Implications of hepatitis C virus subtype 1a migration patterns for virus genetic sequencing policies in Italy

Phylodynamic evolution of HIV-1 A6 sub-subtype epidemics in Poland

The human immunodeficiency virus type 1 (HIV-1) A6 sub-subtype is highly prevalent in Eastern Europe. Over the past decade, the dissemination of the A6 lineage has been expanding in Poland. The recent Russian invasion of Ukraine may further escalate the spread of this sub-subtype. While evolutionary studies using viral sequences have been instrumental in identifying the HIV epidemic patterns, the origins, and dynamics of the A6 sub-subtype in Poland remain to be explored. We analyzed 1185 HIV-1 A6 pol sequences from Poland, along with 8318 publicly available sequences from other countries. For analyses, phylogenetic tree construction, population dynamics inference, Bayesian analysis, and discrete phylogeographic modeling were employed. Of the introduction events to Poland, 69.94% originated from Ukraine, followed by 29.17% from Russia. Most A6 sequences in Poland (53.16%) formed four large clades, with their introductions spanning 1993-2008. Central and Southern Polish regions significantly influenced migration events. Transmissions among men who have sex with men (MSM) emerged as the dominant risk group for virus circulation, representing 72.92% of migration events. Sequences from migrants were found primarily outside the large clades. Past migration from Ukraine has fueled the spread of the A6 sub-subtype and the current influx of war-displaced people maintains the growing national epidemic.

Phylodynamics of HIV in the Mexico City Metropolitan Region

Evolutionary analyses of viral sequences can provide insights into transmission dynamics, which in turn can optimize prevention interventions. Here, we characterized the dynamics of HIV transmission within the Mexico City metropolitan area. HIV pol sequences from persons recently diagnosed at the largest HIV clinic in Mexico City (between 2016 and 2021) were annotated with demographic/geographic metadata. A multistep phylogenetic approach was applied to identify putative transmission clades. A data set of publicly available sequences was used to assess international introductions. Clades were analyzed with a discrete phylogeographic model to evaluate the timing and intensity of HIV introductions and transmission dynamics among municipalities in the region. A total of 6,802 sequences across 96 municipalities (5,192 from Mexico City and 1,610 from the neighboring State of Mexico) were included (93.6% cisgender men, 5.0% cisgender women, and 1.3% transgender women); 3,971 of these sequences formed 1,206 clusters, involving 78 municipalities, including 89 clusters of ≥10 sequences. Discrete phylogeographic analysis revealed (i) 1,032 viral introductions into the region, over one-half of which were from the United States, and (ii) 354 migration events between municipalities with high support (adjusted Bayes factor of ≥3). The most frequent viral migrations occurred between northern municipalities within Mexico City, i.e., Cuauhtémoc to Iztapalapa (5.2% of events), Iztapalapa to Gustavo A. Madero (5.4%), and Gustavo A. Madero to Cuauhtémoc (6.5%). Our analysis illustrates the complexity of HIV transmission within the Mexico City metropolitan area but also identifies a spatially active transmission area involving a few municipalities in the north of the city, where targeted interventions could have a more pronounced effect on the entire regional epidemic. IMPORTANCE Phylogeographic investigation of the Mexico City HIV epidemic illustrates the complexity of HIV transmission in the region. An active transmission area involving a few municipalities in the north of the city, with transmission links throughout the region, is identified and could be a location where targeted interventions could have a more pronounced effect on the entire regional epidemic, compared with those dispersed in other manners.

Molecular Epidemiology and Baseline Resistance of Hepatitis C Virus to Direct Acting Antivirals in Croatia

Molecular epidemiology of hepatitis C virus (HCV) is exceptionally complex due to the highly diverse HCV genome. Genetic diversity, transmission dynamics, and epidemic history of the most common HCV genotypes were inferred by population sequencing of the HCV NS3, NS5A, and NS5B region followed by phylogenetic and phylodynamic analysis. The results of this research suggest high overall prevalence of baseline NS3 resistance associate substitutions (RAS) (33.0%), moderate prevalence of NS5A RAS (13.7%), and low prevalence of nucleoside inhibitor NS5B RAS (8.3%). Prevalence of RAS significantly differed according to HCV genotype, with the highest prevalence of baseline resistance to NS3 inhibitors and NS5A inhibitors observed in HCV subtype 1a (68.8%) and subtype 1b (21.3%), respectively. Phylogenetic tree reconstructions showed two distinct clades within the subtype 1a, clade I (62.4%) and clade II (37.6%). NS3 RAS were preferentially associated with clade I. Phylogenetic analysis demonstrated that 27 (9.0%) HCV sequences had a presumed epidemiological link with another sequence and classified into 13 transmission pairs or clusters which were predominantly comprised of subtype 3a viruses and commonly detected among intravenous drug users (IDU). Phylodynamic analyses highlighted an exponential increase in subtype 1a and 3a effective population size in the late 20th century, which is a period associated with an explosive increase in the number of IDU in Croatia.

Comparative Dynamics of Delta and Omicron SARS-CoV-2 Variants across and between California and Mexico

Evolutionary analysis using viral sequence data can elucidate the epidemiology of transmission. Using publicly available SARS-CoV-2 sequence and epidemiological data, we developed discrete phylogeographic models to interrogate the emergence and dispersal of the Delta and Omicron variants in 2021 between and across California and Mexico. External introductions of Delta and Omicron in the region peaked in early July (2021-07-10 [95% CI: 2021-04-20, 2021-11-01]) and mid-December (2021-12-15 [95% CI: 2021-11-14, 2022-01-09]), respectively, 3 months and 2 weeks after first detection. These repeated introductions coincided with domestic migration events with no evidence of a unique transmission hub. The spread of Omicron was most consistent with gravity centric patterns within Mexico. While cross-border events accounted for only 5.1% [95% CI: 4.3-6] of all Delta migration events, they accounted for 20.6% [95% CI: 12.4-29] of Omicron movements, paralleling the increase in international travel observed in late 2021. Our investigations of the Delta and Omicron epidemics in the California/Mexico region illustrate the complex interplay and the multiplicity of viral and structural factors that need to be considered to limit viral spread, even as vaccination is reducing disease burden. Understanding viral transmission patterns may help intra-governmental responses to viral epidemics.

Comparative Circulation Dynamics of the Five Main HIV Types in China

The HIV epidemic in China accounts for 3% of the global HIV incidence. We compared the patterns and determinants of interprovincial spread of the five most prevalent circulating types. HIV pol sequences sampled across China were used to identify relevant transmission networks of the five most relevant HIV-1 types (B and circulating recombinant forms [CRFs] CRF01_AE, CRF07_BC, CRF08_BC, and CRF55_01B) in China. From these, the dispersal history across provinces was inferred. A generalized linear model (GLM) was used to test the association between migration rates among provinces and several measures of human mobility. A total of 10,707 sequences were collected between 2004 and 2017 across 26 provinces, among which 1,962 are newly reported here. A mean of 18 (minimum and maximum, 1 and 54) independent transmission networks involving up to 17 provinces were identified. Discrete phylogeographic analysis largely recapitulates the documented spread of the HIV types, which in turn, mirrors within-China population migration flows to a large extent. In line with the different spatiotemporal spread dynamics, the identified drivers thereof were also heterogeneous but are consistent with a central role of human mobility. The comparative analysis of the dispersal dynamics of the five main HIV types circulating in China suggests a key role of large population centers and developed transportation infrastructures as hubs of HIV dispersal. This advocates for coordinated public health efforts in addition to local targeted interventions.IMPORTANCE While traditional epidemiological studies are of great interest in describing the dynamics of epidemics, they struggle to fully capture the geospatial dynamics and factors driving the dispersal of pathogens like HIV as they have difficulties capturing linkages between infections. To overcome this, we used a discrete phylogeographic approach coupled to a generalized linear model extension to characterize the dynamics and drivers of the across-province spread of the five main HIV types circulating in China. Our results indicate that large urbanized areas with dense populations and developed transportation infrastructures are facilitators of HIV dispersal throughout China and highlight the need to consider harmonized country-wide public policies to control local HIV epidemics.

Dynamics and Dispersal of Local HIV Epidemics Within San Diego and Across The San Diego-Tijuana Border

BACKGROUND

Evolutionary analyses of well-annotated HIV sequence data can provide insights into viral transmission patterns and associated factors. Here, we explored the transmission dynamics of the HIV-1 subtype B epidemic across the San Diego (US) - Tijuana (Mexico) border region to identify factors that could help guide public health policy.

METHODS

HIV pol sequences were collected from people with HIV in San Diego County and from Tijuana between 1996-2018. A multistep phylogenetic approach was used to characterize the dynamics of spread. The contribution of geospatial factors and HIV risk group to the local dynamics were evaluated.

RESULTS

Phylogeographic analyses of the 2,034 sequences revealed an important contribution of local transmission in sustaining the epidemic, as well as a complex viral migration network across the region. Geospatial viral dispersal between San Diego communities occurred predominantly among men-who-have-sex with-men with central San Diego being the main source (34.9%) and recipient (39.5%) of migration events. HIV migration was more frequent from San Diego county towards Tijuana than vice versa. Migrations were best explained by driving time between locations.

CONCLUSION

The US-Mexico border may not be a major barrier to the spread of HIV, which may stimulate coordinated transnational intervention approaches. Whereas a focus on central San Diego has the potential to avert most spread, the substantial viral migration independent of central San Diego shows that county-wide efforts will be more effective. Combined, this work shows that epidemiological information gleaned from pathogen genomes can uncover mechanisms that underlie sustained spread and, in turn, can be a building block of public health decision making.

Evolutionary dynamics and transmission patterns of Newcastle disease virus in China through Bayesian phylogeographical analysis

The Chinese poultry industry has experienced outbreaks of Newcastle disease (ND) dating back to the 1920s. However, the epidemic has exhibited a downtrend in recent years. In this study, both observational and genetic data [fusion (F) and haemagglutinin-neuraminidase genes (HN)] were analyzed, and phylogeographic analysis based on prevalent genotypes of Newcastle disease virus (NDV) was conducted for better understanding of the evolution and spatiotemporal dynamics of ND in China. In line with the observed trend of epidemic outbreaks, the effective population size of F and HN genes of circulating NDV is no longer growing since 2000, which is supported by 95% highest posterior diversity (HPD) intervals. Phylogeographic analysis indicated that the two eastern coastal provinces, Shandong and Jiangsu were the most relevant hubs for NDV migration, and the geographical regions with active NDV diffusion seemed to be constrained to southern and eastern China. The live poultry trade may play an important role in viral spread. Interestingly, no migration links from wild birds to poultry received Bayes factor support (BF > 3), while the migration links from poultry to wild birds accounted for 64% in all effective migrations. This may indicate that the sporadic cases of ND in wild bird likely spillover events from poultry. These findings contribute to predictive models of NDV transmission, and potentially help in the prevention of future outbreaks.

HCV Antibody Prevalence and Genotype Evolution in a Teaching Hospital, Calabria Region, Southern Italy Over A Decade (2008-2018)

Background:

Hepatitis C Virus (HCV) infection is associated with a high risk of developing liver diseases. Globally, HCV prevalence is changing due to improving health care procedures, population movement, and availability of new antiviral therapy. In Italy, data on the prevalence of HCV infection are insufficient, out-dated, and restricted to specific areas.

Objective:

Between 2008 and 2018, we investigated HCV antibody (Ab) seroprevalence and genotypes distribution among patients presenting for testing at our Teaching Hospital.

Methods:

The HCV Ab and genotyping assays were performed by routine diagnostic methods. Chi-square for linear trend was carried out by OpenEpi (v3.01).

Results:

Among 120,009 consecutive patients, 5877 subjects were HCV Ab positive (4.89%). During the observational period 2008-2018, prevalence decreased significantly (p<0.001) from 4.7% in 2008 to 3.6% in 2018. HCV1b was the most prevalent subtype (47.2%) followed by HCV2a/2c (20.2%), and HCV3 (9.7%), while HCV4 showed a rate of 6.1%. HCV infection was more frequent in males (55.4%) than in females (44.6%). Overall, most infected patients were born before 1949.

Conclusion:

Epidemiological analyses are important to understand the evolution of the HCV epidemics under the influence of several factors, such as risk behaviour and therapy with direct-acting antivirals.

Pretreatment HIV drug resistance spread within transmission clusters in Mexico City

BACKGROUND

Pretreatment HIV drug resistance (HIVDR) to NNRTIs has consistently increased in Mexico City during the last decade.

OBJECTIVES

To infer the HIV genetic transmission network in Mexico City to describe the dynamics of the local HIV epidemic and spread of HIVDR.

PATIENTS AND METHODS

HIV pol sequences were obtained by next-generation sequencing from 2447 individuals before initiation of ART at the largest HIV clinic in Mexico City (April 2016 to June 2018). Pretreatment HIVDR was estimated using the Stanford algorithm at a Sanger-like threshold (≥20%). Genetic networks were inferred with HIV-TRACE, establishing putative transmission links with genetic distances <1.5%. We examined demographic associations among linked individuals with shared drug resistance mutations (DRMs) using a ≥ 2% threshold to include low-frequency variants.

RESULTS

Pretreatment HIVDR reached 14.8% (95% CI 13.4%-16.2%) in the cohort overall and 9.6% (8.5%-10.8%) to NNRTIs. Putative links with at least one other sequence were found for 963/2447 (39%) sequences, forming 326 clusters (2-20 individuals). The inferred network was assortative by age and municipality (P < 0.001). Clustering individuals were younger [adjusted OR (aOR) per year = 0.96, 95% CI 0.95-0.97, P < 0.001] and less likely to include women (aOR = 0.46, 95% CI 0.28-0.75, P = 0.002). Among clustering individuals, 175/963 (18%) shared DRMs (involving 66 clusters), of which 66/175 (38%) shared K103N/S (24 clusters). Eight municipalities (out of 75) harboured 65% of persons sharing DRMs. Among all persons sharing DRMs, those sharing K103N were younger (aOR = 0.93, 95% CI 0.88-0.98, P = 0.003).

CONCLUSIONS

Our analyses suggest age- and geographically associated transmission of DRMs within the HIV genetic network in Mexico City, warranting continuous monitoring and focused interventions.

In Search of Covariates of HIV-1 Subtype B Spread in the United States-A Cautionary Tale of Large-Scale Bayesian Phylogeography

Infections with HIV-1 group M subtype B viruses account for the majority of the HIV epidemic in the Western world. Phylogeographic studies have placed the introduction of subtype B in the United States in New York around 1970, where it grew into a major source of spread. Currently, it is estimated that over one million people are living with HIV in the US and that most are infected with subtype B variants. Here, we aim to identify the drivers of HIV-1 subtype B dispersal in the United States by analyzing a collection of 23,588 pol sequences, collected for drug resistance testing from 45 states during 2004-2011. To this end, we introduce a workflow to reduce this large collection of data to more computationally-manageable sample sizes and apply the BEAST framework to test which covariates associate with the spread of HIV-1 across state borders. Our results show that we are able to consistently identify certain predictors of spread under reasonable run times across datasets of up to 10,000 sequences. However, the general lack of phylogenetic structure and the high uncertainty associated with HIV trees make it difficult to interpret the epidemiological relevance of the drivers of spread we are able to identify. While the workflow we present here could be applied to other virus datasets of a similar scale, the characteristic star-like shape of HIV-1 phylogenies poses a serious obstacle to reconstructing a detailed evolutionary and spatial history for HIV-1 subtype B in the US.

Next-generation sequencing for the clinical management of hepatitis C virus infections: does one test fits all purposes?

While the prospect of viral cure is higher than ever for individuals infected with the hepatitis C virus (HCV) due to ground-breaking progress in antiviral treatment, success rates are still negatively influenced by HCV's high genetic variability. This genetic diversity is represented in the circulation of various genotypes and subtypes, mixed infections, recombinant forms and the presence of numerous drug resistant variants among infected individuals. Common misclassifications by commercial genotyping assays in combination with the limitations of currently used targeted population sequencing approaches have encouraged researchers to exploit alternative methods for the clinical management of HCV infections. Next-generation sequencing (NGS), a revolutionary and powerful tool with a variety of applications in clinical virology, can characterize viral diversity and depict viral dynamics in an ultra-wide and ultra-deep manner. The level of detail it provides makes it the method of choice for the diagnosis and clinical assessment of HCV infections. The sequence library provided by NGS is of a higher magnitude and sensitivity than data generated by conventional methods. Therefore, these technologies are helpful to guide clinical practice and at the same time highly valuable for epidemiological studies. The decreasing costs of NGS to determine genotypes, mixed infections, recombinant strains and drug resistant variants will soon make it feasible to employ NGS in clinical laboratories, to assist in the daily care of patients with HCV.

Signature of natural resistance in NS3 protease revealed by deep sequencing of HCV strains circulating in Iran

A tremendous upscale of screening and treatment strategies is required to achieve elimination of the hepatitis C virus (HCV) in Iran by 2030. Among treated patients, at least 5-10% is expected to experience treatment failure. To efficiently retreat cases with prior exposure to NS5A and NS5B drugs, knowledge on the natural prevalence of NS3 resistance is key. The NS3 region of 32 samples from sixteen Iranian HCV patients, among which 6 injecting drug users, was amplified and subjected to deep sequencing. Amplification and sequencing were successful in 29 samples. The reads were assembled to consensus sequences and showed that 6 patients were infected with HCV1a (37.5%), 7 with HCV1b (43.8%) and 3 with HCV3a (18.7%). Nucleotide identities were shared for >97% between intra-host sequences. Two patients were infected with natural resistant viruses, of which one solely comprising low frequency variants. Inferred phylogenies showed that Iranian sequences clustered together for HCV1a and HCV1b, while for HCV3a a potential recombination event was detected. We firstly report the use of deep sequencing for HCV in Iran, demonstrate the use of NS3 inhibitors as salvage therapy in case of retreatment and stress the importance for Iran to prioritize drug users for screening and treatment.

Discussion on critical points for a tailored therapy to cure hepatitis C virus infection

Hepatitis C virus (HCV) infects around 71 million people worldwide and in 2018 it is still a major health problem. Since 2011, anti-HCV therapy with availability of direct-acting antiviral drugs has revolutionized the clinical response and paved the way to eradication strategies. However, despite the high rate of sustained virological response, treatment failure may occur in a limited percentage of patients, possibly due to resistance-associated substitutions (RASs), either emergent or pre-existent even in minority viral populations. Clearly this problem may impair success of eradication strategies. With this background, several questions marks still exist around HCV treatment, including whether pan-genotypic treatments with complete effectiveness in any clinical conditions really exist outside clinical trials, the actual cost-effectiveness of genotyping testing, and utility of RAS detection in viral quasispecies by next generation sequencing approach. In this review, we describe these critical points by discussing recent literature data and our research experience.

Increasing importance of European lineages in seeding the hepatitis C virus subtype 1a epidemic in Spain

BackgroundReducing the burden of the hepatitis C virus (HCV) requires large-scale deployment of intervention programmes, which can be informed by the dynamic pattern of HCV spread. In Spain, ongoing transmission of HCV is mostly fuelled by people who inject drugs (PWID) infected with subtype 1a (HCV1a).AimOur aim was to map how infections spread within and between populations, which could help formulate more effective intervention programmes to halt the HCV1a epidemic in Spain.MethodsEpidemiological links between HCV1a viruses from a convenience sample of 283 patients in Spain, mostly PWID, collected between 2014 and 2016, and 1,317, 1,291 and 1,009 samples collected abroad between 1989 and 2016 were reconstructed using sequences covering the NS3, NS5A and NS5B genes. To efficiently do so, fast maximum likelihood-based tree estimation was coupled to a flexible Bayesian discrete phylogeographic inference method.ResultsThe transmission network structure of the Spanish HCV1a epidemic was shaped by continuous seeding of HCV1a into Spain, almost exclusively from North America and European countries. The latter became increasingly relevant and have dominated in recent times. Export from Spain to other countries in Europe was also strongly supported, although Spain was a net sink for European HCV1a lineages. Spatial reconstructions showed that the epidemic in Spain is diffuse, without large, dominant within-country networks.ConclusionTo boost the effectiveness of local intervention efforts, concerted supra-national strategies to control HCV1a transmission are needed, with a strong focus on the most important drivers of ongoing transmission, i.e. PWID and other high-risk populations.

On the importance of negative controls in viral landscape phylogeography

Phylogeographic reconstructions are becoming an established procedure to evaluate the factors that could impact virus spread. While a discrete phylogeographic approach can be used to test predictors of transition rates among discrete locations, alternative continuous phylogeographic reconstructions can also be exploited to investigate the impact of underlying environmental layers on the dispersal velocity of a virus. The two approaches are complementary tools for studying pathogens' spread, but in both cases, care must be taken to avoid misinterpretations. Here, we analyse rice yellow mottle virus (RYMV) sequence data from West and East Africa to illustrate how both approaches can be used to study the impact of environmental factors on the virus’ dispersal frequency and velocity. While it was previously reported that host connectivity was a major determinant of RYMV spread, we show that this was a false positive result due to the lack of appropriate negative controls. We also discuss and compare the phylodynamic tools currently available for investigating the impact of environmental factors on virus spread.

The global origins of resistance-associated variants in the non-structural proteins 5A and 5B of the hepatitis C virus

New, costly, fast acting, therapies targeting the non-structural proteins 5A and 5B (NS5A and NS5B) regions of the hepatitis C virus (HCV) genome are curative in the majority of cases. Variants with certain mutations in the NS5A and NS5B regions of HCV have been shown to reduce susceptibility to direct-acting NS5A and NS5B therapy and are found in treatment naïve patients. Despite this, the ease with which these variants evolve is poorly known, as are their evolutionary and geographic origins. To address this crucial gap we inferred the evolutionary and geographic origins of resistance-associated variants (RAVs) in the HCV NS5A and NS5B regions of subtypes 1a, 1b, and 3a sequences available from global databases. We found that RAVs in the NS5A region of HCV, when prevalent, were widely dispersed throughout the phylogenetic tree of HCV with multiple independent origins and that these variants are globally distributed. In contrast, most of the NS5B C316N variants came from one of two clades in the phylogenetic tree of HCV subtype 1b. The presence of serine (S) at codon 218 of HCV NS5B appears to facilitate the evolution of the C316N RAV. Other NS5B RAVs did not arise very frequently in our data set, except for S556G in subtype 1b and with respect to geography NS5B RAVs were also globally distributed. The inferred distribution of RAVs in the NS5A region and frequency of their origin suggest a low fitness barrier without the need for co-evolution of compensatory mutations. A low fitness barrier may allow rapid selection of de novo resistance to NS5A inhibitors during therapy.

Accurate quantification of within- and between-host HBV evolutionary rates requires explicit transmission chain modelling

Analyses of virus evolution in known transmission chains have the potential to elucidate the impact of transmission dynamics on the viral evolutionary rate and its difference within and between hosts. Lin et al. (2015, Journal of Virology, 89/7: 3512–22) recently investigated the evolutionary history of hepatitis B virus in a transmission chain and postulated that the ‘colonization–adaptation–transmission’ model can explain the differential impact of transmission on synonymous and non-synonymous substitution rates. Here, we revisit this dataset using a full probabilistic Bayesian phylogenetic framework that adequately accounts for the non-independence of sequence data when estimating evolutionary parameters. Examination of the transmission chain data under a flexible coalescent prior reveals a general inconsistency between the estimated timings and clustering patterns and the known transmission history, highlighting the need to incorporate host transmission information in the analysis. Using an explicit genealogical transmission chain model, we find strong support for a transmission-associated decrease of the overall evolutionary rate. However, in contrast to the initially reported larger transmission effect on non-synonymous substitution rate, we find a similar decrease in both non-synonymous and synonymous substitution rates that cannot be adequately explained by the colonization-adaptation-transmission model. An alternative explanation may involve a transmission/establishment advantage of hepatitis B virus variants that have accumulated fewer within-host substitutions, perhaps by spending more time in the covalently closed circular DNA state between each round of viral replication. More generally, this study illustrates that ignoring phylogenetic relationships can lead to misleading evolutionary estimates.

Cross-border spread, lineage displacement and evolutionary rate estimation of rabies virus in Yunnan Province, China

Background

Rabies is an important but underestimated threat to public health, with most cases reported in Asia. Since 2000, a new epidemic wave of rabies has emerged in Yunnan Province, southwestern China, which borders three countries in Southeast Asia.

Method

We estimated gene-specific evolutionary rates for rabies virus using available data in GenBank, then used this information to calibrate the timescale of rabies virus (RABV) spread in Asia. We used 452 publicly available geo-referenced complete nucleoprotein (N) gene sequences, including 52 RABV sequences that were recently generated from samples collected in Yunnan between 2008 and 2012.

Results

The RABV N gene evolutionary rate was estimated to be 1.88 × 10⁻⁴ (1.37–2.41 × 10⁻⁴, 95% Bayesian credible interval, BCI) substitutions per site per year. Phylogenetic reconstructions show that the currently circulating RABV lineages in Yunnan result from at least seven independent introductions (95% BCI: 6–9 introductions) and represent each of the three main Asian RABV lineages, SEA-1, -2 and -3. We find that Yunnan is a sink location for the domestic spread of RABV and connects RABV epidemics in North China, South China, and Southeast Asia. Cross-border spread from southeast Asia (SEA) into South China, and intermixing of the North and South China epidemics is also well supported. The influx of RABV into Yunnan from SEA was not well-supported, likely due to the poor sampling of SEA RABV diversity. We found evidence for a lineage displacement of the Yunnan SEA-2 and -3 lineages by Yunnan SEA-1 strains, and considered whether this could be attributed to fitness differences.

Conclusion

Overall, our study contributes to a better understanding of the spread of RABV that could facilitate future rabies virus control and prevention efforts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-017-0769-6) contains supplementary material, which is available to authorized users.