Declining ecosystem health and the dilution effect.

Sci Rep. 2016 Aug 8;6:31314. doi: 10.1038/srep31314. Khalil H1, Ecke F1,2, Evander M3, Magnusson M1, Hörnfeldt B1. Author information 1 Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, Skogmarksgränd, SE-901 83 Umeå, Sweden. 2 Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Gerda Nilssons väg 5, SE-756 51 Uppsala Sweden. 3 Department of Clinical Microbiology, Virology, Umeå University, SE-901 85 Umeå, Sweden. Abstract The "dilution effect" implies that where species vary in susceptibility to infection by a pathogen, higher diversity often leads to lower infection prevalence in hosts. For directly transmitted pathogens, non-host species may "dilute" infection directly (1) and indirectly (2). Competitors and predators may (1) alter host behavior to reduce pathogen transmission or (2) reduce host density. In a well-studied system, we tested the dilution of the zoonotic Puumala hantavirus (PUUV) in bank voles (Myodes glareolus) by two competitors and a predator. Our study was based on long-term PUUV infection data (2003-2013) in northern Sweden. The field vole (Microtus agrestis) and the common shrew (Sorex araneus) are bank vole competitors and Tengmalm's owl (Aegolius funereus) is a main predator of bank voles. Infection probability in bank voles decreased when common shrew density increased, suggesting that common shrews reduced PUUV transmission. Field voles suppressed bank vole density in meadows and clear-cuts and indirectly diluted PUUV infection. Further, Tengmalm's owl decline in 1980-2013 may have contributed to higher PUUV infection rates in bank voles in 2003-2013 compared to 1979-1986. Our study provides further evidence for dilution effect and suggests that owls may have an important role in reducing disease risk. PMID: 27499001 PMCID: PMC4976314 DOI: 10.1038/srep31314 [Indexed for MEDLINE] Free PMC Article