Exploration of low-frequency allelic variants of SARS-CoV-2 genomes reveals coinfections in Mexico occurred during periods of VOCs turnover.

A total of 14 973 alleles in 29 661 sequenced samples collected between March 2021 and January 2023 by the Mexican Consortium for Genomic Surveillance (CoViGen-Mex) and collaborators were used to construct a thorough map of mutations of the Mexican SARS-CoV-2 genomic landscape containing Intra-Patient Minor Allelic Variants (IPMAVs), which are low-frequency alleles not ordinarily present in a genomic consensus sequence. This additional information proved critical in identifying putative coinfecting variants included alongside the most common variants, B.1.1.222, B.1.1.519, and variants of concern (VOCs) Alpha, Gamma, Delta, and Omicron. A total of 379 coinfection events were recorded in the dataset (a rate of 1.28 %), resulting in the first such catalogue in Mexico. The most common putative coinfections occurred during the spread of Delta or after the introduction of Omicron BA.2 and its descendants. Coinfections occurred constantly during periods of variant turnover when more than one variant shared the same niche and high infection rate was observed, which was dependent on the local variants and time. Coinfections might occur at a higher frequency than customarily reported, but they are often ignored as only the consensus sequence is reported for lineage identification.

SARS-CoV-2 Omicron variants BA.4 and BA.5 dominated the fifth COVID-19 epidemiological wave in Mexico.

In Mexico, the BA.4 and BA.5 Omicron variants dominated the fifth epidemic wave (summer 2022), superseding BA.2, which had circulated during the inter-wave period. The present study uses genome sequencing and statistical and phylogenetic analyses to examine these variants' abundance, distribution, and genetic diversity in Mexico from April to August 2022. Over 35 % of the sequenced genomes in this period corresponded to the BA.2 variant, 8 % to the BA.4 and 56 % to the BA.5 variant. Multiple subvariants were identified, but the most abundant, BA.2.9, BA.2.12.1, BA.5.1, BA.5.2, BA.5.2.1 and BA.4.1, circulated across the entire country, not forming geographical clusters. Contrastingly, other subvariants exhibited a geographically restricted distribution, most notably in the Southeast region, which showed a distinct subvariant dynamic. This study supports previous results showing that this region may be a significant entry point and contributed to introducing and evolving novel variants in Mexico. Furthermore, a differential distribution was observed for certain subvariants among specific States through time, which may have contributed to the overall increased diversity observed during this wave compared to the previous ones. This study highlights the importance of sustaining genomic surveillance to identify novel variants that may impact public health.

Exploring the Molecular Basis of Vesicular Stomatitis Virus Pathogenesis in Swine: Insights from Expression Profiling of Primary Macrophages Infected with M51R Mutant Virus.

Vesicular stomatitis virus (VSV) is an emergent virus affecting livestock in the US. Previously, using a recombinant VSV carrying the M51R mutation in the matrix protein (rNJ0612NME6-M51R), we evaluated the pathogenesis of this virus in pigs. Our results indicated that rNJ0612NME6-M51R represented an attenuated phenotype in in-vivo and in ex-vivo in pig macrophages, resembling certain clinical features observed in field VSV isolates. In order to gain more insight into the molecular basis leading to the attenuation of rNJ0612NME6-M51R in pigs, we conducted a microarray analysis to assess the gene expression profiles of primary porcine macrophages infected with rNJ0612NME6-M51R compared to its parental virus (rNJ0612NME6). Our results showed an overall higher gene expression in macrophages infected with rNJ0612NME6-M51R. Specifically, we observed that the pathways related with immune cytokine signaling and interferon (IFN)-related responses (including activation, signaling, induction, and antiviral mechanisms) were the ones comprising most of the relevant genes identified during this study. Collectively, the results presented herein highlight the relevance of type I interferon during the pathogenesis of VSV in pigs. The information generated from this study may represent a framework for future studies intended to understand the molecular bases of the pathogenesis of field strains in livestock.

Comparing the evolutionary dynamics of predominant SARS-CoV-2 virus lineages co-circulating in Mexico.

Over 200 different SARS-CoV-2 lineages have been observed in Mexico by November 2021. To investigate lineage replacement dynamics, we applied a phylodynamic approach and explored the evolutionary trajectories of five dominant lineages that circulated during the first year of local transmission. For most lineages, peaks in sampling frequencies coincided with different epidemiological waves of infection in Mexico. Lineages B.1.1.222 and B.1.1.519 exhibited similar dynamics, constituting clades that likely originated in Mexico and persisted for >12 months. Lineages B.1.1.7, P.1 and B.1.617.2 also displayed similar dynamics, characterized by multiple introduction events leading to a few successful extended local transmission chains that persisted for several months. For the largest B.1.617.2 clades, we further explored viral lineage movements across Mexico. Many clades were located within the south region of the country, suggesting that this area played a key role in the spread of SARS-CoV-2 in Mexico.

SARS-CoV-2 BW lineage, a fast-growing Omicron variant from southeast Mexico bearing relevant escape mutations.

PURPOSE: The swift expansion of the BW.1 SARS-CoV-2 variant coincided with a rapid increase of COVID-19 cases occurring in Southeast Mexico in October, 2022, which marked the start of Mexico's sixth epidemiological wave. In Yucatan, up to 92% (58 of 73) of weekly sequenced genomes between epidemiological week 42 and 47 were identified as either BW.1 or its descendant, BW.1.1 in the region, during the last trimester of 2022. In the current study, a comprehensive genomic comparison was carried out to characterize the evolutionary history of the BW lineage, identifying its origins and its most important mutations. METHODS: An alignment of all the genomes of the BW lineage and its parental BA.5.6.2 variant was carried out to identify their mutations. A phylogenetic and ancestral sequence reconstruction analysis with geographical inference, as well as a longitudinal analysis of point mutations, were performed to trace back their origin and contrast them with key RBD mutations in variant BQ.1, one of the fastest-growing lineages to date. RESULTS: Our ancestral reconstruction analysis portrayed Mexico as the most probable origin of the BW.1 and BW.1.1 variants. Two synonymous substitutions, T7666C and C14599T, support their Mexican origin, whereas other two mutations are specific to BW.1: S:N460K and ORF1a:V627I. Two additional substitutions and a deletion are found in its descending subvariant, BW.1.1. Mutations found in the receptor binding domain, S:K444T, S:L452R, S:N460K, and S:F486V in BW.1 have been reported to be relevant for immune escape and are also key mutations in the BQ.1 lineage. CONCLUSIONS: BW.1 appears to have arisen in the Yucatan Peninsula in Southeast Mexico sometime around July 2022 during the fifth COVID-19 wave. Its rapid growth may be in part explained by the relevant escape mutations also found in BQ.1.

Omicron-BA.1 Dispersion Rates in Mexico Varied According to the Regional Epidemic Patterns and the Diversity of Local Delta Subvariants.

PURPOSE: The Omicron subvariant BA.1 of SARS-CoV-2 was first detected in November 2021 and quickly spread worldwide, displacing the Delta variant. In this work, a characterization of the spread of this variant in Mexico is presented. METHODS: The time to fixation of BA.1, the diversity of Delta sublineages, the population density, and the level of virus circulation during the inter-wave interval were determined to analyze differences in BA.1 spread. RESULTS: BA.1 began spreading during the first week of December 2021 and became dominant in the next three weeks, causing the fourth COVID-19 epidemiological surge in Mexico. Unlike previous variants, BA.1 did not exhibit a geographically distinct circulation pattern. However, a regional difference in the speed of the replacement of the Delta variant was observed. CONCLUSIONS: Viral diversity and the relative abundance of the virus in a particular area around the time of the introduction of a new lineage seem to have influenced the spread dynamics, in addition to population density. Nonetheless, if there is a significant difference in the fitness of the variants, or if the time allowed for the competition is sufficiently long, it seems the fitter virus will eventually become dominant, as observed in the eventual dominance of the BA.1.x variant in Mexico.

Dominance of Three Sublineages of the SARS-CoV-2 Delta Variant in Mexico.

In this study, we analyzed the sequences of SARS-CoV-2 isolates of the Delta variant in Mexico, which has completely replaced other previously circulating variants in the country due to its transmission advantage. Among all the Delta sublineages that were detected, 81.5 % were classified as AY.20, AY.26, and AY.100. According to publicly available data, these only reached a world prevalence of less than 1%, suggesting a possible Mexican origin. The signature mutations of these sublineages are described herein, and phylogenetic analyses and haplotype networks are used to track their spread across the country. Other frequently detected sublineages include AY.3, AY.62, AY.103, and AY.113. Over time, the main sublineages showed different geographical distributions, with AY.20 predominant in Central Mexico, AY.26 in the North, and AY.100 in the Northwest and South/Southeast. This work describes the circulation, from May to November 2021, of the primary sublineages of the Delta variant associated with the third wave of the COVID-19 pandemic in Mexico and highlights the importance of SARS-CoV-2 genomic surveillance for the timely identification of emerging variants that may impact public health.

An approach to cellular tropism of SARS-CoV-2 through protein-protein interaction and enrichment analysis.

COVID-19, caused by SARS-CoV-2, is a primarily pulmonary disease that can affect several organs, directly or indirectly. To date, there are many questions about the different pathological mechanisms. Here, we generate an approach to identify the cellular-level tropism of SARS-CoV-2 using human proteomics, virus-host interactions, and enrichment analysis. Through a network-based approach, the molecular context was visualized and analyzed. This procedure was also performed for SARS-CoV-1. We obtained proteomes and interactomes from 145 different cells corresponding to 57 different tissues. We discarded the cells without the proteins known for interacting with the virus, such as ACE2 or TMPRSS2. Of the remaining cells, a gradient of susceptibility to infection was observed. In addition, we identified proteins associated with the coagulation cascade that can be directly or indirectly affected by viral proteins. As a whole we identified 55 cells that could be potentially controlled by the virus, with different susceptibilities, mainly being pneumocytes, heart, kidney, liver, or small intestine cells. These results help to explain the molecular context and provide elements for possible treatments in the current situation. This strategy may be useful for other viruses, especially those with limited reported PPI, such as a new virus.

The Alpha Variant (B.1.1.7) of SARS-CoV-2 Failed to Become Dominant in Mexico.

During the coronavirus disease 2019 (COVID-19) pandemic, the emergence and rapid increase of the B.1.1.7 (Alpha) lineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first identified in the United Kingdom in September 2020, was well documented in different areas of the world and became a global public health concern because of its increased transmissibility. The B.1.1.7 lineage was first detected in Mexico during December 2020, showing a slow progressive increase in its circulation frequency, which reached its maximum in May 2021 but never became predominant. In this work, we analyzed the patterns of diversity and distribution of this lineage in Mexico using phylogenetic and haplotype network analyses. Despite the reported increase in transmissibility of the B.1.1.7 lineage, in most Mexican states, it did not displace cocirculating lineages, such as B.1.1.519, which dominated the country from February to May 2021. Our results show that the states with the highest prevalence of B.1.1.7 were those at the Mexico-U.S. border. An apparent pattern of dispersion of this lineage from the northern states of Mexico toward the center or the southeast was observed in the largest transmission chains, indicating possible independent introduction events from the United States. However, other entry points cannot be excluded, as shown by multiple introduction events. Local transmission led to a few successful haplotypes with a localized distribution and specific mutations indicating sustained community transmission. IMPORTANCE The emergence and rapid increase of the B.1.1.7 (Alpha) lineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) throughout the world were due to its increased transmissibility. However, it did not displace cocirculating lineages in most of Mexico, particularly B.1.1.519, which dominated the country from February to May 2021. In this work, we analyzed the distribution of B.1.1.7 in Mexico using phylogenetic and haplotype network analyses. Our results show that the states with the highest prevalence of B.1.1.7 (around 30%) were those at the Mexico-U.S. border, which also exhibited the highest lineage diversity, indicating possible introduction events from the United States. Also, several haplotypes were identified with a localized distribution and specific mutations, indicating that sustained community transmission occurred in the country.

Two-year follow-up of the COVID-19 pandemic in Mexico.

Background: After the initial outbreak in China (December 2019), the World Health Organization declared COVID-19 a pandemic on March 11th, 2020. This paper aims to describe the first 2 years of the pandemic in Mexico. Design and methods: This is a population-based longitudinal study. We analyzed data from the national COVID-19 registry to describe the evolution of the pandemic in terms of the number of confirmed cases, hospitalizations, deaths and reported symptoms in relation to health policies and circulating variants. We also carried out logistic regression to investigate the major risk factors for disease severity. Results: From March 2020 to March 2022, the coronavirus disease 2019 (COVID-19) pandemic in Mexico underwent four epidemic waves. Out of 5,702,143 confirmed cases, 680,063 were hospitalized (11.9%), and 324,436 (5.7%) died. Even if there was no difference in susceptibility by gender, males had a higher risk of death (CFP: 7.3 vs. 4.2%) and hospital admission risk (HP: 14.4 vs. 9.5%). Severity increased with age. With respect to younger ages (0-17 years), the 60+ years or older group reached adjusted odds ratios of 9.63 in the case of admission and 53.05 (95% CI: 27.94-118.62) in the case of death. The presence of any comorbidity more than doubled the odds ratio, with hypertension-diabetes as the riskiest combination. While the wave peaks increased over time, the odds ratios for developing severe disease (waves 2, 3, and 4 to wave 1) decreased to 0.15 (95% CI: 0.12-0.18) in the fourth wave. Conclusion: The health policy promoted by the Mexican government decreased hospitalizations and deaths, particularly among older adults with the highest risk of admission and death. Comorbidities augment the risk of developing severe illness, which is shown to rise by double in the Mexican population, particularly for those reported with hypertension-diabetes. Factors such as the decrease in the severity of the SARS-CoV2 variants, changes in symptomatology, and advances in the management of patients, vaccination, and treatments influenced the decrease in mortality and hospitalizations.

Genetic Analysis of SARS-CoV-2 Variants in Mexico during the First Year of the COVID-19 Pandemic.

During the first year of the SARS-CoV-2 pandemic in Mexico, more than two million people were infected. In this study, we analyzed full genome sequences from 27 February 2020 to 28 February 2021 to characterize the geographical and temporal distribution of SARS-CoV-2 lineages and identify the most common circulating lineages during this period. We defined six different geographical regions with particular dynamics of lineage circulation. The Northeast and Northwest regions were the ones that exhibited the highest lineage diversity, while the Central south and South/Southeast regions presented less diversity with predominance of a certain lineage. Additionally, by late February 2021, lineage B.1.1.519 represented more than 89% of all circulating lineages in the country.

Positive Selection of ORF1ab, ORF3a, and ORF8 Genes Drives the Early Evolutionary Trends of SARS-CoV-2 During the 2020 COVID-19 Pandemic.

In this study, we analyzed full-length SARS-CoV-2 genomes from multiple countries to determine early trends in the evolutionary dynamics of the novel COVID-19 pandemic. Results indicated SARS-CoV-2 evolved early into at least three phylogenetic groups, characterized by positive selection at specific residues of the accessory proteins ORF3a and ORF8. Also, we are reporting potential relevant sites under positive selection at specific sites of non-structural proteins nsp6 and helicase. Our analysis of co-evolution showed evidence of epistatic interactions among sites in the genome that may be important in the generation of variants adapted to humans. These observations might impact not only public health but also suggest that more studies are needed to understand the genetic mechanisms that may affect the development of therapeutic and preventive tools, like antivirals and vaccines. Collectively, our results highlight the identification of ongoing selection even in a scenario of conserved sequences collected over the first 3 months of this pandemic.

Natural Vertical Transmission of Zika Virus in Larval Aedes aegypti Populations, Morelos, Mexico.

We characterized natural vertical transmission of Zika virus in pools of Aedes aegypti larvae hatched from eggs collected in Jojutla, Morelos, Mexico. Of the 151 pools analyzed, 17 tested positive for Zika virus RNA; infectious Zika virus was successfully isolated from 1 of the larvae pools (31N) in C6/36 cells. Real-time quantitative PCR and indirect immunofluorescence assays confirmed the identity of the isolate, named Zika virus isolate 31N; plaque assays in Vero cells demonstrated the isolate's infectivity in a mammalian cell line. We obtained the complete genome of Zika virus isolate 31N by next-generation sequencing and identified 3 single-nucleotide variants specific to Zika virus isolate 31N using the meta-CATS tool. These results demonstrate the occurrence of natural vertical transmission of Zika virus in wild Ae. aegypti mosquitoes and suggest that this transmission mode could aid in the spread and maintenance of Zika virus in nature.

Complete genome of DENV2 isolated from mosquitoes in Mexico.

Dengue virus is the most prevalent arbovirus in Mexico, and although the diversity of this virus has been studied, the vast majority of sequences have been derived from viruses isolated from the human host. In this work, we aimed to sequence and to analyze DENVs derived from wild mosquitoes captured in Acapulco Guerrero, Mexico. We succeeded in determining three full genome sequences of such viruses and were able to compare them with other reported sequences from human and mosquito-derived DENVs. We found 15 nonsynonymous and 88 synonymous substitutions that were present more frequently in mosquito viruses than what would be expected by chance, although the limited number of genomes reported so far puts a constraint on the conclusions that can be derived from these analyses. Also, given the high depth of coverage attained in one of the genomes a variant analysis was carried out, finding 68 polymorphic sites in this genome. Interestingly, six of them corresponded to SNV that were detected as potentially differential between mosquitoes and humans, indicating that a that at least some positions may be maintained as polymorphic, which may facilitate host transmission.

Postsplicing-Derived Full-Length Intron Circles in the Protozoan Parasite Entamoeba histolytica.

Noncoding circular RNAs are widespread in the tree of life. Particularly, intron-containing circular RNAs which apparently upregulate their parental gene expression. Entamoeba histolytica, the causative agent of dysentery and liver abscesses in humans, codes for several noncoding RNAs, including circular ribosomal RNAs, but no intron containing circular RNAs have been described to date. Divergent RT-PCR and diverse molecular approaches, allowed us to detect bona fide full-length intronic circular RNA (flicRNA) molecules. Self-splicing reactions, RNA polymerase II inhibition with Actinomycin D, and second step of splicing-inhibition with boric acid showed that the production of flicRX13 (one of the flicRNAs found in this work, and our test model) depends on mRNA synthesis and pre-mRNA processing instead of self-splicing. To explore the cues and factors involved in flicRX13 biogenesis in vivo, splicing assays were carried out in amoeba transformants where splicing factors and Dbr1 (intron lariat debranching enzyme 1) were silenced or overexpressed, or where Rabx13 wild-type and mutant 5'ss (splice site) and branch site minigene constructs were overexpressed. Whereas SF1 (splicing factor 1) is not involved, the U2 auxiliary splicing factor, Dbr1, and the GU-rich 5'ss are involved in postsplicing flicRX13 biogenesis, probably by Dbr1 stalling, in a similar fashion to the formation of ciRNAs (circular intronic RNAs), but with distinctive 5'-3'ss ligation points. Different from the reported functions of ciRNAs, the 5'ss GU-rich element of flicRX13 possibly interacts with transcription machinery to silence its own gene in cis. Furthermore, introns of E. histolytica virulence-related genes are also processed as flicRNAs.

Human Virome.

The human virome is composed by the set of all viruses, eukaryotic and prokaryotic, present in the human body; as each body compartment constitutes a different microenvironment, the virome varies with the body part. Additionally, other factors influence the virome composition, such as age, diet, and the presence of other components of the microbiome. The study of the virome takes advantage of the development of next generation sequencing, and has allowed the discovery of novel viruses, and the characterization of the virome in healthy and diseased individuals, allowing the association of viruses with specific diseases. Perhaps the most interesting development of the study of the virome is the interplay that viruses can have with other components of the microbiome, specifically bacteria, that can either up- or down-regulate the antiviral immune response and can therefore modulate viral infectivity. This relationship is reciprocal since viruses can in turn modulate bacterial infections. The complex interactions of the virome with other members of the microbiome in the context of host genetics, and their influence in the health status of the patient have just begun to be investigated and are not completely understood, but the findings so far indicate that the regulation of the immune response by viruses and other members of the microbiome can affect the outcome of infections.

Selective Factors Associated with the Evolution of Codon Usage in Natural Populations of Arboviruses.

Arboviruses (arthropod borne viruses) have life cycles that include both vertebrate and invertebrate hosts with substantial differences in vector and host specificity between different viruses. Most arboviruses utilize RNA for their genetic material and are completely dependent on host tRNAs for their translation, suggesting that virus codon usage could be a target for selection. In the current study we analyzed the relative synonymous codon usage (RSCU) patterns of 26 arboviruses together with 25 vectors and hosts, including 8 vertebrates and 17 invertebrates. We used hierarchical cluster analysis (HCA) and principal component analysis (PCA) to identify trends in codon usage. HCA demonstrated that the RSCU of arboviruses reflects that of their natural hosts, but not that of dead-end hosts. Of the two major components identified by PCA, the first accounted for 62.1% of the total variance, and among the 59 codons analyzed in this study, the leucine codon CTG had the highest correlation with the first principal component, however isoleucine had the highest correlation during amino acid analysis. Nucleotide and dinucleotide composition were the variables that explained most of the total codon usage variance. The results suggest that the main factors driving the evolution of codon usage in arboviruses is based on the nucleotide and dinucleotide composition present in the host. Comparing codon usage of arboviruses and potential vector hosts can help identifying potential vectors for emerging arboviruses.

Phylogeographic characteristics of vesicular stomatitis New Jersey viruses circulating in Mexico from 2005 to 2011 and their relationship to epidemics in the United States.

We analyzed the phylogenetic and time-space relationships (phylodynamics) of 181 isolates of vesicular stomatitis New Jersey virus (VSNJV) causing disease in Mexico and the United States (US) from 2005 through 2012. We detail the emergence of a genetic lineage in southern Mexico causing outbreaks in central Mexico spreading into northern Mexico and eventually into the US. That emerging lineage showed higher nucleotide sequence identity (99.5%) than that observed for multiple lineages circulating concurrently in southern Mexico (96.8%). Additionally, we identified 58 isolates from Mexico that, unlike previous isolates from Mexico, grouped with northern Central America clade II viruses. This study provides the first direct evidence for the emergence and northward migration of a specific VSNJV genetic lineage from endemic areas in Mexico causing VS outbreaks in the US. In addition we document the emergence of a Central American VSNJV genetic lineage moving northward and causing outbreaks in central Mexico.

The R2R3 Myb protein family in Entamoeba histolytica.

The MYB DNA-binding domain is conserved in vertebrates, plants, and fungi. This domain mediates the DNA-binding activity of proteins (that have transcription factor activity) in a sequence-specific manner and is also used for the protection of telomeric regions. The MYB DNA-binding domain contains three imperfect conserved repeats of 52 amino acids (R1, R2, and R3). Within each repeat, there are three tryptophans that are separated by 18 or 19 amino acids. In order to understand the role of Myb transcription factors in Entamoeba histolytica, we searched for MYB DNA-binding domain containing proteins using the amino acid sequence of human c-Myb as the query. We found 34 putative MYB DNA-binding domain containing proteins, which clustered into three monophyletic groups. Family I members conserve only the R2 and R3 repeats in their MYB DNA-binding domain and were dubbed in this report as EhMybR2R3. Family II includes single-repeat proteins related to human telomeric binding proteins. Family III is predicted to comprise proteins with one single repeat where the region corresponding to the conserved tryptophan of the third alpha helix is replaced by a (S)/(T)HAQK(Y)/(F)F motif; this family was named EhMybSHAQKYF. In this work, we focused on proteins that belong to the EhMybR2R3 family. RT-PCR analysis showed that EhMybR2R3 genes were differentially expressed in trophozoites grown in basal culture conditions. Purified rEhMyb10 protein, belonging to the EhMybR2R3 family, was able to bind a consensus Myb recognition element in vitro. In addition, using nuclear extracts from trophozoites of E. histolytica, we were able to detect Myb DNA-binding activity to this sequence. Our in silico surveys demonstrated that this consensus sequence is present in E. histolytica gene promoters. Interestingly, these promoters include different families of genes that are related to signal transduction, vesicular transport, heat shock response, and virulence. Thus, Myb putative transcription factors in E. histolytica could be involved in the transcriptional regulation of genes participating in several different pathways.

Pleocytosis is associated with disruption of HIV compartmentalization between blood and cerebral spinal fluid viral populations.

INTRODUCTION: We hypothesized that pleocytosis, which is a marker of central nervous system (CNS) inflammation, would result in viral genetic equilibration or de-compartmentalization between HIV populations in the blood and cerebrospinal fluid (CSF), suggesting viral trafficking. METHODS: Study subjects, who started or interrupted their antiretroviral treatment, had viral loads measured and clonal viral env sequences generated from HIV RNA extracted from paired blood and CSF samples. White blood counts in CSF were also measured at each timepoint. Degree of inter-compartment segregation was calculated by posterior probability using linear discriminant analysis and multidimensional scaling. Co-receptor usage was determined using a trained support vector machine. RESULTS: Pleocytosis was strongly associated with disruption of viral compartmentalization. CONCLUSIONS: Inflammation in the CNS, marked by pleocytosis, allows HIV populations to mix between blood and CSF, which may increase the overall viral genetic diversity within the CSF.