The reliability of observational approaches for detecting interspecific parasite interactions: comparison with experimental results.
Interactions among coinfecting parasites have the potential to alter host susceptibility to infection, the progression of disease and the efficacy of disease control measures. It is therefore essential to be able to accurately infer the occurrence and direction of such interactions from parasitological data. Due to logistical constraints, perturbation experiments are rarely undertaken to directly detect interactions, therefore a variety of approaches are commonly used to infer them from patterns of parasite association in observational data. However, the reliability of these various approaches is not known. We assess the ability of a range of standard analytical approaches to detect known interactions between infections of nematodes and intestinal coccidia (Eimeria) in natural small-mammal populations, as revealed by experimental perturbations. We show that correlation-based approaches are highly unreliable, often predicting strong and highly significant associations between nematodes and Eimeria in the opposite direction to the underlying interaction. The most reliable methods involved longitudinal analyses, in which the nematode infection status of individuals at one month is related to the infection status by Eimeria the next month. Even then, however, we suggest these approaches are only viable for certain types of infections and datasets. Overall we suggest that, in the absence of experimental approaches, careful consideration be given to the choice of statistical approach when attempting to infer interspecific interactions from observational data.
Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK. Electronic address: A.fenton@liverpool.ac.uk.
Andy
A
Fenton
Department of Infectious Disease Epidemiology, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, UK.
Sarah C L
SC
Knowles
Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Owen L
OL
Petchey
Institute of Evolutionary Biology and Centre for Immunity, Infection and Evolution (CIIE), School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, UK.
Amy B
AB
Pedersen
D000818:Animals; D003048:Coccidiosis / Q000150:complications*; D060085:Coinfection / Q000469:parasitology / Q000662:veterinary*; D051189:Murinae; D009349:Nematode Infections / Q000150:complications*; D064887:Observational Studies as Topic / Q000592:standards*; D010542:Peromyscus; D015203:Reproducibility of Results; D012376:Rodent Diseases / Q000469:parasitology*
Coinfection; Cross-sectional and longitudinal analyses; Experimental perturbation; Field study; Helminths; Polyparasitism; Small mammals