Similar Borrelia burgdorferi infection prevalence and genotype diversity in two highly contrasting biodiversity settings

Background/Question/Methods

Biodiversity’s role in buffering against disease is proposed as an ecosystem service applicable to many infectious diseases.  The dilution effect hypothesizes that increased host diversity reduces pathogen transmission by reducing direct or indirect contact between hosts.  Biodiversity may also influence disease risk if pathogens can adapt, or specialize, to different host species.  Lyme disease, caused by the bacterium Borrelia burgdorferi and transmitted by Ixodes scapularis ticks, is a common zoonotic disease in the northeastern United States.   The dilution effect predicts that Peromyscus leucopus-dominated, species-poor host communities represent the highest risk to humans.  Under the host specialization hypothesis, reduced biodiversity may increase disease risk because some strains can persist longer in P. leucopus and are more likely to be transmitted to larvae.  In a comparative study of a host species-poor and a host species-rich community we evaluated support for two specific predictions of the dilution effect and host specialization hypotheses: 1) B. burgdorferi nymphal infection prevalence and density of infected nymphs is higher in a species-poor community and 2) B. burgdorferi genotype diversity is lower in the species-rich community.  We collected mammal-derived larvae and questing nymphs in 2010 and 2011 to measure infection prevalence and estimate genotype diversity and richness. 

Results/Conclusions

We found no significant difference in nymphal infection prevalence and density of infected nymphs between the two communities, providing no evidence for the dilution effect.  We also found high levels of genetic variation in the species-poor community, refuting the host specialization theory.   Additionally, estimates of genotype diversity and richness of disseminating B. burgdorferi strains found primarily in P. leucopus were not significantly different between species-poor and species-rich communities.  We find little evidence for either the dilution effect or host specialization theories, suggesting a complicated relationship between biodiversity and disease prevalence.