SummaryData on the relationship between the two genotypes of Giardia duodenalis that infect humans, assemblages A and B, their clinical presentation and intestinal inflammation are limited. We analyzed 108 stool samples previously collected for a diarrhoeal study among Brazilian children, representing 71 infections in 47 children. Assemblage B was most prevalent, accounting for 43/58 (74.1%) infections, while assemblage A accounted for 9/58 (15.5%) infections and 6/58 (10.3%) infections were mixed (contained both assemblage A and B). There was no significant difference in diarrhoeal symptoms experienced during assemblage A, B or mixed infections. Children with assemblage B demonstrated greater variability in G. duodenalis cyst shedding but at an overall greater level (n = 43, mean 3.6 × 10 5 , range 5.3 × 10 2 -2.5 × 10 6 cysts/ml) than children infected with assemblage A (n = 9, mean 1.4 × 10 5 , range 1.5 × 10 4 -4.6 × 10 5 cysts/ml; P = 0.009). Children with mixed infections shed more cysts (mean 8.3 × 10 5 , range 3.1 × 10 4 -2.8 × 10 6 cysts/ml) than children with assemblage A or B alone (P = 0.069 and P = 0.046 respectively). This higher rate of cyst shedding in children with assemblage B may propagate its spread, accounting for its increased incidence. Additionally, second and third infections had decreasing faecal lactoferrin, suggesting some protection against severity, albeit not against infection, by prior infection. Authors' contributions: AAML, RLG, AK and OYB designed the study protocol; RDN, AK and OYB carried out the clinical assessment; AK carried out and EH designed and carried out the quantitative PCR of Giardia; AK, RCP, OYB, CLS and RDN carried out the analysis and interpretation of these data; AK, OYB, RDN and CLS drafted the manuscript. All authors read and approved the final manuscript. AK and RLG are guarantors of the paper.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Conflicts of interest: None declared.Ethical approval: The study protocol and informed consent were approved by the human investigations committees of the Federal