Serologic evidence of the circulation of the hepatitis E virus and the prevalence of antibodies against hepatitis A in an indigenous population in northern Argentina.

In 2005 a universal vaccination program against hepatitis A was introduced in Argentina. Nevertheless, there are still some unvaccinated marginal population groups. There are no data about the seroprevalence of hepatitis E in the northern region of Argentina mainly because of lack of awareness of this emergent pathogen. We aimed to determine the seroprevalence of hepatitis A, and hepatitis E in an indigenous population in northern Argentina. One hundred and twenty six (126) donor serum samples collected near San Salvador de Jujuy were analyzed for anti-HAV IgG and HEV IgG and IgM, alkaline phosphatase and transaminase values. Volunteers were interviewed about their living conditions, animal farming, consumption of tap water or river water, and level of education. Seroprevalence of specific anti-HAV antibodies was high (80.2%, 95% confidence interval, 72.1-86.7%) in children under 5 years of age, indicating early infection in life. Seroprevalence of anti-HEV antibodies was 5.6% (95% CI: 2.3-11.2%), being slightly higher than the values found in healthy patients from other regions of the country. Although we could not characterize the genotype of the circulating HEV strain, the clear epidemiological difference between seroprevalence of HAV and HEV in a community with poor sanitary conditions suggest that the circulating HEV strains spread through a different transmission route than HAV. Furthermore a significant correlation between anti-HEV IgG and swine farming was found (p<0.05), which supports a zoonotic transmission path. We reassessed the epidemiological pattern of HAV infection and reported evidence of HEV infection for the first-time in a community belonging to the Guarani ethnic group, highlighting the need to include hepatitis E testing in routine diagnostics in the region.

Role of HLA-DP and HLA-DQ on the clearance of hepatitis B virus and the risk of chronic infection in a multiethnic population.

BACKGROUND & AIMS: HBV infection exhibits geographical variation in its distribution in South America. While HBV rates are low in central Argentina, the north-western region exhibits intermediate HBV rates. Unfortunately, the reasons that could explain this difference are still unknown. METHODS: A total of 1440 Argentines were recruited and grouped into HBV patients, HBV-resolved individuals and healthy controls. Genetic ancestry was assessed by analysis of biparental lineages and ancestry autosomal typing. SNPs of HLA-DPA1 (rs3077), HLA-DPB1 (rs9277542), HLA-DQB1 (rs2856718) and HLA-DQB2 (rs7453920) were determined, and HBV genotyping was performed by phylogenetic analysis in HBV patients. RESULTS: Native American ancestry prevailed in the north-western region when compared with central Argentina (P<.0001). However, no differences were observed among the three groups of each region. The distribution of HBV genotypes revealed significant differences (P<.0001). Three SNPs (rs3077, rs9277542 and rs7453920) showed a significant association with protection against chronic HBV and viral clearance in both regions. The remaining SNP showed a significant association with susceptibility to chronic HBV. The frequency rates of rs3077-T, related to protection against chronic HBV and viral clearance, were lower in north-western Argentina when compared with central Argentina. The same uneven frequency rates were observed for SNP rs9277542. CONCLUSIONS: This is the first study addressing the associations between the HLA-DP and HLA-DQ loci and the protection against chronic HBV and viral clearance in a multiethnic South American population. The uneven distribution of HLA-DP and HLA-DQ supports the HBV epidemiological differences observed in these two regions of Argentina with dissimilar ancestry genetic background.

Correlation of HTLV-1 Tax genetic diversity with HTLV-1 associated myelopathy/tropical spastic paraparesis progression and HTLV-1a genotypes in an HTLV-1 endemic region in Argentina.

The oncoprotein Tax was characterized genetically from a large cohort of human T-cell lymphotropic virus type 1 (HTLV-1) seropositive individuals from the most endemic region of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and HTLV-1 infection in Argentina, the province of San Salvador de Jujuy. Sixteen HAM/TSP patients and 47 HTLV-1 healthy carriers were evaluated. Six Tax genetic polymorphisms were identified and observed in 70.8% of healthy carriers and 62.5% of HAM/TSP patients. Tax genetic polymorphisms were not associated with clinical status but A8344C polymorphism statistically provide a borderline protective effect of HAM/TSP outcome. Nucleotide diversity in healthy carriers was 0.00549, whereas HAM/TSP virus population revealed a low diversity of 0.00379, suggests a positive selection for Tax protein conservation in this group. It is concluded that tax genetic polymorphisms do not increase the risk of developing HAM/TSP in this endemic region. However, in spite of the low prevalence of HTLV-1aB genotype, statistical analysis revealed an important correlation of tax genetic signatures with HTLV-1aA trans-continental subgroup.

First Description of Seronegative HTLV-1 Carriers in Argentina.

In some areas of Argentina endemic for human T-lymphotropic virus type 1 (HTLV-1), tropical spastic paraparesis is frequent in subjects who lack antibodies against the virus; however, the relevance of this seronegative status in the country has not been investigated. In neighboring countries, HTLV-1 seronegative status has been described in patients with different diseases; however, data regarding features of seronegative HTLV-1 carriers are scarce. We investigated the seronegative status in 124 relatives of 28 HTLV-1 infected subjects from an endemic area in Northwest Argentina. Blood samples and clinical/epidemiological data were collected. Human T-lymphotropic virus type 1 infection was diagnosed by serology and long terminal repeat (LTR) sequence, env and tax gene detection. IgG anti-Tax HTLV-1 antibody, tax gene sequence, and DNA proviral load were also evaluated. Seventy-five percent of the 124 relatives were negative for HTLV-1/2 antibodies; 35.5% were also negative by molecular assays and 64.5% were negative for HTLV-1 LTR and env sequences, but positive for two sequences of HTLV-1 tax gene. Also, 35.7% of these subjects had IgG anti-Tax antibodies. The seronegative HTLV-1 status was significantly associated with male gender, youth, and sensory symptoms/autonomic nervous system dysfunction. High rates of seronegative symptomatic and asymptomatic HTLV-1 carriers in Argentina are described. The evidence highlights that HTLV-1 prevalence may be underestimated worldwide. Larger cohort studies are required to assess disease outcome in these seronegative subjects. Also, the findings emphasize the limitations of ongoing screening assays for diagnosis and blood safety. Therefore, algorithms for HTLV-1 diagnosis should include not only serological but also molecular assays.

Genetic diversity and phylogeographic analysis of human herpesvirus type 8 (HHV-8) in two distant regions of Argentina: Association with the genetic ancestry of the population.

BACKGROUND: The genetic diversity of persistent infectious agents, such as HHV-8, correlates closely with the migration of modern humans out of East Africa which makes them useful to trace human migrations. However, there is scarce data about the evolutionary history of HHV-8 particularly in multiethnic Latin American populations. OBJECTIVES: The aims of this study were to characterize the genetic diversity and the phylogeography of HHV-8 in two distant geographic regions of Argentina, and to establish potential associations with pathogenic conditions and the genetic ancestry of the population. STUDY DESIGN: A total of 101 HIV-1 infected subjects, 93 Kaposi's Sarcoma (KS) patients and 411 blood donors were recruited in the metropolitan (MET) and north-western regions of Argentina (NWA). HHV-8 DNA was detected by ORF-26 PCR in whole blood, saliva and FFPE tissues. Then, ORF-26 and ORF-K1 were analyzed for subtype assignment. Mitochondrial DNA and Y chromosome haplogroups, as well as autosomal ancestry markers were evaluated in samples in which subtypes could be assigned. Phylogeographic analysis was performed in the ORF-K1 sequences from this study combined with 388 GenBank sequences. RESULTS: HHV-8 was detected in 50.7%, 59.2% and 8% of samples from HIV-1 infected subjects, KS patients and blood donors, respectively. ORF-K1 phylogenetic analyses showed that subtypes A (A1-A5), B1, C (C1-C3) and F were present in 46.9%, 6.25%, 43.75% and 3.1% of cases, respectively. Analyses of ORF-26 fragment revealed that 81.95% of strains were subtypes A/C followed by J, B2, R, and K. The prevalence of subtype J was more commonly observed among KS patients when compared to the other groups. Among KS patients, subtype A/C was more commonly detected in MET whereas subtype J was the most frequent in NWA. Subtypes A/C was significantly associated with Native American maternal haplogroups (p = 0.004), whereas subtype J was related to non-Native American haplogroups (p < 0.0001). Sub-Saharan Africa, Europe and Latin America were the most probable locations from where HHV-8 was introduced to Argentina. CONCLUSIONS: These results give evidence of the geographic circulation of HHV-8 in Argentina, suggest the association of ORF-26 subtype J with KS development and provide new insights about its relationship with ancient and modern human migrations and identify the possible origins of this virus in Argentina.

Relevance of HTLV-1 proviral load in asymptomatic and symptomatic patients living in endemic and non-endemic areas of Argentina.

HTLV-1 proviral load (pVL) in peripheral blood mononuclear cell (PBMCs) is proposed as a marker of disease progression but its role still remains controversial. The aim of this study was to evaluate the levels of HTLV-1 pVL in symptomatic patients and asymptomatic HTLV-1 carriers. In this cross-sectional study the pVL was measured by Real Time PCR in 102 asymptomatic carriers and 22 symptomatic patients (5ATLL, 15 TSP and 2 uveitis). We observed that the HTLV-1 pVL was significantly higher in symptomatic patients (median = 4.99 log10 HTLV-1 copies /106 PBMCs) compared to asymptomatic HTLV-1 carriers (median = 4.38 log10 HTLV-1 copies /106 PBMCs; p = 0.0030). A wide variation on the HTLV-1 pVL levels among asymptomatic HTLV-1 carriers was observed with some pVL as high as those observed in symptomatic patients. The asymptomatic HTLV-1 carriers were divided according to the place of birth and the highest levels of pVL were detected among patients from endemics areas from the North of Argentina. Our results reinforce the usefulness of the proviral load would be a prognostic marker of HTLV-1 disease progression. Moreover, host, viral or socio-environmental factors cannot be excluded as determinant of high proviral load.

Hepatitis B virus genetic diversity in Argentina: dissimilar genotype distribution in two different geographical regions; description of hepatitis B surface antigen variants.

BACKGROUND: The hepatitis B virus (HBV) molecular epidemiological data of Argentina are still scarce, since most of the previous analyses have been performed in the Metropolitan Region. OBJECTIVES: To deepen the current molecular and epidemiological information about the geographical distribution of HBV genotypes and subgenotypes, and to describe the hepatitis B surface antigen (HBsAg) variants circulating in Argentina. STUDY DESIGN: Eighty-eight Argentine partial HBsAg sequences from both the Northern and the Metropolitan Regions of the country were analyzed along with 67 Argentine HBV sequences existing in GenBank. RESULTS: Phylogenetic and amino acid sequence analysis grouped the 88 samples as genotypes A (14.8%), D (21.6%) and F (63.6%). In the Northern Region, 44 out of the 48 sequences analyzed (91.7%) grouped as genotype F. Differently, in the Metropolitan Region, the 40 samples grouped as genotype F (30.0%), genotype D (42.5%), and genotype A (27.5%). An elevated proportion (14.8%) of the genomes presented mutations in the major hydrophilic region (MHR). CONCLUSIONS: The different genotype distribution in both Argentine regions indicates that the epidemiological landscape of HBV infection appears to be the result of the diverse human migratory movements that have given shape to the present population. Our findings show that the prevalence of HBsAg variants is quite significant among the Argentine population.

Silent dissemination of HTLV-1 in an endemic area of Argentina. Epidemiological and molecular evidence of intrafamilial transmission.

BACKGROUND: Molecular and epidemiological studies of transmission routes and risk factors for infection by HTLV-1 are extremely important in order to implement control measures, especially because of the high prevalence of HTLV-1 in several regions of the world. San Salvador de Jujuy, Northwest Argentina, is a highly endemic area for HTLV-1 and foci of tropical spastic paraparesis/HTLV-1-associated myelopathy. OBJECTIVE: To gain further insight into the role of intrafamilial transmission of HTLV-1 in a highly endemic region in Argentina. METHOD: Cross-sectional study in Northwest Argentina. Epidemiological data and blood samples were collected from 28 HTLV-1 infected subjects (index cases) and 92 close relatives/cohabitants. HTLV-1 infection was diagnosed by detection of antibodies and proviral DNA. The LTR region was sequenced and analyzed for genetic distances (VESPA software), in addition to determination and identification of polymorphisms to define HTLV-1 family signatures. RESULTS: Fifty seven of the 120 subjects enrolled had antibodies against HTLV-1 and were typified as HTLV-1 by PCR. The prevalence rate of HTLV-1 infection in family members of infected index cases was 31.52% (29/92). The infection was significantly associated with gender, age and prolonged lactation. Identity of LTR sequences and presence of polymorphisms revealed high prevalence of mother-to-child and interspousal transmission of HTLV-1 among these families. CONCLUSION: There is an ongoing and silent transmission of HTLV-1 through vertical and sexual routes within family clusters in Northwest Argentina. This evidence highlights that HTLV-1 infection should be considered as a matter of public health in Argentina, in order to introduce preventive measures as prenatal screening and breastfeeding control.

Proposal for diagnostic criteria of tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM).

After the first description of TSP/HAM in 1985 and the elaboration of WHO's diagnostic criteria in 1988, the experience of the professionals in this field has increased so that a critical reappraisal of these diagnostic guidelines was considered timely. Brazilian neurologists and observers from other countries met recently to discuss and propose a modified model for diagnosing TSP/HAM with levels of ascertainment as definite, probable, and possible, according to myelopathic symptoms, serological findings, and/or detection of HTLV-I DNA and exclusion of other disorders.

Probable segundo evento por SARS-CoV-2: 12 casos / Probable second event due to SARS-CoV-2: 12 cases

Con el avance de la pandemia por COVID-19, la aparición de pacientes con un segundo episodio confirmado por reacción en cadena de la polimerasa, con transcripción inversa (rt-PCR) compatible con reinfección, puso de manifiesto la falta de recomendaciones para su abordaje.Presentamos un estudio descriptivo multicéntrico retro-prospectivo de una serie de doce casos atendidos entre el 01/06/2020 y el 20/10/2020. En la misma, diez casos presentaron el segundo episodio en un período de tiempo menor a 90 días.Por su complejidad, la confirmación de una reinfección no está al alcance en la práctica diaria. Esto requiere de estudios que incluyan comparaciones genómicas de cepas virales involucradas en ambos episodios, determinación de la infectividad del ARN por cultivo viral y análisis molecular.Es necesario establecer definiciones operativas y algoritmos clínicos para la atención de los segundos episodios

As COVID-19 pandemic progresses, patients with a second confirmed episode by reverse transcription-polymerase chain reaction (RT PCR) compatible with reinfection reveals the lack of recommendations for its approach.A multicenter retro-prospective descriptive work was done of a series of 12 cases evaluated between June 1, 2020 and October 20, 2020. In this study, 10 out of 12 cases presented the second episode occurred in less than 90 days.Due to the diagnosing reinfection complexity, its confirmation is not available in the daily practice, this requires studies, which include viral strains genomic comparisons involved in both episodes, ARN determination infectivity by viral culture and molecular analysis.It is necessary to establish operational and clinical algorithms definitions to assist second episodes

Tick paralysis cases in Argentina.

Tick paralysis (TP) occurs worldwide and is caused by a neurotoxin secreted by engorged female ticks that affects the peripheral and central nervous system. The clinical manifestations range from mild or nonspecific symptoms to manifestations similar to Guillain-Barré syndrome, bulbar involvement, and death in 10% of the patients. The diagnosis of TP is clinical. To our knowledge, there are no formal reports of TP in humans in South America, although clusters of TP among hunting dogs in Argentina have been identified recently. In this paper, clinical features of two cases of TP occurring during 1994 in Jujuy Province, Argentina, are described.

Acute retroviral syndrome and high baseline viral load are predictors of rapid HIV progression among untreated Argentinean seroconverters.

BACKGROUND: Diagnosis of primary HIV infection (PHI) has important clinical and public health implications. HAART initiation at this stage remains controversial. METHODS: Our objective was to identify predictors of disease progression among Argentinean seroconverters during the first year of infection, within a multicentre registry of PHI-patients diagnosed between 1997 and 2008. Cox regression was used to analyze predictors of progression (LT-CD4 < 350 cells/mm3, B, C events or death) at 12 months among untreated patients. RESULTS: Among 134 subjects, 74% presented with acute retroviral syndrome (ARS). Seven opportunistic infections (one death), nine B events, and 10 non-AIDS defining serious events were observed. Among the 92 untreated patients, 24 (26%) progressed at 12 months versus three (7%) in the treated group (p = 0.01). The 12-month progression rate among untreated patients with ARS was 34% (95% CI 22.5-46.3) versus 13% (95% CI 1.1-24.7) in asymptomatic patients (p = 0.04). In univariate analysis, ARS, baseline LT-CD4 < 350 cells/mm3, and baseline and six-month viral load (VL) > 100,000 copies/mL were associated with progression. In multivariate analysis, only ARS and baseline VL > 100,000 copies/mL remained independently associated; HR: 8.44 (95% CI 0.97-73.42) and 9.44 (95% CI 1.38-64.68), respectively. CONCLUSIONS: In Argentina, PHI is associated with significant morbidity. HAART should be considered in PHI patients with ARS and high baseline VL to prevent disease progression.

Latrodectismo en la provincia de Jujuy: Aspectos epidemiológicos y clínicos / Latrodectism in the province of Jujuy: Epidemiological and clinical aspects

En Argentina, las especies de arañas de importancia sanitaria pertenecen a los géneros Loxosceles, Phoneutria y Latrodectus. El objetivo del presente trabajo fue relevar los accidentes producidos por el género Latrodectus atendidos en el centro de referencia y derivación provincial de animales venenosos de Jujuy (Hospital San Roque) en el período: 1 de enero de 1998 al 31 de diciembre de 2014. En los diecisiete años analizados se registraron 30 historias clínicas con diagnóstico de latrodectismo, el 83 % de los casos procede de zonas semiáridas y áridas de la provincia de Jujuy. Se registró un valor medio de 1.8 casos/año; la mayoría de los accidentados (63 %) fueron de sexo masculino y la franja etaria más afectada se ubicó entre 16-25 años (50 %). La visualización del arácnido fue confirmada por 18 pacientes, de los cuales el 67 % (n=12) lo identificó como "huayruro" o "viuda negra". Entre las manifestaciones clínicas predominaron: dolor local, dolor generalizado, dolor abdominal, diaforesis e hipertensión arterial. El periodo de internación fue corto (2,7 días) y no hubo complicaciones ni óbitos. Este es el primer estudio clínico-epidemiológico de latrodectismo en el noroeste argentino.

In Argentina, the species of spiders of sanitary importance belong to the Loxosceles, Latrodectus and Phoneutria genera. The objective of this study was to survey accidents caused by the spiders of Latrodectus genus treated at the Jujuy provincial venomous animal reference and referral center (San Roque Hospital) between January 1, 1998 and December 31, 2014. In the seventeen years analyzed, 30 medical records with a diagnosis of latrodectism were analyzed, 83% of the cases came from semi-arid and arid areas of the province of Jujuy. An average of 1.8 cases/year was established. Most of the injured (63%) were male and the most affected age group was between 16-25 years (50%). The arachnid depiction was confirmed by 18 patients, of which 67% (n=12) identified it as "huayruro" or "black widow". Predominant clinical manifestations were local pain, generalized pain, abdominal pain, diaphoresis and hypertension. The length of hospitalization was short (2,7 days) and there were no complications or deaths. This is the first clinical-epidemiological study of latrodectism in northwestern Argentina

Rocky Mountain spotted fever in Argentina.

We describe the first molecular confirmation of Rickettsia rickettsii, the cause of Rocky Mountain spotted fever (RMSF), from a tick vector, Amblyomma cajennense, and from a cluster of fatal spotted fever cases in Argentina. Questing A. cajennense ticks were collected at or near sites of presumed or confirmed cases of spotted fever rickettsiosis in Jujuy Province and evaluated by polymerase chain reaction assays for spotted fever group rickettsiae. DNA of R. rickettsii was amplified from a pool of A. cajennense ticks and from tissues of one of four patients who died during 2003-2004 after illnesses characterized by high fever, severe headache, myalgias, and petechial rash. The diagnosis of spotted fever rickettsiosis was confirmed in the other patients by indirect immunofluorescence antibody and immunohistochemical staining techniques. These findings show the existence of RMSF in Argentina and emphasize the need for clinicians throughout the Americas to consider RMSF in patients with febrile rash illnesses.

HTLV type 1 genetic types among native descendants in Argentina.

The province of San Salvador de Jujuy, located in the northwest of Argentina, is a highly endemic area for HTLV-1 infection and a foci of tropical spastic paraparesis/HTLV-1-associated myelopathy (HAM/TSP). Therefore, to better understand this, we carried out a genetic characterization of a large set of HTLV-1 strains (n = 65) of descendants of Amerindians from this region. The LTR and env regions were analyzed. The genetic analysis showed that all of these new HTLV-1 isolates from Argentina belong to the Transcontinental subgroup A of the HTLV-1a Cosmopolitan subtype, with the exception of three isolates that cluster within the Japanese subgroup B. Interestingly, the majority of the sequences from Jujuy province belonged to a distinct cluster within the Latin America Transcontinental subgroup, referred to here as the Jujuy subcluster, and were characterized by specific signatures in the LTR. Given that the samples analyzed in this study belong to the Amerindian population and the high prevalence of HTLV-1 in Jujuy in contrast to the low prevalence of this virus in the country, it could be that HTLV-1aA was spread in Argentina from the Amerindians to the cosmopolitan population. Moreover, this is the first report of an HTLV-1aB or Japanese subgroup in descendants of non-Japanese people in South America.

Tick paralysis cases in Argentina / Casos de paralisia por carrapato na Argentina

Tick paralysis (TP) occurs worldwide and is caused by a neurotoxin secreted by engorged female ticks that affects the peripheral and central nervous system. The clinical manifestations range from mild or nonspecific symptoms to manifestations similar to Guillain-Barré syndrome, bulbar involvement, and death in 10% of the patients. The diagnosis of TP is clinical. To our knowledge, there are no formal reports of TP in humans in South America, although clusters of TP among hunting dogs in Argentina have been identified recently. In this paper, clinical features of two cases of TP occurring during 1994 in Jujuy Province, Argentina, are described.

A paralisia por carrapatos (PC) ocorre mundialmente e é causada por uma neurotoxina secretada por carrapatos fêmea engolidores de sangue que afeta o sistema nervoso periférico e central. As manifestações clínicas variam de suave ou sintomas não específicos a manifestações semelhantes à síndrome de Guillain-Barré, envolvimento de bulbar, e morte em 10% dos pacientes. O diagnóstico de PC é clínico. A nosso conhecimento, não há nenhum relatório formal em seres humanos na América do Sul, embora grupos de PC entre cães de caça na Argentina, tenham sido identificados recentemente. Neste artigo, descrevo dois casos de PC ocorridos durante o ano de 1994 na província de Jujuy, Argentina.

Molecular characterization of hepatitis A virus isolates from Argentina.

Hepatitis A, a vaccine preventable disease, is now of transitional or intermediate endemicity in Argentina, as the epidemiologic pattern of the disease has shifted with improvements in living conditions in some parts of the country. Increase in the susceptibility of older children and adults has led to increasing disease incidence. Molecular epidemiology has played an important role in the understanding of HAV infection by identifying modes of spreading and by permitting the monitoring of changes in circulating virus brought about by prevention programs. South American isolates characterized are limited. Eighty-two sporadic and outbreak isolates from Argentina were sequenced in the VP1/2A region of HAV genome over a 9-year period. All the isolates belonged to subgenotype IA. All our sequences grouped into two big clusters. Apparently, at least two lineages have been co-circulating in the same place at the same time. Despite great genetic variability, few point amino acid changes could be deduced. Four sequences showed an Arg --> Lys substitution at 1-297 which characterized the genotype IB at the amino acid level. Many isolates carried a conservative amino acid substitution Leu --> Ile at position 42 of the 2A domain, previously described as a possible fingerprint of HAV sequences in Brazil. The other rare changes have been found before, except for a 1-277 Asn --> Ser substitution displayed in two isolates that has not been previously reported. Argentina recently implemented universal vaccination in 1-year-old children. Molecular tools would be useful in an active surveillance program.

Adult T-cell leukemia/lymphoma in Jujuy, north-west Argentina.

Human T-cell leukemia virus type 1 (HTLV-1) infection is prevalent in native Americans living in the Andes. Some of their malignant lymphomas (ML) show a peculiar histology suggestive of adult T-cell leukemia/lymphoma (ATLL). To determine whether ML resembling ATLL are indeed ATLL, re-analysis of 34 cases occurring in Jujuy, a province of Argentina, was conducted, concentrating on immunological phenotype, integration of HTLV-1 proviral DNA, expression of HTLV-1 p40Tax and p27Rex, and infection of Epstein-Barr virus (EBV). The ML were 22 cases of mature peripheral T-cell and natural killer (NK)-cell neoplasm (mT/NKN), 11 B-cell malignant neoplasms and one Hodgkin's lymphoma. Polymerase chain reaction against the HTLV-1 proviral DNA, using DNA extracted from paraffin sections, indicated integration of the HTLV-1 proviral DNA in three cases of eight mT/NKN. Two other cases of mT/NKN were positive for anti-HTLV-1 antibodies. Expression of p40Tax and p27Rex was detected in all five of these mT/NKN cases associated with HTLV-1. As such, these five mT/NKN were rediagnosed as ATLL. In situ hybridization signals for EBV-encoded small nuclear early region-1 were detected in nine cases of mT/NKN, of which five cases of NK-cell lymphoma were found to have cytoplasmic CD3 expression, a CD56 phenotype and positivity of TIA1. According to the new World Health Organization classification, the mT/NKN class includes five cases of ATLL and five cases of NK-cell lymphomas. The five cases of ATLL were of native American extraction from an HTLV-1-endemic area around Jujuy, north-west Argentina.