Dilution effects in disease ecology

For decades, people have reduced the transmission of pathogens by adding low-quality hosts to managed environments like agricultural fields. More recently, there has been interest in whether similar 'dilution effects' occur in natural disease systems, and whether these effects are eroded as diversity declines. For some pathogens of plants, humans and other animals, the highest-quality hosts persist when diversity is lost, so that high-quality hosts dominate low-diversity communities, resulting in greater pathogen transmission. Meta-analyses reveal that these natural dilution effects are common. However, studying them remains challenging due to limitations on the ability of researchers to manipulate many disease systems experimentally, difficulties of acquiring data on host quality and confusion about what should and should not be considered a dilution effect. Because dilution effects are widely used in managed disease systems and have been documented in a variety of natural disease systems, their existence should not be considered controversial. Important questions remain about how frequently they occur and under what conditions to expect them. There is also ongoing confusion about their relationships to both pathogen spillover and general biogeographical correlations between diversity and disease, which has resulted in an inconsistent and confusing literature. Progress will require rigorous and creative research.

Automated summary

The dilution effect is a common phenomenon in reducing pathogen transmission in both managed and natural disease systems. However, challenges remain in studying the frequency and conditions of occurrence, as well as the relationship between dilution effects and pathogen spillover. Further research is needed to clarify these aspects and address the inconsistencies in the existing literature.