Enterotoxin-producing bacteria and parasites in stools of Ethiopian children with diarrhoeal disease.
Enterotoxinogenic bacteria were isolated from 131 (37%) of 354 Ethiopian infants and children with acute gastrointestinal symptoms. Only one of these isolates belonged to the classical enteropathogenic serotypes of Esch. coli. Two colonies from each patient were isolated and tested for production of enterotoxin by the rabbit ileal loop test, the rabbit skin test, and an adrenal cell assay. However, only 38% of the isolated enterotoxinogenic strains were Esch. coli; the others belonged to Klebsiella, Enterobacter, Proteus, Citrobacter, Serratia, and Aeromonas. In 18 patients both isolates were toxinogenic and belonged to different species. The incidence of intestinal parasites was 35% with no apparent correlation to the occurrence of toxinogenic bacteria in the stools. (+info)
Glycosaminoglycan-binding microbial proteins in tissue adhesion and invasion: key events in microbial pathogenicity.
Glycosaminoglycans such as heparin, heparan sulphate and dermatan sulphate, are distributed widely in the human body. Several glycosaminoglycans form part of the extracellular matrix and heparan sulphate is expressed on all eukaryotic surfaces. The identification of specific binding to different glycosaminoglycan molecules by bacteria (e.g., Helicobacter pylori, Bordetella pertussis and Chlamydia trachomatis), viruses (e.g., herpes simplex and dengue virus), and protozoa (e.g., Plasmodium and Leishmania), is therefore of great interest. Expression of glycosaminoglycan-binding proteins depends on growth and culture conditions in bacteria, and differs in various phases of parasite development. Glycosaminoglycan-binding microbial proteins may mediate adhesion of microbes to eukaryotic cells, which may be a primary mechanism in mucosal infections, and are also involved in secondary effects such as adhesion to cerebral endothelia in cerebral malaria or to synovial membranes in arthritis caused by Borrelia burgdorferi. It has been suggested that they may enhance intracellular survival in macrophages. Microbial binding of heparin may interfere with heparin-dependent growth factors. Whether or not glycosaminoglycan-binding proteins mediate invasion of epithelial cells is a matter of controversy. Heparin and other glycosaminoglycans may have potential uses as therapeutic agents in microbial infections and could form part of future vaccines against such infections. (+info)
Redescription of Rhamnocercus stichospinus Seamster and Monaco, 1956 (Monogenea: Diplectanidae), parasitic on Menticirrhus americanus (Osteichthyes: Sciaenidae) from the coastal zone of the State of Rio de Janeiro, Brazil.
Rhamnocercus stichospinus Seamster and Monaco, 1956 (Diplectanidae) parasitic on the sciaenid fish Menticirrhus americanus from the coastal zone of the State of Rio de Janeiro, is redescribed and recorded for the first time in the South American Atlantic Ocean. The generic diagnosis of Rhamnocercus is emended to accommodate the presence of confluent intestinal ceca in R. stichospinus. (+info)
Evaluation of Streck tissue fixative, a nonformalin fixative for preservation of stool samples and subsequent parasitologic examination.
We undertook a study to evaluate Streck tissue fixative (STF) as a substitute for formalin and polyvinyl alcohol (PVA) in fecal preservation. A comparison of formalin, PVA, (mercuric chloride based), and STF was done by aliquoting fecal samples into each fixative. Stool specimens were collected in Haiti, and parasites included Cyclospora cayetanensis, Giardia intestinalis, Entamoeba coli, Iodamoeba butschlii, Endolimax nana, Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis, and Necator americanus. Preserved stools were examined at various predetermined times (1 week, 1 month, and 3 months) to establish the quality of the initial preservation as well as the suitability of the fixative for long-term storage. At each time point, stool samples in fixatives were examined microscopically as follows: (i) in wet mounts (with bright-field and epifluorescence microscopy), (ii) in modified acid-fast-, trichrome-, and safranin-stained smears, and (iii) with two commercial test kits. At the time points examined, morphologic features remained comparable for samples fixed with 10% formalin and STF. For comparisons of STF- and 10% formalin-fixed samples, specific findings showed that Cyclospora oocysts retained full fluorescence, modified acid-fast- and safranin-stained smears of Cryptosporidium and Cyclospora oocysts were equal in staining quality, and results were comparable in the immunofluorescence assay and enzyme immunoassay commercial kits. Stool fixed in STF and stained with trichrome showed less-than-acceptable staining quality compared with stool fixed in PVA. STF provides an excellent substitute for formalin as a fixative in routine examination of stool samples for parasites. However, modifications to the trichrome staining procedures will be necessary to improve the staining quality for protozoal cysts fixed in STF to a level comparable to that with PVA. (+info)
Manipulation of host behaviour by parasites: a weakening paradigm?
New scientific paradigms often generate an early wave of enthusiasm among researchers and a barrage of studies seeking to validate or refute the newly proposed idea. All else being equal, the strength and direction of the empirical evidence being published should not change over time, allowing one to assess the generality of the paradigm based on the gradual accumulation of evidence. Here, I examine the relationship between the magnitude of published quantitative estimates of parasite-induced changes in host behaviour and year of publication from the time the adaptive host manipulation hypothesis was first proposed. Two independent data sets were used, both originally gathered for other purposes. First, across 137 comparisons between the behaviour of infected and uninfected hosts, the estimated relative influence of parasites correlated negatively with year of publication. This effect was contingent upon the transmission mode of the parasites studied. The negative relationship was very strong among studies of parasites which benefit from host manipulation (transmission to the next host occurs by predation on an infected intermediate host), i.e. among studies which were explicit tests of the adaptive manipulation hypothesis. There was no correlation with year of publication among studies on other types of parasites which do not seem to receive benefits from host manipulation. Second, among 14 estimates of the relative, parasite-mediated increase in transmission rate (i.e. increases in predation rates by definitive hosts on intermediate hosts), the estimated influence of parasites again correlated negatively with year of publication. These results have several possible explanations, but tend to suggest biases with regard to what results are published through time as accepted paradigms changed. (+info)
The currently available preparations used as antigen in the serological investigation of parasitic diseases are ill-defined heterogeneous mixtures, and there is an evident need for better characterized reagents. Antigens of different parasite species (schistosomes, filariae, trypanosomes, and plasmodia) are discussed and parasite sources enumerated. Modern methods for the preparation of antigenic extracts and their fractionation are described, together with certain guidelines as to their biochemical characterization and their immunological activity. In order to implement this endeavour and to make better use of serological techniques in parasitic diseases, proposals are made concerning collaborative research and field application among a number of laboratories on schistosome, onchocercal, trypanosome, and plasmodial antigens. (+info)
Evolution of parasite virulence against qualitative or quantitative host resistance.
We analysed the effects of two different modes of host resistance on the evolution of parasite virulence. Hosts can either adopt an all-or-nothing qualitative response (i.e. resistant hosts cannot be infected) or a quantitative form of resistance (i.e. which reduces the within-host growth rate of the parasite). We show that the mode of host resistance greatly affects the evolutionary outcome. Specifically, a qualitative form of resistance reduces parasite virulence, while a quantitative form of resistance generally selects for higher virulence. (+info)
Mammalian metabolism, longevity and parasite species richness.
Basal metabolic rate (BMR) scales allometrically with body mass in mammals, but the reasons why some species have higher or lower metabolic rates than predicted from their body mass remain unclear. We tested the idea that parasite species richness may be a contributory factor by performing a comparative analysis on 23 species of mammals for which data were available on parasite species richness, BMR, body mass and two potentially confounding variables, i.e. host density and host longevity. Parasite species richness was positively correlated with BMR and negatively correlated with host longevity independent of body mass. (+info)