Autochthonous Crimean-Congo Hemorrhagic Fever in Spain.

Crimean-Congo hemorrhagic fever (CCHF) is a widely distributed, viral, tickborne disease. In Europe, cases have been reported only in the southeastern part of the continent. We report two autochthonous cases in Spain. The index patient acquired the disease through a tick bite in the province of Ávila - 300 km away from the province of Cáceres, where viral RNA from ticks was amplified in 2010. The second patient was a nurse who became infected while caring for the index patient. Both were infected with the African 3 lineage of this virus. (Funded by Red de Investigación Cooperativa en Enfermedades Tropicales [RICET] and Efficient Response to Highly Dangerous and Emerging Pathogens at EU [European Union] Level [EMERGE].).

Survey of Crimean-Congo Hemorrhagic Fever Enzootic Focus, Spain, 2011-2015.

During 2011-2015, we conducted a Crimean-Congo hemorrhagic fever virus (CCHFV) survey in captured ticks that were feeding mainly on wild and domestic ungulates in Spain, where presence of this virus had been reported previously. We detected CCHFV RNA in Hyalomma lusitanicum and H. marginatum ticks for 3 of the 5 years. The rate of infected ticks was 2.78% (44/1,579), which was similar to those for other countries in Europe with endemic foci for CCHFV (Kosovo, Bulgaria, and Albania). These data confirm the established spread of CCHFV into western Europe. Phylogenetic study of the small RNA segment showed Africa-3 clade as the only genotype identified, although we observed cocirculation of genetic variants during 2011 and 2015. We could not rule out genetic reassortments because of lack of sequence data for the medium and large RNA segments of the virus genome.

Ribavirin Had Demonstrable Effects on the Crimean-Congo Hemorrhagic Fever Virus (CCHFV) Population and Load in a Patient With CCHF Infection.

The use of ribavirin to treat Crimean-Congo hemorrhagic fever virus (CCHFV) infection has been controversial, based on uncertainties about its antiviral efficacy in clinical case studies. We studied the effect of ribavirin treatment on viral populations in a recent case by deep-sequencing analysis of plasma samples obtained from a CCHFV-infected patient before, during, and after a 5-day regimen of ribavirin treatment. The CCHFV load dropped during ribavirin treatment, and subclonal diversity (transitions) and indels increased in viral genomes during treatment. Although the results are based on a single case, these data demonstrate the mutagenic effect of ribavirin on CCHFV in vivo.

Phylogenetic Characterization of Crimean-Congo Hemorrhagic Fever Virus, Spain.

Two cases of Crimean-Congo hemorrhagic fever were reported in Spain during 2016. We obtained the virus from a patient sample and characterized its full genomic sequence. Phylogenetic analysis indicated that the virus corresponds to the African genotype III, which includes viruses previously found in West and South Africa.

Chikungunya virus infections among travellers returning to Spain, 2008 to 2014.

Since the first documented autochthonous transmission of chikungunya virus in the Caribbean island of Saint Martin in 2013, the infection has been reported within the Caribbean region as well as North, Central and South America. The risk of autochthonous transmission of chikungunya virus becoming established in Spain may be elevated due to the large numbers of travellers returning to Spain from countries affected by the 2013 epidemic in the Caribbean and South America, as well as the existence of the Aedes albopictus vector in certain parts of Spain. We retrospectively analysed the laboratory diagnostic database of the National Centre for Microbiology, Institute of Health Carlos III (CNM-ISCIII) from 2008 to 2014. During the study period, 264 confirmed cases, of 1,371 suspected cases, were diagnosed at the CNM-ISCIII. In 2014 alone, there were 234 confirmed cases. The highest number of confirmed cases were reported from the Dominican Republic (n = 136), Venezuela (n = 30) and Haiti (n = 11). Six cases were viraemic in areas of Spain where the vector is present. This report highlights the need for integrated active case and vector surveillance in Spain and other parts of Europe where chikungunya virus may be introduced by returning travellers.

Clinical, microbiological, and molecular characterization of pediatric invasive infections by Streptococcus pyogenes in Spain in a context of global outbreak.

In December 2022, an alert was published in the UK and other European countries reporting an unusual increase in the incidence of Streptococcus pyogenes infections. Our aim was to describe the clinical, microbiological, and molecular characteristics of group A Streptococcus invasive infections (iGAS) in children prospectively recruited in Spain (September 2022-March 2023), and compare invasive strains with strains causing mild infections. One hundred thirty isolates of S. pyogenes causing infection (102 iGAS and 28 mild infections) were included in the microbiological study: emm typing, antimicrobial susceptibility testing, and sequencing for core genome multilocus sequence typing (cgMLST), resistome, and virulome analysis. Clinical data were available from 93 cases and 21 controls. Pneumonia was the most frequent clinical syndrome (41/93; 44.1%), followed by deep tissue abscesses (23/93; 24.7%), and osteoarticular infections (11/93; 11.8%). Forty-six of 93 cases (49.5%) required admission to the pediatric intensive care unit. iGAS isolates mainly belonged to emm1 and emm12; emm12 predominated in 2022 but was surpassed by emm1 in 2023. Spread of M1UK sublineage (28/64 M1 isolates) was communicated for the first time in Spain, but it did not replace the still predominant sublineage M1global (36/64). Furthermore, a difference in emm types compared with the mild cases was observed with predominance of emm1, but also important representativeness of emm12 and emm89 isolates. Pneumonia, the most frequent and severe iGAS diagnosed, was associated with the speA gene, while the ssa superantigen was associated with milder cases. iGAS isolates were mainly susceptible to antimicrobials. cgMLST showed five major clusters: ST28-ST1357/emm1, ST36-ST425/emm12, ST242/emm12.37, ST39/emm4, and ST101-ST1295/emm89 isolates. IMPORTANCE: Group A Streptococcus (GAS) is a common bacterial pathogen in the pediatric population. In the last months of 2022, an unusual increase in GAS infections was detected in various countries. Certain strains were overrepresented, although the cause of this raise is not clear. In Spain, a significant increase in mild and severe cases was also observed; this study evaluates the clinical characteristics and the strains involved in both scenarios. Our study showed that the increase in incidence did not correlate with an increase in resistance or with an emm types shift. However, there seemed to be a rise in severity, partly related to a greater rate of pneumonia cases. These findings suggest a general increase in iGAS that highlights the need for surveillance. The introduction of whole genome sequencing in the diagnosis and surveillance of iGAS may improve the understanding of antibiotic resistance, virulence, and clones, facilitating its control and personalized treatment.

Carbapenemase-Producing Klebsiella pneumoniae in COVID-19 Intensive Care Patients: Identification of IncL-VIM-1 Plasmid in Previously Non-Predominant Sequence Types.

During the COVID-19 pandemic, intensive care units (ICUs) operated at or above capacity, and the number of ICU patients coinfected by nosocomial microorganisms increased. Here, we characterize the population structure and resistance mechanisms of carbapenemase-producing Klebsiella pneumoniae (CP-Kpn) from COVID-19 ICU patients and compare them to pre-pandemic populations of CP-Kpn. We analyzed 84 CP-Kpn isolates obtained during the pandemic and 74 CP-Kpn isolates obtained during the pre-pandemic period (2019) by whole genome sequencing, core genome multilocus sequence typing, plasmid reconstruction, and antibiotic susceptibility tests. More CP-Kpn COVID-19 isolates produced OXA-48 (60/84, 71.4%) and VIM-1 (18/84, 21.4%) than KPC (8/84, 9.5%). Fewer pre-pandemic CP-Kpn isolates produced VIM-1 (7/74, 9.5%). Cefiderocol (97.3-100%) and plazomicin (97.5-100%) had the highest antibiotic activity against pandemic and pre-pandemic isolates. Sequence type 307 (ST307) was the most widely distributed ST in both groups. VIM-1-producing isolates belonging to ST307, ST17, ST321 and ST485, (STs infrequently associated to VIM-1) were detected during the COVID-19 period. Class 1 integron Int1-blaVIM-1-aac(6')-1b-dfrB1-aadAI-catB2-qacEΔ1/sul1, found on an IncL plasmid of approximately 70,000 bp, carried blaVIM-1 in ST307, ST17, ST485, and ST321 isolates. Thus, CP-Kpn populations from pandemic and pre-pandemic periods have similarities. However, VIM-1 isolates associated with atypical STs increased during the pandemic, which warrants additional monitoring and surveillance.

An increase in erythromycin resistance in methicillin-susceptible Staphylococcus aureus from blood correlates with the use of macrolide/lincosamide/streptogramin antibiotics. EARS-Net Spain (2004-2020).

Objectives: To describe and analyse erythromycin resistance trends in blood isolates of Staphylococcus aureus (EARS-Net Spain, 2004-2020) and the association of these trends with the consumption of macrolide, lincosamide, and streptogramin B (MLSB) antibiotics. To assess molecular changes that could be involved in erythromycin resistance trends by whole genome analysis of representative isolates. Materials and methods: We collected antibiotic susceptibility data for all first-blood S. aureus isolates in patients from 47 Spanish hospitals according to EARS-Net criteria. MLSB antibiotic consumption was obtained from the Spanish Agency for Medicines and Medical Devices (2008-2020). We sequenced 137 representative isolates for core genome multilocus sequence typing, resistome and virulome analysis. Results: For the 36,612 invasive S. aureus isolates, methicillin resistance decreased from 26.4% in 2004 to 22.4% in 2020. Erythromycin resistance in methicillin-susceptible S. aureus (MSSA) increased from 13.6% in 2004 to 28.9% in 2020 (p < 0.001); however, it decreased from 68.7 to 61.8% (p < 0.0001) in methicillin-resistant S. aureus (MRSA). Total consumption of MLSB antibiotics increased from 2.72 defined daily doses per 1,000 inhabitants per day (DID) in 2014 to 3.24 DID in 2016. By WGS, the macrolide resistance genes detected were erm (59.8%), msrA (46%), and mphC (45.2%). The erm genes were more prevalent in MSSA (44/57, 77.2%) than in MRSA (38/80, 47.5%). Most of the erm genes identified in MSSA after 2013 differed from the predominant ermC gene (17/22, 77.3%), largely because ermT was significantly associated with MSSA after 2013 (11/29, 37.9%). All 13 ermT isolates in this study, except one, belonged to ST398 and came from 10 hospitals and six Spanish provinces. Conclusion: The significant increase in erythromycin resistance in blood MSSA correlated with the consumption of the MLSB antibiotics in Spain. These preliminary data seem support the hypothesis that the human ST398 MSSA clade with ermT-mediated resistance to erythromycin may be involved in this trend.

Widespread Detection of Yersiniabactin Gene Cluster and Its Encoding Integrative Conjugative Elements (ICEKp) among Nonoutbreak OXA-48-Producing Klebsiella pneumoniae Clinical Isolates from Spain and the Netherlands.

In this study, we determined the presence of virulence factors in nonoutbreak, high-risk clones and other isolates belonging to less common sequence types associated with the spread of OXA-48-producing Klebsiella pneumoniae clinical isolates from The Netherlands (n = 61) and Spain (n = 53). Most isolates shared a chromosomally encoded core of virulence factors, including the enterobactin gene cluster, fimbrial fim and mrk gene clusters, and urea metabolism genes (ureAD). We observed a high diversity of K-Locus and K/O loci combinations, KL17 and KL24 (both 16%), and the O1/O2v1 locus (51%) being the most prevalent in our study. The most prevalent accessory virulence factor was the yersiniabactin gene cluster (66.7%). We found seven yersiniabactin lineages-ybt 9, ybt 10, ybt 13, ybt 14, ybt 16, ybt 17, and ybt 27-which were chromosomally embedded in seven integrative conjugative elements (ICEKp): ICEKp3, ICEKp4, ICEKp2, ICEKp5, ICEKp12, ICEKp10, and ICEKp22, respectively. Multidrug-resistant lineages-ST11, ST101, and ST405-were associated with ybt 10/ICEKp4, ybt 9/ICEKp3, and ybt 27/ICEKp22, respectively. The fimbrial adhesin kpi operon (kpiABCDEFG) was predominant among ST14, ST15, and ST405 isolates, as well as the ferric uptake system kfuABC, which was also predominant among ST101 isolates. No convergence of hypervirulence and resistance was observed in this collection of OXA-48-producing K. pneumoniae clinical isolates. Nevertheless, two isolates, ST133 and ST792, were positive for the genotoxin colibactin gene cluster (ICEKp10). In this study, the integrative conjugative element, ICEKp, was the major vehicle for yersiniabactin and colibactin gene clusters spreading. IMPORTANCE Convergence of multidrug resistance and hypervirulence in Klebsiella pneumoniae isolates has been reported mostly related to sporadic cases or small outbreaks. Nevertheless, little is known about the real prevalence of carbapenem-resistant hypervirulent K. pneumoniae since these two phenomena are often separately studied. In this study, we gathered information on the virulent content of nonoutbreak, high-risk clones (i.e., ST11, ST15, and ST405) and other less common STs associated with the spread of OXA-48-producing K. pneumoniae clinical isolates. The study of virulence content in nonoutbreak isolates can help us to expand information on the genomic landscape of virulence factors in K. pneumoniae population by identifying virulence markers and their mechanisms of spread. Surveillance should focus not only on antimicrobial resistance but also on virulence characteristics to avoid the spread of multidrug and (hyper)virulent K. pneumoniae that may cause untreatable and more severe infections.

Titers of lentiviral vectors encoding shRNAs and miRNAs are reduced by different mechanisms that require distinct repair strategies.

RNAi-based gene therapy is a powerful approach to treat viral infections because of its high efficiency and sequence specificity. The HIV-1-based lentiviral vector system is suitable for the delivery of RNAi inducers to HIV-1 susceptible cells due to its ability to transduce nondividing cells, including hematopoietic stem cells, and its ability for stable transgene delivery into the host cell genome. However, the presence of anti-HIV short hairpin RNA (shRNA) and microRNA (miRNA) cassettes can negatively affect the lentiviral vector titers. We show that shRNAs, which target the vector genomic RNA, strongly reduced lentiviral vector titers but inhibition of the RNAi pathway via saturation could rescue vector production. The presence of miRNAs in the vector RNA genome (sense orientation) results in a minor titer reduction due to Drosha processing. A major cause for titer reduction of miRNA vectors is due to incompatibility of the cytomegalovirus promoter with the lentiviral vector system. Replacement of this promoter with an inducible promoter resulted in an almost complete restoration of the vector titer. We also showed that antisense poly(A) signal sequences can have a dramatic effect on the vector titer. These results show that not all sequences are compatible with the lentiviral vector system and that care should be taken in the design of lentiviral vectors encoding RNAi inducers.

Novel association of five HLA alleles with HIV-1 progression in Spanish long-term non progressor patients.

Certain host genetic variants, especially in the human leucocyte antigen (HLA) region, are associated with different progression of HIV-1-induced diseases and AIDS. Long term non progressors (LTNP) represent only the 2% of infected patients but are especially relevant because of their efficient HIV control. In this work we present a global analysis of genetic data in the large national multicenter cohort of Spanish LTNP, which is compared with seronegative individuals and HIV-positive patients. We have analyzed whether several single-nucleotide polymorphisms (SNPs) including in key genes and certain HLA-A and B alleles could be associated with a specific HIV phenotype. A total of 846 individuals, 398 HIV-1-positive patients (213 typical progressors, 55 AIDS patients, and 130 LTNPs) and 448 HIV-negative controls, were genotyped for 15 polymorphisms and HLA-A and B alleles. Significant differences in the allele frequencies among the studied populations identified 16 LTNP-associated genetic factors, 5 of which were defined for the first time as related to LTNP phenotype: the protective effect of HLA-B39, and the detrimental impact of HLA-B18, -A24, -B08 and -A29. The remaining eleven polymorphisms confirmed previous publications, including the protective alleles HLA-B57, rs2395029 (HCP5), HLA bw4 homozygosity, HLA-B52, HLA-B27, CCR2 V64I, rs9264942 (HLA-C) and HLA-A03; and the risk allele HLA bw6 homozygosity. Notably, individual Spanish HIV-negative individuals had an average of 0.12 protective HLA alleles and SNPs, compared with an average of 1.43 protective alleles per LTNP patient, strongly suggesting positive selection of LTNP. Finally, stratification of LTNP according to viral load showed a proportional relationship between the frequency of protective alleles with control of viral load. Interestingly, no differences in the frequency of protection/risk polymorphisms were found between elite controllers and LTNPs maintaining viral loads <2.000 copies/mL throughout the follow-up.

First Evidence of Antibodies Against Lloviu Virus in Schreiber's Bent-Winged Insectivorous Bats Demonstrate a Wide Circulation of the Virus in Spain.

Although Lloviu virus (LLOV) was discovered in the carcasses of insectivorous Schreiber's Bent-winged bats in the caves of Northern Spain in 2002, its infectivity and pathogenicity remain unclear. We examined the seroprevalence of LLOV in potentially exposed Schreiber's Bent-winged bats (n = 60), common serotine bats (n = 10) as controls, and humans (n = 22) using an immunoblot assay. We found antibodies against LLOV GP2 in all of Schreiber's Bent-winged bats serum pools, but not in any of the common serotine bats and human pools tested. To confirm this seroreactivity, 52 serums were individually tested using Domain Programmable Arrays (DPA), a phage display based-system serology technique for profiling filovirus epitopes. A serological signature against different LLOV proteins was obtained in 19/52 samples tested (36.5%). The immunodominant response was in the majority specific to LLOV-unique epitopes, confirming that the serological response detected was to LLOV. To our knowledge, this is the first serological evidence of LLOV exposure in live captured Schreiber's Bent-winged bats, dissociating LLOV circulation as the cause of the previously reported die-offs.

Efficacy of antiretroviral therapy in individuals infected with HIV-1 non-B subtypes.

The impact of HIV-1 subtype on clinical outcome following exposure to antiretroviral therapy is currently not well known. Natural polymorphisms are often present in HIV-1 non-B subtypes at positions known to be associated with drug resistance in clade B viruses. These changes might influence the emergence of drug-resistant viruses, modifying drug susceptibility and/or the virus replicative capacity. Moreover, different pathways may lead to drug resistance according to HIV-1 clade. Finally, the influence of subtype on the performance of phenotypic assays and in the interpretation of algorithms for genotypic resistance is currently a matter of debate. All these aspects explain why the response to antiretroviral therapy might vary in subjects infected with different HIV-1 clades.

New findings on transcription regulation across different HIV-1 subtypes.

Transcriptional activation of gene expression in HIV-1 is controlled by the interaction of sequence-specific transcription factors with the long terminal repeat (LTR) of the provirus. The identification and characterization of cellular proteins involved in the process has provided a basic understanding about both general eukaryotic and HIV-1 proviral transcription regulation. The HIV-1 epidemic is expanding worldwide with an increasing number of distinct viral subtypes as well as intersubtype recombinant viruses. LTR-specific sequence variability among different HIV-1 variants could affect LTR binding to cellular and/or viral factors, influencing the extent of transcription. In vitro assays have demonstrated subtype-specific functional differences between the LTR regions of distinct HIV-1 subtypes. This observation could have consequences on the biology of the different HIV-1 clades and influence HIV-1 disease progression. Finally, the knowledge of the molecular mechanisms of transcription regulation events could help in the search for new compounds targeting the critical steps of viral transcription.

Cell entry by a novel European filovirus requires host endosomal cysteine proteases and Niemann-Pick C1.

Lloviu virus (LLOV), a phylogenetically divergent filovirus, is the proposed etiologic agent of die-offs of Schreibers's long-fingered bats (Miniopterus schreibersii) in western Europe. Studies of LLOV remain limited because the infectious agent has not yet been isolated. Here, we generated a recombinant vesicular stomatitis virus expressing the LLOV spike glycoprotein (GP) and used it to show that LLOV GP resembles other filovirus GP proteins in structure and function. LLOV GP must be cleaved by endosomal cysteine proteases during entry, but is much more protease-sensitive than EBOV GP. The EBOV/MARV receptor, Niemann-Pick C1 (NPC1), is also required for LLOV entry, and its second luminal domain is recognized with high affinity by a cleaved form of LLOV GP, suggesting that receptor binding would not impose a barrier to LLOV infection of humans and non-human primates. The use of NPC1 as an intracellular entry receptor may be a universal property of filoviruses.

Prevalence of HIV-1 dual infection in long-term nonprogressor-elite controllers.

INTRODUCTION: Human immunodeficiency virus type 1 (HIV-1) dual infection (DI) in long-term nonprogressor-elite controller patients (LTNP-EC) has been described only in sporadic cases and then, consequences in disease progression are not clearly established. To fill-up this limited knowledge, we analyzed, for the first time, the prevalence, host genetic polymorphisms, and clinical consequences of HIV-1 DI in a group of LTNP-EC. METHODS: For DI detection, nucleotide sequences in env gene from viruses from 20 LTNP-EC were analyzed by maximum likelihood. Epidemiological and clinical parameters and host factors of patients were also studied. RESULTS: DI was detected in 4 (20%) of the 20 LTNP-EC, of which 3 maintained the elite controller status. CD4⁺ T-cell counts were not different between single and DI patients although higher CD8⁺ T-cell counts were observed in DI patients, and, consequently, the CD4⁺/CD8⁺ ratios were lower in LTNP-EC DI patients. CONCLUSIONS: Prevalence of HIV-1 DIs in LTNP-EC is similar to other groups of HIV-1 patients; in addition, DI was not associated with loss of disease control in the patients. These DI LTNP-EC patients showed, in comparison with single infected patients, higher numbers of CD8⁺ T cells and lower CD4⁺/CD8⁺ ratios.

Differential prevalence of the HLA-C -- 35 CC genotype among viremic long term non-progressor and elite controller HIV+ individuals.

Susceptibility to HIV infection and disease progression are complex traits modulated by environmental and genetic factors, affecting innate and adaptive immune responses, among other cellular processes. A single nucleotide polymorphism (SNP) 35 kb upstream of the HLA-C gene locus (-35C/T) was previously shown to correlate with increased HLA-C expression and improved control of HIV-1. Here, we genotyped the -35C/T SNP in 639 subjects (180 uninfected patients, 304 HIV progressors and 155 LTNP) and confirmed the association of the -35C/T variant with the LTNP phenotype. The genotype frequencies in the general population subjects did not differ significantly from those seen in HIV progressors (p-value=0.472). However, a significant higher frequency of the protective CC genotype was identified when LTNP were compared either with HIV progressors alone (p-value<0.0001) or progressors and uninfected subjects together (p-value<0.0001). When considering aviremic LTNP alone (elite controllers; viral load below 50 copies/ml), the -35 CC genotype was not overrepresented compared to HIV progressors. Conversely, a significant association was found with the viremic LTNP groups (viral loads below 10,000 copies/ml). These results suggest that other factors alone or in combination with the -35 CC genotype may play an important role in differentiating the elite controller status from LTNP. Combination of different genetic variants may have additive or epistatic effects determining the HIV course of infection.

Genetic analysis of the long terminal repeat (LTR) promoter region in HIV-1-infected individuals with different rates of disease progression.

The long terminal repeat (LTR) region of HIV-1 promotes and modulates proviral transcription. LTR genetic variability might influence viral replication and disease progression. Proviral LTR sequences from 32 HIV-1-infected individuals showing different rates of disease progression were examined. Non-progressors (NP, n = 11) were individuals with high and stable CD4 counts and persistently low or undetectable plasma HIV-RNA. Slow progressors (SP, n = 6) were subjects with minimal CD4 decays over time and low plasma HIV-RNA. Typical progressors (TP, n = 15) were individuals with chronic infection showing CD4 counts repeatedly below 500 cells/mul. The mutation frequency within distinct LTR functional regions involved in HIV-1 transcription were compared in these three groups of patients. No significant differences were observed in the mutation frequency in most LTR regulatory sites when comparing the three groups. However, changes in USF regulatory binding sites were more frequent in TP than in SP/NP, while changes in Sp1 binding sites were less common in the former. This is the first study examining the genetic variability of the HIV-1 LTR region in long-term non-progressors showing further divergent outcomes.

[Regulation of transcription in different HIV-1 subtypes]. / Regulación de la transcripción en los diferentes subtipos del VIH-1.

Transcriptional activation of HIV-1 gene expression is controlled in part by the interaction of viral and cellular transcription factors with the HIV-1 long terminal repeat (LTR) sequences. LTR variability among different HIV-1 subtypes could affect LTR binding of either cellular or viral elements, influencing the transcription level. This effect, in turn, may have consequences on the biology of the different HIV-1 clades and on disease progression. In some circumstances, a relationship between replication capacity in vitro and changes in binding sequences for transcription factors located at the LTR has been proven.

Tratamiento antirretroviral según tipos y subtipos del virus de la inmunodeficiencia humana / Antiviral therapy according to HIV type and subtype

Los virus del subtipo B del grupo M son las variantes más prevalentes del virus de la inmunodeficiencia humana (VIH) tipo 1 en los países occidentales. El desarrollo del tratamiento antirretroviral y la mayoría de los datos que conocemos sobre mecanismos de resistencia del VIH se han basado en el estudio de cepas del subtipo B. Sin embargo, en el global de la epidemia, predominan otros subtipos como el A y el C, así como formas recombinantes entre subtipos como son las variantes CRF01_AE y CRF02_AG, entre otros. Además, la prevalencia de estos subtipos no-B y de recombinantes está aumentando en los países desarrollados, favorecido principalmente por los movimientos migratorios y el turismo. Las diferencias genéticas entre subtipos podrían tener impacto en la respuesta al tratamiento antirretroviral y en el desarrollo de distintas vías de resistencia, aunque las evidencias clínicas en este sentido son aún limitadas. Se revisan a continuación algunas características de los diferentes subtipos que pueden tener influencia en la respuesta al tratamiento antirretroviral

HIV-1 group M subtype B viruses are the most prevalent variants in Western countries. Antiretroviral therapies have been developed using subtype B isolates. Most data on HIV drug resistance mechanisms are from clade B viruses. However, overall, subtypes A and C and circulating recombinant forms such as CRF01_AE y CRF02_AG predominate in the global epidemic. In addition, the prevalence of these non-B subtypes and of recombinant forms is increasing in developed countries, mainly due to migration and tourism. Genetic variability among subtypes could have an impact on therapy outcome and on the development of drug resistance, although clinical evidence remains limited. We review some characteristics of the various subtypes that could influence therapy outcome