Ecosystem dynamics, biological diversity and emerging infectious diseases

Abstract

In this article, we summarize the major scientific developments of the last decade on the transmission of infectious agents in multi-host systems. Almost sixty percent of the pathogens that have emerged in humans during the last 30-40 years are of animal origin and about sixty percent of them show an important variety of host species besides humans (3 or more possible host species). In this review, we focus on zoonotic infections with vector-borne transmission and dissect the contrasting effects that a multiplicity of host reservoirs and vectors can have on their disease dynamics. We discuss the effects exerted by host and vector species richness and composition on pathogen prevalence (i.e., reduction, including the dilution effect, or amplification). We emphasize that, in multiple host systems and for vector-borne zoonotic pathogens, host reservoir species and vector species can exert contrasting effect locally. The outcome on disease dynamics (reduced pathogen prevalence in vectors when the host reservoir species is rich and increased pathogen prevalence when the vector species richness increases) may be highly heterogeneous in both space and time. We then ask briefly how a shift towards a more systemic perspective in the study of emerging infectious diseases, which are driven by a multiplicity of hosts, may stimulate further research developments. Finally, we propose some research avenues that take better into account the multi-host species reality in the transmission of the most important emerging infectious diseases, and, particularly, suggest, as a possible orientation, the careful assessment of the life-history characteristics of hosts and vectors in a community ecology-based perspective.

Characterising African tick communities at a wild–domestic interface using repeated sampling protocols and models

“…Our results are also compatible with the "dilution effect" hypothesis (Schmidt and Ostfeld, 2001) which states that a highly diversified host system, including hosts on which tick survival and reproductive success are highly variable, could decrease the density of tick populations as compared to a less diversified host system only composed of hosts on which tick survival and reproductive success are homogeneously high (Keesing et al, 2006, Roche andGuegan, 2011). Indeed, host diversity as quantified using the Shannon index is higher in the protected and mixed compartments than in the communal compartment (Fig.…”

Pangloss revisited: a critique of the dilution effect and the biodiversity-buffers-disease paradigm

“…gov/ncidod/dvbid/westnile/), in contrast to the much more limited range of competent species and smaller sporadic outbreaks in southern Europe (Murgue et al 2001). A new multi-host/multi-vector model indicates that increased richness of vector species, and therefore increased vector abundance, may compensate for any wasted contacts between vectors and poorly competent vertebrate hosts, and may even result in amplification rather than dilution (Roche and Guégan, 2011) (Fig. 4).…”

“…These authors point out that even within a single vector species, mosquito abundance will increase with blood-meal host abundance, whether the latter is competent or not, just as in the tick-borne disease systems (above). Indeed, "local richness and composition in host reservoirs and vectors may lead to different combinatorial effects of disease transmission", whatever the relative competence levels of vertebrate and vector species (Roche and Guégan, 2011). Amongst many other disease systems that rely on multiple vector species, viruses that cause dengue and chikungunya are each transmitted differentially by 2 species of Aedes mosquitoes with different host relationships in each part of their increasingly extensive ranges.…”

“…In natural conditions, these two antagonistic effects can lead to contrasting epidemiological situations depending on the characteristics of the local ecosystems and their biological diversity. Reproduced from Roche and Guégan (2011), with permission. the longer-established A. aegypti, may be contributing to the emerging epidemics of dengue there (Marina et al 2011).…”

“…Furthermore, WNV offers a good example of transmission potential being affected by community composition, rather than biodiversity per se; the identity of each suite of species is evidently significant. An important theoretical advance is the incorporation of the impact of vector diversity on the outcome, dilution or amplification, of WNV transmission (Roche and Guégan, 2011). The high diversity of mosquito species in the New World (Turell et al 2005), together with nonrandom avian host selection (above), contributes to transmission cycles and the spectacular epidemic of the early 21st century (CDC, 2007, http://www.cdc.…”