More than three quarters of new, emerging or re-emerging human diseases are caused by pathogens from animals, according to the World Health Organization.
But a widely accepted theory of risk reduction for these pathogens one of the most important ideas in disease ecology is likely wrong, according to a new study co-authored by Stanford Woods Institute for the Environment Senior Fellow James Holland Jones and former Woods-affiliated ecologist Dan Salkeld.
The dilution effect theorizes that disease risk for humans decreases as the variety of species in an area increases. For example, it postulates that a tick has a higher chance of infecting a human with Lyme disease if the tick has previously had few animal host options beyond white-footed mice, which are carriers of Lyme disease-causing bacteria.
If many other animal hosts had been available to the tick, the tick's likelihood of being infected and spreading that infection to a human host would go down, according to the theory.
If true, the dilution effect would mean that conservation and public health agendas could be united in a common purpose: to protect biodiversity and guard against disease risk. "However, its importance to the field or the beauty of the idea do not guarantee that it is actually scientifically correct," said Jones, an associate professor of Anthropology.
In the first study to formally assess the dilution effect, Jones, Salkeld and California Department of Public Health researcher Kerry Padgett tested the hypothesis through a meta-analysis of studies that evaluate links between host biodiversity and disease risk for disease agents that infect humans.
The analysis, published in the journal Ecology Letters, allowed the researchers to pool estimates from studies and test for any bias against publishing studies with "negative results" that contradict the dilution effect.
The analysis found "very weak support, at best" for
|Contact: James Holland Jones|