Evolution of virulence when transmission occurs before disease
Erik E Osnas1, Andrew P Dobson
1Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA. erik.osnas@gmail.com
Biology Letters
|February 12, 2010
Summary
Pathogen evolution of virulence depends on the timing of transmission and disease. Virulence may increase or decrease after a pathogen emerges in a new host, challenging existing evolutionary models.
Area of Science:
- Evolutionary biology
- Epidemiology
- Pathogen dynamics
Background:
- Current models of virulence evolution often assume constant transmission and virulence during infection.
- Many pathogens, including viruses (HIV, influenza), bacteria (TB), and prions (BSE, CWD), exhibit delayed mortality post-infection, with transmission occurring earlier.
Purpose of the Study:
- To develop a mathematical model exploring virulence evolution with distinct infected host classes.
- To investigate how the evolutionarily stable strategy (ESS) for virulence is influenced by transmission rates, virulence levels, transition rates between classes, and recovery rates.
Main Methods:
- Construction of a mathematical model with two distinct infected host classes.
- Analysis of the model to determine the ESS for virulence based on varying parameters such as transmission rates, virulence, transition, and recovery rates.
Main Results:
- ESS virulence decreases when pathology is expressed early or transmission occurs late in infection.
- When virulence is similar across classes and recovery occurs, ESS virulence increases with higher transition rates.
- In scenarios with low early virulence and rapid recovery, ESS virulence shows a complex pattern, initially increasing then decreasing with transition rate.
Conclusions:
- Pathogen virulence evolution is highly sensitive to the temporal dynamics of transmission and pathology.
- Pathogens may evolve to increase or decrease virulence following introduction into a new host population.
- The timing of disease symptoms and infectiousness significantly shapes the evolutionary trajectory of pathogen virulence.
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