title: Antagonism between two intestinal parasites in humans: the importance of co-infection for infection risk and recovery dynamics.
abstract: 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.
authors.affiliation: Department of Anthropology, University of California, Santa Barbara, CA 93106-3210, USA. blackwell@anth.ucsb.edu
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Blackwell
authors.forename: Melanie
authors.initials: M
authors.lastname: Martin
authors.forename: Hillard
authors.initials: H
authors.lastname: Kaplan
authors.forename: Michael
authors.initials: M
authors.lastname: Gurven
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D000898:Antibiosis; D001838:Bolivia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D060085:Coinfection / Q000453:epidemiology* / Q000469:parasitology; D003430:Cross-Sectional Studies; D005243:Feces / Q000469:parasitology; D005260:Female; D005872:Giardia / Q000302:isolation & purification* / Q000502:physiology; D005873:Giardiasis / Q000453:epidemiology* / Q000469:parasitology; D006373:Helminthiasis / Q000453:epidemiology* / Q000469:parasitology; D006376:Helminths / Q000302:isolation & purification* / Q000502:physiology; D006801:Humans; D007199:Indians, South American; D007223:Infant; D007411:Intestinal Diseases, Parasitic / Q000453:epidemiology* / Q000469:parasitology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D055815:Young Adult
keywords: Bolivia; Tsimane; co-infection; giardia; helminths; state-based modelling