Giardia duodenalis assemblage, clinical presentation and markers of intestinal inflammation in Brazilian children

Data 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 × 10⁵, range 5.3 × 10²-2.5 × 10⁶ cysts/ml) than children infected with assemblage A (n = 9, mean 1.4 × 10⁵, range 1.5 × 10⁴-4.6 × 10⁵ cysts/ml; P = 0.009). Children with mixed infections shed more cysts (mean 8.3 × 10⁵, range 3.1 × 10⁴-2.8 × 10⁶ 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 promote 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.