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Biomedical subjects

M Isaacson

Publications and source records attributed to M Isaacson.

29 records · Page 2Linked to original sources
PubMed1978

Epidemiologic investigation of Marburg virus disease, Southern Africa, 1975.

During the first 10 days of February 1975, an Australian hitchhiker contracted Marburg virus disease while traveling through Rhodesia and died; the infection was subsequently passed to two other persons, who recovered. Investigators retraced the hitchhiker's steps in March and again in June 1975 in an effort to uncover the natural reservoir of the virus and determine how it was transmitted. Serum samples were collected from humans and animals wherever the patient had come in close contact with animals or insects. Arthropods of various types were collected in June 1975 and again in February 1976 for virus isolation attempts; at no time did the patient come in direct contact with nonhuman primates of any kind, or any other animals. Indirect contact with bats, monkeys, and birds through aerosols was possible, though at some distance. Direct contact with arthropods occurred throughout the trip; on several occasions it was notably severe. We believe that during this outbreak the first Marburg virus infection occurred by vector-borne transmission from an arthropod yet to be identified, and that patients 2 and 3 acquired the disease by exposure to the oropharyngeal secretions of patients 1 and 2, respectively. Studies are underway to identify the species of arthropod involved in this transmission.

Adult↗
PubMed1975

The microanalysis of light elements using transmitted energy loss electrons.

The use of transmitted energy loss electrons is shown to hold considerable promise for the elemental analysis of light elements. In this technique, those electrons which have lost energy in exciting characteristic inner shell atomic levels are detected rather than X-rays resulting from the decay of the excited levels. The advantages of this technique are (1) a large fraction (0.1-1) of the information-carrying energy loss electrons can be detected, and (2) for each excited level, one energy loss electron is produced independent of the fluorescent yield. Thus the technique potentially offers higher sensitivity than X-ray analysis. We have begun a program to evaluate this technique both theoretically and experimentally for electron probe devices. First, we have developed the necessary theoretical framework to make predictions concerning relevant quantities of elemental analysis such as the minimum detectable mass (MDM) and mimimum detectable mass fraction (MMF). The results of these calculations for thin specimens indicate a potential reduction in the MDM by up to three orders of magnitude and in the MMF by up to 500 through the use of transmitted energy loss electrons rather than X-rays; the advantages over X-ray detection being greater for lower atomic number. Second, we have begun experimental measurements to verify our predictions. These experiments were performed in a field emission scanning microscope with known limitations in collection efficiency, but the results indicate the validity of the basic assumptions and also aid in the design of an instrument which can fully exploit this technique. The experimental results obtained indicate the ease of detection of characteristic K-shell energy levels in elements as light as lithium and indicate the mass detectability of less than 10(-18)g.

Aorta↗
PubMed1974

Scanning transmission electron microscopy at high resolution.

We have shown that a scanning transmission electron microscope with a high brightness field emission source is capable of obtaining better than 3 A resolution using 30 to 40 keV electrons. Elastic dark field images of single atoms of uranium and mercury are shown which demonstrate this fact as determined by a modified Rayleigh criterion. Point-to-point micrograph resolution between 2.5 and 3.0 A is found in dark field images of micro-crystallites of uranium and thorium compounds. Furthermore, adequate contrast is available to observe single atoms as light as silver.

Crystallography↗
PubMedDate not supplied

Molecular characterization of a hepatitis E virus isolate from Namibia.

Hepatitis E virus (HEV) causes sporadic and epidemic acute viral hepatitis in many developing countries. In Africa, hepatitis E has been documented by virus detection (reverse transcriptase polymerase chain reaction, RT-PCR) in Egypt, Chad, Algeria, Morocco and Tunisia. Cases of presumptive hepatitis E also have been documented by detection of antibody to HEV in the Sudan, Kenya, Ethiopia, Somalia, Djibouti and South Africa. Recently, we reported the recovery of 9 isolates of HEV from feces collected during an outbreak of jaundice in Namibia. These specimens were stored frozen for many years at the South African Institute for Medical Research awaiting new methods to determine the etiology of jaundice. HEV genomic sequences were detected by antigen-capture RT-PCR with primers that amplified 2 independent regions of the HEV genome (ORF-2 and ORF-3). To further characterize the HEV 83-Namibia isolates, we determined the nucleotide (nt) sequence of the 3' end of the capsid gene (296 of 1, 980 nt in ORF-2) and ORF-3 for 1 isolate. The capsid gene sequence shared 86% identity with the prototype Burma strain and up to 96% identity with other African strains at the (nt) level, and 99% identity with Burma or other Africa strains at the amino acid level. A 188 (nt) fragment amplified from ORF-3 was also highly homologous to other HEV but was too short for meaningful comparison. Phylogenetic analysis indicated that HEV 83-Namibia is closely related to other African isolates, and differs from Burmese, Mexican and Chinese HEV. These data link the HEV causing the 1983 Namibia outbreak to more recent HEV transmission in northern and sub-Saharan Africa, suggesting this subgenotype of HEV is firmly established throughout the continent.

Capsid↗