Disease invasion: Impacts on biodiversity and human health

Institute of Zoology, Zoological Society of London, , Regent's Park, London NW1 4RY, UK.
Philosophical Transactions of The Royal Society B Biological Sciences (Impact Factor: 7.06). 10/2012; 367(1604):2804-6. DOI: 10.1098/rstb.2012.0331
Source: PubMed


An introduction to the theme issue that includes papers that identify how, where and why infectious diseases in wildlife emerge, while also addressing their possible conservation impacts.

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    • "Th e application of the EMS framework and determination of variables associated with metacommunity structure is new to host – parasite systems and is particularly important for understanding relationships between hosts, which may be reservoirs for emerging diseases, and their parasites, which may be vectors that transmit disease to humans or agriculturally important domestic animals (Daszak et al. 2000, Cunningham et al. 2012). Only host traits associated with the environment were signifi cantly associated with variation in species composition, indicating that responses to the same type of environmental variation can be associated with multiple types of metacommunity structure. "
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    ABSTRACT: Identification of mechanisms that shape parasite community and metacommunity structures have important implications to host health, disease transmission, and the understanding of community assembly in general. Using a long-term dataset on parasites from desert rodents, we examined the relative contributions of host traits that represent important aspects of parasite environment, transmission probability between host species, and host phylogeny to the structure of a parasite metacommunity as well as for taxonomically restricted parasite metacommunities (coccidians, ectoparasites and helminths). This was done using a combination of metacommunity analysis and variance partitioning based on canonical correspondence analysis. Coccidian and ectoparasite metacommunities did not exhibit coherent structure. In contrast, helminths and the full parasite metacommunity had Clementsian and quasi-Clementsian structure, respectively, indicating that parasite species distributions for these metacommunities were compartmentalized along a dominant gradient. Variance decomposition indicated that characteristics associated with the host environment consistently explained more variation than did host traits associated with transmission opportunities or host phylogeny, indicating that the host environment is primary in shaping parasite species distributions among host species. Moreover, the importance of different types of host traits in structuring parasite metacommunities was consistent among taxonomic groups (i.e. full metacommunity, coccidians, and helminths) despite manifest differences in emergent structures (i.e. Clementsian, quasi-Clementsian, and random) that arose in response to variation in host environment.
    Full-text · Article · Feb 2014 · Oikos
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    ABSTRACT: Hosts species for multi-host pathogens show considerable variation in the species' reservoir competence, which is usually used to measure species' potential to maintain and transmit these pathogens. Although accumulating research has proposed a trade-off between life-history strategies and immune defences, only a few studies extended this to host species' reservoir competence. Using a phylogenetic comparative approach, we studied the relationships between some species' life-history traits and reservoir competence in three emerging infectious vector-borne disease systems, namely Lyme disease, West Nile Encephalitis (WNE) and Eastern Equine Encephalitis (EEE). The results showed that interspecific variation in reservoir competence could be partly explained by the species' life histories. Species with larger body mass (for hosts of Lyme disease and WNE) or smaller clutch size (for hosts of EEE) had a higher reservoir competence. Given that both larger body mass and smaller clutch size were linked to higher extinction risk of local populations, our study suggests that with decreasing biodiversity, species with a higher reservoir competence are more likely to remain in the community, and thereby increase the risk of transmitting these pathogens, which might be a possible mechanism underlying the dilution effect.
    Full-text · Article · Sep 2013 · PLoS ONE
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    ABSTRACT: Many pathogens infect a wide range of host species. However, variation in the outcome of infection often exists amongst hosts and is shaped by intrinsic host traits. For example, contact with pathogens may trigger changes in hosts directed toward preventing, fighting, or tolerating infection. Host responses to infection are dynamic; they change over time and vary depending on health, condition and within the context of the environment.Immunological defences are an important class of responses that mediate host–pathogen dynamics. Here, we examined temporal patterns of immunity in two amphibian species, Pacific tree frogs (Pseudacris regilla) and Cascades frogs (Rana cascadae), exposed to control conditions or experimental inoculation with the emerging infectious fungal pathogen, Batrachochytrium dendrobatidis (Bd). For each species, we compared bacterial killing ability of blood and differential white blood cell counts at four different time-points after pathogen inoculation. We also quantified infection load over time and monitored survival.We detected qualitative and quantitative differences in species responses to Bd. Pseudacris regilla exhibited an increase in infection load over time and 16% of Bd-exposed animals died during the experiment. Tree frogs lacked robust treatment differences in immune responses, but Bd-exposed P. regilla tended to display weaker bacterial killing responses than unexposed control animals. Neutrophil counts did not vary consistently with treatment and lymphocytes tended to be less abundant in Bd-exposed animals at the later sampling time-points.In contrast, Bd-exposed R. cascadae exhibited a decrease in infection load over time and no mortality occurred in the Bd treatment. Bd-exposed Cascades frogs showed stronger bacterial killing responses and an elevated number of neutrophils in blood when compared with control animals, and both responses were upregulated within 48 h of pathogen exposure. Lymphocyte counts did not vary significantly with treatment.Although only statistically significant in Cascades frogs, neutrophil:lymphocyte ratios showed a trend of being elevated in Bd-exposed animals of both species and are indicative of pathogen-induced physiological stress.Our results suggest that variation in systemic immunological responses of two syntopic amphibian species is associated with and may contribute to differential patterns of survival and infection load during exposure to the chytrid fungus. Species variation in immunological responses as soon as 48 h after pathogen exposure suggests that initial host–pathogen interactions may set the stage for subsequent infection and disease progression. Variation in host responses can drive disease dynamics and comparative studies of host responses to pathogens are critical for making predictions about pathogen emergence, spread and persistence.
    Full-text · Article · Nov 2013 · Functional Ecology
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