Serosurvey of Blood Donors to Assess West Nile Virus Exposure, South-Central Spain.

We analyzed West Nile Virus (WNV) exposure from 1,222 blood donors during 2017-2018 from an area of south-central Spain. Results revealed WNV seroprevalence of 0.08% (95% CI 0.004%-0.4%) in this population. Our findings underscore the need for continued surveillance and research to manage WNV infection in this region.

Detection of Rat Hepatitis E Virus in Pigs, Spain, 2023.

We identified rat hepatitis E virus (HEV) RNA in farmed pigs from Spain. Our results indicate that pigs might be susceptible to rat HEV and could serve as viral intermediaries between rodents and humans. Europe should evaluate the prevalence of rat HEV in farmed pigs to assess the risk to public health.

Acute Hepatitis in Children Due to Rat Hepatitis E Virus.

Two of 11 children with acute hepatitis of unknown origin were found to have rat hepatitis E virus infection. This infection should be considered in the differential diagnosis of children with acute hepatitis of unknown origin.

Molecular detection of Enterocytozoon bieneusi in bats from Portugal.

Enterocytozoon bieneusi is a microsporidia commonly found in the gastrointestinal tract of humans and a wide range of other animals, constituting a major cause of microsporidiosis in humans. Although E. bieneusi has been detected in humans, domestic, and wild animals in Portugal, and its presence in bats has been linked to zoonotic characteristics, its occurrence in bats within the country has not been reported. In this study, we investigated the presence of E. bieneusi in 380 bat fecal samples collected in mainland Portugal through a nested PCR assay targeting the internal transcribed spacer region and the flanking small and large subunits of the ribosomal RNA. Enterocytozoon bieneusi was detected in one bat sample (i.e., 0.26%; Pipistrellus pipistrellus). Additionally, another sample tested positive for Enterocytozoon sp. Phylogenetic analysis of the obtained ITS sequence of E. bieneusi revealed clustering within the potentially zoonotic Group 1. This study represents the first report of E. bieneusi in a bat from Europe. Findings presented here contribute to an enhanced understanding of E. bieneusi epidemiology.

Enterocytozoon bieneusi is the most frequent cause of microsporidiosis in humans. In this study, E. bieneusi, belonging to a potentially zoonotic Group, was detected in 0.26% bat samples from Portugal, highlighting bats' potential role in transmitting this microsporidia to humans and other animals.

Hepatitis E Virus Infections in Free-Ranging and Captive Cetaceans, Spain, 2011-2022.

Epidemiologic surveillance of hepatitis E virus in over 300 free-ranging and captive cetaceans in waters off Spain revealed extensive exposure to this pathogen. We suggest the persistent and widespread presence of hepatitis E in the marine environment off the coast of Spain may be driven by terrestrial sources of contamination.

Orthohepevirus C infection as an emerging cause of acute hepatitis in Spain: First report in Europe.

BACKGROUND & AIM: Hepatitis E virus (HEV) was considered the only member of the Hepeviridae family with zoonotic potential. Nevertheless, this consideration has been reassessed owing to several reported cases of acute and chronic hepatitis linked to the Orthohepevirus C genus. Because the circulation of Orthohepevirus C in rodents has been described worldwide, the risk of zoonotic transmission is plausibly global. METHODS: Orthohepevirus C RNA was retrospectively evaluated in 2 cohorts of patients in Spain. The first cohort included patients with acute hepatitis without etiological diagnosis after screening for hepatotropic virus infection. The second cohort included patients diagnosed with acute HEV infection, defined as positivity for anti-HEV-IgM antibodies and/or detectable HEV RNA in serum. RESULTS: Cohort 1 comprised 169 patients (64.4% male, median age 43 years) and cohort 2 comprised 98 individuals (68.3% male, median age 45 years). Of the individuals included in Cohort 1, two (1.18%; 95% CI 0.2-3.8) had detectable Orthohepevirus C RNA in serum. In Cohort 2, of the 98 included patients, 58 showed detectable HEV RNA, while 40 only showed positivity for IgM antibodies. Among those bearing only IgM antibodies, Orthohepevirus C RNA was detected in 1 (2.5%; 95% CI 0.06-13.1) individual. All strains were consistent with genotype C1. The infection resulted in mild self-limiting acute hepatitis in 2 patients. Infection caused severe acute hepatitis in the remaining patient who died as a result of liver and renal failure. CONCLUSIONS: We described 3 cases of Orthohepevirus C in patients with acute hepatitis, resulting in the first description of this infection in Europe. The prevalence obtained in our study suggests that Orthohepevirus C could be an emerging disease in Europe. LAY SUMMARY: We describe the first cases of acute hepatitis related to rat hepatitis E virus in Europe. The prevalence found in our study suggest that rat hepatitis E virus could be considered an emerging disease in Europe.

Zoonotic Enterocytozoon bieneusi genotypes in free-ranging and farmed wild ungulates in Spain.

Microsporidia comprises a diverse group of obligate, intracellular, and spore-forming parasites that infect a wide range of animals. Among them, Enterocytozoon bieneusi is the most frequently reported species in humans and other mammals and birds. Data on the epidemiology of E. bieneusi in wildlife are limited. Hence, E. bieneusi was investigated in eight wild ungulate species present in Spain (genera Ammotragus, Capra, Capreolus, Cervus, Dama, Ovis, Rupicapra, and Sus) by molecular methods. Faecal samples were collected from free-ranging (n = 1058) and farmed (n = 324) wild ungulates from five Spanish bioregions. The parasite was detected only in red deer (10.4%, 68/653) and wild boar (0.8%, 3/359). Enterocytozoon bieneusi infections were more common in farmed (19.4%, 63/324) than in wild (1.5%, 5/329) red deer. A total of 11 genotypes were identified in red deer, eight known (BEB6, BEB17, EbCar2, HLJD-V, MWC_d1, S5, Type IV, and Wildboar3) and three novel (DeerSpEb1, DeerSpEb2, and DeerSpEb3) genotypes. Mixed genotype infections were detected in 15.9% of farmed red deer. Two genotypes were identified in wild boar, a known (Wildboar3) and a novel (WildboarSpEb1) genotypes. All genotypes identified belonged to E. bieneusi zoonotic Groups 1 and 2. This study provides the most comprehensive epidemiological study of E. bieneusi in Spanish ungulates to date, representing the first evidence of the parasite in wild red deer populations worldwide. Spanish wild boars and red deer are reservoir of zoonotic genotypes of E. bieneusi and might play an underestimated role in the transmission of this microsporidian species to humans and other animals.

The fungal-related intracellular parasite Enterocytozoon bieneusi is a worldwide public health and veterinary problem. Here we demonstrated that it was present in wild boar, and wild and farmed red deer in Spain, with genotypes potentially capable of infecting humans, posing a public health risk.

Orthohepevirus C as causal agent of acute hepatitis in Spain.

Recently, it has been reported the first cases of acute hepatitis linked to Orthohepevirus C, supposing the first cases in Europe. In this editorial, we summarized the main findings of this study, evidence of the viral circulation among human and animal populations, as well as the research points that need to be assessed regarding the epidemiology, clinical management and diagnosis of this emerging virus.

Development and Clinical Validation of a Pangenotypic PCR-Based Assay for the Detection and Quantification of Hepatitis E Virus (Orthohepevirus A Genus).

The objective of this study was to design a pangenotypic PCR-based assay for the detection and quantification of hepatitis E virus (HEV) RNA from across the entire spectrum of described genotypes belonging to the Orthohepevirus A genus. The optimal conditions and the performance of the assay were determined by testing the WHO standard strain (6219/10) and the WHO HEV panel (8578/13). Similarly, performance comparisons were made with two commercial assays (Real Star HEV RT-PCR 2.0 and ampliCube HEV 2.0 Quant) to detect HEV RNA at concentrations below 1,000 IU/ml with viral strains from the WHO and to test samples from 54 patients with acute hepatitis. The assay presented in this study was able to detect the entire spectrum of described genotypes belonging to the Orthohepevirus A genus, demonstrating better performance than both commercial kits. This procedure may represent a significant improvement in the molecular diagnosis of HEV infection.

First molecular characterization of the hepatitis E virus in humans in Cameroon: Confirmation of the HEV outbreak in Touboro, North-Cameroon.

Hepatitis E virus (HEV) is a major causative agent of acute viral hepatitis in many regions of the world including Africa. In Cameroon, there is no published molecular study on HEV in humans. However, based on serological assays, the first outbreak of HEV was detected in North-Cameroon. The objective of this study was to determine the molecular characterization of HEV that circulated during this period. A retrospective study design was used to select serum samples among those collected during the outbreak period. immunoglobulin M positive samples available in sufficient volumes to amplify HEV RNA were selected. RNA was extracted and then amplified by a real-time reverse transcription polymerase chain reaction (real time RT-PCR) assay, followed by a nested reverse transcription polymerase chain reaction (nested RT-PCR) assay for sequencing and phylogenetic analysis. Overall, 24 samples were selected and HEV RNA was amplified by real-time RT-PCR in 20 samples. Amongst these, 12 samples were positive for HEV RNA by nested RT-PCR and yielded good sequencing products. Phylogenetic analysis showed that 10 samples clustered with HEV genotype 1 (subtype 1e) and two samples clustered with HEV genotype 3 (subtype 3f). This study fills the gap of knowledge on the molecular epidemiology of HEV in Cameroon and confirms the first report of the hepatitis E outbreak in North-Cameroon.

Classification Accuracy of Hepatitis C Virus Infection Outcome: Data Mining Approach.

BACKGROUND: The dataset from genes used to predict hepatitis C virus outcome was evaluated in a previous study using a conventional statistical methodology. OBJECTIVE: The aim of this study was to reanalyze this same dataset using the data mining approach in order to find models that improve the classification accuracy of the genes studied. METHODS: We built predictive models using different subsets of factors, selected according to their importance in predicting patient classification. We then evaluated each independent model and also a combination of them, leading to a better predictive model. RESULTS: Our data mining approach identified genetic patterns that escaped detection using conventional statistics. More specifically, the partial decision trees and ensemble models increased the classification accuracy of hepatitis C virus outcome compared with conventional methods. CONCLUSIONS: Data mining can be used more extensively in biomedicine, facilitating knowledge building and management of human diseases.

Prediction of Esophageal Varices by Liver Stiffness and Platelets in Persons With Human Immunodeficiency Virus Infection and Compensated Advanced Chronic Liver Disease.

BACKGROUND: People living with human immunodeficiency virus (PLWH) are at increased risk of cirrhosis and esophageal varices. Baveno VI criteria, based on liver stiffness measurement (LSM) and platelet count, have been proposed to avoid unnecessary esophagogastroduodenoscopy (EGD) screening for esophageal varices needing treatment (EVNT). This approach has not been validated in PLWH. METHODS: PLWH from 8 prospective cohorts were included if they fulfilled the following criteria: (1) compensated advanced chronic liver disease (LSM >10 kPa); (2) availability of EGD within 6 months of reliable LSM. Baveno VI (LSM <20 kPa and platelets >150 000/µL), expanded Baveno VI (LSM <25 kPa and platelets >110 000/µL), and Estudio de las Hepatitis Víricas (HEPAVIR) criteria (LSM <21 kPa) were applied to identify patients not requiring EGD screening. Criteria optimization was based on the percentage of EGDs spared, while keeping the risk of missing EVNT <5%. RESULTS: Five hundred seven PLWH were divided into a training (n = 318) and a validation set (n = 189). EVNT were found in 7.5%. In the training set, Baveno VI, expanded Baveno VI, and HEPAVIR criteria spared 10.1%, 25.5%, and 28% of EGDs, while missing 0%, 1.2%, and 2.2% of EVNT, respectively. The best thresholds to rule out EVNT were platelets >110 000/µL and LSM <30 kPa (HIV cirrhosis criteria), with 34.6% of EGDs spared and 0% EVNT missed. In the validation set, HEPAVIR and HIV cirrhosis criteria spared 54% and 48.7% of EGDs, while missing 4.9% and 2.2% EVNT, respectively. CONCLUSIONS: Baveno VI criteria can be extended to HEPAVIR and HIV cirrhosis criteria while sparing a significant number of EGDs, thus improving resource utilization for PLWH with compensated advanced chronic liver disease.

What is needed to achieve HCV microelimination among HIV-infected populations in Andalusia, Spain: a modeling analysis.

BACKGROUND: Scale-up of hepatitis C virus (HCV) treatment for HIV/HCV coinfected individuals is occurring in Spain, the vast majority (> 85%) with a reported history of injecting drug use and a smaller population of co-infected men who have sex with men (MSM). We assess impact of recent treatment scale-up to people living with HIV (PLWH) and implications for achieving the WHO HCV incidence elimination target (80% reduction 2015-2030) among PLWH and overall in Andalusia, Spain, using dynamic modeling. METHODS: A dynamic transmission model of HCV/HIV coinfection was developed. The model was stratified by people who inject drugs (PWID) and MSM. The PWID component included dynamic HCV transmission from the HCV-monoinfected population. The model was calibrated to Andalusia based on published data and the HERACLES cohort (prospective cohort of HIV/HCV coinfected individuals representing > 99% coinfected individuals in care in Andalusia). From HERACLES, we incorporated HCV treatment among diagnosed PLWH of 10.5%/year from 2004 to 2014, and DAAs at 33%/year from 2015 with 94.8% SVR. We project the impact of current and scaled-up HCV treatment for PLWH on HCV prevalence and incidence among PLWH and overall. RESULTS: Current treatment rates among PLWH (scaled-up since 2015) could substantially reduce the number of diagnosed coinfected individuals (mean 76% relative reduction from 2015 to 2030), but have little impact on new diagnosed coinfections (12% relative reduction). However, DAA scale-up to PWLH in 2015 would have minimal future impact on new diagnosed coinfections (mean 9% relative decrease from 2015 to 2030). Similarly, new cases of HCV would only reduce by a mean relative 29% among all PWID and MSM due to ongoing infection/reinfection. Diagnosing/treating all PLWH annually from 2020 would increase the number of new HCV infections among PWLH by 28% and reduce the number of new HCV infections by 39% among the broader population by 2030. CONCLUSION: Targeted scale-up of HCV treatment to PLWH can dramatically reduce prevalence among this group but will likely have little impact on the annual number of newly diagnosed HIV/HCV coinfections. HCV microelimination efforts among PWLH in Andalusia and settings where a large proportion of PLWH have a history of injecting drug use will require scaled-up HCV diagnosis and treatment among PLWH and the broader population at risk.

A Knockout IFNL4 Variant Is Associated With Protection From Sexually Transmitted HIV-1 Infection.

An interferon λ4 gene (IFNL4) knockout allele (rs368234815; TT) is associated with spontaneous and IFN-α-dependent cure of hepatitis C virus infection. The role of this polymorphism in the susceptibility to human immunodeficiency virus type 1 (HIV-1) infection is controversial. This study aimed to assess the association of this knockout IFNL4 variant and sexually transmitted HIV-1 infection. A total of 228 HIV-1-positive individuals and 136 HIV-exposed seronegative individuals were investigated for their association with IFNL4 rs368234815 genotypes. The IFNL4 ΔG functional allele is associated with increased susceptibility to HIV-1 infection through the sexual route (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.2-3.6; P = .004). A meta-analysis including a population of injection drug users suggests a codominant mode of inheritance of this risk factor (OR, 2.0; 95% CI, 1.3-3.2; P = .001).

Response to direct-acting antiviral therapy among ongoing drug users and people receiving opioid substitution therapy.

BACKGROUND & AIMS: People who inject drugs (PWID) and are on opioid agonist therapy (OAT) might have lower adherence to direct-acting antivirals (DAAs) against hepatitis C virus (HCV) and, therefore, lower rates of sustained virologic response (SVR). Because of this, we compared the SVR rates to interferon-free DAA combinations in individuals receiving OAT and those not receiving OAT in a real-world setting. METHODS: The HEPAVIR-DAA cohort, recruiting HIV/HCV-coinfected patients (NCT02057003), and the GEHEP-MONO cohort (NCT02333292), including HCV-monoinfected individuals, are ongoing prospective multicenter cohorts of patients receiving DAAs in clinical practice. We compared SVR 12 weeks after treatment (SVR12) in non-drug users and PWID, including those receiving or not receiving OAT. Intention-to-treat and per protocol analyses were performed. RESULTS: Overall, 1,752 patients started interferon-free DAA treatment. By intention-to-treat analysis, 778 (95%, 95% CI 93%-96%) never injectors, 673 (92%, 95% CI 89%-93%) PWID not on OAT and 177 (89%, 95% CI 83%-92%) PWID on OAT achieved SVR12 (p = 0.002). SVR12 rates for ongoing drug users (with or without OAT) were 68 (79%) compared with 1,548 (95%) for non-drug users (p <0.001). Among ongoing drug users, 15 (17%) were lost-to-follow-up, and 3 (3.5%) became reinfected. In the per protocol analysis, 97% never injectors, 95% PWID not on OAT and 95% PWID on OAT achieved SVR12 (p = 0.246). After adjustment, ongoing drug use was associated with SVR12 (intention-to-treat) and OAT use was not. CONCLUSIONS: HCV-infected PWID achieve high SVR12 rates with DAAs whether they are on OAT or not, but their response rates are lower than those of patients who never used drugs. This is mainly attributable to more frequent loss to follow-up. Accounting for active drug use during DAA therapy nearly closed the gap in SVR rates between the study groups. LAY SUMMARY: Patients with hepatitis C virus infection who are on opioid agonist therapy can achieve high cure rates with current treatments. The use of illicit drugs during treatment can drive drop-outs and reduce cure rates. However, hepatitis C can be cured in most of those using drugs who complete treatment and follow-up. Clinical trial number: HEPAVIR-DAA cohort, NCT02057003; GEHEP-MONO cohort, NCT02333292.

High efficacy of resistance-guided retreatment of HCV patients failing NS5A inhibitors in the real world.

BACKGROUND & AIMS: Most hepatitis C virus (HCV)-infected patients failing NS5A inhibitors develop resistance-associated substitutions (RASs). Here we report the use of resistance-guided retreatment of patients who failed prior NS5A inhibitor-containing regimens in the GEHEP-004 cohort. This is the largest direct-acting antiviral (DAA)-resistance cohort study conducted in Spain. We aim to provide indications on how to use resistance information in settings where sofosbuvir/velpatasvir/voxilaprevir may not be available. METHODS: GEHEP-004 is a prospective multicenter cohort enrolling HCV-infected patients treated with interferon (IFN)-free DAA regimens. Prior to retreatment, population-based sequencing of HCV NS3, NS5A and NS5B genes was performed. After receiving a comprehensive resistance interpretation report, the retreatment regimen was chosen and the sustained virological response (SVR) at 12 weeks after treatment completion (SVR12) was recorded. RESULTS: A total of 342 patients experiencing virological failure after treatment with sofosbuvir/ledipasvir±ribavirin (54%), sofosbuvir/daclatasvir±ribavirin (23%), or paritaprevir-ritonavir/ombitasvir±dasabuvir±ribavirin (20%) were studied. After a resistance report, 186 patients were retreated. An SVR12 was achieved for 88.1% of the patients who failed after sofosbuvir/ledipasvir±ribavirin, 83.3% of the patients who failed after sofosbuvir/daclatasvir±ribavirin, 93.7% of the patients who failed after paritaprevir-ritonavir+ombitasvir±dasabuvir±ribavirin. CONCLUSIONS: In our study, we show how resistance-guided retreatment in conjunction with an interpreted report allows patients to achieve SVR rates close to 90%. We hypothesize that SVR rates may even be improved if resistance data are discussed between experienced virologists and treating clinicians. We believe that our data may be relevant for countries where the access to new DAA combination regimens is limited. LAY SUMMARY: Hepatitis C infection can be cured with currently available antiviral agents. Only a small proportion of patients experience treatment failure, however, in absolute numbers, a high number of patients may require retreatment. Highly effective combinations of antivirals are also available for retreatment. However, these antivirals might not be available in resource-limited settings. Herein, we show how, by analyzing the cause of resistance, retreatment efficacy with old drugs can get very close to the efficacy of new drug combinations.

Early emergence of opportunistic infections after starting direct-acting antiviral drugs in HIV/HCV-coinfected patients.

Varicella-zoster virus and hepatitis B virus reactivations have been reported after starting interferon-free direct-acting antiviral agent (DAA) combinations. HIV/HCV-coinfected patients could be a high-risk group for the reactivation of latent infections. Because of these, we report the occurrence of severe infections after starting DAA regimens in HIV/HCV-coinfected patients. Individuals included in the HEPAVIR-DAA (NCT02057003) cohort were selected if they had received all-oral DAA combinations. A retrospective review of clinical events registered between the start of DAAs and 12 months after SVR12 was carried out. Overall, 38 (4.5%) of 848 patients presented infections. The incidence (95% confidence interval) of infections was 4.6 (3.3-6.3) cases per 100 person-years. The median (Q1-Q3) time to the infection since baseline was 23 (7.3-33) weeks. Five (13%) of the patients with infections died; four of them had cirrhosis. The frequency of previous AIDS was 21 (54%) for patients with infections and 324 (40%) for those without infections (P = 0.084). The median (Q1-Q3) nadir CD4 cell count of individuals with and without infections was 75 (53-178) and 144 (67-255) cells/µL, respectively (P = 0.047). Immunodepression-associated infections were observed in 9 (1.1%) patients. All of them had suppressed HIV replication with antiretroviral therapy. In conclusion, severe infections are relatively common among HIV/HCV-coinfected patients receiving all-oral DAA combinations. Some unusual reactivations of latent infections in patients with suppressed HIV replication seem to be temporally linked with DAA use.

Hepatitis E virus in Spanish donors and the necessity for screening.

Hepatitis E virus (HEV) represents a major health problem worldwide. As the course of HEV cases is often subclinical, asymptomatic infections could represent an important source of viral spread and infection via routes such as blood donations. Before universal screening for HEV in blood donations can be implemented, studies evaluating the incidence of infection are needed to establish the potential risk of viral transmission. This is a prospective longitudinal study that included blood donors recruited at the Hospital de Ciudad Real Transfusion Service between October 2017 and January 2018. Pools of eight donations were tested for HEV viremia by PCR. Positive pools were individually evaluated following the same procedure. Positive samples were tested for anti-HEV IgG and IgM. Recipients of blood transfusions obtained from HEV-positive donors were retrospectively evaluated. The prevalence of HEV was calculated. A total of 11 313 healthy donors were analysed during the study period. Four blood donations from four different donors were HEV RNA-reactive. The prevalence of HEV infection was 0.035% (95% CI: 0.01%-0.09%), which meant a ratio of one positive donation per 2828 donations. All donors were negative for anti-HEV IgM at the time of the donation. Five patients received transfusions from HEV-positive blood donations, none of them showed an increase in alanine aminotransferase levels after transfusion. In conclusion, our study found a high prevalence of HEV infection in blood donors from south-central Spain. In view of the prevalence, Spanish blood banks should carefully consider including screening for HEV.

A genome-wide association study on low susceptibility to hepatitis C virus infection (GEHEP012 study).

BACKGROUND: A low proportion of individuals repeatedly exposed to the hepatitis C virus (HCV) remain uninfected. This condition could have a genetic basis but it is not known whether or not it is mainly driven by a high-penetrance common allele. OBJECTIVE: To explore whether low susceptibility to HCV infection is mainly driven by a high-penetrance common allele. METHODS: In this genome-wide association study (GWAS), a total of 804 HCV-seropositive individuals and 27 high-risk HCV-seronegative (HRSN) subjects were included. Plink and Magma software were used to carry out single nucleotide polymorphism (SNP)-based and gene-based association analyses respectively. RESULTS: No SNP nor any gene was associated with low susceptibility to HCV infection after multiple testing correction. However, SNPs previously associated with this trait and allocated within the LDLR gene, rs5925 and rs688, were also associated with this condition in our study under a dominant model (24 out of 27 [88.9%] rs5925-C carriers in the HRSN group vs 560 of 804 [69.6%] rs5925-C carriers in the HCV-seropositive group, P = 0.031, odds ratio [OR] = 3.48; 95% confidence interval [CI] = 1.04-11.58; and 24 out of 27 [88.9%] rs688-T carriers in the HRSN group vs 556 of 804 [69.1%] rs688-T carriers in the HCV-seropositive group, P = 0.028, OR = 3.57, 95% CI = 1.65-11.96). CONCLUSIONS: Low susceptibility to HCV infection does not seem to be mainly driven by a high-penetrant common allele. By contrast, it seems a multifactorial trait where genes such as LDLR could be involved.

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

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