Phylodynamics of the HIV-1 CRF02_AG clade in Cameroon

The rates of global bacterial and archaeal dispersal

The phylogenetic resolution at which microorganisms display geographic endemism, the rates at which they disperse at global scales, and the role of humans on global microbial dispersal are largely unknown. Answering these questions is necessary for interpreting microbial biogeography, ecology, and macroevolution and for predicting the spread of emerging pathogenic strains. To resolve these questions, I analyzed the geographic and evolutionary relationships between 36,795 bacterial and archaeal ("prokaryotic") genomes from ∼7000 locations around the world. I find clear signs of continental-scale endemism, including strong correlations between phylogenetic divergence and geographic distance. However, the phylogenetic scale at which endemism generally occurs is extremely small, and most "species" (defined by an average nucleotide identity ≥ 95%) and even closely related strains (average nucleotide identity ≥ 99.9%) are globally distributed. Human-associated lineages display faster dispersal rates than other terrestrial lineages; the average net distance between any two human-associated cell lineages diverging 50 years ago is roughly 580 km. These results suggest that many previously reported global-scale microbial biogeographical patterns are likely the result of recent or current environmental filtering rather than geographic endemism. For human-associated lineages, estimated transition rates between Europe and North America are particularly high, and much higher than for non-human associated terrestrial lineages, highlighting the role that human movement plays in global microbial dispersal. Dispersal was slowest for hot spring- and terrestrial subsurface-associated lineages, indicating that these environments may act as "isolated islands" of microbial evolution.

The Role of Phylogenetics in Discerning HIV-1 Mixing among Vulnerable Populations and Geographic Regions in Sub-Saharan Africa: A Systematic Review

To reduce global HIV-1 incidence, there is a need to understand and disentangle HIV-1 transmission dynamics and to determine the geographic areas and populations that act as hubs or drivers of HIV-1 spread. In Sub-Saharan Africa (sSA), the region with the highest HIV-1 burden, information about such transmission dynamics is sparse. Phylogenetic inference is a powerful method for the study of HIV-1 transmission networks and source attribution. In this review, we assessed available phylogenetic data on mixing between HIV-1 hotspots (geographic areas and populations with high HIV-1 incidence and prevalence) and areas or populations with lower HIV-1 burden in sSA. We searched PubMed and identified and reviewed 64 studies on HIV-1 transmission dynamics within and between risk groups and geographic locations in sSA (published 1995-2021). We describe HIV-1 transmission from both a geographic and a risk group perspective in sSA. Finally, we discuss the challenges facing phylogenetic inference in mixed epidemics in sSA and offer our perspectives and potential solutions to the identified challenges.

Elucidation of Early Evolution of HIV-1 Group M in the Congo Basin Using Computational Methods

The Congo Basin region is believed to be the site of the cross-species transmission event that yielded HIV-1 group M (HIV-1M). It is thus likely that the virus has been present and evolving in the region since that cross-species transmission. As HIV-1M was only discovered in the early 1980s, our directly observed record of the epidemic is largely limited to the past four decades. Nevertheless, by exploiting the genetic relatedness of contemporary HIV-1M sequences, phylogenetic methods provide a powerful framework for investigating simultaneously the evolutionary and epidemiologic history of the virus. Such an approach has been taken to find that the currently classified HIV-1 M subtypes and Circulating Recombinant Forms (CRFs) do not give a complete view of HIV-1 diversity. In addition, the currently identified major HIV-1M subtypes were likely genetically predisposed to becoming a major component of the present epidemic, even before the events that resulted in the global epidemic. Further efforts have identified statistically significant hot- and cold-spots of HIV-1M subtypes sequence inheritance in genomic regions of recombinant forms. In this review we provide ours and others recent findings on the emergence and spread of HIV-1M variants in the region, which have provided insights into the early evolution of this virus.

[Phylodynamic characteristics of the Russian population of rotavirus А (Reoviridae: Sedoreovirinae: Rotavirus) based on the VP6 gene]

INTRODUCTION

Rotavirus A is one of the leading causes of acute gastroenteritis in children in the first years of life. Rotavirus infection is currently classified as a preventable infection. The most abundant rotavirion protein is VP6.

MATERIAL AND METHODS

Phylogenetic analysis and calculation of phylodynamic characteristics were carried out for 262 nucleotide sequences of the VP6 gene of rotavirus species A, isolated in Russia, using the BEAST v.1.10.4 software package. The derivation and analysis of amino acid sequences was performed using the MEGAX program.

RESULTS

This study provides phylodynamic characteristics of the rotaviruses in Russia based on the sequences coding VP6 protein. Bayesian analysis showed the circulation of rotaviruses of three sublineages of genotype I1 and three sublineages of genotype I2 in Russia. The level of accumulation of mutations was established, which turned out to be similar for genotypes I1 and I2 and amounted to 7.732E-4 and 1.008E-3 nucleotides/site/year, respectively. The effective population sizes based on nucleotide sequences of the VP6 I1 and I2 genotypes are relatively stable while after the 2000s there is a tendency of its decreasing. Comparative analysis of the amino acid sequences in the region of the intracellular neutralization sites A (231-260 aa) and B (265-292 aa) made it possible to reveal a mutation in position V252I in a proportion of Russian strains of genotype I1 some strains of genotypes I1 and I2 had mutation I281V. These substitutions were not associated with any sublineages to which the strains belong. The analysis of three T-cell epitopes revealed four amino acid differences (in aa positions 305, 315, 342, 348) that were associated with the first or second genogroup.

CONCLUSION

Based on the phylodynamic characteristics and amino acid composition of antigenic determinants, it was concluded that the VP6 protein is highly stable and could potentially be a good model for development of a rotavirus vaccine.

Sampling bias and model choice in continuous phylogeography: Getting lost on a random walk

Phylogeographic inference allows reconstruction of past geographical spread of pathogens or living organisms by integrating genetic and geographic data. A popular model in continuous phylogeography—with location data provided in the form of latitude and longitude coordinates—describes spread as a Brownian motion (Brownian Motion Phylogeography, BMP) in continuous space and time, akin to similar models of continuous trait evolution. Here, we show that reconstructions using this model can be strongly affected by sampling biases, such as the lack of sampling from certain areas. As an attempt to reduce the effects of sampling bias on BMP, we consider the addition of sequence-free samples from under-sampled areas. While this approach alleviates the effects of sampling bias, in most scenarios this will not be a viable option due to the need for prior knowledge of an outbreak’s spatial distribution. We therefore consider an alternative model, the spatial Λ-Fleming-Viot process (ΛFV), which has recently gained popularity in population genetics. Despite the ΛFV’s robustness to sampling biases, we find that the different assumptions of the ΛFV and BMP models result in different applicabilities, with the ΛFV being more appropriate for scenarios of endemic spread, and BMP being more appropriate for recent outbreaks or colonizations.

Phylogeography studies past location and migration using information from current geographic locations of genetic sequences. For example, phylogeography can be used to reconstruct the history of geographical spread of an outbreak using the genetic sequences of the pathogen collected at different times and locations. Here, we investigate the effects of different model assumptions on phylogeographic inference. In particular, we examine the effects of the strategy used to collect samples. We show that sample collection biases can have a strong impact on the quality of phylogeographic reconstruction: geographically biased sampling scheme can be very detrimental for popular continuous phylogeography models. We consider different ways to counter these effects, from utilising alternative phylogeographic models, to the inclusion of partially informative samples (known cases without genetic sequences). While these strategies do alleviate the effects of sampling biases, they also lead to considerable additional computational burden. We also investigate the intrinsic differences of different phylogeographic models, and their effects on reconstructed patterns in different scenarios.

Genomic Surveillance of Yellow Fever Virus Epizootic in São Paulo, Brazil, 2016 - 2018

São Paulo, a densely inhabited state in southeast Brazil that contains the fourth most populated city in the world, recently experienced its largest yellow fever virus (YFV) outbreak in decades. YFV does not normally circulate extensively in São Paulo, so most people were unvaccinated when the outbreak began. Surveillance in non-human primates (NHPs) is important for determining the magnitude and geographic extent of an epizootic, thereby helping to evaluate the risk of YFV spillover to humans. Data from infected NHPs can give more accurate insights into YFV spread than when using data from human cases alone. To contextualise human cases, identify epizootic foci and uncover the rate and direction of YFV spread in São Paulo, we generated and analysed virus genomic data and epizootic case data from NHPs in São Paulo. We report the occurrence of three spatiotemporally distinct phases of the outbreak in São Paulo prior to February 2018. We generated 51 new virus genomes from YFV positive cases identified in 23 different municipalities in São Paulo, mostly sampled from NHPs between October 2016 and January 2018. Although we observe substantial heterogeneity in lineage dispersal velocities between phylogenetic branches, continuous phylogeographic analyses of generated YFV genomes suggest that YFV lineages spread in São Paulo at a mean rate of approximately 1km per day during all phases of the outbreak. Viral lineages from the first epizootic phase in northern São Paulo subsequently dispersed towards the south of the state to cause the second and third epizootic phases there. This alters our understanding of how YFV was introduced into the densely populated south of São Paulo state. Our results shed light on the sylvatic transmission of YFV in highly fragmented forested regions in São Paulo state and highlight the importance of continued surveillance of zoonotic pathogens in sentinel species.

Phylogeographic Estimation and Simulation of Global Diffusive Dispersal

The analysis of time-resolved phylogenies (timetrees) and geographic location data allows estimation of dispersal rates, for example, for invasive species and infectious diseases. Many estimation methods are based on the Brownian Motion model for diffusive dispersal on a 2D plane; however, the accuracy of these methods deteriorates substantially when dispersal occurs at global scales because spherical Brownian motion (SBM) differs from planar Brownian motion. No statistical method exists for estimating SBM diffusion coefficients from a given timetree and tip coordinates, and no method exists for simulating SBM along a given timetree. Here, I present new methods for simulating SBM along a given timetree, and for estimating SBM diffusivity from a given timetree and tip coordinates using a modification of Felsenstein's independent contrasts and maximum likelihood. My simulation and fitting methods can accommodate arbitrary time-dependent diffusivities and scale efficiently to trees with millions of tips, thus enabling new analyses even in cases where planar BM would be a sufficient approximation. I demonstrate these methods using a timetree of marine and terrestrial Cyanobacterial genomes, as well as timetrees of two globally circulating Influenza B clades. My methods are implemented in the R package "castor." [Independent contrasts; phylogenetic; random walk; simulation; spherical Brownian motion.].

High HIV burden and recent transmission chains in rural forest areas in southern Cameroon, where ancestors of HIV-1 have been identified in ape populations

We studied HIV prevalence and genetic diversity in rural forest areas in Cameroon, where chimpanzee and gorilla populations infected with the ancestors of the different HIV-1 groups have been identified and transmitted to humans during the 20th century. A total of 2812 individuals were studied, 924 from south-central, 1116 from south-east and 772 from south-west Cameroon. Of 208 (7.4%) samples that were confirmed for HIV-1 infection all belong to HIV-1 group M. In all sites and in all age categories, HIV-1 prevalence was higher in women (160/1599 (10.0%)) as compared to men (48/1213 (4.0%)) with the highest prevalence in women aged between 25 and 34 years (>17%). For 188/208 (92.3%) HIV-1 positive individuals, a fragment of the pol gene was successfully amplified and sequenced. Phylogenetic analysis showed predominance of CRF02_AG (58%), a large diversity of subtypes (A, D, F2 and G), nine different CRFs and more than 12% URFs. Interestingly, 35/188 (18.6%) HIV-1 strains form 12 recent transmission chains. The majority of the clusters are composed of two (n = 8) or three (n = 3) sequences but one cluster included ten HIV-1 strains from women living in four different villages on a major road for logging concessions in the south-east (60 km distance). In the three regions of Cameroon where the ancestors of the four HIV-1 groups have been transmitted to humans, we observed a high HIV prevalence, especially in the southeast where HIV-1 M originated. Many factors allowing rapid establishment in the human population and subsequent rapid spread to urban areas of a new retrovirus or other pathogens of zoonotic origin are now present. Our study shows clearly that some rural areas should also be considered as hot-spots for HIV infection. Prevention efforts together with growing access to HIV diagnosis and antiretroviral treatment are urgently needed in these remote areas.

HIV-1 Transmission Patterns Within and Between Risk Groups in Coastal Kenya

HIV-1 transmission patterns within and between populations at different risk of HIV-1 acquisition in Kenya are not well understood. We investigated HIV-1 transmission networks in men who have sex with men (MSM), injecting drug users (IDU), female sex workers (FSW) and heterosexuals (HET) in coastal Kenya. We used maximum-likelihood and Bayesian phylogenetics to analyse new (N = 163) and previously published (N = 495) HIV-1 polymerase sequences collected during 2005-2019. Of the 658 sequences, 131 (20%) were from MSM, 58 (9%) IDU, 109 (17%) FSW, and 360 (55%) HET. Overall, 206 (31%) sequences formed 61 clusters. Most clusters (85%) consisted of sequences from the same risk group, suggesting frequent within-group transmission. The remaining clusters were mixed between HET/MSM (7%), HET/FSW (5%), and MSM/FSW (3%) sequences. One large IDU-exclusive cluster was found, indicating an independent sub-epidemic among this group. Phylodynamic analysis of this cluster revealed a steady increase in HIV-1 infections among IDU since the estimated origin of the cluster in 1987. Our results suggest mixing between high-risk groups and heterosexual populations and could be relevant for the development of targeted HIV-1 prevention programmes in coastal Kenya.

Characterisation of HIV-1 Molecular Epidemiology in Nigeria: Origin, Diversity, Demography and Geographic Spread

Nigeria has the highest number of AIDS-related deaths in the world. In this study, we characterised the HIV-1 molecular epidemiology by analysing 1442 HIV-1 pol sequences collected 1999-2014 from four geopolitical zones in Nigeria using state-of-the-art maximum-likelihood and Bayesian phylogenetic analyses. The main circulating forms were the circulating recombinant form (CRF) 02_AG (44% of the analysed sequences), CRF43_02G (16%), and subtype G (8%). Twenty-three percent of the sequences represented unique recombinant forms (URFs), whereof 37 (11%) could be grouped into seven potentially novel CRFs. Bayesian phylodynamic analysis suggested that five major Nigerian HIV-1 sub-epidemics were introduced in the 1960s and 1970s, close to the Nigerian Civil War. The analysis also indicated that the number of effective infections decreased in Nigeria after the introduction of free antiretroviral treatment in 2006. Finally, Bayesian phylogeographic analysis suggested gravity-like dynamics in which virus lineages first emerge and expand within large urban centers such as Abuja and Lagos, before migrating towards smaller rural areas. This study provides novel insight into the Nigerian HIV-1 epidemic and may have implications for future HIV-1 prevention strategies in Nigeria and other severely affected countries.

Distinct rates and patterns of spread of the major HIV-1 subtypes in Central and East Africa

Since the ignition of the HIV-1 group M pandemic in the beginning of the 20th century, group M lineages have spread heterogeneously throughout the world. Subtype C spread rapidly through sub-Saharan Africa and is currently the dominant HIV lineage worldwide. Yet the epidemiological and evolutionary circumstances that contributed to its epidemiological expansion remain poorly understood. Here, we analyse 346 novel pol sequences from the DRC to compare the evolutionary dynamics of the main HIV-1 lineages, subtypes A1, C and D. Our results place the origins of subtype C in the 1950s in Mbuji-Mayi, the mining city of southern DRC, while subtypes A1 and D emerged in the capital city of Kinshasa, and subtypes H and J in the less accessible port city of Matadi. Following a 15-year period of local transmission in southern DRC, we find that subtype C spread at least three-fold faster than other subtypes circulating in Central and East Africa. In conclusion, our results shed light on the origins of HIV-1 main lineages and suggest that socio-historical rather than evolutionary factors may have determined the epidemiological fate of subtype C in sub-Saharan Africa.

Comparing patterns and scales of plant virus phylogeography: Rice yellow mottle virus in Madagascar and in continental Africa

Rice yellow mottle virus (RYMV) in Madagascar Island provides an opportunity to study the spread of a plant virus disease after a relatively recent introduction in a large and isolated country with a heterogeneous host landscape ecology. Here, we take advantage of field survey data on the occurrence of RYMV disease throughout Madagascar dating back to the 1970s, and of virus genetic data from ninety-four isolates collected since 1989 in most regions of the country to reconstruct the epidemic history. We find that the Malagasy isolates belong to a unique recombinant strain that most likely entered Madagascar through a long-distance introduction from the most eastern part of mainland Africa. We infer the spread of RYMV as a continuous process using a Bayesian statistical framework. In order to calibrate the time scale in calendar time units in this analysis, we pool the information about the RYMV evolutionary rate from several geographical partitions. Whereas the field surveys and the phylogeographic reconstructions both point to a rapid southward invasion across hundreds of kilometers throughout Madagascar within three to four decades, they differ on the inferred origin location and time of the epidemic. The phylogeographic reconstructions suggest a lineage displacement and unveil a re-invasion of the northern regions that may have remained unnoticed otherwise. Despite ecological differences that could affect the transmission potential of RYMV in Madagascar and in mainland Africa, we estimate similar invasion and dispersal rates. We could not identify environmental factors that have a relevant impact on the lineage dispersal velocity of RYMV in Madagascar. This study highlights the value and complementarity of (historical) nongenetic and (more contemporaneous) genetic surveillance data for reconstructing the history of spread of plant viruses.

Geographically-stratified HIV-1 group M pol subtype and circulating recombinant form sequences

Accurate classification of HIV-1 group M lineages, henceforth referred to as subtyping, is essential for understanding global HIV-1 molecular epidemiology. Because most HIV-1 sequencing is done for genotypic resistance testing pol gene, we sought to develop a set of geographically-stratified pol sequences that represent HIV-1 group M sequence diversity. Representative pol sequences differ from representative complete genome sequences because not all CRFs have pol recombination points and because complete genome sequences may not faithfully reflect HIV-1 pol diversity. We developed a software pipeline that compiled 6,034 one-per-person complete HIV-1 pol sequences annotated by country and year belonging to 11 pure subtypes and 70 CRFs and selected a set of sequences whose average distance to the remaining sequences is minimized for each subtype/CRF and country to generate a Geographically-Stratified set of 716 Pol Subtype/CRF (GSPS) reference sequences. We provide extensive data on pol diversity within each subtype/CRF and country combination. The GSPS reference set will also be useful for HIV-1 pol subtyping.

Reconstructing the recent West Nile virus lineage 2 epidemic in Europe and Italy using discrete and continuous phylogeography

West Nile virus lineage 2 (WNV-2) was mainly confined to sub-Saharan Africa until the early 2000s, when it was identified for the first time in Central Europe causing outbreaks of human and animal infection. The aim of this study was to reconstruct the origin and dispersion of WNV-2 in Central Europe and Italy on a phylodynamic and phylogeographical basis. To this aim, discrete and continuous space phylogeographical models were applied to a total of 33 newly characterised full-length viral genomes obtained from mosquitoes, birds and humans in Northern Italy in the years 2013–2015 aligned with 64 complete sequences isolated mainly in Europe. The European isolates segregated into two highly significant clades: a small one including three sequences and a large clade including the majority of isolates obtained in Central Europe since 2004. Discrete phylogeographical analysis showed that the most probable location of the root of the largest European clade was in Hungary a mean 12.78 years ago. The European clade bifurcated into two highly supported subclades: one including most of the Central/East European isolates and the other encompassing all of the isolates obtained in Greece. The continuous space phylogeographical analysis of the Italian clade showed that WNV-2 entered Italy in about 2008, probably by crossing the Adriatic sea and reaching a central area of the Po Valley. The epidemic then spread simultaneously eastward, to reach the region of the Po delta in 2013, and westward to the border area between Lombardy and Piedmont in 2014; later, the western strain changed direction southward, and reached the central area of the Po valley once again in 2015. Over a period of about seven years, the virus spread all over an area of northern Italy by following the Po river and its main tributaries.

Genetic characterization of human immunodeficiency virus type 1 transmission in the Middle East and North Africa

BACKGROUND

The HIV-1 spread in the Middle East and North Africa (MENA) has not been previously characterised using the phylogenetic approach. The aim of the current study was to investigate the genetic diversity and domestic transmission of HIV-1 in the MENA.

METHODS

A total of 2036 HIV-1 sequences available in Genbank and collected in the MENA during 1988-2016 were used together with 715 HIV-1 reference sequences that were retrieved from Genbank based on genetic similarity with the MENA sequences. The REGA and COMET tools were used to determine HIV-1 subtypes and circulating recombinant forms. Maximum Likelihood and Bayesian phylogenetic analyses were used to identify and date HIV-1 transmission clusters.

RESULTS

At least 21 HIV-1 subtypes and recombinant forms were prevalent in the MENA. Subtype B was the most common variant (39%), followed by CRF35_AD (19%) and CRF02_AG (14%). The most common genetic region was pol, and 675 partial pol sequences (average of 1005 bp) were eligible for detailed phylogenetic analysis. Fifty-four percent of the MENA sequences formed HIV-1 transmission clusters. Whereas numerous clusters were country-specific, some clusters indicated transmission links between countries for subtypes B, C and CRF02_AG. This was more common in North Africa compared with the Middle East (p < 0.001). Recombinant forms had a larger proportion of clustering compared to pure subtypes (p < 0.001). The largest MENA clusters dated back to 1991 (an Algerian CRF06_cpx cluster of 43 sequences) and 2002 (a Tunisian CRF02_AG cluster of 48 sequences).

CONCLUSIONS

We found an extensive HIV-1 diversity in the MENA and a high proportion of sequences in transmission clusters. This study highlights the need for preventive measures in the MENA to limit HIV-1 spread in this region.

Phylodynamic applications in 21st century global infectious disease research

BACKGROUND

Phylodynamics, the study of the interaction between epidemiological and pathogen evolutionary processes within and among populations, was originally defined in the context of rapidly evolving viruses and used to characterize transmission dynamics. The concept of phylodynamics has evolved since the early 21st century, extending its reach to slower-evolving pathogens, including bacteria and fungi, and to the identification of influential factors in disease spread and pathogen population dynamics.

RESULTS

The phylodynamic approach has now become a fundamental building block for the development of comparative phylogenetic tools capable of incorporating epidemiological surveillance data with molecular sequences into a single statistical framework. These innovative tools have greatly enhanced scientific investigations of the temporal and geographical origins, evolutionary history, and ecological risk factors associated with the growth and spread of viruses such as human immunodeficiency virus (HIV), Zika, and dengue and bacteria such as Methicillin-resistant Staphylococcus aureus.

CONCLUSIONS

Capitalizing on an extensive review of the literature, we discuss the evolution of the field of infectious disease epidemiology and recent accomplishments, highlighting the advancements in phylodynamics, as well as the challenges and limitations currently facing researchers studying emerging pathogen epidemics across the globe.

The epidemic dynamics of hepatitis C virus subtypes 4a and 4d in Saudi Arabia

The relatedness between viral variants sampled at different locations through time can provide information pertinent to public health that cannot readily be obtained through standard surveillance methods. Here, we use virus genetic data to identify the transmission dynamics that drive the hepatitis C virus subtypes 4a (HCV4a) and 4d (HCV4d) epidemics in Saudi Arabia. We use a comprehensive dataset of newly generated and publicly available sequence data to infer the HCV4a and HCV4d evolutionary histories in a Bayesian statistical framework. We also introduce a novel analytical method for an objective assessment of the migration intensity between locations. We find that international host mobility patterns dominate over within country spread in shaping the Saudi Arabia HCV4a epidemic, while this may be different for the HCV4d epidemic. This indicates that the subtypes 4a and 4d burden can be most effectively reduced by combining the prioritized screening and treatment of Egyptian immigrants with domestic prevention campaigns. Our results highlight that the joint investigation of evolutionary and epidemiological processes can provide valuable public health information, even in the absence of extensive metadata information.

Emerging Concepts of Data Integration in Pathogen Phylodynamics

Phylodynamics has become an increasingly popular statistical framework to extract evolutionary and epidemiological information from pathogen genomes. By harnessing such information, epidemiologists aim to shed light on the spatio-temporal patterns of spread and to test hypotheses about the underlying interaction of evolutionary and ecological dynamics in pathogen populations. Although the field has witnessed a rich development of statistical inference tools with increasing levels of sophistication, these tools initially focused on sequences as their sole primary data source. Integrating various sources of information, however, promises to deliver more precise insights in infectious diseases and to increase opportunities for statistical hypothesis testing. Here, we review how the emerging concept of data integration is stimulating new advances in Bayesian evolutionary inference methodology which formalize a marriage of statistical thinking and evolutionary biology. These approaches include connecting sequence to trait evolution, such as for host, phenotypic and geographic sampling information, but also the incorporation of covariates of evolutionary and epidemic processes in the reconstruction procedures. We highlight how a full Bayesian approach to covariate modeling and testing can generate further insights into sequence evolution, trait evolution, and population dynamics in pathogen populations. Specific examples demonstrate how such approaches can be used to test the impact of host on rabies and HIV evolutionary rates, to identify the drivers of influenza dispersal as well as the determinants of rabies cross-species transmissions, and to quantify the evolutionary dynamics of influenza antigenicity. Finally, we briefly discuss how data integration is now also permeating through the inference of transmission dynamics, leading to novel insights into tree-generative processes and detailed reconstructions of transmission trees. [Bayesian inference; birth–death models; coalescent models; continuous trait evolution; covariates; data integration; discrete trait evolution; pathogen phylodynamics.

Phylodynamic and Phylogeographic Profiles of Subtype B HIV-1 Epidemics in South Spain

BACKGROUND

Since 1982, HIV-1 epidemics have evolved to different scenarios in terms of transmission routes, subtype distribution and characteristics of transmission clusters. We investigated the evolutionary history of HIV-1 subtype B in south Spain.

PATIENTS & METHODS

We studied all newly diagnosed HIV-1 subtype B patients in East Andalusia during the 2005-2012 period. For the analysis, we used the reverse transcriptase and protease sequences from baseline resistance, and the Trugene® HIV Genotyping kit (Siemens, Barcelona, Spain). Subtyping was done with REGA v3.0. The maximum likelihood trees constructed with RAxML were used to study HIV-1 clustering. Phylogeographic and phylodynamic profiles were studied by Bayesian inference methods with BEAST v1.7.5 and SPREAD v1.0.6.

RESULTS

Of the 493 patients infected with HIV-1 subtype B, 234 grouped into 55 clusters, most of which were small (44 clusters ≤ 5 patients, 31 with 2 patients, 13 with 3). The rest (133/234) were grouped into 11 clusters with ≥ 5 patients, and most (82%, 109/133) were men who have sex with men (MSM) grouped into 8 clusters. The association with clusters was more frequent in Spanish (p = 0.02) men (p< 0.001), MSM (p<0.001) younger than 35 years (p = 0.001) and with a CD4+ T-cell count above 350 cells/ul (p<0.001). We estimated the date of HIV-1 subtype B regional epidemic diversification around 1970 (95% CI: 1965-1987), with an evolutionary rate of 2.4 (95%CI: 1.7-3.1) x 10-3 substitutions/site/year. Most clusters originated in the 1990s in MSMs. We observed exponential subtype B HIV-1 growth in 1980-1990 and 2005-2008. The most significant migration routes for subtype B went from inland cities to seaside locations.

CONCLUSIONS

We provide the first data on the phylodynamic and phylogeographic profiles of HIV-1 subtype B in south Spain. Our findings of transmission clustering among MSMs should alert healthcare managers to enhance preventive measures in this risk group in order to prevent future outbreaks.

Time-scale of minor HIV-1 complex circulating recombinant forms from Central and West Africa

Background

Several HIV-1 circulating recombinant forms with a complex mosaic structure (CRFs_cpx) circulate in central and western African regions. Here we reconstruct the evolutionary history of some of these complex CRFs (09_cpx, 11_cpx, 13_cpx and 45_cpx) and further investigate the dissemination dynamic of the CRF11_cpx clade by using a Bayesian coalescent-based method.

Results

The analysis of two HIV-1 datasets comprising 181 pol (36 CRF09_cpx, 116 CRF11_cpx, 20 CRF13_cpx and 9 CRF45_cpx) and 125 env (12 CRF09_cpx, 67 CRF11_cpx, 17 CRF13_cpx and 29 CRF45_cpx) sequences pointed to quite consistent onset dates for CRF09_cpx (~1966: 1958–1979), CRF11_cpx (~1957: 1950–1966) and CRF13_cpx (~1965: 1958–1973) clades; while some divergence was found for the estimated date of origin of CRF45_cpx clade [pol = 1970 (1964–1976); env = 1960 (1952–1969)]. Phylogeographic reconstructions indicate that the HIV-1 CRF11_cpx clade most probably emerged in Cameroon and from there it was first disseminated to the Central Africa Republic and Chad in the early 1970s and to other central and western African countries from the early 1980s onwards. Demographic reconstructions suggest that the CRF11_cpx epidemic grew between 1960 and 1990 with a median exponential growth rate of 0.27 year⁻¹, and stabilized after.

Conclusions

These results reveal that HIV-1 CRFs_cpx clades have been circulating in Central Africa for a period comparable to other much more prevalent HIV-1 group M lineages. Cameroon was probably the epicenter of dissemination of the CRF11_cpx clade that seems to have experienced a long epidemic growth phase before stabilization. The epidemic growth of the CRF11_cpx clade was roughly comparable to other HIV-1 group M lineages circulating in Central Africa.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0824-8) contains supplementary material, which is available to authorized users.

Understanding Past Population Dynamics: Bayesian Coalescent-Based Modeling with Covariates

Effective population size characterizes the genetic variability in a population and is a parameter of paramount importance in population genetics and evolutionary biology. Kingman's coalescent process enables inference of past population dynamics directly from molecular sequence data, and researchers have developed a number of flexible coalescent-based models for Bayesian nonparametric estimation of the effective population size as a function of time. Major goals of demographic reconstruction include identifying driving factors of effective population size, and understanding the association between the effective population size and such factors. Building upon Bayesian nonparametric coalescent-based approaches, we introduce a flexible framework that incorporates time-varying covariates that exploit Gaussian Markov random fields to achieve temporal smoothing of effective population size trajectories. To approximate the posterior distribution, we adapt efficient Markov chain Monte Carlo algorithms designed for highly structured Gaussian models. Incorporating covariates into the demographic inference framework enables the modeling of associations between the effective population size and covariates while accounting for uncertainty in population histories. Furthermore, it can lead to more precise estimates of population dynamics. We apply our model to four examples. We reconstruct the demographic history of raccoon rabies in North America and find a significant association with the spatiotemporal spread of the outbreak. Next, we examine the effective population size trajectory of the DENV-4 virus in Puerto Rico along with viral isolate count data and find similar cyclic patterns. We compare the population history of the HIV-1 CRF02_AG clade in Cameroon with HIV incidence and prevalence data and find that the effective population size is more reflective of incidence rate. Finally, we explore the hypothesis that the population dynamics of musk ox during the Late Quaternary period were related to climate change. [Coalescent; effective population size; Gaussian Markov random fields; phylodynamics; phylogenetics; population genetics.

Spatio-Temporal History of HIV-1 CRF35_AD in Afghanistan and Iran

HIV-1 Circulating Recombinant Form 35_AD (CRF35_AD) has an important position in the epidemiological profile of Afghanistan and Iran. Despite the presence of this clade in Afghanistan and Iran for over a decade, our understanding of its origin and dissemination patterns is limited. In this study, we performed a Bayesian phylogeographic analysis to reconstruct the spatio-temporal dispersion pattern of this clade using eligible CRF35_AD gag and pol sequences available in the Los Alamos HIV database (432 sequences available from Iran, 16 sequences available from Afghanistan, and a single CRF35_AD-like pol sequence available from USA). Bayesian Markov Chain Monte Carlo algorithm was implemented in BEAST v1.8.1. Between-country dispersion rates were tested with Bayesian stochastic search variable selection method and were considered significant where Bayes factor values were greater than three. The findings suggested that CRF35_AD sequences were genetically similar to parental sequences from Kenya and Uganda, and to a set of subtype A1 sequences available from Afghan refugees living in Pakistan. Our results also showed that across all phylogenies, Afghan and Iranian CRF35_AD sequences formed a monophyletic cluster (posterior clade credibility> 0.7). The divergence date of this cluster was estimated to be between 1990 and 1992. Within this cluster, a bidirectional dispersion of the virus was observed across Afghanistan and Iran. We could not clearly identify if Afghanistan or Iran first established or received this epidemic, as the root location of this cluster could not be robustly estimated. Three CRF35_AD sequences from Afghan refugees living in Pakistan nested among Afghan and Iranian CRF35_AD branches. However, the CRF35_AD-like sequence available from USA diverged independently from Kenyan subtype A1 sequences, suggesting it not to be a true CRF35_AD lineage. Potential factors contributing to viral exchange between Afghanistan and Iran could be injection drug networks and mass migration of Afghan refugees and labours to Iran, which calls for extensive preventive efforts.

Molecular Genotyping of HIV-1 Strains from Newly Infected Men Who Have Sex with Men in Harbin, China

In this study, blood samples from newly HIV-1 infected men who have sex with men (MSM) were collected, and HIV-1 genotypes were identified based on gag p17-p24 and nef gene regions. We found that participants aged from 20 to 40 years old were the major infection group in Harbin. CRF01_AE was the predominant genotype, contributing to 84.7% of HIV-1 infections, followed by subtype B (4.7%), CRF07_BC (3.5%), and subtype B' (Thai B, 1.2%). Moreover, five unique recombinant forms (5.9%) were also identified, including genotypes 01B, 01C, and 01/02. The recombinant CRF01_AE/CRF02_AG was first reported in China. These results suggested that current HIV-1 genotype epidemic among MSM in Harbin is more complicated and that intersubtype recombinants have emerged. Therefore, timely regional epidemiological surveillance of HIV-1 genotype and development of prevention measures for new HIV-1 infections among MSM are quite important.

Phylodynamics of the major HIV-1 CRF02_AG African lineages and its global dissemination

The HIV-1 CRF02_AG clade is the most prevalent HIV variant in West and West-Central Africa and its detection outside Africa is increasingly common. Little is known, however, about the number and phylodynamics of major CRF02_AG lineages circulating worldwide. To this end, a total of 3170 HIV-1 CRF02_AG-like pol sequences isolated around the world, over a period of 25years (1989 to 2013), were analyzed using Maximum Likelihood and Bayesian coalescent-based methods. Our results suggest that most of the current CRF02_AG diversity comes from the dissemination of a few founder strains out of Central Africa into West Africa and Cameroon between the late 1960s and the middle 1980s. The CRF02_AG strain introduced into West Africa established a large regional epidemic with low phylogeographic structure. This strain was also successfully disseminated out of the West African region and originated at least three large secondary outbreaks in Cameroon at around the late 1970s, in the former Soviet Union (FSU) countries at around the late 1990s, and in Bulgaria/Germany at around the early 2000s. The CRF02_AG African lineages introduced into Cameroon remained mostly restricted to this country and its neighbors. Demographic reconstructions indicate that major CRF02_AG clades circulating in Africa exhibited a decline in growth rate since the middle 1980s/1990s, whereas CRF02_AG clades in Europe and the FSU countries continue to grow exponentially until the middle to late 2000s. Substantial differences in the median estimated growth rate of the same CRF02_AG clade circulating in different regions (0.63-2.00year^-1), and of different CRF02_AG clades circulating in the same country (0.41-0.75year^-1) were observed. Thus, the cause of the epidemic outcome of the different HIV-1 CRF02_AG lineages is probably multifactorial.

Reconstructing the HIV-1 CRF02_AG and CRF06_cpx epidemics in Burkina Faso and West Africa using early samples

BACKGROUND

HIV-1 circulating recombinant forms (CRFs) represent viral recombinant lineages that play a significant role in the global epidemic. Two of them dominate the epidemic in Burkina Faso: CRF06_cpx (first described in this country) and CRF02_AG. We reconstructed the phylodynamics of both recombinant viruses in Burkina Faso and throughout West Africa.

METHODS

We analysed CRF06_cpx and CRF02_AG sequences (protease/gp41) from early samples collected in Burkina Faso in 1986 together with other GenBank sequences (1984-2013) in 4 datasets: African CRF06_cpx (210/60); down-sampled CRF06_cpx (146/45); Burkina Faso CRF02_AG (130/39) and West/Central African CRF02_AG (691/298). For each dataset, we analysed both protease and gp41 jointly using the BEAST multilocus analysis and conducted phylogeographic analysis to reconstruct the early migration routes between countries.

RESULTS

The time to the most recent common ancestor (tMRCA) of CRF06_cpx was 1979 (1973-1983) for protease and 1981 (1978-1983) for gp41. The gp41 analysis inferred the origin of CRF06_cpx (or at least its parental subtype G lineage) in the Democratic Republic of Congo but migrated to Burkina Faso soon after (1982). Both genes showed that CRF06_cpx radiated to the rest of West Africa predominantly after around 1990. These results were robust to the oversampling of Burkina Faso sequences as they were confirmed in the down-sampled dataset. The tMRCA of the Burkina Faso CRF02_AG lineage was 1979 (1977-1983) for protease and 1980 (1978-1981) for gp41. However, we reconstructed its presence in West Africa much earlier (mid-1960s), with an initial origin in Cameroon and/or Nigeria, and its phylogeographic analysis revealed much interconnection within the region with a lack of country-specific phylogenetic patterns, which prevents tracking its exact migration routes.

CONCLUSIONS

Burkina Faso presents a relatively young HIV epidemic, with the diversification of the current in-country CRF02_AG and CRF06_cpx lineages taking place around 1980. This country represents the main source of CRF06_cpx in West Africa. The CRF02_AG epidemic started at least a decade earlier and showed much interchange between West African countries (especially involving coastal countries) suggesting great population mobility and an extensive viral spread in the region.

Short Communication: Reassessing the Origin of the HIV-1 CRF02_AG Lineages Circulating in Brazil

HIV-1 CRF02_AG is responsible for at least 8% of the HIV-1 infections worldwide and is distributed mainly in West Africa. CRF02_AG has recently been reported in countries where it is not native, including Brazil. In a previous study including 10 CRF02_AG Brazilian samples, we found at least four independent introductions and two autochthonous transmission networks of this clade in Brazil. As more CRF02_AG samples have been identified in Brazil, we performed a new phylogeographic analysis using a larger dataset than before. A total of 20 Brazilian (18 from Rio de Janeiro and two from São Paulo) and 1,485 African HIV-1 CRF02_AG pol sequences were analyzed using maximum likelihood (ML). The ML tree showed that the Brazilian sequences were distributed in five different lineages. The Bayesian phylogeographic analysis of the Brazilian and their most closely related African sequences (n = 212) placed the origin of all Brazilian lineages in West Africa, probably Ghana, Senegal, and Nigeria. Two monophyletic clades were identified, comprising only sequences from Rio de Janeiro, and their date of origin was estimated at around 1985 (95% highest posterior density: 1979-1992). These results support the existence of at least five independent introductions of the CRF02_AG lineage from West Africa into Brazil and further indicate that at least two of these lineages have been locally disseminated in the Rio de Janeiro state over the past 30 years.

The Two-Phase Emergence of Non Pandemic HIV-1 Group O in Cameroon

Unlike the pandemic form of HIV-1 (group M), group O viruses are endemic in west central Africa, especially in Cameroon. However, little is known about group O's genetic evolution, and why this highly divergent lineage has not become pandemic. Using a unique and large set of group O sequences from samples collected from 1987 to 2012, we find that this lineage has evolved in successive slow and fast phases of diversification, with a most recent common ancestor estimated to have existed around 1930 (1914-1944). The most rapid periods of diversification occurred in the 1950s and in the 1980s, and could be linked to favourable epidemiological contexts in Cameroon. Group O genetic diversity reflects this two-phase evolution, with two distinct populations potentially having different viral properties. The currently predominant viral population emerged in the 1980s, from an ancient population which had first developed in the 1950s, and is characterized by higher growth and evolutionary rates, and the natural presence of the Y181C resistance mutation, thought to confer a phenotypic advantage. Our findings show that although this evolutionary pattern is specific to HIV-1 group O, it paralleled the early spread of HIV-1 group M in the Democratic Republic of Congo. Both viral lineages are likely to have benefited from similar epidemiological contexts. The relative role of virological and social factors in the distinct epidemic histories of HIV-1 group O and M needs to be reassessed.

Phylogenetic studies of transmission dynamics in generalized HIV epidemics: an essential tool where the burden is greatest?

Efficient and effective HIV prevention measures for generalized epidemics in sub-Saharan Africa have not yet been validated at the population level. Design and impact evaluation of such measures requires fine-scale understanding of local HIV transmission dynamics. The novel tools of HIV phylogenetics and molecular epidemiology may elucidate these transmission dynamics. Such methods have been incorporated into studies of concentrated HIV epidemics to identify proximate and determinant traits associated with ongoing transmission. However, applying similar phylogenetic analyses to generalized epidemics, including the design and evaluation of prevention trials, presents additional challenges. Here we review the scope of these methods and present examples of their use in concentrated epidemics in the context of prevention. Next, we describe the current uses for phylogenetics in generalized epidemics and discuss their promise for elucidating transmission patterns and informing prevention trials. Finally, we review logistic and technical challenges inherent to large-scale molecular epidemiological studies of generalized epidemics and suggest potential solutions.

Spatiotemporal dynamics of dissemination of non-pandemic HIV-1 subtype B clades in the Caribbean region

The Human immunodeficiency virus type-1 (HIV-1) epidemic in the Caribbean region is mostly driven by subtype B; but information about the pattern of viral spread in this geographic region is scarce and different studies point to quite divergent models of viral dissemination. In this study, we reconstructed the spatiotemporal and population dynamics of the HIV-1 subtype B epidemic in the Caribbean. A total of 1,806 HIV-1 subtype B pol sequences collected from 17 different Caribbean islands between 1996 and 2011 were analyzed together with sequences from the United States (n = 525) and France (n = 340) included as control. Maximum Likelihood phylogenetic analyses revealed that HIV-1 subtype B infections in the Caribbean are driven by dissemination of the pandemic clade (BPANDEMIC) responsible for most subtype B infections across the world, and older non-pandemic lineages (BCAR) characteristics of the Caribbean region. The non-pandemic BCAR strains account for >40% of HIV-1 infections in most Caribbean islands; with exception of Cuba and Puerto Rico. Bayesian phylogeographic analyses indicate that BCAR strains probably arose in the island of Hispaniola (Haiti/Dominican Republic) around the middle 1960s and were later disseminated to Trinidad and Tobago and to Jamaica between the late 1960s and the early 1970s. In the following years, the BCAR strains were also disseminated from Hispaniola and Trinidad and Tobago to other Lesser Antilles islands at multiple times. The BCAR clades circulating in Hispaniola, Jamaica and Trinidad and Tobago appear to have experienced an initial phase of exponential growth, with mean estimated growth rates of 0.35-0.45 year(-1), followed by a more recent stabilization since the middle 1990s. These results demonstrate that non-pandemic subtype B lineages have been widely disseminated through the Caribbean since the late 1960s and account for an important fraction of current HIV-1 infections in the region.

Phylogenetic analysis of HIV type 1 CRF02_AG in multiple genes in Italian and African patients living in Italy

Human immunodeficiency virus type 1 (HIV-1) circulating recombinant form (CRF) 02_AG is a major recombinant variant in different geographic areas and is predominant in West and Central Africa. Of particular interest is the increased frequency of CRF02_AG in patients living in Italy. In the present study, phylogenetic analyses were performed on gag, pol (integrase), and env (gp120 and gp41) gene sequences from 34 CRF02_AG-infected patients living in Italy. Thirty out of 34 (89.4%) patients were from western Africa, 3/34 (8.8%) were born in Italy, and 1/34 (2.9%) was from Cuba. Phylogenetic analysis revealed the presence of a well-supported clade (aLRT score>0.75) of sequences only in gp120 and gp41 trees. Evolutionary rate estimation showed a faster evolution for the gp120 gene with respect to the gag, integrase, and gp41 genes. This finding was confirmed by the analysis of interpatient variability. Intrapatient variability was greater in gp120 gene sequences; 10/19 (52.6%; p<0.001) patients had a ratio of dN/dS>1 as compared with gag, integrase, and gp41 gene sequences with dN/dS ratios<1. In summary, phylogenetic analyses of CRF02_AG strains offer a perspective on intrapatient and interpatient variability among CRF02_AG-infected patients living in Italy. In addition, divergent phylogenetic relationships were observed among different genomic regions.

Spatiotemporal dynamics of the HIV-1 subtype G epidemic in West and Central Africa

The human immunodeficiency virus type 1 (HIV-1) subtype G is the second most prevalent HIV-1 clade in West Africa, accounting for nearly 30% of infections in the region. There is no information about the spatiotemporal dynamics of dissemination of this HIV-1 clade in Africa. To this end, we analyzed a total of 305 HIV-1 subtype G pol sequences isolated from 11 different countries from West and Central Africa over a period of 20 years (1992 to 2011). Evolutionary, phylogeographic and demographic parameters were jointly estimated from sequence data using a Bayesian coalescent-based method. Our analyses indicate that subtype G most probably emerged in Central Africa in 1968 (1956–1976). From Central Africa, the virus was disseminated to West and West Central Africa at multiple times from the middle 1970s onwards. Two subtype G strains probably introduced into Nigeria and Togo between the middle and the late 1970s were disseminated locally and to neighboring countries, leading to the origin of two major western African clades (G_WA-I and G_WA-II). Subtype G clades circulating in western and central African regions displayed an initial phase of exponential growth followed by a decline in growth rate since the early/middle 1990s; but the mean epidemic growth rate of G_WA-I (0.75 year⁻¹) and G_WA-II (0.95 year⁻¹) clades was about two times higher than that estimated for central African lineages (0.47 year⁻¹). Notably, the overall evolutionary and demographic history of G_WA-I and G_WA-II clades was very similar to that estimated for the CRF06_cpx clade circulating in the same region. These results support the notion that the spatiotemporal dissemination dynamics of major HIV-1 clades circulating in western Africa have probably been shaped by the same ecological factors.

Phylogeographic analysis of rabies viruses in the Philippines

Rabies still remains a public health threat in the Philippines. A significant number of human rabies cases, about 200-300 cases annually, have been reported, and the country needs an effective strategy for rabies control. To develop an effective control strategy, it is important to understand the transmission patterns of the rabies viruses. We conducted phylogenetic analyses by considering the temporal and spatial evolution of rabies viruses to reveal the transmission dynamics in the Philippines. After evaluating the molecular clock and phylogeographic analysis, we estimated that the Philippine strains were introduced from China around the beginning of 20th century. Upon this introduction, the rabies viruses evolved within the Philippines to form three major clades, and there was no indication of introduction of other rabies viruses from any other country. However, within the Philippines, island-to-island migrations were observed. Since then, the rabies viruses have diffused and only evolved within each island group. The evolutionary pattern of these viruses was strongly shaped by geographical boundaries. The association index statistics demonstrated a strong spatial structure within the island group, indicating that the seas were a significant geographical barrier for viral dispersal. Strong spatial structure was also observed even at a regional level, and most of the viral migrations (79.7% of the total median number) in Luzon were observed between neighboring regions. Rabies viruses were genetically clustered at a regional level, and this strong spatial structure suggests a geographical clustering of transmission chains and the potential effectiveness of rabies control that targets geographical clustering. Dog vaccination campaigns have been conducted independently by local governments in the Philippines, but it could be more effective to implement a coordinated vaccination campaign among neighboring areas to eliminate geographically-clustered rabies transmission chains.

HIV Type 1 transmission networks among men having sex with men and heterosexuals in Kenya

We performed a molecular phylogenetic study on HIV-1 polymerase sequences of men who have sex with men (MSM) and heterosexual patient samples in Kenya to characterize any observed HIV-1 transmission networks. HIV-1 polymerase sequences were obtained from samples in Nairobi and coastal Kenya from 84 MSM, 226 other men, and 364 women from 2005 to 2010. Using Bayesian phylogenetics, we tested whether sequences clustered by sexual orientation and geographic location. In addition, we used trait diffusion analyses to identify significant epidemiological links and to quantify the number of transmissions between risk groups. Finally, we compared 84 MSM sequences with all HIV-1 sequences available online at GenBank. Significant clustering of sequences from MSM at both coastal Kenya and Nairobi was found, with evidence of HIV-1 transmission between both locations. Although a transmission pair between a coastal MSM and woman was confirmed, no significant HIV-1 transmission was evident between MSM and the comparison population for the predominant subtype A (60%). However, a weak but significant link was evident when studying all subtypes together. GenBank comparison did not reveal other important transmission links. Our data suggest infrequent intermingling of MSM and heterosexual HIV-1 epidemics in Kenya.

TB and HIV in the Central African region: current knowledge and knowledge gaps

PURPOSE

Reliable and comprehensive data on the HIV/AIDS and TB co-pandemics from Central Africa remain scarce. This systematic review provides a comprehensive overview on current and past research activities in the region and provides a basis for future research work to close knowledge gaps.

METHODS

The scientific literature was searched for publications meeting the following search terms: "tuberculosis" or "HIV" or "acquired immunodeficiency syndrome", combined with "Central Africa", or the names of individual countries within the region. Original studies, reviews and case series were included, and a selection of relevant articles was made.

RESULTS

Most research in the field of HIV and TB has been conducted in Cameroon, where the epidemics have been described fairly well. The Democratic Republic of Congo ranked second on the amount of publications, despite the civil wars over the past several decades. Very little has been published on HIV and TB in the other countries, possibly due to the poor infrastructure of health care systems, lack of scientific capacity building or shortage of laboratory equipment.

CONCLUSIONS

Despite the relatively high burden of HIV and TB in the Central African region, the amount of research activities on these topics is limited. A better understanding of the co-epidemics in this region is urgently needed. The occurrence of opportunistic infections, treatment complications and drug resistance in TB and HIV need to be better described; the failure of public health systems needs to be understood, and research infrastructure needs to be developed. Only then will it be possible to turn the tide against the HIV and TB epidemics in this region.

Description of HIV-1 group M molecular epidemiology and drug resistance prevalence in Equatorial Guinea from migrants in Spain

Background

The HIV epidemic is increasing in Equatorial Guinea (GQ), West Central Africa, but few studies have reported its HIV molecular epidemiology. We aimed to describe the HIV-1 group M (HIV-1M) variants and drug-resistance mutations in GQ using sequences sampled in this country and in Spain, a frequent destination of Equatoguinean migrants.

Methods

We collected 195 HIV-1M pol sequences from Equatoguinean subjects attending Spanish clinics during 1997-2011, and 83 additional sequences sampled in GQ in 1997 and 2008 from GenBank. All (n = 278) were re-classified using phylogeny and tested for drug-resistance mutations. To evaluate the origin of CRF02_AG in GQ, we analyzed 2,562 CRF02_AG sequences and applied Bayesian MCMC inference (BEAST program).

Results

Most Equatoguinean patients recruited in Spain were women (61.1%) or heterosexuals (87.7%). In the 278 sequences, the variants found were CRF02_AG (47.8%), A (13.7%), B (7.2%), C (5.8%), G (5.4%) and others (20.1%). We found 6 CRF02_AG clusters emerged from 1983.9 to 2002.5 with origin in GQ (5.5 sequences/cluster). Transmitted drug-resistance (TDR) rate among naïve patients attended in Spain (n = 144) was 4.7%: 3.4% for PI (all with M46IL), 1.8% for NRTI (all with M184V) and 0.9% for NNRTI (Y188L). Among pre-treated patients, 9/31 (29%) presented any resistance, mainly affecting NNRTI (27.8%).

Conclusions

We report a low (<5%) TDR rate among naïve, with PI as the most affected class. Pre-treated patients also showed a low drug-resistance prevalence (29%) maybe related to the insufficient treatment coverage in GQ. CRF02_AG was the prevalent HIV-1M variant and entered GQ through independent introductions at least since the early 1980s.

Spatiotemporal dynamics of the HIV-1 CRF06_cpx epidemic in Western Africa

OBJECTIVE

To investigate the origin and spatiotemporal dynamics of dissemination of the HIV-1 CRF06_cpx clade in western Africa.

DESIGN

A total of 180 HIV-1 CRF06_cpx-like pol sequences isolated from 12 different countries from west and west-central Africa over a period of 16 years (1995-2010) were analyzed.

METHODS

Evolutionary, phylogeographic and demographic parameters were jointly estimated from sequence data using a Bayesian coalescent-based method and combined with molecular epidemiology and spatial accessibility data.

RESULTS

The CRF06_cpx most probably emerged in Burkina Faso in 1979 (1970-1985). From Burkina Faso, the virus was first disseminated to Mali and Nigeria during the 1980s and later to other countries from west and west-central Africa. Demographic reconstruction indicates that the CRF06_cpx epidemic grew exponentially during the 1980s, with a median growth rate of 0.82 year (0.60-1.09 year), and after stabilize. We found a negative correlation between CRF06_cpx prevalence and the geographical distance to Burkina Faso's capital. Regional accessibility information agrees with the overall geographical range of the CRF06_cpx, but not fully explains the highly heterogeneous distribution pattern of this CRF at regional level.

CONCLUSION

The CRF06_cpx epidemic in western Africa probably emerged at the late 1970s and grew during the 1980s at a rate comparable to the HIV-1 epidemics in the United States and Europe. Burkina Faso seems to be the most important epicenter of dissemination of the HIV-1 CRF06_cpx strain at regional level. The explanation for the current geographical distribution of CRF06_cpx is probably multifactorial.

Automated subtyping of HIV-1 genetic sequences for clinical and surveillance purposes: performance evaluation of the new REGA version 3 and seven other tools

BACKGROUND

To investigate differences in pathogenesis, diagnosis and resistance pathways between HIV-1 subtypes, an accurate subtyping tool for large datasets is needed. We aimed to evaluate the performance of automated subtyping tools to classify the different subtypes and circulating recombinant forms using pol, the most sequenced region in clinical practice. We also present the upgraded version 3 of the Rega HIV subtyping tool (REGAv3).

METHODOLOGY

HIV-1 pol sequences (PR+RT) for 4674 patients retrieved from the Portuguese HIV Drug Resistance Database, and 1872 pol sequences trimmed from full-length genomes retrieved from the Los Alamos database were classified with statistical-based tools such as COMET, jpHMM and STAR; similarity-based tools such as NCBI and Stanford; and phylogenetic-based tools such as REGA version 2 (REGAv2), REGAv3, and SCUEAL. The performance of these tools, for pol, and for PR and RT separately, was compared in terms of reproducibility, sensitivity and specificity with respect to the gold standard which was manual phylogenetic analysis of the pol region.

RESULTS

The sensitivity and specificity for subtypes B and C was more than 96% for seven tools, but was variable for other subtypes such as A, D, F and G. With regard to the most common circulating recombinant forms (CRFs), the sensitivity and specificity for CRF01_AE was ~99% with statistical-based tools, with phylogenetic-based tools and with Stanford, one of the similarity based tools. CRF02_AG was correctly identified for more than 96% by COMET, REGAv3, Stanford and STAR. All the tools reached a specificity of more than 97% for most of the subtypes and the two main CRFs (CRF01_AE and CRF02_AG). Other CRFs were identified only by COMET, REGAv2, REGAv3, and SCUEAL and with variable sensitivity. When analyzing sequences for PR and RT separately, the performance for PR was generally lower and variable between the tools. Similarity and statistical-based tools were 100% reproducible, but this was lower for phylogenetic-based tools such as REGA (~99%) and SCUEAL (~96%).

CONCLUSIONS

REGAv3 had an improved performance for subtype B and CRF02_AG compared to REGAv2 and is now able to also identify all epidemiologically relevant CRFs. In general the best performing tools, in alphabetical order, were COMET, jpHMM, REGAv3, and SCUEAL when analyzing pure subtypes in the pol region, and COMET and REGAv3 when analyzing most of the CRFs. Based on this study, we recommend to confirm subtyping with 2 well performing tools, and be cautious with the interpretation of short sequences.

Characterization of HIV-1 gag and nef in Cameroon: further evidence of extreme diversity at the origin of the HIV-1 group M epidemic

BACKGROUND

Cameroon, in west central Africa, has an extraordinary degree of HIV diversity, presenting a major challenge for the development of an effective HIV vaccine. Given the continuing need to closely monitor the emergence of new HIV variants in the country, we analyzed HIV-1 genetic diversity in 59 plasma samples from HIV-infected Cameroonian blood donors. Full length HIV gag and nef sequences were generated and phylogenetic analyses were performed.

FINDINGS

All gag and nef sequences clustered within HIV-1M. Circulating recombinant form CRF02_AG predominated, accounting for 50% of the studied infections, followed by clade G (11%), clade D and CRF37_cpx (4% each), and clades A, F, CRF01_AE and CRF36_cpx (2% each). In addition, 22% of the studied viruses apparently had nef and gag genes from viruses belonging to different clades, with the majority (8/10) having either a nef or gag gene derived from CRF02_AG. Interestingly, five gag sequences (10%) and three (5%) nef sequences were neither obviously recombinant nor easily classifiable into any of the known HIV-1M clades.

CONCLUSION

This suggests the widespread existence of highly divergent HIV lineages in Cameroon. While the genetic complexity of the Cameroonian HIV-1 epidemic has potentially serious implications for the design of biomedical interventions, detailed analyses of divergent Cameroonian HIV-1M lineages could be crucial for dissecting the earliest evolutionary steps in the emergence of HIV-1M.

Population dynamics of HIV-2 in rural West Africa: comparison with HIV-1 and ongoing transmission at the heart of the epidemic

OBJECTIVES

To compare the population dynamics of HIV-2 and HIV-1, and to characterize ongoing HIV-2 transmission in rural Guinea-Bissau.

DESIGN

Phylogenetic and phylodynamic analyses using HIV-2 gag and env, and HIV-1 env sequences, combined with epidemiological data from a community cohort.

METHODS

Samples were obtained from surveys in 1989-1991, 1996-1997, 2003 and 2006-2007. Phylogenies were reconstructed using sequences from 103 HIV-2-infected and 56 HIV-1-infected patients using Bayesian Evolutionary Analysis by Sampling Trees (BEAST), a relaxed molecular clock and a Bayesian skyline coalescent model.

RESULTS

Bayesian skyline plots showed a strong increase in the 1990s of the HIV-1 effective population size (Ne) in the same period that the Ne of HIV-2 came into a plateau phase. The population dynamics of both viruses were remarkably similar following initial introduction. Incident infections were found more often in HIV-2 transmission clusters, with 55-58% of all individuals contributing to ongoing transmission. Some phylogenetically linked sexual partners had discordant viral loads (undetectable vs. detectable), suggesting host factors dictate the risk of disease progression in HIV-2. Multiple HIV-2 introductions into the cohort are evident, but ongoing transmission has occurred predominantly within the community.

CONCLUSION

Comparison of HIV-1 and HIV-2 phylodynamics in the same community suggests both viruses followed similar growth patterns following introduction, and is consistent with the hypothesis that HIV-1 may have played a role in the decline of HIV-2 via competitive exclusion. The source of ongoing HIV-2 transmission in the cohort appears to be new HIV-2 cases, rather than the pool of older infections established during the early growth of HIV-2.

Spatial accessibility and the spread of HIV-1 subtypes and recombinants

OBJECTIVE/DESIGN

The global spread of HIV-1 main group (group M) has resulted in differential distributions of subtypes and recombinants, with the greatest diversity being found in sub-Saharan Africa. The explanations for the current subtype distribution patterns are likely multifactorial, but the promotion of human migrations and movements through transportation link availability and quality, summarized through 'accessibility', have been consistently cited as strong drivers. We sought to address the question of whether accessibility has been a significant factor in HIV-1 spread across mainland Africa through spatial analyses of molecular epidemiology, transport network and land cover data.

METHODS

The distribution of HIV-1 subtypes and recombinants in sub-Saharan Africa for the period 1998-2008 was mapped using molecular epidemiology data at a finer level of detail than ever before. Moreover, hypotheses on the role of distance, road network structure and accessibility in explaining the patterns seen were tested using spatial datasets representing African transport infrastructure, land cover and an accessibility model of landscape travel speed.

RESULTS

Coherent spatial patterns in HIV-1 subtype distributions across the continent exist, and a substantial proportion of the variance in the distribution and diversity pattern seen can be explained by variations in regional spatial accessibility.

CONCLUSION

The study confirms quantitatively the influence of transport infrastructure on HIV-1 spread within Africa, presents an approach for examining potential future impacts of road development projects and, more generally, highlights the importance of accessibility in the spread of communicable diseases.

Improving Bayesian population dynamics inference: a coalescent-based model for multiple loci

Effective population size is fundamental in population genetics and characterizes genetic diversity. To infer past population dynamics from molecular sequence data, coalescent-based models have been developed for Bayesian nonparametric estimation of effective population size over time. Among the most successful is a Gaussian Markov random field (GMRF) model for a single gene locus. Here, we present a generalization of the GMRF model that allows for the analysis of multilocus sequence data. Using simulated data, we demonstrate the improved performance of our method to recover true population trajectories and the time to the most recent common ancestor (TMRCA). We analyze a multilocus alignment of HIV-1 CRF02_AG gene sequences sampled from Cameroon. Our results are consistent with HIV prevalence data and uncover some aspects of the population history that go undetected in Bayesian parametric estimation. Finally, we recover an older and more reconcilable TMRCA for a classic ancient DNA data set.

HIV-1 drug resistance genotyping from antiretroviral therapy (ART) naïve and first-line treatment failures in Djiboutian patients

Abstract

In this study we report the prevalence of antiretroviral drug resistant HIV-1 genotypes of virus isolated from Djiboutian patients who failed first-line antiretroviral therapy (ART) and from ART naïve patients.

Patients and methods

A total of 35 blood samples from 16 patients who showed first-line ART failure (>1000 viral genome copies/ml) and 19 ART-naïve patients were collected in Djibouti from October 2009 to December 2009. Both the protease (PR) and reverse transcriptase (RT) genes were amplified and sequenced using National Agency for AIDS Research (ANRS) protocols. The Stanford HIV database algorithm was used for interpretation of resistance data and genotyping.

Results

Among the 16 patients with first-line ART failure, nine (56.2%) showed reverse transcriptase inhibitor-resistant HIV-1 strains: two (12.5%) were resistant to nucleoside (NRTI), one (6.25%) to non-nucleoside (NNRTI) reverse transcriptase inhibitors, and six (37.5%) to both. Analysis of the DNA sequencing data indicated that the most common mutations conferring drug resistance were M184V (38%) for NRTI and K103N (25%) for NNRTI. Only NRTI primary mutations K101Q, K103N and the PI minor mutation L10V were found in ART naïve individuals. No protease inhibitor resistant strains were detected. In our study, we found no detectable resistance in ∼ 44% of all patients who experienced therapeutic failure which was explained by low compliance, co-infection with tuberculosis and malnutrition. Genotyping revealed that 65.7% of samples were infected with subtype C, 20% with CRF02_AG, 8.5% with B, 2.9% with CRF02_AG/C and 2.9% with K/C.

Conclusion

The results of this first study about drug resistance mutations in first-line ART failures show the importance of performing drug resistance mutation test which guides the choice of a second-line regimen. This will improve the management of HIV-infected Djiboutian patients.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2051206212753973

Toward a quantitative understanding of viral phylogeography

Phylogeographic approaches help uncover the imprint that spatial epidemiological processes leave in the genomes of fast evolving viruses. Recent Bayesian inference methods that consider phylogenetic diffusion of discretely and continuously distributed traits offer a unique opportunity to explore genotypic and phenotypic evolution in greater detail. To provide a taste of the recent advances in viral diffusion approaches, we highlight key findings arising at the intrahost, local and global epidemiological scales. We also outline future areas of research and discuss how these may contribute to a quantitative understanding of the phylodynamics of RNA viruses.