RESUMEN
Pulmonary cryptosporidiosis is a rare complication of intestinal cryptosporidiosis in AIDS patients. We report the epidemiological, clinical, radiological, microbiological and immunological findings in 5 AIDS patients with pulmonary cryptosporidiosis. Diagnosis was based on the detection of acid-fast oocysts in sputum or aspirated bronchial material using the Kinyoun technique. Microbiology laboratories should be alert to the possibility of Cryptosporidium spp oocysts presence in respiratory specimens from patients with advanced HIV/AIDS disease and pulmonary involvement.
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Síndrome de Inmunodeficiencia Adquirida/complicaciones , Criptosporidiosis/etiología , Enfermedades Pulmonares Parasitarias/etiología , Adulto , Humanos , MasculinoAsunto(s)
Vértebras Cervicales , Discitis/microbiología , Vértebras Lumbares , Vértebras Torácicas , Tuberculosis de la Columna Vertebral/complicaciones , Adulto , Anciano , Anciano de 80 o más Años , Discitis/diagnóstico , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estudios Retrospectivos , Tuberculosis de la Columna Vertebral/diagnósticoRESUMEN
Disseminated histoplasmosis in AIDS patients is the focus of this paper. Cutaneous lesions are reported as a frequent clinical sign. Bone marrow aspiration and biopsy, blood cultures (lysis-centrifugation technique), bronchoalveolar lavage, and skin lesion scrapings are the most effective diagnostic methods. The identification of a specific antigen in blood and urine may be a rapid means of evaluation and follow-up of patients with this disease.
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Infecciones Oportunistas Relacionadas con el SIDA/diagnóstico , Fungemia/diagnóstico , Histoplasmosis/diagnóstico , Infecciones Oportunistas Relacionadas con el SIDA/tratamiento farmacológico , Infecciones Oportunistas Relacionadas con el SIDA/epidemiología , Antifúngicos/administración & dosificación , Argentina/epidemiología , Femenino , Fungemia/tratamiento farmacológico , Fungemia/epidemiología , Histoplasmosis/tratamiento farmacológico , Histoplasmosis/epidemiología , Humanos , Incidencia , Masculino , Pronóstico , Factores de RiesgoRESUMEN
Intermediate and highly malignant non-Hodgkin and primary central nervous system lymphomas are marker diseases for AIDS. Cavum and oropharynx involvement by these tumors is uncommon. Although there are few cases reported in the literature, these may be primary localizations of the tumor. We present a hemophilic HIV+ patient with non-Hodgkin lymphoma of the cavum. The histologic diagnosis was high-grade, pleomorphic, centroblastic lymphoma. The patient was treated with chemotherapy plus intrathecal chemotherapy and highly active antiretroviral therapy (HAART). His evolution has been excellent. One year after diagnosis, the patient is asymptomatic with no evidence of residual tumor, and responding well to HAART.
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Síndrome de Inmunodeficiencia Adquirida/complicaciones , Hemofilia A/complicaciones , Linfoma Relacionado con SIDA/diagnóstico , Linfoma no Hodgkin/diagnóstico , Neoplasias Nasofaríngeas/diagnóstico , Adulto , Humanos , Linfoma Relacionado con SIDA/complicaciones , Linfoma Relacionado con SIDA/tratamiento farmacológico , Linfoma no Hodgkin/complicaciones , Linfoma no Hodgkin/tratamiento farmacológico , Masculino , Neoplasias Nasofaríngeas/complicaciones , Neoplasias Nasofaríngeas/tratamiento farmacológico , Tomografía Computarizada por Rayos XRESUMEN
As HIV seropositive patients with undetectable CSF viral load have a lower likelihood of developing neurologic disease, the determination of CSF viral load levels may be useful to evaluate the efficacy of HAART. We compared plasma viral load levels with HIV-1 RNA CSF levels in 18 hemophilic patients without neurocognitive involvement under HAART. We detected a significant correlation between plasma viral load levels and CSF viral load levels. Fourteen patients with undetectable plasma viral load had undetectable RNA HIV-1 CSF levels as well. Four patients with detectable plasma viral load had detectable HIV-RNA in CSF, but the latter were significantly lower. Viral load is usually lower in non-blood fluids and HAART decreases the viral load in CSF as well as in blood.
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Terapia Antirretroviral Altamente Activa , Infecciones por VIH/líquido cefalorraquídeo , VIH-1 , Hemofilia A/virología , ARN Viral/líquido cefalorraquídeo , Carga Viral , Infecciones por VIH/complicaciones , Infecciones por VIH/tratamiento farmacológico , Hemofilia A/sangre , Hemofilia A/líquido cefalorraquídeo , Humanos , ARN Viral/sangreRESUMEN
We conducted a retrospective evaluation to determine the clinical and microbiological characteristics of 61 episodes of infective endocarditis (IE) in intravenous drug abusers (IDA), HIV seropositive patients. Forty-nine males and 6 females between 15 and 42 years of age were included in the study. All the included patients presented 61 episodes of IE. Fever and cardiac murmur were present in all episodes; 43 (70.4%) had hepatomegaly; 29 (47.5%) had splenomegaly. Thirty-eight (62.3%) presented cough (9 with hemoptysis); 25 (41%) had dyspnea, and 5 (8.2%) had jugular ingurgitation. Fundoscopy showed alterations in 3 patients (4.9%). Bacteriological confirmation was obtained in 41 episodes (67.2%); blood cultures revealed Staphylococcus aureus in 30 cases (73.1%), Streptococcus viridans in 8 (19.5%) patients, Staphylococcus epidermidis in 1 (2.4%), Staphylococcus hominis in 1 (2.4%) and Streptococcus pneumoniae in one case (2.4%). The tricuspid valve was involved in 51 episodes (83.6%), the aorta in 6 (9.8%), the mitral valve in 3 (4.9%) and the pulmonary valve in one (1.6%). There was evidence of right bivalvular involvement in 2 patients (3.2%) and tricuspid and mitral involvement in another (1.6%). Pericardial effusion was detected in 19 episodes (31.1%). Six patients (10.9%) died during the acute episode of IE.
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Endocarditis Bacteriana/complicaciones , Infecciones por VIH/complicaciones , Abuso de Sustancias por Vía Intravenosa/complicaciones , Adolescente , Adulto , Endocarditis Bacteriana/diagnóstico , Endocarditis Bacteriana/microbiología , Femenino , VIH-1 , Humanos , Masculino , Estudios RetrospectivosRESUMEN
In the context of HIV infection, cryptococcal meningitis is the most common mycosis threatening the patient's life. We conducted a retrospective evaluation to determine the epidemiological, microbiological, immunological and clinical characteristics of disseminated cryptococcosis in 51 hospitalised HIV seropositive patients. All the individuals (n = 51) presented reactive serology for HIV (ELISA and/or Western blot) and none fulfilled strict HAART treatment, previous to the opportunistic infection. CD4+ lymphocyte T counts showed levels between 361 and 0 cells/microliter (mean = 45). All patients but one had counts lower than 100 cells/microliter. Cryptococcosis presented as unique episode in 35 patients (68.6%) and in 16 as relapse (31.3%). In all of them we detected central nervous system involvement. The induction treatment was carried out with amphotericin B (AMB), continued with maintenance therapy with fluconazole. Lethality rate was 36.7%, slightly superior among patients in relapse (40%) compared to those who presented a first episode of the mycosis (35.2%). In those individuals for whom data were available, 65.2% of blood cultures, 94.1% of CSF cultures and 79.06% of microscopic CSF examination with India ink were positive. Titers of Cryptococcus neoformans capsular antigen in CSF > or = 1/1000 were found in 36.1% and > or = 1/1000 in 73.6% of serum samples. In conclusion, manifestations and severity of disseminated cryptococcosis continue maintaining the characteristics of half a decade behind, in those patients who are not treated with HAART. Neurological involvement existed in all patients of this cohort. Treatment is not able to modify the parameters of mortality seen in previous communications. Diagnostic methods applied in this study are in accordance with those in the bibliography.
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Infecciones Oportunistas Relacionadas con el SIDA/epidemiología , Criptococosis/epidemiología , Infecciones Oportunistas Relacionadas con el SIDA/inmunología , Infecciones Oportunistas Relacionadas con el SIDA/microbiología , Enfermedad Aguda , Adulto , Anfotericina B/uso terapéutico , Antifúngicos/uso terapéutico , Antígenos Fúngicos/sangre , Antígenos Fúngicos/líquido cefalorraquídeo , Terapia Antirretroviral Altamente Activa , Argentina/epidemiología , Recuento de Linfocito CD4 , Criptococosis/tratamiento farmacológico , Criptococosis/inmunología , Criptococosis/microbiología , Cryptococcus neoformans/inmunología , Cryptococcus neoformans/aislamiento & purificación , Fluconazol/uso terapéutico , Anticuerpos Anti-VIH/sangre , VIH-1 , Humanos , Pacientes Internos , Masculino , Meningitis Criptocócica/líquido cefalorraquídeo , Meningitis Criptocócica/tratamiento farmacológico , Meningitis Criptocócica/epidemiología , Meningitis Criptocócica/inmunología , Meningitis Criptocócica/microbiología , Persona de Mediana Edad , Recurrencia , Estudios RetrospectivosRESUMEN
Esophageal disease is a common complication in patients infected with human immunodeficiency virus type-1 (HIV-1). Dysphagia, odynophagia and retrosternal pain are the most common symptons associated with the esophageal compromise. Esophageal candidiasis, the most frequent opportunistic infection, may occur in patients with long-standing infection or may be a manifestation of the seroconversion. Cytomegalovirus and Herpes simplex virus are more likely to produce esophageal ulcers or erosions. HIV itself may be responsible for ulcerative esophagitis. Neoplasms as Kaposi's sarcoma, are an infrequent cause of symptomatic disease. Barium esophagography and specially upper endoscopy are the most commonly employed diagnostic modalities for the evaluation of symptomatic patients. Endoscopy may be warranted to make a rapid diagnosis such that specific therapy will not be delayed. The use of a combination of histologic, cytologic, mycologic and virologic studies is necessary to provide an etiologic diagnosis of these lesions.
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Infecciones Oportunistas Relacionadas con el SIDA/complicaciones , Esofagitis/microbiología , VIH-1 , Antifúngicos/uso terapéutico , Candidiasis/complicaciones , Candidiasis/tratamiento farmacológico , Infecciones por Citomegalovirus/complicaciones , Esofagitis/clasificación , Esofagitis/terapia , Esofagitis Péptica/etiología , Herpes Simple/complicaciones , HumanosRESUMEN
Primary esophageal lymphomas are extremely rare. We report a primary esophageal T cell lymphoma of a diffuse large cell phenotype B in a patient with AIDS. Also we reviewed other published cases. The diagnosis of this complication should be considered in HIV seropositive patients with progressive displagia and endoscopic findings of masses, polyps or ulcerations and, specially in those unresponsive to antifungal or antiviral therapy. Biopsy and histopathologic studies are needed to confirm the diagnosis.
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Neoplasias Esofágicas/diagnóstico , Linfoma Relacionado con SIDA/diagnóstico , Linfoma de Células B Grandes Difuso/diagnóstico , Adulto , Neoplasias Esofágicas/patología , Humanos , Linfoma Relacionado con SIDA/patología , Linfoma de Células B Grandes Difuso/patología , MasculinoRESUMEN
El colapso dinámico excesivo de la vía aérea (CDEVA) se caracteriza por una invaginación exagerada de la pared posterior de la tráquea que compromete la luz de la vía aérea, especialmente durante la espiración. La obstrucción es dinámica, por tanto, pueden presentarse hiperinsuflación y atrapamiento de aire, dificultando la ventilación1, 2. En condiciones normales la luz de la vía aérea puede disminuir hasta el 35% con la tos o las maniobras de espiración forzada, pero una disminución mayor al 50% es considerada anormal. El CDEVA es una entidad clínica subdiagnosticada, por lo que algunos pacientes son asintomáticos y otros presentan síntomas crónicos como tos, disnea, infecciones recurrentes y aumento de las secreciones. Usualmente se confunde con otras enfermedades comunes, como enfermedad pulmonar obstructiva crónica (EPOC) o asma, con las que puede coexistir agravándolas4, 5. Es más frecuente en individuos de mediana edad y ancianos con exposición previa al cigarrillo6, 7. Si bien es benigna, puede causar morbilidad progresiva y, ocasionalmente, falla respiratoria y muerte. La discusión de esta entidad surge a partir de la presentación de un caso clínico cuya detección precoz durante la agudización del paciente, permitió optimizar el manejo ventilatorio y la desvinculación de la ventilación mecánica
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Respiración Artificial , Enfermedad Pulmonar Obstructiva Crónica , Manejo de la Vía AéreaRESUMEN
Progressive multifocal leukoencephalopathy causes an infection of the central nervous system by JC virus (JCV), a polyomavirus that destroys oligodendrocytes and their myelin processes. Here, we describe a patient with AIDS who developed a progressive multifocal leucoencephalopathy with the clinical and neuroimaging characteristics of the immune inflammatory reconstitution syndrome. Unlike other opportunistic infections, this disease can present when CD4 T cell counts are higher than those associated with AIDS and also when patients are receiving combined antiretroviral therapy. Clinical suspicion of this form of the disease is based on clinical examination that shows focal neurological deficits associated with magnetic resonance images findings. The histopathological examination of brain biopsy smears and the identification of JCV in cerebrospinal fluid or brain tissue are definitive for the diagnosis.
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Síndrome de Inmunodeficiencia Adquirida/complicaciones , Síndrome Inflamatorio de Reconstitución Inmune/fisiopatología , Leucoencefalopatía Multifocal Progresiva/diagnóstico , Leucoencefalopatía Multifocal Progresiva/etiología , Adulto , Astrocitos/patología , Encéfalo/patología , Humanos , Imagen por Resonancia Magnética , MasculinoRESUMEN
Introducción: La vigilancia epidemiológica de la morbilidad y la mortalidad relacionadas a los desastres, es fundamental para organizar y gestionar los recursos, equipos y personal necesarios para responder efectivamente a las situaciones de emergencia. Se describe la implementación del sistema de vigilancia intensificada en poblaciones desplazadas por inundaciones en Paraguay, período 2015/2016. Materiales y métodos: Estudio descriptivo de corte trasversal, entre el 28/12/2015 y 12/07/2016, en todo el territorio nacional. Como fuentes de datos se utilizaron la planilla de notificación diaria de enfermedades, el consolidado de situación de albergues. Se diseñó un sistema de carga de datos por la web. Para el análisis de datos se utilizó el programa informático Epi Info 7.1.5, con medidas estadísticas de tendencia central como medias, medianas, proporciones. Resultados: Se registraron 68.699 personas afectadas. De las cuales, 32,4% eran menores de 5 años. Un 48,0 % se alojaron en refugios formales y 36,7% en campamentos informales, en ambos se identificó déficit de condiciones sanitarias básicas. Se registraron 23.877 consultas. Las enfermedades más frecuentes: Infección respiratoria aguda no neumonía (33%), hipertensión arterial (19%), enfermedad tipo influenza (14%), lesiones de la piel (6%) y diarreas (6%). Un 3% correspondió al síndrome febril agudo, dos casos confirmados de leptospirosis. No se registraron brotes de enfermedades infecciosas. Conclusión: La aplicación de la vigilancia intensificada durante el evento de inundación permitió la identificación de grupos de riesgo y sus problemas de salud más frecuentes. Esto fue fundamental en la orientación de los esfuerzos de prevención y control durante del desastre. Palabras claves: Desastres naturales, inundaciones, vigilancia en salud pública, epidemiología, Paraguay.
Introduction: The importance of epidemiological surveillance of morbidity and mortality related to disasters is that it is essential to organize and manage resources, equipment and personnel necessary to respond effectively to emergencies. The implementation of an intensified surveillance system in populations displaced by flooding in the affected regions of Paraguay during the 2015/2016 period is described. Materials and methods: Descriptive study of cross section, between 12/28/2015 and 7/12/2016, throughout the national territory. As data sources, the planning of the daily notifications of diseases is used, the consolidation of the situation of the shelters. A web data loading system was designed. For the analysis of the data, it is the Epi Info 7.1.5 computer program, with measures of central tendency such as means, medians, and proportions. Results: 68,699 affected people were registered. Of which, 32.4% were under 5 years old; 48.0% were housed in formal shelters and 36.7% in informal camps, both of which identified a deficit of basic sanitary conditions. There were 23,877 queries. The most frequent diseases: Acute respiratory infection, pneumonia (33%), hypertension (19%), influenza-like illness (14%), skin lesions (6%) and diarrhea (6%). 3% corresponded to the acute febrile syndrome, two confirmed cases of leptospirosis. There were no outbreaks of infectious diseases. Conclusion: The implementation of intensified surveillance during the flooding event allowed a better understanding of the general situation of the displaced population, as well as the identification of risk groups and their most frequent health problems. This was instrumental in guiding the prevention and control efforts during the disaster. Keywords: Natural disasters, floods, public health surveillance, epidemiology, Paraguay.
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Humanos , Masculino , Femenino , Embarazo , Recién Nacido , Lactante , Preescolar , Niño , Adolescente , Adulto , Persona de Mediana Edad , Anciano , Anciano de 80 o más Años , Refugiados , Inundaciones , Vigilancia en Salud Pública , Migración Humana , Paraguay/epidemiología , Grupos de Riesgo , Estudios TransversalesRESUMEN
El síndrome de Sweet es una dermatosis neutrofílica aguda y febril que puede ser desencadenada por diferentes noxas. El diagnóstico es clínico a partir de una dermatosis aguda, con fiebre, leucocitosis y lesiones cutáneas localizadas en cara, cuello y extremidades. La histopatología muestra un denso infiltrado inflamatorio de la dermis a predominio neutrofílico, sin signos de vasculitis. Se presenta un paciente con síndrome de Sweet asociado a infección por el virus de la inmunodeficiencia humana
Sweet's syndrome associated with human immunodeficiency virus infection Sweet's syndrome is a neutrophilic and acute febrile dermatosis that can be triggered by different noxas. Diagnosis should be suspected in a patient with fever, leukocytosis and cutaneous lesions located on the face, the neck and the extremities. Cutaneous biopsy confirms the diagnosis of Sweet syndrome, with typical features of a neutrophilic dermatosis in the absence of vasculitis. Here we present a case of Sweet syndrome associated with human immunodeficiency virus infection
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Humanos , Masculino , Adulto , Infecciones por VIH/fisiopatología , VIH , Síndrome de Sweet/diagnósticoRESUMEN
La sífilis es una enfermedad infectocontagiosa causada por una espiroqueta: el Treponema pallidum. Se transmite por contacto directo (generalmente sexual) con las lesiones cutáneo-mucosas durante el estadio primario y secundario, por vía transplacentaria durante el embarazo o a través del pasaje por el canal uterino y por sangre. Se trata de una enfermedad sistémica con una gran variedad de manifestaciones clínicas. La sífilis secundaria cursa con manifestaciones generales de un síndrome infeccioso inespecífico y lesiones mucocutáneas características. La presentación clínica de los 20 pacientes que se describen en este trabajo es singular ya que solo poseían lesiones en la cavidad oral. Es importante considerar esta patología en el diagnóstico diferencial de lesiones mucosas orales, para realizar un diagnóstico temprano, tratamiento precoz y evitar el contagio, así como siempre descartar la asociación con infección por el retrovirus VIH
Syphilis is a sexually transmitted disease caused by the spirochete bacterium named as Treponema pallidum. Syphilis is transmitted by direct contact (generally non-protect sexual contact) with cutaneous and mucosal lesions during the primary and secondary periods, by trans-placental transmission if the mother develop the infection during pregnancy and by blood. Syphilis is a systemic disease with a wide variety of clinical manifestations. Secondary syphilis is characterized by a nonspecific infectious syndrome and mucocutaneous lesions. Here we describe a serie of 20 patients with secondary syphilis as the unique clinical manifestation. Secondary syphilis should be included in the differential diagnosis of oral cavity mucosal lesions to achieve an early diagnosis and avoid the contagion. Human immunodeficiency virus infection should be always considered
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Humanos , Adolescente , Adulto , Persona de Mediana Edad , Sífilis Cutánea/terapia , Sífilis/diagnóstico , Diagnóstico Precoz , Sexo Inseguro , Boca/lesionesRESUMEN
Plasmablastic lymphoma (PBL) is a distinct disease entity of the diffuse large B-cell lymphoma, which often occurs in HIV-positive patients. The immunophenotype of this lymphoid neoplasm is characterized by the presence of plasma cell-associated markers VS38c and CD138 antigens and the absence of B-cell markers such as CD20 and CD45. The most frequent site of involvement is the oral cavity and the jaw, while several reports describe the development of PBL in extra-oral sites including the lymph nodes, the anal canal, the soft tissue, the skin and the gastrointestinal tract as less frequent. Epstein-Barr virus is often associated with PBL pathogenesis and the neoplastic cells contain this virus genome. Here we review the epidemiological, clinical, immunological, histopathological and virological characteristics and their prognosis and outcome in a series of five patients with diagnoses of HIV/AIDS and PBL.
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Infecciones por VIH/patología , Linfoma Relacionado con SIDA/patología , Linfoma de Células B Grandes Difuso/virología , Adulto , Femenino , Humanos , Hígado/patología , Linfoma Relacionado con SIDA/diagnóstico , Linfoma Relacionado con SIDA/virología , Linfoma de Células B Grandes Difuso/diagnóstico , Linfoma de Células B Grandes Difuso/patología , Masculino , Persona de Mediana Edad , Boca/patología , Pronóstico , Piel/patologíaRESUMEN
Paracoccidioidomycosis is a systemic disease endemic to subtropical areas in Central and South America caused by a dimorphic fungus known as Paracoccidioides brasiliensis. Central nervous system involvement is a severe complication of the systemic disease, and has been found in approximately 13% of patients. This paper describes the case of a patient whose computed tomography scan and magnetic resonance imaging showed a single tumor-like lesion in the brainstem. Histopathological and mycological examinations of stereotactic biopsy smears showed the characteristic yeast cells that confirmed the diagnosis of neuroparacoccidioidomycosis.
RESUMEN
OBJECTIVE: Assessment of HIV prevalence and associated risk behaviours among female commercial sex workers (FCSW) across major cities in South America. METHODS: Seroepidemiological, cross sectional studies of 13 600 FCSW were conducted in nine countries of South America during the years 1999-2002. Participants were recruited in brothels, massage parlours, hotels, and streets where anonymous questionnaires and blood samples were collected. HIV infection was determined by enzyme linked immunosorbent assay (ELISA) screening and western blot confirmatory tests. RESULTS: The overall HIV seroprevalence was 1.2% (range 0.0%-4.5%). The highest HIV seroprevalences were reported in Argentina (4.5%) and Paraguay (2.6%); no HIV infected FCSW were detected in Venezuela and Chile. Consistent predictors of HIV seropositivity were: (1) a previous history of sexually transmitted infections (STI, AORs = 3.8-8.3), and (2) 10 years or more in commercial sex work (AORs = 2.2-24.8). In addition, multiple (> or =3) sexual contacts (AOR = 5.0), sex with foreigners (AOR = 6.9), use of illegal drugs (AOR = 3.2), and marijuana use (AOR = 8.2) were associated with HIV seropositivity in Southern Cone countries. CONCLUSIONS: Consistently low HIV seroprevalences were detected among FCSW in South America, particularly in the Andean region. Predictors of HIV infection across the continent were STI and length of commercial sex work; however, use of illegal drugs, especially marijuana, and sexual contacts with foreigners were also found to be associated risk factors in the Southern Cone region. Interventions for the control of HIV and other STI need to be region and country specific; drug use appears to have an ever increasing role in the spread of HIV among heterosexually active populations.
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Infecciones por VIH/epidemiología , Seroprevalencia de VIH , VIH-1 , Trabajo Sexual/estadística & datos numéricos , Adulto , Western Blotting , Ensayo de Inmunoadsorción Enzimática , Métodos Epidemiológicos , Femenino , Humanos , Factores de Riesgo , América del Sur/epidemiologíaRESUMEN
Cytochrome oxidase is a multisubunit, intrinsic membrane protein with a complex function that includes oxidation of cytochrome c, reduction of oxygen and generation of a membrane potential. To clarify the relationship of its normal function to protein and membrane structure, we have examined the kinetic behavior of rat liver cytochrome oxidase in the intact inner mitochondrial membrane and in detergent solubilized states. Dissolution of rat liver mitochondrial membranes alters the kinetic parameters of the oxidase in a manner dependent in part on the dispersing agent, and characterized by a large increase in maximal activity which is not attributable to exposure of more oxidase or diminished affinity for cytochrome c. The most profound effect of solubilization of the membrane is seen on the low affinity reaction of cytochrome c, suggesting that the electron transfer pathway from this site to oxygen is sensitive to alterations in hydrophobic interactions within the oxidase. Purified rat liver and beef heart oxidase exists predominantly in a monodisperse, 300 kilodalton form in laurylmaltoside (Rosevear et al., 1980). However, a smaller, 130 kd species that exhibits high turnover rates equal to the 300 kd form is detected in some beef heart preparations, implying that the dimer may not be essential for high activity. Radiation inactivation studies on purified oxidase reveal a molecular weight for the functional unit of approximately 70 kd. It is concluded that less than a complete set of subunits may be sufficient for both normal binding of cytochrome c and rapid electron transfer to oxygen.