We conducted a longitudinal study of
cryptosporidiosis from birth to three years of age in an urban slum of Dhaka Bangladesh. Fecal
DNA was extracted from monthly surveillance samples and diarrheal stool samples collected from 392 infants from birth to three years. A pan-Cryptosporidium qPCR assay was used to identify sub-clinical and symptomatic
cryptosporidiosis. Anthropometric measurements were collected quarterly to assess child nutritional status. 31% (121/392) of children experienced a single and 57% (222/392) multiple
infections with Cryptosporidium. Repeat
infections had a lower burden of parasites in the stool (Cq slope = -1.85; p<0.0001) and were more likely to be sub-clinical (Chi square test for trend; p = 0.01). Repeat
infections were associated with the development of growth faltering (Pearson correlation = -0.18; p = 0.0004). High levels of fecal
IgA antibodies against the Cryptosporidium Cp23 sporozoite
protein at one year of life were associated with a delay in
reinfection and amelioration of growth faltering through three years of life (HAZ
IgA high responders -1.323 ± 0.932 versus HAZ -1.731 ± 0.984 p = 0.0001). We concluded that nonsterile immunity to
cryptosporidiosis in young children was associated with high levels of mucosal
IgA anti-Cp23 and protection from
diarrhea and growth faltering. Trial Registration: NCT02764918.