Biomedical subjects

Gonzalo Alvarez

Publications and source records attributed to Gonzalo Alvarez.

15 recordsLinked to original sources

PubMed2006

Identification of pectenotoxins in plankton, filter feeders, and isolated cells of a Dinophysis acuminata with an atypical toxin profile, from Chile.

A bloom of Dinophysis acuminata produced, in autumn of 2005, a closure of the scallop harvesting in Bahía Inglesa, in the Chilean III region. Isolated cells of this Dinophysis species were shown to contain 180 pg cell(-1) of pectenotoxin 2 but neither okadaic acid nor any of its analogs or derivatives (at least at a detectable level). Examination of plankton and filter-feeder samples covering an area of ca. 350 km, from the location where the toxicity was recorded to Bahía Tongoy, showed that the unique toxin profile found in the first bloom was widespread over that part of Chile and persisted for months. The analysis were carried out by HPLC-ESI-MS using positive ionization mode, with a detection limit below 2 ng of OA mL(-1) of methanolic extract. This is the first report of the presence of pectenotoxins in the plankton of the Pacific coast of America and in the studied filter feeders. This is also the first report of a Dinophysis species containing pectenotoxins and not any toxin of the okadaic acid group.

Animals↗

PubMed2006

Analysis of security problems in a medical image encryption system.

Recently, a new system for the secure transmission and efficient storage of medical images interleaved with patient information has been proposed in 2003 by Rajendra Acharya et al. In this paper, we analyse the security of this system, showing how to improve it to obtain a truly secure system.

Algorithms↗

PubMed2006

Therapeutic efficacy test in malaria falciparum in Antioquia, Colombia.

OBJECTIVE: Evaluate the frequency of failure of eight treatments for non-complicated malaria caused by Plasmodium falciparum in patients from Turbo (Urabá region), El Bagre and Zaragoza (Bajo Cauca region), applying the 1998 protocol of the World Health Organization (WHO). Monotherapies using chloroquine (CQ), amodiaquine (AQ), mefloquine (MQ) and sulphadoxine-pyrimethamine (SP), and combinations using chloroquine-sulphadoxine-pyrimethamine (CQ-SP), amodiaquine-sulphadoxine-pyrimethamine (AQ-SP), mefloquine-sulphadoxine-pyrimethamine (MQ-SP) and artesunate-sulphadoxine-pyrimethamine (AS-SP), were examined. METHODOLOGY: A balanced experimental design with eight groups. Samples were selected based on statistical and epidemiological criteria. Patients were followed for 21 to 28 days, including seven or eight parasitological and clinical evaluations, with an active search for defaulting patients. A non-blinded evaluation of the antimalarial treatment response (early failure, late failure, adequate response) was performed. RESULTS: Initially, the loss of patients to follow-up was higher than 40%, but the immediate active search for the cases and the monetary help for transportation expenses of patients, reduced the loss to 6%. The treatment failure was: CQ 82%, AQ 30%, MQ 4%, SP 24%, CQ-SP 17%, AQ-SP 2%, MQ-S-P 0%, AS-SP 3%. CONCLUSION: The characteristics of an optimal epidemiological monitoring system of antimalarial treatment response in Colombia are discussed. It is proposed to focus this on early failure detection, by applying a screening test every two to three years, based on a seven to 14-day follow-up. Clinical and parasitological assessment would be carried out by a general physician and a field microscopist from the local hospital, with active measures to search for defaulter patients at follow-up.

Adolescent↗

PubMed2006

Efficacy of three chloroquine-primaquine regimens for treatment of Plasmodium vivax malaria in Colombia.

Plasmodium vivax malaria is an important cause of morbidity in Central and South America. In Colombia, this is the most prevalent malaria infection, representing 75% of the reported cases. To define the efficacy of the chloroquine and primaquine regimen to eliminate hypnozoites and prevent relapses, we conducted a random controlled clinical trial of three primaquine regimens in an open-label study. We evaluated the anti-relapse efficacy of total primaquine doses of 45, 105, and 210 mg administered at a dosage of 15 mg/day in 210 adults with P. vivax infection from the northwestern region of Colombia. Cure rates for blood-stage P. vivax malaria by day 28 of follow-up were 100% in all groups. Post-treatment reappearance of parasitemia during the six months of follow-up was 45%, 36.6% and 17.6%, respectively, for each group. When compared with other groups, administration of 210 mg was a significant protection factor for reappearance of parasitemia in a malaria-endemic area.

Adult↗

PubMed2006

[Plasmodium vivax malaria: treatment of primary attacks with primaquine, in three different doses, and a fixed dose of chloroquine, Antioquia, Colombia, 2003-2004].

INTRODUCTION: Chloroquine (CQ) and primaquine (PQ) are used in Colombia for treatment of uncomplicated vivax malaria but there are few efficacy studies of this scheme. OBJECTIVES: (a) to investigate the clinical picture of vivax malaria in adult patients; (b) to evaluate the antimalarial treatment response to the standard scheme CQ-PQ; (c) to compare the efficacy of the standard scheme and two alternative schemes with equal dose of CQ and different PQ dose; (d) to identify the adverse effects of CQ-PQ treatment. MATERIALS AND METHODS: Randomized, nonblind design; three groups, defined according to total dose of PQ: 45, 105 and 210 mg. All patients received CQ (1500 mg, in 48 hours), which was followed by PQ. Patients were recruited in Turbo and El Bagre. The follow-up period was 28 days. Antimalarial treatment response was classified according to the WHO-2001 protocol (early failure, late failure, adequate response). RESULTS: In total 228 patients were recruited, 18 were lost between days 4 and 27; the antimalarial treatment response was evaluated in 210. The clinical findings were similar to those described by other authors. Parasitaemia clearance was confirmed during the first 24 hours of CQ treatment in 11% of patients. At 48 hours 66% and at 72 hours 97% of patients were negative. All patients (210) displayed adequate treatment response to the CQ-PQ treatment. The different doses of PQ did not affect this response. CONCLUSIONS: CQ-PQ should be conserved as the first treatment choice and should be evaluated in other areas. Simultaneous administration of CQ and PQ is proposed.

Acute Disease↗

PubMed2005

Phase fluctuations in strongly coupled d-wave superconductors.

We present a numerically exact solution for the BCS Hamiltonian at any temperature, including the degrees of freedom associated with classical phase, as well as amplitude fluctuations via a Monte Carlo integration. This allows for an investigation over the whole range of couplings: from weak attraction, as in the well-known BCS limit, to the mainly unexplored strong-coupling regime of pronounced phase fluctuations. In the latter, two characteristic temperatures T(*) and T(c), associated with short- and long-range ordering, respectively, can be identified in a mean-field-motivated Hamiltonian. T(*) at the same time corresponds to the opening of a gap in the excitation spectrum. In addition to introducing a novel procedure to study strongly coupled d-wave superconductors, our results indicate that classical phase fluctuations are not sufficient to explain the pseudogap features of high-temperature superconductors.

Journal Article↗

PubMed2005

Models of general frequency-dependent selection and mating-interaction effects and the analysis of selection patterns in Drosophila inversion polymorphisms.

We investigate mechanisms of balancing selection by extending two deterministic models of selection in a one-locus two-allele genetic system to allow for frequency-dependent fitnesses. Specifically we extend models of constant selection to allow for general frequency-dependent fitness functions for sex-dependent viabilities and multiplicative fertilities, while non-multiplicative mating-dependent components remain constant. We compute protected polymorphism conditions that take the form of harmonic means involving both the frequency- and the mating-dependent parameters. This allows for a direct comparison of the equilibrium properties of the frequency-dependent models with those of the constant models and for an analysis of equilibrium of the general model of constant fertility. We then apply the theory to analyze the maintenance of inversion polymorphisms in Drosophila subobscura and D. pseudoobscura, for which data on empirical fitness component estimates are available in the literature. Regression on fitness estimates obtained at different starting frequencies enables us to implement explicit fitness functions in the models and therefore to perform complete studies of equilibrium and stability for particular sets of data. The results point to frequency dependence of fitness components as the main mechanism responsible for the maintenance of the inversion polymorphisms considered, particularly in relation to heterosis, although we also discuss the contribution of other selection mechanisms.

Animals↗

PubMed2005

Breaking a chaos-noise-based secure communication scheme.

This paper studies the security of a secure communication scheme based on two discrete-time intermittently chaotic systems synchronized via a common random driving signal. Some security defects of the scheme are revealed: 1) The key space can be remarkably reduced; 2) the decryption is insensitive to the mismatch of the secret key; 3) the key-generation process is insecure against known/chosen-plaintext attacks. The first two defects mean that the scheme is not secure enough against brute-force attacks, and the third one means that an attacker can easily break the cryptosystem by approximately estimating the secret key once he has a chance to access a fragment of the generated keystream. Yet it remains to be clarified if intermittent chaos could be used for designing secure chaotic cryptosystems.

Algorithms↗

PubMed2004

Evaluation of clastogenic potential of the antimalarial plant Solanum nudum.

Compounds isolated from Solanum nudum have shown in vitro antimalarial activity against the FCB-2 strain of Plasmodium falciparum. Diosgenone (C27H40O3) the main component isolated from the hexane extract and an aqueous extract were evaluated to measure their clastogenic potential using the micronucleus test. Three concentrations (16, 32 and 64 g/kg of weight) of the aqueous extract were administered intraperitoneally into mice, (the highest concentration corresponded to 80% LD50) and diosgenone solubilized in olive oil was inoculated at the highest concentration possible (11.187 g/kg of weight). After administration of the compounds, no induction of micronucleus was observed either in polychromatic or normochromatic erythrocytes. Interestingly, a reduction of 51% in the young/mature erythrocytes ratio was seen in cells treated with aqueous extract. We conclude that neither diosgenone nor the aqueous extract have clastogenic activity, and that the aqueous extract showed some toxicity at the above mentioned concentrations. These results are significant since diosgenone could be a new therapeutic alternative for the treatment of malaria.

Animals↗

PubMed2003

Serological and parasitological study and report of the first case of human babesiosis in Colombia.

A study on the presence of Babesia in humans was performed in Puerto Berr o (Latitude 6.50deg. Longitude: -74.38deg. River: Magdalena. Area: 74.410km , Colombia-South America). Indirect immunofluorescence, thin and thick blood smears were used to study 194 individuals. Patients were grouped according to their risk-factors for Babesia infection: (group 1) individuals with fever, chills, sweating and other malaria-type symptoms; (group 2) symptomatic and asymptomatic individuals from local cattle ranches, which were enrolled in an active form, and (group 3) workers from the local slaughterhouse. Seven individuals were serologically positive for Babesia: Three individuals presented IgM antibodies against B. bovis, while one had IgG against this species; one individual had IgM against B. bigemina, another had IgG and a third both IgM and IgG against this species. Only one individual was parasitologically positive for Babesiaand serologically positive for Babesia bovis (IgM 1:64)

Adolescent↗

PubMed2003

Clinical and laboratory findings of Plasmodium vivax malaria in Colombia, 2001.

A descriptive study was carried out in 104 patients with Plasmodium vivax malaria, from the region of Turbo (Antioquia, Colombia). Clinical features and levels of hemoglobin, glycemia, serum bilirubin, alanine-aminotransferase (ALT), aspartate-aminotransferase (AST), creatinine and complete blood cell profile were established. 65% of the studied individuals were men and their mean age was 23. Of all individuals 59% had lived in the region for > 1 year and 91% were resident in the rural area. 42% were farmers and 35% had a history of malaria. The mean parasitaemia was 5865 parasites/mm3. The evolution of the disease was short (average of 4.0 days). Fever, headache and chills were observed simultaneously in 91% of the cases while the most frequent signs were palmar pallor (46%), jaundice (15%), hepatomegaly (17%), and spleen enlargement (12%). Anemia was found in 39% of the women and in 51% of the men, 8% of individuals had thrombocytopaenia and 41% had hypoglycemia.

Adolescent↗

PubMed2002

Phase diagram of a model for diluted magnetic semiconductors beyond mean-field approximations.

A lattice spin-fermion model for diluted magnetic semiconductors (DMS) is investigated numerically, improving on previously used mean-field approximations. Curie temperatures are obtained varying the Mn spin x and hole n densities, and the impurity-hole exchange J in units of the hop-ping t. Optimal values are found in the subtle intermediate regime between itinerant and localized carriers. At intermediate and large J/t, a "clustered" state is observed above the Curie temperature and ferromagnetism is suppressed. Formal analogies between DMS and manganites are discussed.

Journal Article↗

PubMed2002

Application of proteomics for fast identification of species-specific peptides from marine species.

In this work, a novel approach based on proteomics is applied for the analysis of the three European marine mussel species: Mytilus edulis (ME), Mytilus galloprovincialis (MG) and Mytilus trossulus (MT), which are of interest in biotechnology and food industry. The proteomes of these species are poorly described in databases, are difficult to diagnose, and have a controversial taxonomy, To characterise species-specific peptides, we compared 51 matrix-assisted laser desorption/ioization-time of flight peptide mass maps generated from 6 random selected prominent spots derived from the two-dimensional electrophoresis analysis of foot protein extracts from several individuals. Minor species-specific differences in the peptide maps were detected in only one of the spots, corresponding to tropomyosin. Two peptides were unique to ME and MG individuals, whereas another peptide was present only in MT individuals. The sequence of these peptides was characterised by, nanoelectrospray ionization-ion trap (nanoESI-IT) tandem mass spectrometry (MS/MS) analysis followed by database searching and de novo sequence interpretation. We detected a single T to D amino acid substitution in MT tropomyosin. Unambiguous and highly-specific species identification was then demonstrated by analysing peptide extracts from tropomyosin spots by micro high-performande liquid chromatography (microHPL) ESI-IT mass spectrometry using the selected ion monitoring configuration, focused on these peptides, in continuous MS/MS operation. Our results suggest that proteomics may be successfully applied for the identification of species whose proteome is not present in databases.

Amino Acid Sequence↗

PubMed2002

Factors influencing the adoption of blood alternatives to minimize allogeneic transfusion: the perspective of eight Ontario hospitals.

OBJECTIVE: To identify and describe the factors influencing the use and nonuse of blood-sparing methods such as preoperative autologous donation, acute normovolemic hemodilution, and the use of cell salvage devices, hemostatic agents and erythropoietin. DESIGN: An interview survey. SETTING: Eight Ontario hospitals. METHOD: Interviews were conducted with chiefs of surgery, orthopedics, cardiac surgery and anesthesia, and with heads of transfusion medicine and pharmacy. Hospitals were selected using the qualitative sampling strategy of maximum variation based on their use of the methods (as reported in a previous mail survey). RESULTS: Use of blood-sparing methods was influenced by diverse factors often operating simultaneously. These included the following: characteristics of the method (e.g., evidence of its effectiveness, ease of use, cost); perceptions and experiences of the potential adopters (experience with the method, perception of the current safety of allogeneic blood, perceived convenience or inconvenience of using the method); aspects of the practice setting (inability to move resources between hospital departments, presence of a local clinical champion); and the external environment (patient and public expectations, funding of the blood system, blood shortages). INTERPRETATION: More rational and evidence-based use of blood-sparing methods could be promoted by the adoption of an interdisciplinary, comprehensive, coordinated approach tailored to each patient's needs.

Blood Transfusion↗

PubMedDate not supplied

Incidence, 30-day case-fatality rate, and prognosis of stroke in Iquique, Chile: a 2-year community-based prospective study (PISCIS project).

BACKGROUND: The epidemiology of stroke in Latin-American populations and variation of subtypes between communities are unclear. Our aim was to ascertain prospectively the incidence of first-ever stroke in the predominantly Hispanic-Mestizo population of Iquique, a city in the northern desert region of Chile. METHODS: We prospectively identified all possible cases of stroke and transient ischaemic attacks between July 1, 2000, and June 30, 2002, from several overlapping sources. Patients were rapidly assessed by two field neurologists. Standard definitions for incident cases, stroke, transient ischaemic attack, pathological type, and infarction subtype were used. All cases identified were adjudicated by at least two stroke neurologists and followed up at 6 months. Incidence rates of first-ever strokes were calculated from the population of Iquique (214 526) according to the national census of 2002. FINDINGS: Of 380 cases of stroke identified, 292 were incident. CT scans were done in 267 (91%) patients and the mean time to scan was 2.2 days. The hospital admission rate was 71% (207/292). The overall age-adjusted incidence rate of first-ever stroke was 140.1 per 100,000 (95% CI 124.0-156.2). The incidence rates per 100,000 according to pathological type were: infarcts 87.3, intracerebral haemorrhage 27.6, and subarachnoid haemorrhage 6.2. The 30 day and 6-month case-fatality rates were 23.3% and 33.0%, respectively. INTERPRETATION: Our results show incidence rates of stroke similar to those reported in other community studies. Although the proportion of intracerebral haemorrhages was higher than reported in previous studies, the overall incidence was not, which could indicate a slightly lower incidence of ischaemic strokes in this population than in other countries. The prognosis was similar to that found in other population-based studies.

Adult↗