The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Effects of Parasitism on Fecundity and Life History in Human Females


1Department of Anthropology, University of California - Santa Barbara, 2Department of Anthropology, University of Missouri, 3Department of Anthropology, University of New Mexico

March 27, 2015 2:00, Grand Ballroom A/B Add to calendar

In animal studies, parasitism decreases overall reproductive effort, consistent with costs of both parasitism and reproduction. Yet when examined across the lifespan, parasitism can increase precocious reproduction, as effort is shifted earlier due to increased mortality or reproductive senescence, a response known as fecundity compensation. To date, studies have largely examined short-lived birds and rodents, and no studies have examined effects in humans. Here, we investigate whether intestinal parasites affect human fecundity with seven years of longitudinal data from the Tsimane, Bolivian forger-horticulturalists experiencing both 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 IBI 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). Although parasitism affected pregnancy, odds of infection were not affected by reproductive state. While the effect of hookworm suggests overall costs, infection with A. lumbricoides, which often co-occurs with hookworm, suggests fecundity compensation. Our results suggest that helminths have consequences for human fertility, and provide an additional avenue for understanding demographic changes with modernization.

National Institutes of Health/National Institute on Aging [R01AG024119 and R56AG024119] and the National Science Foundation [BCS-0422690].