Increased Host Species Diversity and Decreased Prevalence of Sin Nombre Virus

Portland State University, Portland, Oregon 97207-0751, USA.
Emerging Infectious Diseases (Impact Factor: 6.75). 08/2009; 15(7):1012-8. DOI: 10.3201/eid1507.081083
Source: PubMed


Emerging outbreaks of zoonotic diseases are affecting humans at an alarming rate. Until the ecological factors associated with zoonoses are better understood, disease emergence will continue. For Lyme disease, disease suppression has been demonstrated by a dilution effect, whereby increasing species diversity decreases disease prevalence in host populations. To test the dilution effect in another disease, we examined 17 ecological variables associated with prevalence of the directly transmitted Sin Nombre virus (genus Hantavirus, etiologic agent of hantavirus pulmonary syndrome) in its wildlife host, the deer mouse (Peromyscus maniculatus). Only species diversity was statistically linked to infection prevalence: as species diversity decreased, infection prevalence increased. The increase was moderate, but prevalence increased exponentially at low levels of diversity, a phenomenon described as zoonotic release. The results suggest that species diversity affects disease emergence.

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Available from: Luis A. Ruedas, Jan 10, 2014
    • "The structure of host communities can also affect parasites. Increased host diversity can decrease parasitism through a " dilution effect " (Dizney & Ruedas, 2009; Hall et al., 2009; Johnson & Thieltges, 2010; Ostfeld & Keesing, 2000; Schmidt & Ostfeld, 2001; Venesky, Liu, Sauer, & Rohr, 2014; but see Randolph & Dobson, 2012), where an increase in the relative or absolute abundance of unsusceptible host species reduces the rates of parasite encounter and transmission in susceptible species. Of course, species composition of the host community is critical; a low-diversity host community lacking a susceptible ( " competent " ) host will have a lower parasitism rate than a species-rich host community that contains a competent host. "
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    ABSTRACT: Water mites (Arrenurus spp.) parasitize adult dragonflies. We collected dragonflies weekly at 11 waterbodies in Greenville Co. and Pickens Co., SC, USA, to: (1) compare parasitism prevalence across species, sites, and sampling periods; (2) test the hypothesis that prevalence correlates with host abundance; (3) test the hypothesis that prevalence is inversely related to host diversity (the “dilution effect”); and (4) test the hypothesis that prevalence and intensity vary with ecological conditions. Parasitism prevalence varied among well-sampled (N > 30) hosts; Perithemis tenera, Plathemis lydia, and Celithemis ornata had no mites, whereas prevalence exceeded 20% for Argia fumipennis, Celithemis elisa, and C. fasciata. Differences among species, however, varied across sites and through time, suggesting patchy or species-specific relationships not captured by our diffuse analysis at the generic level. Prevalence was positively correlated with species abundance and host site occupancy, as expected for generalist parasites. There was no evidence of a dilution effect: there were no significant negative relationships between prevalence and three measures of species richness (observed richness, extrapolated Sest, or CHAO2 estimated richness), considering all odonate species, parasitized species, or only species in the parasitized families Libellulidae or Coenagrionidae. Odonate communities in more pristine sites had higher mean prevalence (18.4 ± 6.0) and median intensity (4.5) than those in disturbed sites (13.1 ± 7.0; 3.0), but only intensities were marginally significantly different. Parasitism by Arrenurus spp. met the criteria for a dilution effect, but did not exhibit this effect as a diffuse community-level response.
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    • "A concurrent extension of this research has investigated the diversity of system components beyond the host community, including predators, competitors and coinfecting symbionts. Reductions in predator diversity have been correlated with increased prevalence of Sin Nombre hantavirus in deer mice (Peromyscus maniculatus) (Dizney & Ruedas 2009; Orrock et al. 2011) and higher infectious disease levels in coral reefs (Raymundo et al. 2009; see also Rohr et al. 2015). The experimental exclusion of large herbivores in East African savanna ecosystems led to a doubling in the density of their competitors, rodents and their associated fleas (McCauley et al. 2008; Keesing & Young 2014; Young et al. 2014; but see Borer et al. 2009). "
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    ABSTRACT: Global losses of biodiversity have galvanised efforts to understand how changes to communities affect ecological processes, including transmission of infectious pathogens. Here, we review recent research on diversity-disease relationships and identify future priorities. Growing evidence from experimental, observational and modelling studies indicates that biodiversity changes alter infection for a range of pathogens and through diverse mechanisms. Drawing upon lessons from the community ecology of free-living organisms, we illustrate how recent advances from biodiversity research generally can provide necessary theoretical foundations, inform experimental designs, and guide future research at the interface between infectious disease risk and changing ecological communities. Dilution effects are expected when ecological communities are nested and interactions between the pathogen and the most competent host group(s) persist or increase as biodiversity declines. To move beyond polarising debates about the generality of diversity effects and develop a predictive framework, we emphasise the need to identify how the effects of diversity vary with temporal and spatial scale, to explore how realistic patterns of community assembly affect transmission, and to use experimental studies to consider mechanisms beyond simple changes in host richness, including shifts in trophic structure, functional diversity and symbiont composition. © 2015 John Wiley & Sons Ltd/CNRS.
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    • "). For rodents, the impact of host community structure has been investigated for Lyme disease (Kilpatrick & Kramer 2006; Keesing et al. 2006, 2009), hantaviruses (Tersago et al. 2008; Clay et al. 2009a; Dizney & Ruedas 2009; Blasdell et al. 2011), anaplasmosis (a tick-borne disease for which the agent is the bacteria Anaplasma phagocytophilum) and bartonellosis (another arthropod-borne disease for which the agents are bacteria of the genus Bartonella) (Bai et al. 2009; Foley et al. 2009). For all these studies, the key concept was the " dilution effect " hypothesis (Schmidt & Ostfeld 2001). "
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