Giardia: a pathogen or commensal for children in high-prevalence settings?

Abstract

Purpose of review Giardia is a common intestinal parasite worldwide, and infection can be associated with clear and sometimes persistent symptomatology. However, in children in high prevalence settings, it is not associated with or is perhaps even protective against acute diarrhea, and the association with long-term outcomes has been difficult to discern. Recent findings Recent studies have made progress in helping us disentangle this apparent paradox. First, prospective, well-characterized cohort studies have added to the data on the association between Giardia and diarrhea in these settings and have further characterized associations between Giardia infection and nutrition, gut function, and growth. Second, animal models have further characterized the host response to Giardia and helped elucidate mechanisms by which Giardia could impair child development. Finally, new work has shed light on the heterogeneity of human Giardia strains, which may both explain discrepant findings in the literature and help guide higher-resolution analyses of this pathogen in the future. Summary The true clinical impact of endemic pediatric giardiasis remains unclear, but recent prospective studies have confirmed a high prevalence of persistent, subclinical Giardia infections and associated growth shortfalls. Integrating how nutritional, microbial, metabolic, and pathogen-strain variables influence these outcomes could sharpen delineations between pathogenic and potentially beneficial attributes of this enigmatic parasite.

Subclinical Enteric Parasitic Infections and Growth Faltering in Infants in São Tomé, Africa: A Birth Cohort Study

“…The physiopathology of growth faltering in enteric parasitic infection could be related to several mechanisms, including microbial-driven nutrient deficiencies, intestinal inflammation, gut dysfunction, and increased intestinal permeability [ 48 ]. In experimental models, Giardia lamblia and Cryptosporidium spp.…”

Identification of the NADP+ Structural Binding Site and Coenzyme Effect on the Fused G6PD::6PGL Protein from Giardia lamblia

“…The clinical manifestations of the disease can range from asymptomatic conditions to acute diarrhea or even malabsorption syndrome [7]. Children and immunocompromised patients are more exposed to the clinical consequences of infection by Giardia lamblia due to the high colonization capacity and the evasion of the immune system [8].…”

Biochemical Characterization and Structural Modeling of Fused Glucose-6-Phosphate Dehydrogenase-Phosphogluconolactonase from Giardia lamblia

“…This parasite is the most common enteric pathogen in humans that causes giardiasis [ 3 , 4 , 5 , 6 ]. Children and immunocompromised patients are the most susceptible to the serious clinical consequences of G. lamblia infection [ 3 , 7 , 8 ]. G. lamblia is an early divergent eukaryotic microorganism that shares many characteristics with anaerobic prokaryotes, including some metabolic pathways [ 1 ] and the absence of organelles, such as peroxisomes and mitochondria, that are replaced by closely-related organelles called mitosomes that do not perform oxidative phosphorylation [ 9 ].…”