Heterogeneous host susceptibility enhances prevalence of mixed-genotype micro-parasite infections

Area of Science:

• * Ecology and Evolutionary Biology
• * Infectious Disease Epidemiology
• * Virology

Background:

• * Standard micro-parasite infection models often fail to predict observed shallow dose-response curves and higher-than-expected prevalence of mixed-genotype infections.
• * Existing models assume independent action of infectious units and homogeneous host susceptibility, which do not fully capture real-world infection dynamics.
• * A gap exists in probabilistic models explaining the simultaneous occurrence of shallow dose response and increased mixed-genotype infection prevalence.

Purpose of the Study:

• * To identify a probabilistic model that accurately explains both shallow dose response and high prevalence of mixed-genotype infections.
• * To investigate the roles of dependent versus independent action of infectious units and homogeneous versus heterogeneous host susceptibility.
• * To elucidate the impact of host susceptibility heterogeneity on mixed-genotype infection prevalence.

Main Methods:

• * Model selection was employed, comparing four alternative probabilistic models of micro-parasite infection.
• * Experimental data were generated by challenging Spodoptera exigua larvae with two genotypes of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV).
• * Infection dose-response and mixed-genotype prevalence were analyzed using the selected models.

Main Results:

• * An independent action model incorporating host susceptibility heterogeneity successfully explained both the shallow dose response and the high prevalence of mixed-genotype infections.
• * Theoretical analysis confirmed a strong link between host susceptibility variation and increased mixed-genotype infection prevalence.
• * No evidence supported dependent action of infectious units; virions appeared to act independently.

Conclusions:

• * Heterogeneity in host susceptibility is a critical factor driving both dose-response patterns and the prevalence of mixed-genotype infections.
• * This study demonstrates, for the first time, the specific influence of host susceptibility heterogeneity on mixed-genotype infection dynamics.
• * The findings underscore the importance of considering host heterogeneity in micro-parasite transmission models and have broad implications for infectious disease management.