Biomedical subjects
G Sperber
Publications and source records attributed to G Sperber.
[Effect of 2 vaccination strategies on developments during the epidemic of meningococcal A meningitis in N'Djamena (Chad) in 1988].
From February till May 1988, during an epidemic of group-A meningococcal disease, 4542 cases of meningitis were reported in N'Djamena, the capital of Chad (550,000 inhabitants). A first selective vaccination campaign was carried out between 5 and 14 March; 156,500 vaccine doses (polyvalent: group A and C: Institut Mérieux) were given using jet injectors. The target population for this first campaign consisted of groups such as school-children and the armed forces. As the epidemic continued, a mass vaccination campaign was implemented one month later between 8 and 14 April 1988; this was targeted at the whole population above 1 year of age, not previously immunized, and 266,738 doses of vaccine were injected. One week after the start of the second campaign, the number of reported cases fell sharply and, within four weeks, the epidemic was halted. The vaccination coverage rate, evaluated by a WHO cluster survey method in people above one year of age, was 95.5%. These results show (i) the failure of selective vaccination, restricted to only at-risk groups, to halt the epidemic; (ii) the efficacy of the mass vaccination campaign aimed at the whole population; and (iii) the feasibility in tropical Africa of such a mass campaign which must be carried out in a few days.
DNA fingerprinting in the epidemiology of African serogroup A Neisseria meningitidis.
The restriction endonuclease (RE) technique was used to compare 172 meningococcal group A strains collected between 1969 and 1990, mainly from countries of the so-called African Meningitis Belt, the Gambia and Ethiopia. The 64 strains from various African countries (Niger, Chad, Burkina Faso, Cameroon, Morocco, Djibouti) were distributed within 3 main restriction enzyme patterns (REPs); the 77 Gambian strains fell into 5 REPs and the 24 Ethiopian strains into 2 such patterns. Several of the main REPs were formed by clusters of closely related clones. Clones, very similar to dominating REPs of the 1960s in Niger, Burkina Faso and Cameroon, were in the 1980s found to be strongly represented in the Gambia to the extreme west of the Meningitis Belt. One of the Gambian clones from 1983-86 was identical to an Indian clone recovered in New Delhi 1986-87. Another clone was detected in 1983 in the Gambia, in 1989 again in the Gambia as well as in Ethiopia, and in 1990 in Tanzania. Our results are largely in line with those of previous studies based on modern techniques of protein and isoenzyme electrophoresis. The RE method is useful mainly for the exact genotypic differentiation of closely related clones, and seems to be a valuable complement to phenotypic tools for epidemiological mapping of Group A meningococcal infection.
[Comparative study of 3 bacteriological tests of cerebrospinal meningitis during the epidemiological period].
During an outbreak of group A meningococcal meningitis in Chad in 1988, a comparative study of three bacteriological techniques (direct microscopic examination, latex agglutination, and culture) was conducted with 120 samples of cerebrospinal fluid (CSF) for diagnosis. The results correlated well with cloudy or purulent CSF specimens. Direct microscopic examination was as good a diagnostic indicator as the other tests. The authors recommend using direct microscopic examination, which is easy to perform under field conditions and accurate enough for a rapid diagnosis of cerebrospinal meningitis during an epidemic. However, complete identification of the first cases in the epidemic is important in order to establish control measures as soon as possible.
[Reliability of the diagnosis of cerebrospinal meningitis during an epidemic. The epidemic in Chad in 1988].
The authors analysed the positive predictive value (PPV) of the clinical diagnosis during an epidemic of meningococcal meningitidis in Africa. This PPV was globally 73.3 +/- 11.2%. This PPV was fluctuating according to the standards of the diagnosis. Typical clinical meningitic syndrome without spinal picture: 85.7 +/- 10.3%, Non typical syndrome and macroscopical aspect of cerebrospinal fluid: 62.5 +/- 16.4%.
[Epidemiological notes: meningococcal meningitis of serogroup X in Niamey (Niger)].
From 19th February to 15th April 1990, 22 strains of meningococcus belonging to serogroup X have been identified by the Centre for Study and Research on meningitidis and Schistosomiases (CERMES) at Niamey (Niger). Serogroup X has been confirmed by the Centre Collaborating WHO of Reference and Training for Meningococci (CCOMSRFM) at Marseille (France). These strains have been isolated from cerebrospinal fluid of patients suffering from cerebrospinal meningitis and living in different neighbourhoods of Niamey. Apparition of cases of meningococcal meningitis with other serogroups than A implies identification of serogroup of meningococcus in intertropical Africa.
Serological study of meningococcal isolates in Switzerland and France 1980-1986.
A study was performed of 342 disease-related strains of meningococci isolated in Switzerland and France between 1980 and 1986, including more than 50% of all strains isolated in Switzerland in 1986. Using a newly developed spot-blot enzyme-linked immunoassay and a panel of monoclonal anti-meningococcal antibodies, 96% of all strains were shown to react with at least one antibody. In both countries more than 50% of the strains were group B. In France serotype 2a was the prevalent serotype and was often associated with subtype P1.2. In Switzerland serological markers of epidemic strains recently described in Northern Europe (serotype 15 and subtype P1.16) were observed with increasing frequency in 1986. However, serotype 4 has been prevalent in Switzerland since 1980 and no clonal population was seen to emerge.
T1, T2, and relative proton density at 0.35 T for spleen, liver, adipose tissue, and vertebral body: normal values.
An MRI installation (Magnetom, Siemens, software version B1 of NUMARIS) working at 0.35 T was used to estimate T1, T2, and relative proton density in the spleen, liver, adipose tissue, and vertebral body in 14 healthy volunteers. Two double-echo sequences were applied for all subjects: TR = 500 ms, TE1 = 35 and TE2 = 70 ms; and TR = 1600 ms, TE1 = 35 and TE2 = 70 ms. The images were sampled in regions of interest and appropriate relaxation expressions fitted to the ROI data yielding relaxation parameters and relative proton densities. Relaxation expressions, included in standard software (Siemens), were compared to more elaborate functions, developed in parallel to this study. The latter were found more appropriate, especially for high T1 values, and gave the following mean values for the four tissues (estimated uncertainty of mean in parentheses) T1 (ms) 915(36), 428(5), 261(7), and 501(11); T2 (ms) 79.7(8.8), 51.0(0.2), 59.8(1.0), and 64.7(0.8); and corresponding relative proton density (rho, arbitrary units) 2088(136), 2182(10), 2915(49), and 2136(21). The uncertainty in the values was estimated in the fitting procedure and does not include systematic errors. The relative noise in the ROIs was about 9% and the reproducibility of the ROI mean values about 8%.
Subtraction in magnetic resonance imaging.
Subtraction of images recorded with multiple echo, spin echo (SE) techniques was performed in phantom and clinical studies of patients with pituitary adenomas and gliomas. The tissue differentiation was enhanced in the subtracted images.
Method for quantification of low flow velocities by magnetic resonance phase imaging.
The aim of this study was to compare the influence of flow in the velocity range 0 to 25 mm/s on modulus, phase, real and imaginary images obtained with a standard magnetic resonance scanner (Siemens Magnetom, 0.5 T), and to develop a simple method for determination of flow velocities in vivo from this information. Using a flow phantom, the flow dependent magnetic resonance imaging (MRI) signal has been studied as a function of flow perpendicular to the image slice with non-doped water (simulating moving cerebrospinal fluid) as well as with water doped with Mn2+ (simulating moving blood) for each of the four mentioned image types. The results show a marked flow dependence on all types of images studied. The variation of the signal with flow in the modulus images is relaxation-time dependent in the studied velocity range and it is non-monotone for non-doped water. In the phase images, however, the variations are monotone and not dependent on relaxation times. In modulus images the curve shape is relatively independent on flow direction, while phase images are clearly dependent on flow direction in the studied velocity range. The signal versus velocity curves for the real and imaginary images show resemblance to those for the modulus and the phase images, respectively. It is concluded that the phase information can be used to generate a signal versus velocity calibration curve, which can be used to quantify low flow velocities in vivo.
Cerebrospinal fluid flow studied with gated magnetic resonance imaging during the various parts of the cardiac cycle.
The pulsatile movement of cerebrospinal fluid (CSF) through the Sylvian aqueduct has been studied in two normal volunteers. A standard magnetic resonance scanner was used as well as a routine spin echo sequence. Series of ECG-gated axial images were obtained perpendicular to the long axis of the Sylvian aqueduct. Previously it has been demonstrated by flow phantom experiments that the phase information can be used to obtain a linear relation between phase and flow velocity. By multiplying the CSF flow velocity by the cross-sectional area of the aqueduct of Sylvius obtained in each image, the CSF flow variation during the cardiac cycle could be demonstrated and measured.
[Magnetic resonance tomography completes the radiologic diagnosis].
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Metabolism and tissue distribution of tobacco-specific N-nitrosamines in the marmoset monkey (Callithrix jacchus).
Three male marmoset monkeys (Callithrix jacchus) were injected i.v. with the tobacco-specific carcinogen [2'-14C]N'-nitrosonornicotine (NNN) (20.3 mumol/kg body weight) or [carbonyl-14C]4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) (18.8 or 420 mumol/kg body weight). They were sacrificed 4 h later. Tissue distribution was studied in two monkeys by whole-body autoradiography and by computer-assisted densitometric analysis of the autoradiograms. The autoradiograms showed a high level of radioactivity in the liver, nasal mucosa, kidneys, melanin of the eyes, hair-follicles of the skin and in the ceruminous ear glands of the monkeys. Total level of radioactivity was 5.7 times higher in the liver of the [carbonyl-14C]NNK-injected monkey than in that of [2'-14C]-NNN-injected monkey. Washing the sections with trichloroacetic acid and organic solvents selectively removed free metabolites leaving metabolites bound to cellular macromolecules. Level of bound metabolites was 1.5 times higher in the nasal mucosa than in the liver of the [2'-14C]NNN monkey. Levels of bound metabolites were similar in the liver of NNN- and NNK-treated monkeys. The results indicate that the liver and nasal mucosa of C. jacchus can activate NNN and NNK to alkylating species. Unbound metabolites present in the liver, lung, kidneys, eye, blood and urine were extracted and separated by h.p.l.c. Hydroxylation of the carbons alpha to the N-nitroso group of NNN were the major metabolic pathways. Unmetabolized NNN was the major radioactive component in the liver, lung, eye and blood. Reduction of the carbonyl of NNK yields 4-(methylnitrosamino)-1-(3-pyridyl)butan-1-ol (NNAl). NNAl was present in all tissues analyzed and was the major radioactive component in the eye and stomach lumen. It was also excreted in the urine. NNK and NNAl were metabolized by alpha-carbon hydroxylation. These results suggest that in C. jacchus, NNN, NNK and NNAl are activated to alkylating species by alpha-carbon hydroxylation. In the third monkey injected with NNK, DNA methylation was observed in the liver and nasal mucosa but not in the lung and kidneys. Pulmonary tissues of C. jacchus, unlike those of F344 rats, do not have the enzymic capacities to activate NNK to methylating species.
Physiology of the choroidal vascular bed.
The choroidal vascular bed has many interesting features such as relatively wide but flat capillaries, fenestrated capillary walls and an enormous blood flow. The high flow rate results in a high oxygen tension in the tissue and is also of importance in the temperature control of the eye. The capillary wall is permeable to plasma proteins which is probably of great importance for the supply of vitamin A to the pigment epithelium. The permeability to low molecular weight substances is very high which results in a tissue fluid similar to plasma with respect to small molecules. It is not clear whether the choriocapillaris is normally reabsorbing fluid transported into the choroid from the retina and from the anterior chamber or if there is a net filtration from the choriocapillaris. Fluid can pass from the choroid through the suprachoroid into the episcleral tissues via the scleral substance and spaces around the blood vessels and nerves.
Changes in the electrical resistivity of lecithin coacervates as a model for olfactory transduction.
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Study of the hydrogen bonding in the adenine-thymine, adenine-cytosine, and guanine-thymine base pairs.
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A method for MR quantification of flow velocities in blood and CSF using interleaved gradient-echo pulse sequences.
The aim of this study was to establish a rapid method for in vivo quantification of a large range of flow velocities using phase information. A basic gradient-echo sequence was constructed, in which flow was encoded along the slice selection direction by variation of the amplitude of a bipolar gradient without changes in sequence timings. The influence of field inhomogeneities and eddy currents was studied in a 1.5 T interleaved sequences for calibration and in vivo flow determination were constructed, and flow information was obtained by pairwise subtraction of velocity-encoded from velocity non-encoded phase images. Calibration was performed in a nongated mode using flow phantoms, and the results were compared with theoretically calculated encoding efficiencies. In vivo flow was studied in healthy volunteers in three different areas using cardiac gating; central blood flow in the great thoracic vessels, peripheral blood flow in the popliteal vessels, and flow of cerebrospinal fluid (CSF) in the cerebral aqueduct. The results show good agreement with results obtained with other techniques. The proposed method for flow determination was shown to be rapid and flexible, and we thus conclude that it seems well suited for routine clinical MR examinations.
Cardiac gated MR imaging of cerebrospinal fluid flow.
This is a preliminary investigation of the cerebrospinal fluid (CSF) spaces using cardiac gated magnetic resonance imaging. A variation of intensity of the signal from the cerebral aqueduct is demonstrated during the cardiac cycle. The pattern of this variation suggests pulsatile CSF flow. Calculations that have been verified by phantom measurements show that CSF flow rates less than 1 mm/s may be detectable. Magnetic resonance may therefore offer a new method for the demonstration and measurement of CSF flow.