Immunity-driven evolution of virulence and diversity in respiratory diseases

Area of Science:

• Evolutionary biology
• Pathogen dynamics
• Epidemiology

Background:

• Traditional virulence evolution theory posits a positive link between infectivity and harmfulness.
• Respiratory diseases, however, often show a negative correlation: lower respiratory tract infections are less infectious but more harmful.

Purpose of the Study:

• To explore the evolutionary consequences of virulence in respiratory diseases using a mathematical model.
• To investigate the role of cross-immunity and host population density in pathogen diversification.

Main Methods:

• A simple mathematical model was developed to simulate pathogen evolution.
• The model incorporates cross-immunity that decreases with pathogen distance in the respiratory tract.
• Docking rates were modeled based on cell surface compatibility and pathogen surface similarity.

Main Results:

• Virulent strains in lower airways tend to evolve towards milder, more transmissible variants.
• Limited cross-immunity increases pathogen diversification, especially with higher host population density.
• Pathogen diversity is predicted to be highest in the upper respiratory tract.

Conclusions:

• Emerging respiratory diseases may initially be virulent and evolve towards milder forms.
• The model provides insights into the diversification differences between various common cold viruses like rhinoviruses and coronaviruses.