111 research outputs found
The Resilience of Clusters in the Context of Increasing Globalization: The Basque Wind Energy Value Chain
No full textIn this paper, we study how globalization impacts on the structure and governance
patterns of value chains and on the resilience of local clusters. We study the value chains
related to two Basque (Spain) companies in the wind energy industry, Iberdrola and Gamesa,
and the local cluster to which they belong. We find that firms within the cluster have different
types of relationships with lead companies depending on their competences and the complexity
of their products. As a consequence, firms also present different potential for growth and/or
resilience: some have the capacity to internationalize their operations and/or shift to the
offshore wind market, others are vulnerable to competition from providers in the emerging
countries. Against this context, we discuss how the cluster responds to these challenges and the
role of policy
Solvation Dynamics in Acetonitrile: A Study Incorporating Solute Electronic Response and Nuclear Relaxation
No full textThe solvent reorganization process after electronic excitation of a polar solute in a polar solvent such as acetonitrile is related mainly to the time evolution of the solute-solvent electrostatic interaction. Modern laser-based techniques have sufficient time resolution to follow this decay in real time, providing information to be confirmed and interpreted by theories and models. We present here a study aimed at the investigation of the different steps involved in the process taking place after a vertical S0 f S1 excitation of a large size chromophore, coumarin 153 (C153), in acetonitrile, from both the solute and the solvent points of view. To do this, we use accurate quantum mechanical calculations for the solute properties within the polarizable continuum model (PCM) and classical molecular dynamics (MD) simulations, both equilibrium and nonequilibrium, for C153 in the presence of the solvent. The geometry of the solute is allowed to change in order to study the role of internal motions in the time-dependent solvation process. The solvent response function has been obtained from the simulation data and compared to experiment, while the comparison between equilibrium and nonequilibrium MD results for the solvation response confirms the validity of the linear response approximation in the C153-acetonitrile system. The MD trajectories have also been used to monitor the structure of the solvation shell and to determine its change in response to the change in the solute partial charges
Do clusters follow the industry life cycle? An exploratory meta-study of Basque clusters from the 1970s to 2008
No full textAlthough clusters life cycles tend to co-evolve with the life cycle of its dominant industry (Bergman, 2008; Menzel and Fornahl, 2010), the stylized life cycle model does not capture the full complexity of cluster evolution (Martin and Sunley, 2011). Empirical studies indicate that clusters do not necessarily follow the life cycles of their dominant industries, as different clusters that belong to the same industry life cycle follow different evolutionary paths (Saxenian, 1994). Thus, clusters are not just a local representation of an industry and local peculiarities also matter for the evolution of a particular cluster (Menzel and Fornahl, 2010). Empirical studies have pointed out that local factors such as factor endowment, entrepreneurship and firms? capabilities, an existing market, or institutions and social capital may have an impact on it (Belussi and Sedita, 2009; Elola et al., 2012). The Basque Country is an old industrialized European region that successfully managed to escape from a lock-in situation in the 1980s renewing its industrial base by upgrading some of its mature clusters and by promoting new high tech ones. Based on the experience of the Basque Country, in this paper, we aim at analyzing whether clusters co-evolve with their corresponding industry or deviate from it. In addition, we also study which are the local factors that explain such behaviors. For that purpose, we draw on a meta-study of six clusters of the Basque Country: papermaking, maritime industries, machine-tools, electronics and ICTs, aeronautics and energy. References BELUSSI, R. and SEDITA, C. (2009) Life Cycle vs. Multiple Path Dependency in Industrial Districts, European Planning Studies, 17, 4, pp. 505-528. BERGMAN, E. M. (2008) Cluster life-cycles: an emerging synthesis, in C. KARLSSON (Ed.), Handbook of Research on Cluster Theory, Edward Elgar: Cheltenham. ELOLA, A., VALDALISO, J. M., ARANGUREN, M. J., and LÓPEZ, S. (2012) Cluster Life Cycles, Path Dependency and Regional Economic Development. Insights from a Meta-Study on Basque Clusters, European Planning Studies, 20, 2, 257-279. MARTIN, R., and SUNLEY, P. (2011) Conceptualizing Cluster Evolution: Beyond the Life Cycle Model? Regional Studies, 45, 10, 1299-1318. MENZEL, P., and FORNAHL, D. (2010) Cluster life cycles ?dimensions and rationales of cluster evolution, Industrial and Corporate Change 19, 1: 205-238. SAXENIAN, A. (1994) Regional Advantage: Culture and Competition in Silicon Valley and Route 128. Harvard University Press: Cambridge
Equilibrium and dynamical characteristics of Imidazole Langmuir monolayers on graphite sheets
No full textUsing molecular dynamics techniques, we examine structural and dynamical characteristics of liquid-like, Imidazole(Im) monolayers physisorbed onto a planar graphite sheet, at T = 384K. Our simulations reveal that molecular orientations in the saturated monolayer exhibit a bistable distribution, characterized by an inner parallel arrangement of the molecules in close contact with the substrate and a slanted alignment, in those lying in adjacent, outer locations. Compared to the results found in three dimensional, bulk phases, the analysis of the spatial correlations between sites participating in hydrogen bonding shows a clear enhancement of the intermolecular interactions, which also leads to stronger dipolar correlations. As a result, the gross structural features of the monolayer can be cast in terms of mesoscopic domains, comprising units articulated via winding hydrogen bonds, that persist along typical time intervals of a few tens of picoseconds. On the dynamical side, a similar comparison of the characteristic decorrelation time for orientational motions shows a 4-fold increment. Contrasting, the reduction of the system dimensionality leads to a larger diffusion constant. Possible substrate-induced anisotropies in the diffusive motions are also investigated.Fil: Rodriguez, Javier. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Núcleo de Investigación en Educacion Ciencia y Tecnologia; ArgentinaFil: Elola, Maria Dolores. Comisión Nacional de Energía Atómica; ArgentinaFil: Laria, Daniel Hector. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentin
Structure and dynamics of nanoconfined water and aqueous solutions
No full textAbstract: This review is devoted to discussing recent progress on the structure, thermodynamic, reactivity, and dynamics of water and aqueous systems confined within different types of nanopores, synthetic and biological. Currently, this is a branch of water science that has attracted enormous attention of researchers from different fields interested to extend the understanding of the anomalous properties of bulk water to the nanoscopic domain. From a fundamental perspective, the interactions of water and solutes with a confining surface dramatically modify the liquid’s structure and, consequently, both its thermodynamical and dynamical behaviors, breaking the validity of the classical thermodynamic and phenomenological description of the transport properties of aqueous systems. Additionally, man-made nanopores and porous materials have emerged as promising solutions to challenging problems such as water purification, biosensing, nanofluidic logic and gating, and energy storage and conversion, while aquaporin, ion channels, and nuclear pore complex nanopores regulate many biological functions such as the conduction of water, the generation of action potentials, and the storage of genetic material. In this work, the more recent experimental and molecular simulations advances in this exciting and rapidly evolving field will be reported and critically discussed. Graphic abstract: [Figure not available: see fulltext.
Structure and dynamics of liquid methanol confined within functionalized silica nanopores
No full textMolecular dynamics simulations have been carried out to investigate the structure and dynamics of liquid methanol confined in 3.3 nm diameter cylindrical silica pores. Three cavities differing in the characteristics of the functional groups at their walls have been examined: (i) smooth hydrophobic pores in which dispersive forces prevail, (ii) hydrophilic cavities with surfaces covered by polar silanol groups, and (iii) a much more rugged pore in which 60% of the previous interfacial hydroxyl groups were replaced by the bulkier trimethylsilyl ones. Confinement promotes a considerable structure at the vicinity of the pore walls which is enhanced in the case of hydroxylated surfaces. Moreover, in the presence of the trimethylsilyl groups, the propagation of this interface-induced spatial ordering extends down to the central region of the pore. Concerning the dynamical modes, we observed an overall slowdown in both the translational and rotational motions. An analysis of these mobilities from a local perspective shows that the largest retardations operate at the vicinity of the interfaces. The gross features of the rotational dynamics were analyzed in terms of contributions arising from bulk and surface states. Compared to the bulk dynamical behavior, the characteristic timescales associated with the rotational motions show the most dramatic increments. A dynamical analysis of hydrogen bond formation and breaking processes is also included. © 2010 American Institute of Physics.Fil:Elola, M.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Rodriguez, J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Laria, D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Exploring Heritage Speakers, L2s, and Monolinguals\u27 Typed Writing Strategies: Evidence from Stimulated Recalls
No full textComposing and writing development is an area of investigation that has been severely understudied in the field of heritage language (HL) studies. Yet while HL speakers have robust production skills, writing in their HL tends to be far less developed due to inaccessibility of formal education in their HL (Potowski, 2021; Potowski & Marshall, 2021). Understanding how students compose is essential to drive evidence-based pedagogy that will help HL speakers improve their writing (Colombi, 1997) and to inform theoretical writing frameworks.
Within literacy development, recent HL studies in Spanish (e.g., Bowles & Bello-Uriarte, 2019; Hurtado & Gastañaga, 2021) have primarily focused on exploring individual writing development through product-centric indicators (i.e., lexical density, sophistication, and diversity). Furthermore, research on Spanish HL speakers’ writing behavior has been limited to HL college students (Schwartz, 2003, 2005; Mikulski & Elola, 2011; Elola & Mikulski, 2013; Torres, 2023). Yet, there is a significant gap concerning second language learners (L2ers), younger HL speakers (Bowles & Torres, 2021), and non-college-educated HL speakers.
The goal of this study is to assess what typing strategies and previous knowledge participants used when typing a dictation task. By integrating stimulated recalls post-dictation task, this study examined monolingually-raised Spanish speakers (n=18), L2ers (n=8), and Spanish HL speakers in college (n=8), high school (n=4), and non-college educated (n=6) from a major university in the Midwest and from Southern California.
Preliminary main findings indicate that L2ers and monolingually-raised speakers relied on metalinguistic strategies, with both referring to classroom-based knowledge. The former focused more on form focused strategies (e.g., placing two vowels to remember it has an accent) while the latter more on meaning (e.g., abbreviations as placeholders). HL speakers focused more on meaning, with strategies drawn from their HL courses such as sounding out the words and focusing more on the context (e.g., skipping lines for different sentences). Younger and non-college educated HL speakers used descriptive based strategies (e.g., lexical chunking).
Bowles, M. A., & Torres, J. (2021). Instructed Heritage Language Acquisition. In S. Montrul & M. Polinsky (Eds.), The Cambridge Handbook of Heritage Languages and Linguistics (1st ed., pp. 826–850). Cambridge University Press. https://doi.org/10.1017/9781108766340.037
Bowles, M. A., & Bello-Uriarte, J. (2019). What Impact Does Heritage Language Instruction Have on Spanish Heritage Learners’ Writing? In M. Sato & S. Loewen (Eds.), Evidence-based second language pedagogy (pp. 219–239). New York: Routledge.
Colombi, M. C. (1997). Perfil del discurso escrito: Teoría y práctica. In M. C. Colombi & F. X. Alarcón (Eds.), La enseñanza del español a hispanohablantes: Praxis y teoría (pp. 175–189). Houghton Mifflin.
Elola, I., & Mikulski, A. (2013). Revisions in real time: Spanish heritage language learners’ writing processes in English and Spanish. Foreign Language Annals, 46, 646–660.
Hurtado, I., & Gastañaga, K. (2021). Influence of Writing Instruction on Spanish Heritage Learners in Heritage-Only and Mixed Courses: A Longitudinal Study. Languages, 6(2), 109. https://doi.org/10.3390/languages6020109
Mikulski, A., & Elola, I. (2011). Spanish heritage language learners’ allocation of time to writing processes in English and Spanish. Hispania, 94, 715–733.
Potowski, K. (2021). Elementary School Heritage Language Educational Options and Outcomes. In S. Montrul & M. Polinsky (Eds.), The Cambridge Handbook of Heritage Languages and Linguistics (1st ed., pp. 761–776). Cambridge University Press. https://doi.org/10.1017/9781108766340.034
Potowski, K. and M. Marshall. 2021. The Spanish Proficiency of Latino Dual Immersion Students Compared to Peers in an All English Program: A Pseudo-Longitudinal Study across Multiple Domains. International Symposium on Bilingualism ISB13
Schwartz, A. M. (2003). ¡No me suena! Heritage Spanish speakers’ writing strategies. In A. Roca & M. C. Colombi (Eds.), Mi lengua: Spanish as a heritage language in the United States (pp. 235–256). Georgetown University Press.
Schwartz, A. M. (2005). Exploring differences and similarities in the writing strategies used by students in SNS courses. In L. A. Ortiz López & M. Lacorte (Eds.), Contactos y contextos lingüísticos: El español en los Estados Unidos y en contacto con otras lenguas (pp. 323–333). Lingüística Iberoamericana.
Torres, J. (2023). Exploring working memory and language dominance in heritage bilinguals’ writing processes. Studies in Second Language Acquisition, 45(3), 710–736. https://doi.org/10.1017/S027226312300013
Aireztapenen maiztasunaren neurketa bihotz biriketako berpiztean kapnografia erabiliz.
No full text[EN]Hyperventilation, which is common both in-hospital and out-of-hospital cardiac arrest,
decreases coronary and cerebral perfusion contributing to poorer survival rates in both
animals and humans. Current resucitation guidelines recommend continuous monitoring of
exhaled carbon dioxide (CO2) during cardiopulmonary resucitation (CPR) and emphasize
good quality of CPR, including ventilations at 8-10 min1. Most of commercial monitors/de-
brilators incorporate methods to compute the respiratory rate based on capnography since
it shows
uctuations caused by ventilations. Chest compressions may induce artifacts in this
signal making the calculation of the respiratory rate di cult. Nevertheless, the accuracy of
these methods during CPR has not been documented yet.
The aim of this project is to analyze whether the capnogram is reliable to compute
ventilation rate during CPR. A total of 91 episodes, 63 out-of-hospital cardiac arrest episodes
( rst database) and 28 in-hospital cardiac arrest episodes (second database) were used to
develop an algorithm to detect ventilations in the capnogram, and the nal aim is to provide
an accurate ventilation rate for feedback purposes during CPR.
Two graphic user interfaces were developed to make the analysis easier and another
two were adapted to carry out this project. The use of this interfaces facilitates the managment
of the databases and the calculation of the algorithm accuracy. In the rst database,
as gold standard every ventilation was marked by visual inspection of both the impedance,
which shows
uctuations with every ventilation, and the capnography signal. In the second
database, volume of the respiratory
ow signal was used as gold standard to mark ventilation
instants since it is not a ected by chest compressions.
The capnogram was preprocessed to remove high frequency noise, and the rst di erence
was computed to de ne the onset of inspiration and expiration. Then, morphological
features were extracted and a decission algorithm built based on the extracted features to detect
ventilation instants. Finally, ventilation rate was calculated using the detected instants
of ventilation.
According to the results obtained in this project, the capnogram can be reliably
used to give feedback ventilation rate, and therefore, on hyperventilation in a resucitation
scenario.[ES]La hiperventilaci on, muy com un durante la resucitaci on cardiopulmonar (RCP), disminuye
la presi on de la perfusi on coronaria y cerebral, reduciendo la tasa de supervivencia
tanto en animales como en personas. Las gu as de resucitaci on actuales, recomiendan la constante
monitorizaci on del di oxido de carbono exhalado por el paciente y enfatizan la buena
calidad del RCP, incluyendo ventilaciones con una frecuencia de 8-10 min1. La mayor a
de los des briladores y monitores comercialmente disponibles a d a de hoy, usan la se~nal de
capnograf a para el c alculo de dicha frecuencia, puesto que muestra
uctuaciones con cada
ventilaci on. El problema es que esta se~nal sufre interferencias causadas por las compresiones
tor acicas, y la precisi on de los m etodos durante la RCP no ha sido documentada.
En este contexto, el objetivo de este proyecto es analizar la abilidad del capnograma
para la medida de la frecuencia de las ventilaciones durante la RCP. Para ello, se ha desarrollado
un algoritmo que determina los instantes de ventilaci on a partir del capnograma,
incluyendo los intervalos en los que se est an aplicando compresiones tor acicas. El objetivo
nal es mostrar la frecuencia de ventilaciones. La base de se~nales utilizada incluye 91 episodios,
de los cuales 63 pertenecen a paradas card acas extrahospitalarias (primera base de
datos) y 28 intrahospitalarias (segunda base de datos).
El desarrollo del proyecto incluye la implementaci on de dos herramientas gr a cas
para la de nici on de la base de se~nales de prueba y para la evaluaci on del algoritmo de
detecci on de ventilaciones. Adem as, se han adaptado otras dos herramientas gr a cas con
el n de facilitar el proceso. Usando estas herramientas, la gesti on de las bases de datos
y la medida de la precisi on del algoritmo ser an m as c omodas de realizar. En la primera
base de datos, se han usado como referencia el capnograma y la se~nal de impedancia (la
cual muestra
uctuaciones en cada ventilaci on) para marcar las ventilaciones. En la segunda
base de datos, se ha usado como referencia la se~nal de volumen del
ujo respiratorio (la cual
no se ve afectada por las compresiones tor acicas) para marcar las ventilaciones.
El algoritmo preprocesa la se~nal para suprimir el ruido de alta frecuencia, y se calcula
la primera diferencia para marcar los posibles instantes de inspiraci on/expiraci on. A partir
de esta informaci on, se calculan ciertos par ametros y un algoritmo de decisi on descarta los
falsos instantes de ventilaci on.
Analizando los resultados, se puede concluir que el capnograma es able para la
medida de la frecuencia respiratoria durante la resucitaci on cardiopulmonar. Adem as, en
este documento se propone un algoritmo nuevo para conseguirlo.[EU]Hiperbentilazioak, oso ohikoa bai ospitale-barruko (OB) eta bai ospitale-kanpoko
(OK) bihotz-geldialdietan, biziraupen probabilitatea jaisten du. Egungo berpizte gomendioek,
gaixoak botatako karbono dioxidoaren (CO2) etengabeko monitorizazioa gomendatzen
dute bat-bateko bihotz geldialdi (BBG) eszenario batean, eta kalitate oneko bihotzbiriketako
berpizte (BBB) bat bermatzeko, minutuko 8-10 aireztapen ematea gomendatzen
dute. Egun merkatuan dauden monitore/des briladore gehienek, aireztapenen maiztasuna
kapnograman oinarrituriko algoritmoen bidez kalkulatzen dute, baina sakadek interferentzia
bat eragiten dute seinalearengan eta algoritmoen zehaztasuna ez da dokumentatu interferentzia
hau ageri denean.
Honen harira, proiektu honen helburua kapnogramaren zehaztasuna aztertzea da aireztapenen
maiztasunaren kalkulurako, sakadak dauden testuinguru batean. Helburu hau
betetzeko, algoritmo bat diseinatu da aireztapenak detektatzeko kapnograman BBB masajea
aplikatzen ari den bitartean. Honetarako, guztira 91 episodioz osaturiko datu-multzoa
erabili da, 63 OK geldialdiak ziren (lehenengo datu-basea) eta 28 OB geldialdiak (bigarren
datu-basea).
Prozesua errazteko asmoz, bi tresna gra ko garatu dira eta beste bi tresna proiektu
honen betebeharrak asetzeko moldatu dira. Tresna hauek erabiliz, datu-baseen kudeaketa,
algoritmoaren optimizazioa eta algoritmoaren zehaztasunaren analisia errazago gauzatzen
dira. Lehenengo datu-basean, aireztapen guztiak inpedantzia-seinalea (zeinak
uktuazioak
erakusten dituen aireztapen bakoitzean) eta kapnograma erabiliz markatu dira. Bigarren
datu-basean, bolumen-seinalea erabili da erreferentzi gisa aireztapenak markatzeko, sakadek
sorturiko interferentziek gutxiago eragiten diote seinale honi eta aireztapenak erraz markatzen
dira.
Kapnograma aurreprozesatu egiten da goi-maiztasuneko zarata ezabatzeko, eta lehenengo
diferentzia kalkulatzen da gaixoak arnasa hartu eta botatzen dituen uneak estimatzeko.
Ondoren, parametro batzuk kalkulatzen dira eta deliberamendu algoritmo batek aireztapen
uneak identi katzen ditu. Azkenik, aireztapenen maiztasuna kalkulatzen da.
Emaitzak begiratuz, kapnograma aireztapenen maiztasunaren kalkulurako erabili daitekeela
ondorioztatu daiteke, eta dokumentu honetan algoritmo berri bat proposatzen da
hau lortzeko
La sinusite fongique. A propos de 6 cas dans le service ORL du CHU-YO de Ouagadougou
No full textLa sinusite fongique regroupe des aspects anatomo-cliniques variés. Le plus fréquent est la « balle aspergillaire ». En rapportant ces 6 cas, nous voulous souligner les caractéristiques épidémio-cliniques, thérapeutiques et évolutives de cette pathologie dans notre pratique.Il s’est agi d’une étude rétrospective à partir des dossiers cliniques du service d’ORL et de chirurgie cervico-faciale du CHU Yalgado Ouédraogo de 2002 à 2008. En 7 ans, nous avons colligé 6 cas de sinusite fongique. La symptomatologie d’appel non spécifique était celle d’une rhinosinusite mais remarquable par son évolution chronique « désespérante » et son unilatéralité. Il s’est agi de sinusite fongique localisée dans 5 cas ; dans 1 cas, une ostéite avec fistulisation paralatéro-nasale était associée.Le traitement a été médico-chirurgical avec une association systématique d’antifongique par voie générale chez tous les malades. L’examen anatomo- pathologique du spécimen opératoire a montré la présence de filaments mycéliens d’aspergillus fumigatus dans 5 cas. Un aspect de pseudotumeur inflammatoire évoquant une actinomycose a été noté dans un cas. L’examen mycologique n’a été possible que dans deux casisolant aspergillus fumigatus. L’évolution a été favorable dans tous les cas avec un recul de 1 à 4 ans. La sinusite fongique est relativement rare dans notre pratique, mais vraisemblablement sous diagnostiquée. Il faut y penser de parti pris devant toute sinusite chronique rebelle au traitement habituel et demander au mieux une tomodensitométrie des sinus de la face. Le traitement est médico-chirurgical accordant une place pour les antifongiques par voie générale.Mots clés : sinusite, fongique, signes, traitement
Prevalencia de las infecciones por virus de las hepatitis B, C, D y E en Bolivia Prevalence of viral hepatitis B, C, D, and E in Bolivia
No full textEn Bolivia no se han realizado estudios específicos sobre los virus de la hepatitis, por lo que su prevalencia y patrones de circulación son prácticamente desconocidos. De 1992 a 1996 se realizó un estudio seroepidemiológico con el fin de adquirir una primera visión de conjunto sobre las prevalencias de las infecciones por virus de la hepatitis B (VHB), C (VHC), D (VHD) y E (VHE) en distintas poblaciones de Bolivia. Sobre la base de los datos obtenidos en otros lugares de América Latina, se prestó atención especial al estudio de las comunidades autóctonas de la región amazónica. En las zonas rurales del altiplano andino, la infección por VHB presentó una prevalencia general que correspondería a una situación de endemia media o baja (11,2%) y no se encontró ningún portador de anticuerpos contra VHC o VHD. En dos poblaciones de alto riesgo de la ciudad de Cochabamba (niños sin hogar y trabajadoras del sexo), la prevalencia de infección por VHB fue similar (11,6%) y podría considerarse baja en comparación con la de otras poblaciones análogas de núcleos urbanos en América Latina. La correspondiente al VHC (un caso positivo, 0,5%) sería parecida a la descrita en esas mismas poblaciones, si bien el escaso número de muestras estudiadas no permite extraer conclusiones más firmes. En concordancia con observaciones anteriores de comunidades similares de zonas tropicales de Suramérica, en las poblaciones autóctonas de la Amazonia boliviana la infección por VHB es sumamente endémica (prevalencia general de 74,0%), pero no se ha detectado la circulación de VHC. Se sabe que la transmisión de VHB es horizontal y tiene lugar desde edades muy tempranas, pero se desconocen los mecanismos de esa actividad. A los 10 años de edad, más de la mitad de la población ya ha experimentado la infección natural que, 10 años más tarde, se habrá difundido a prácticamente toda la población. La tasa muy baja de individuos positivos al HbsAg (1,6%), la ausencia de ADN vírico en las muestras con reactividad aislada a anti-HBc y la alta prevalencia de anti-HBs entre los individuos que presentan marcadores de infección natural (92,4%) excluyen la participación de la transmisión vertical en el mantenimiento de la endemia. Hasta el momento, no se ha documentado ningún brote de infección por VHD en estas comunidades, pero la alta endemia de infección por VHB alerta sobre el riesgo de posibles brotes en el futuro. Los resultados obtenidos con las pruebas de anticuerpos contra VHE sugieren que este virus circula ampliamente en Bolivia y que podría haber producido brotes recientes en el departamento de Cochabamba. Se recomienda vacunar contra VHB en las poblaciones endémicas como medida de corto plazo; buscar activamente en todo el país brotes y casos esporádicos de hepatitis E y continuar realizando estudios que permitan evaluar las repercusiones sanitarias de la situación documentada en este estudio.In Bolivia, no studies have been carried out specifically on hepatitis viruses. Thus, their prevalence and circulation patterns are virtually unknown. A seroepidemiologic study was performed from 1992 to 1996 to generate a preliminary idea of the overall prevalence of infection from hepatitis B, C, D, and E viruses (HBV, HCV, HDV, and HEV, respectively) in different Bolivian population groups. Prompted by the data obtained in other areas of Latin America, the study focused on indigenous communities in the Amazon region. In rural areas of the high Andean plateau, HBV infection showed an overall prevalence compatible with medium to low endemicity (11.2%), and no carriers of HCV or HDV antibodies were found. In two high-risk groups in the city of Cochabamba (homeless children and sexual workers), the prevalence of HBV infection was similar (11.6%) and could be considered low by comparison to that of similar population groups in Latin American urban centers. The prevalence of HCV (one positive case, or 0.5%) was similar to that found in similar population groups, although the small number of samples precludes drawing more definite conclusions. As has been noted previously with similar communities in tropical areas of South America, HBV infection is highly endemic in indigenous populations of the Bolivian Amazon (with an overall prevalence of 74.0%), but circulation of HCV has not been detected. It is a well-known fact that HBV is horizontally transmitted and that transmission can take place very early in life, but the mechanisms involved are unknown. By 10 years of age, more than half the population has already had the natural infection that, in approximately 10 more years will have affected virtually the entire population. The very low rate of positivity to HBsAg (1.6%), the absence of viral DNA in samples showing isolated positivity to anti-HBc, and the high prevalence of anti-HBs among individuals who show markers for natural infection (92.4%) suggest vertical transmission plays no role in persistent endemi city. So far, no outbreak of HDV infection has been documented in these communities, but the high endemicity shown by HBV points to the po ssibility of future outbreaks. Results obtained with tests for the detection of antibodies against HEV suggest that this virus is circulating widely in Bolivia and that it could have caused recent outbreaks in Cochabamba state. Vaccination against HBV in endemic populations is recommended as a short-term measure. Also recommended are actively searching for outbreaks and sporadic cases of hepatitis E in the entire country and performing additional research that will help in assessing the public health consequences of the situation described in this article
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