was followed to 8 years of age for the presence of G. lamblia in stools by quantitative PCR and A and B assemblages by Taqman assay or Sanger sequencing. We explored risk factors associated with infection using generalized estimating equations applied to longitudinal binary outcomes, and longitudinal panel data analysis to estimate effects of infection on diarrhea and growth trajectories.

RESULTS

2,812 stool samples collected between 1 month and 8 years of age from 498 children were analyzed and showed high rates of infection: 79.7% were infected at least once with peak prevalence (53.9%) at 5 years. Assemblage B was accounted for 56.8% of genotyped infections. Risk factors for infection included male sex (P = 0.001), daycare attendance (P<0.001), having a household latrine (P = 0.04), childhood (P<0.001) and maternal soil-transmitted helminth (P = 0.029) infections, and exposures to donkeys (age interaction P = 0.034). G. lamblia was associated with increased risk of diarrhea (per episode, RR 1.03, 95% CI 1.01-1.06, P = 0.011) during the first 3 years of life and a transient impairment of weight (age interaction P = 0.017) and height-for-age (age interaction P = 0.025) trajectories between 1 and 4 years of age. There was no increased risk of either assemblage being associated with outcomes.

CONCLUSION

Our data show a relatively high edemicity of G. lamblia transmission during childhood in coastal Ecuador, and evidence that infection is associated with a transiently increased risk of diarrhea during the first 3 years of life and impairment of weight and height between 1 and 4 years.

Enhancing Giardicidal Activity and Aqueous Solubility through the Development of "RetroABZ", a Regioisomer of Albendazole: In Vitro, In Vivo, and In Silico Studies

Parasitic diseases, including giardiasis caused by Giardia lamblia (G. lamblia), present a considerable global health burden. The limited effectiveness and adverse effects of current treatment options underscore the necessity for novel therapeutic compounds. In this study, we employed a rational design strategy to synthesize retroalbendazole (RetroABZ), aiming to address the limitations associated with albendazole, a commonly used drug for giardiasis treatment. RetroABZ exhibited enhanced in vitro activity against G. lamblia trophozoites, demonstrating nanomolar potency (IC50 = 83 nM), outperforming albendazole (189 nM). Moreover, our in vivo murine model of giardiasis displayed a strong correlation, supporting the efficacy of RetroABZ, which exhibited an eleven-fold increase in potency compared to albendazole, with median effective dose (ED50) values of 5 µg/kg and 55 µg/kg, respectively. A notable finding was RetroABZ's significantly improved water solubility (245.74 µg/mL), representing a 23-fold increase compared to albendazole, thereby offering potential opportunities for developing derivatives that effectively target invasive parasites. The molecular docking study revealed that RetroABZ displays an interaction profile with tubulin similar to albendazole, forming hydrogen bonds with Glu198 and Cys236 of the β-tubulin. Additionally, molecular dynamics studies demonstrated that RetroABZ has a greater number of hydrophobic interactions with the binding site in the β-tubulin, due to the orientation of the propylthio substituent. Consequently, RetroABZ exhibited a higher affinity compared to albendazole. Overall, our findings underscore RetroABZ's potential as a promising therapeutic candidate not only for giardiasis but also for other parasitic diseases.