Biomedical subjects
Publications and source records attributed to D M Gordon.
We have reported a case of group B streptococcal vertebral osteomyelitis in a 55-year-old alcoholic man. This may be the first reported case of group B streptococcal osteomyelitis in an adult that was not secondary to surgery, ischemic peripheral vascular disease, or a contiguous infection.
The paper examines the factors which generate various patterns of dispersion in the distribution of parasites within their host populations. Particular emphasis is placed on the role played by chance elements in the growth and decay of parasite populations and on the influence of different types of demographic processes. It is argued that observed distributions are dynamic, rather than static, entities generated by opposing forces, some acting to create over-dispersion and others acting to generate under-dispersion. Monte Carlo simulation experiments, based on probability models of the growth and decay of host and parasite populations, are used to study the dynamics of parasite dispersion. Attention is specifically focused on the role played by parasite-induced host mortality. It is shown that, for certain types of host-parasite associations, convex curves of mean parasite abundance in relation to age (age-intensity curves), concomitant with a decline in the degree of dispersion in the older age, classes of hosts, may be evidence of the induction in host mortality by parasite infection. Empirical evidence is examined in light of this prediction. In general, however, simulation studies highlight the technical difficulties inherent in establishing clear evidence of parasite-induced host mortality from ecological studies of hosts and parasites in their natural habitats.
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Studies were performed to evaluate several methods for the artificial removal of Plasmodium berghei merozoites from infected mouse erythrocytes. These methods, many of which have been reported to yield free parasites capable of establishing a patent infection when injected into a suitable host, included NH4C1-mediated lysis, complement-mediated immune lysis, pressure filtration, and multiple-burst and continuous-flow sonication. Free parasites isolated from infected mouse blood were examined in vitro under conditions known to support merozoite invasion, and were found to be noninvasive, irrespective of the method used for their isolation. Although all methods tested achieved high degrees of lysis, none removed all intact parasitized erythrocytes. Using multiple-burst and continuous-flow sonication, the infective potential of free parasite preparations could be accounted for solely on the basis of the intact parasitized cells contaminating the free parasite preparations.
Mouse erythrocytes parasitized with Plasmodium berghei or Plasmodium yoelii were separated by ultracentrifugation using preformed isodensity gradients of the discontinuous type. Three fractions were obtained following centrifugation, the upper of which contained greater than 90% of all schizont-infected cells added to the gradient. The gradient material, Stractan II, is an arabinogalactan polysaccharide and appears to yield results similar to those available using gradients of bovine serum albumin. Cells are not altered morphologically or physiologically (as assessed by infectivity) by the treatment.
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