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1.  The role of viral evolution in rabies host shifts and emergence 
Highlights
•Rabies virus has a broad host range, but transmission cycles are species-specific.•Significant barriers limit viral establishment in new host species, but are poorly characterised.•Viral preadaptation may facilitate emergence, but does not rule out host adaptation.•Several lines of evidence point to adaptation of Rabies virus to specific hosts.
Despite its ability to infect all mammals, Rabies virus persists in numerous species-specific cycles that rarely sustain transmission in alternative species. The determinants of these species-associations and the adaptive significance of genetic divergence between host-associated viruses are poorly understood. One explanation is that epidemiological separation between reservoirs causes neutral genetic differentiation. Indeed, recent studies attributed host shifts to ecological factors and selection of ‘preadapted’ viral variants from the existing viral community. However, phenotypic differences between isolates and broad scale comparative and molecular evolutionary analyses indicate multiple barriers that Rabies virus must overcome through adaptation. This review assesses various lines of evidence and proposes a synthetic hypothesis for the respective roles of ecology and evolution in Rabies virus host shifts.
doi:10.1016/j.coviro.2014.07.004
PMCID: PMC4199325  PMID: 25064563
3.  Simultaneously reconstructing viral cross-species transmission history and identifying the underlying constraints 
The factors that determine the origin and fate of cross-species transmission events remain unclear for the majority of human pathogens, despite being central for the development of predictive models and assessing the efficacy of prevention strategies. Here, we describe a flexible Bayesian statistical framework to reconstruct virus transmission between different host species based on viral gene sequences, while simultaneously testing and estimating the contribution of several potential predictors of cross-species transmission. Specifically, we use a generalized linear model extension of phylogenetic diffusion to perform Bayesian model averaging over candidate predictors. By further extending this model with branch partitioning, we allow for distinct host transition processes on external and internal branches, thus discriminating between recent cross-species transmissions, many of which are likely to result in dead-end infections, and host shifts that reflect successful onwards transmission in the new host species. Our approach corroborates genetic distance between hosts as a key determinant of both host shifts and cross-species transmissions of rabies virus in North American bats. Furthermore, our results indicate that geographical range overlap is a modest predictor for cross-species transmission, but not for host shifts. Although our evolutionary framework focused on the multi-host reservoir dynamics of bat rabies virus, it is applicable to other pathogens and to other discrete state transition processes.
doi:10.1098/rstb.2012.0196
PMCID: PMC3678322  PMID: 23382420
Bayesian diffusion models; branch partitioning; cross-species transmission; rabies virus
4.  Ecological and anthropogenic drivers of rabies exposure in vampire bats: implications for transmission and control 
Despite extensive culling of common vampire bats in Latin America, lethal human rabies outbreaks transmitted by this species are increasingly recognized, and livestock rabies occurs with striking frequency. To identify the individual and population-level factors driving rabies virus (RV) transmission in vampire bats, we conducted a longitudinal capture–recapture study in 20 vampire bat colonies spanning four regions of Peru. Serology demonstrated the circulation of RV in vampire bats from all regions in all years. Seroprevalence ranged from 3 to 28 per cent and was highest in juvenile and sub-adult bats. RV exposure was independent of bat colony size, consistent with an absence of population density thresholds for viral invasion and extinction. Culling campaigns implemented during our study failed to reduce seroprevalence and were perhaps counterproductive for disease control owing to the targeted removal of adults, but potentially greater importance of juvenile and sub-adult bats for transmission. These findings provide new insights into the mechanisms of RV maintenance in vampire bats and highlight the need for ecologically informed approaches to rabies prevention in Latin America.
doi:10.1098/rspb.2012.0538
PMCID: PMC3396893  PMID: 22696521
culling; disease thresholds; longitudinal; Lyssavirus; chiroptera; Desmodus
5.  Enzootic and Epizootic Rabies Associated with Vampire Bats, Peru 
Emerging Infectious Diseases  2013;19(9):1463-1469.
During the past decade, incidence of human infection with rabies virus (RABV) spread by the common vampire bat (Desmodus rotundus) increased considerably in South America, especially in remote areas of the Amazon rainforest, where these bats commonly feed on humans. To better understand the epizootiology of rabies associated with vampire bats, we used complete sequences of the nucleoprotein gene to infer phylogenetic relationships among 157 RABV isolates collected from humans, domestic animals, and wildlife, including bats, in Peru during 2002–2007. This analysis revealed distinct geographic structuring that indicates that RABVs spread gradually and involve different vampire bat subpopulations with different transmission cycles. Three putative new RABV lineages were found in 3 non–vampire bat species that may represent new virus reservoirs. Detection of novel RABV variants and accurate identification of reservoir hosts are critically important for the prevention and control of potential virus transmission, especially to humans.
doi:10.3201/eid1909.130083
PMCID: PMC3810916
rabies; molecular epidemiology; bats; Peru; viruses; zoonoses; vampire bats
6.  Simultaneously reconstructing viral cross-species transmission history and identifying the underlying constraints 
The factors that determine the origin and fate of cross-species transmission events remain unclear for the majority of human pathogens despite being central for the development of predictive models and assessing the efficacy of prevention strategies. Here, we describe a flexible Bayesian statistical framework to reconstruct virus transmission between different host species based on viral gene sequences while simultaneously testing and estimating the contribution of several potential predictors of cross-species transmission. Specifically, we employ a generalized linear model extension of phylogenetic diffusion to perform Bayesian model averaging over candidate predictors. By further extending this model with branch partitioning, we allow for distinct host transition processes on external and internal branches, thus discriminating between recent cross-species transmissions, many of which are likely to result in dead-end infections, and host shifts that reflect successful onwards transmission in the new host species. Our approach corroborates genetic distance between hosts as a key determinant of both host shifts and cross-species transmissions of rabies virus in North American bats. Furthermore, our results indicate that geographical range overlap is a modest predictor for cross-species transmission but not for host shifts. Although our evolutionary framework focused on the multi-host reservoir dynamics of bat rabies virus, it is applicable to other pathogens and to other discrete state transition processes.
doi:10.1098/rstb.2012.0196
PMCID: PMC3678322  PMID: 23382420
7.  Molecular Inferences Suggest Multiple Host Shifts of Rabies Viruses from Bats to Mesocarnivores in Arizona during 2001–2009 
PLoS Pathogens  2012;8(6):e1002786.
In nature, rabies virus (RABV; genus Lyssavirus, family Rhabdoviridae) represents an assemblage of phylogenetic lineages, associated with specific mammalian host species. Although it is generally accepted that RABV evolved originally in bats and further shifted to carnivores, mechanisms of such host shifts are poorly understood, and examples are rarely present in surveillance data. Outbreaks in carnivores caused by a RABV variant, associated with big brown bats, occurred repeatedly during 2001–2009 in the Flagstaff area of Arizona. After each outbreak, extensive control campaigns were undertaken, with no reports of further rabies cases in carnivores for the next several years. However, questions remained whether all outbreaks were caused by a single introduction and further perpetuation of bat RABV in carnivore populations, or each outbreak was caused by an independent introduction of a bat virus. Another question of concern was related to adaptive changes in the RABV genome associated with host shifts. To address these questions, we sequenced and analyzed 66 complete and 20 nearly complete RABV genomes, including those from the Flagstaff area and other similar outbreaks in carnivores, caused by bat RABVs, and representatives of the major RABV lineages circulating in North America and worldwide. Phylogenetic analysis demonstrated that each Flagstaff outbreak was caused by an independent introduction of bat RABV into populations of carnivores. Positive selection analysis confirmed the absence of post-shift changes in RABV genes. In contrast, convergent evolution analysis demonstrated several amino acids in the N, P, G and L proteins, which might be significant for pre-adaptation of bat viruses to cause effective infection in carnivores. The substitution S/T242 in the viral glycoprotein is of particular merit, as a similar substitution was suggested for pathogenicity of Nishigahara RABV strain. Roles of the amino acid changes, detected in our study, require additional investigations, using reverse genetics and other approaches.
Author Summary
Host shifts of the rabies virus (RABV) from bats to carnivores are important for our understanding of viral evolution and emergence, and have significant public health implications, particularly for the areas where “terrestrial” rabies has been eliminated. In this study we addressed several rabies outbreaks in carnivores that occurred in the Flagstaff area of Arizona during 2001–2009, and caused by the RABV variant associated with big brown bats (Eptesicus fuscus). Based on phylogenetic analysis we demonstrated that each outbreak resulted from a separate introduction of bat RABV into populations of carnivores. No post-shift changes in viral genomes were detected under the positive selection analysis. Trying to answer the question why certain bat RABV variants are capable for host shifts to carnivores and other variants are not, we developed a convergent evolution analysis, and implemented it for multiple RABV lineages circulating worldwide. This analysis identified several amino acids in RABV proteins which may facilitate host shifts from bats to carnivores. Precise roles of these amino acids require additional investigations, using reverse genetics and animal experimentation. In general, our approach and the results obtained can be used for prediction of host shifts and emergence of other zoonotic pathogens.
doi:10.1371/journal.ppat.1002786
PMCID: PMC3380930  PMID: 22737076
8.  Rates of Viral Evolution Are Linked to Host Geography in Bat Rabies 
PLoS Pathogens  2012;8(5):e1002720.
Rates of evolution span orders of magnitude among RNA viruses with important implications for viral transmission and emergence. Although the tempo of viral evolution is often ascribed to viral features such as mutation rates and transmission mode, these factors alone cannot explain variation among closely related viruses, where host biology might operate more strongly on viral evolution. Here, we analyzed sequence data from hundreds of rabies viruses collected from bats throughout the Americas to describe dramatic variation in the speed of rabies virus evolution when circulating in ecologically distinct reservoir species. Integration of ecological and genetic data through a comparative Bayesian analysis revealed that viral evolutionary rates were labile following historical jumps between bat species and nearly four times faster in tropical and subtropical bats compared to temperate species. The association between geography and viral evolution could not be explained by host metabolism, phylogeny or variable selection pressures, and instead appeared to be a consequence of reduced seasonality in bat activity and virus transmission associated with climate. Our results demonstrate a key role for host ecology in shaping the tempo of evolution in multi-host viruses and highlight the power of comparative phylogenetic methods to identify the host and environmental features that influence transmission dynamics.
Author Summary
Rapid evolution of RNA viruses is intimately linked to their success in overcoming the defenses of their hosts. Several studies have shown that rates of viral evolution can vary dramatically among distantly related viral families. Variability in the speed of evolution among closely related viruses has received less attention, but could be an important determinant of the geographic or host species origins of viral emergence if certain species or regions promote especially rapid evolution. Here, using a dataset of rabies virus sequences collected from bat species throughout the Americas, we test the role of inter-specific differences in reservoir host biology on the tempo of viral evolution. We show the annual rate of molecular evolution to be a malleable trait of viruses that is accelerated in subtropical and tropical bats compared to temperate species. The association between geography and the speed of evolution appears to reflect differences in the seasonality of rabies virus transmission in different climatic zones. Our results illustrate that the viral mechanisms that are commonly invoked to explain heterogeneous rates of evolution among viral families may be insufficient to explain evolution in multi-host viruses and indicate a role for host biology in shaping the speed of viral evolution.
doi:10.1371/journal.ppat.1002720
PMCID: PMC3355098  PMID: 22615575
9.  Differential sources of host species heterogeneity influence the transmission and control of multihost parasites 
Ecology Letters  2013;16(8):975-984.
Controlling parasites that infect multiple host species often requires targeting single species that dominate transmission. Yet, it is rarely recognised that such ‘key hosts’ can arise through disparate mechanisms, potentially requiring different approaches for control. We identify three distinct, but not mutually exclusive, processes that underlie host species heterogeneity: infection prevalence, population abundance and infectiousness. We construct a theoretical framework to isolate the role of each process from ecological data and to explore the outcome of different control approaches. Applying this framework to data on 11 gastrointestinal parasites in small mammal communities across the eastern United States reveals variation not only in the magnitude of transmission asymmetries among host species but also in the processes driving heterogeneity. These differences influence the efficiency by which different control strategies reduce transmission. Identifying and tailoring interventions to a specific type of key host may therefore enable more effective management of multihost parasites.
doi:10.1111/ele.12122
PMCID: PMC4282463  PMID: 23714379
Coccidia; community epidemiology; helminth; management; parasitism; species heterogeneity; super-shedder; susceptibility

Results 1-9 (9)