Effects of Parasitism on Fecundity and Life History in Human Females

Aaron D. Blackwell, University of California, Santa Barbara
Marilyne Tamayo, University of Missouri, Columbia
Hillard S. Kaplan, University of New Mexico
Michael D. Gurven, University of California, Santa Barbara

We investigate whether intestinal parasites affect human fecundity with seven years of longitudinal data from the Tsimane, Bolivian forger-horticulturalists experiencing natural fertility and a 70% helminth infection prevalence. We observed 184 nulliparous women, 45 of whom became pregnant during the study period, and 511 intervals following births for 432 women. Cox proportional hazard models were used to examine the effects of infection on pregnancy hazard, controlling for BMI. Hookworm was associated with both delayed first pregnancy (HR=0.38; p=0.003, median age 19.1 vs. 15.9) and extended interbirth intervals (HR=0.77, p=0.042; median at age 20: 36.8 vs 33.9 months). In contrast, A. lumbricoides was associated with earlier first pregnancy (HR=2.24, p=0.002, median age 14.6) and shortened IBIs at younger, but not older, ages (at age 20: HR=2.33, p<0.001, median 27.1 months). Our results suggest that helminths have consequences for human fertility, and provide an additional avenue for understanding demographic changes with modernization.