Abstract
Many emerging infections are RNA virus spillovers from animal reservoirs. Reservoir identification is necessary for predicting the geographic extent of infection risk, but rarely are taxonomic levels below the animal species considered as reservoir, and only key circumstances in nature and methodology allow intrinsic virus-host associations to be distinguished from simple geographic (co-)isolation. We sampled and genetically characterized in detail a contact zone of two subtaxa of the rodent Mastomys natalensis in Tanzania. We find two distinct arenaviruses, Gairo and Morogoro virus, each spatially confined to a single M. natalensis subtaxon, only co-occurring at the contact zone’s centre. Inter-subtaxon hybridization at this centre and a continuum of quality habitat for M. natalensis show that both viruses have the ecological opportunity to spread into the other substaxon’s range, but do not, strongly suggesting host-intrinsic barriers. Such barriers could explain why human cases of another M. natalensis-borne arenavirus, Lassa virus, are limited to West Africa.
Highlights
Most emerging RNA virus infections originate from wild animals [1]
Ongoing hybridization shows that individuals of the subtaxa are in direct physical contact, in principle allowing viral exchange, yet neither of the two arenaviruses -Gairo and Morogoro virus- were found to have crossed the zone
We previously found within the B-V matrilineage range that nuclear markers are further substructured in relation to an urban-rural contrast, and that the region varies in landscape features that likely translate into spatially varying M. natalensis densities [57]
Summary
Outbreaks of many such infections are geographically restricted, e.g. MERS coronavirus in the Middle East, Marburg filovirus in central and southern Africa, and Nipah henipavirus in south-east Asia This restriction is most likely due to dependence on particular host reservoir species (single or multiple) for persistence in nature–those hosts themselves having restricted distributions. Species with a wide geographic range are often (cryptically) genetically subdivided into subtaxa, yet it is rarely assessed whether a local intraspecific taxon may represent the reservoir instead of the entire species Such associations between intraspecific animal taxa and particular viral taxa could explain why the distribution of some viruses appears smaller than the range of the reservoir species, for example in the case of distinct hantaviruses of the widespread rodent species Peromyscus leucopus [4, 5], P. maniculatus [4, 6, 7] and Oligoryzomys flavescens [8], and the Simian Immunodeficiency viruses (SIV) and Simian Foamy viruses (SFV) of chimpanzees (Pan troglodytes) [9,10,11,12]. The association between virus and host taxa must be evaluated in areas where distinct host (sub)taxa carrying distinct viral taxa are in direct physical contact
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