Antagonism between two intestinal parasites in humans: the importance of co-infection for infection risk and recovery dynamics

Proc Biol Sci. 2013 Aug 28;280(1769):20131671. doi: 10.1098/rspb.2013.1671. Print 2013 Oct 22.


Co-infection may affect transmission and recovery from infection, but remains an understudied element of disease ecology, particularly with regard to antagonism between parasites sharing a host. Helminth and giardia infections are often endemic in the same populations and both occupy the small intestine; yet few studies have examined interactions between these parasites. We report on helminth-giardia co-infections in a panel study of forager-horticulturalists in the Bolivian lowlands. Parasites were identified in faecal samples from 3275 participants, collected during 5235 medical exams over 6 years. Longitudinal co-infection patterns were examined using logistic mixed and multi-state Markov models. The most prevalent infections were hookworm (56%), Giardia lamblia (30%) and Ascaris lumbricoides (15%). Cross-sectionally, hookworm and A. lumbricoides were negatively associated with G. lamblia (OR = 0.60; OR = 0.65, respectively). Longitudinally, giardia infection was less likely in helminth-infected individuals (HR: 0.46). Infection with helminths was also less likely for individuals infected with giardia (HR: 0.71). Finally, treatment with mebendazole reduced subsequent hookworm infections, but resulted in a marginal increase in the odds of G. lamblia infection. Our results provide evidence for an antagonistic relationship between helminths and giardia, and suggest that co-infection should be considered in disease transmission models and treatment decisions.

Keywords: Bolivia; Tsimane; co-infection; giardia; helminths; state-based modelling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Animals
  • Antibiosis
  • Bolivia / epidemiology
  • Child
  • Child, Preschool
  • Coinfection / epidemiology*
  • Coinfection / parasitology
  • Cross-Sectional Studies
  • Feces / parasitology
  • Female
  • Giardia / isolation & purification*
  • Giardia / physiology
  • Giardiasis / epidemiology*
  • Giardiasis / parasitology
  • Helminthiasis / epidemiology*
  • Helminthiasis / parasitology
  • Helminths / isolation & purification*
  • Helminths / physiology
  • Humans
  • Indians, South American
  • Infant
  • Intestinal Diseases, Parasitic / epidemiology*
  • Intestinal Diseases, Parasitic / parasitology
  • Longitudinal Studies
  • Male
  • Middle Aged
  • Prevalence
  • Young Adult