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Published on: June 21, 2018
Coinfections by noninteracting pathogens are not independent and require new tests of interaction
Frédéric M Hamelin1, Linda J S Allen2, Vrushali A Bokil3
1IGEPP, Agrocampus Ouest, INRA, Université de Rennes 1, Université Bretagne-Loire, Rennes, France.
Abstract:
If pathogen species, strains, or clones do not interact, intuition suggests the proportion of coinfected hosts should be the product of the individual prevalences. Independence consequently underpins the wide range of methods for detecting pathogen interactions from cross-sectional survey data. However, the very simplest of epidemiological models challenge the underlying assumption of statistical independence. Even if pathogens do not interact, death of coinfected hosts causes net prevalences of individual pathogens to decrease simultaneously. The induced positive correlation between prevalences means the proportion of coinfected hosts is expected to be higher than multiplication would suggest. By modelling the dynamics of multiple noninteracting pathogens causing chronic infections, we develop a pair of novel tests of interaction that properly account for nonindependence between pathogens causing lifelong infection. Our tests allow us to reinterpret data from previous studies including pathogens of humans, plants, and animals. Our work demonstrates how methods to identify interactions between pathogens can be updated using simple epidemic models.
Insights
Even when pathogens do not interact, host deaths can create a false positive correlation. New epidemiological models and tests reveal true pathogen interactions, improving disease analysis in humans, plants, and animals.
Area of Science:
- Epidemiology
- Disease Ecology
- Mathematical Biology
Background:
- Statistical independence is commonly assumed when analyzing pathogen interactions using cross-sectional data.
- This assumption is challenged by basic epidemiological models, particularly concerning coinfection dynamics.
Purpose of the Study:
- To develop novel statistical tests for detecting pathogen interactions that account for non-independence.
- To re-evaluate existing studies on pathogen interactions using updated methodologies.
Main Methods:
- Modeling the dynamics of multiple non-interacting pathogens causing chronic infections.
- Developing a pair of novel tests to identify true pathogen interactions by correcting for induced correlations.
Main Results:
- Host mortality in coinfected individuals can create a positive correlation between pathogen prevalences, even without direct interaction.
- The developed tests correctly identify interactions by properly accounting for this non-independence.
Conclusions:
- Simple epidemiological models reveal that statistical independence is not always a valid assumption in coinfection studies.
- The novel tests offer a more accurate approach to identifying pathogen interactions across various species, including humans, plants, and animals.
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