The prevalence of Entamoeba histolytica in lactating women and in their infants in Bangladesh

Entamoeba histolytica was studied in 33 lactating women and their infants in a periurban village in Bangladesh. Infant-mother pairs were followed for a period of 10-15 months: 67% of mothers excreted E. histolytica during the observation period, the majority for 3 months or more. Only one mother was symptomatic, with a mild, non-dysenteric diarrhoea. 58% of mothers were seropositive, several of them continuously and with a high titre, indicating past invasive infection. 67% had detectable antibodies in breast milk and 36% in saliva. Despite the high prevalence of E. histolytica in these mothers, infants were mostly uninfected: E. histolytica cysts in small numbers were found in only 2 of 1200 samples from infants aged 6 and 10 months. Several of the children were infected with Giardia lamblia. Although lower exposure to E. histolytica than to Giardia may account for the difference in infant infection rates with these parasites, defence mechanisms possibly exist which protect against E. histolytica but are ineffective against Giardia.

Giardia lamblia infections in a cohort of Bangladeshi mothers and infants followed for one year

Giardia lamblia infection in an endemic area was investigated by following a cohort of 33 lactating mothers and their infants in a semiurban community of Bangladesh for one year. Eighty-two percent of mothers and 42% of infants excreted Giardia at least once during the study period. Infants became infected as early as 3 months of age, and 86% of the infected infants had diarrhea, suggesting that the first exposure to the parasite results in disease. Only one of the infected mothers had diarrhea, indicating that with repeated exposure to Giardia, mothers in an endemic area may develop partial immunity that protects against disease but not infection. An interrelationship between maternal and infant colonization was not found. Local and systemic immune responses to Giardia correlated poorly with infection, but milk antibodies were a better reflection of infection than serum antibodies were. Infection with G. lamblia was significantly lower in infants younger than 6 months (9%), an age when many are totally breast-fed. However, we were unable to establish clear-cut protection related to human milk antibodies, and suggest that the lower infection rate in younger infants results mainly from decreased exposure to Giardia cysts.