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Biomedical subjects

H V Smith

Publications and source records attributed to H V Smith.

At least 73 records · Page 4Linked to original sources
PubMed1992

Viability of Cryptosporidium parvum oocysts: correlation of in vitro excystation with inclusion or exclusion of fluorogenic vital dyes.

A viability assay for oocysts of Cryptosporidium parvum based on the inclusion or exclusion of two fluorogenic vital dyes, 4',6-diamidino-2-phenylindole (DAPI) and propidium iodide, was developed by using several different isolates of oocysts. Correlation of this assay with viability measured by in vitro excystation was highly statistically significant, with a calculated correlation coefficient of 0.997. In this research, two similar excystation protocols were utilized, and no significant difference between excystation protocols was detected. Percent excystation of oocyst suspensions could be increased or reduced by inclusion of a preincubation treatment in either excystation protocol, and this alteration was also demonstrated in the viability assay. Oocysts which excluded both dyes would not excyst in vitro unless a further trigger was provided and were more resistant to acid or alkali treatment. The results of this research provide a reproducible, user-friendly assay which is applicable to individual oocysts and also provides a useful adjunct for identification of oocysts in water and environmental samples.

Animals↗
PubMed1992

Survival of Cryptosporidium parvum oocysts under various environmental pressures.

The survival of various isolates of Cryptosporidium parvum oocysts under a range of environmental pressures including freezing, desiccation, and water treatment processes and in physical environments commonly associated with oocysts such as feces and various water types was monitored. Oocyst viability was assessed by in vitro excystation and by a viability assay based on the exclusion or inclusion of two fluorogenic vital dyes. Although desiccation was found to be lethal, a small proportion of oocysts were able to withstand exposure to temperatures as low as -22 degrees C. The water treatment processes investigated did not affect the survival of oocysts when pH was corrected. However, contact with lime, ferric sulfate, or alum had a significant impact on oocyst survival if the pH was not corrected. Oocysts demonstrated longevity in all water types investigated, including seawater, and when in contact with feces were considered to develop an enhanced impermeability to small molecules which might increase the robustness of the oocysts when exposed to environmental pressures.

Animals↗
PubMed1992

Characterization of IgE antibody binding profiles of sera from patients with atopic dermatitis to allergens of the domestic mites Dermatophagoides pteronyssinus and Euroglyphus maynei, using enhanced chemiluminescent immunoblotting.

A rapid, sensitive, chemiluminescent immunoblotting method was used to identify IgE-binding components of Dermatophagoides pteronyssinus and Euroglyphus maynei that were recognized by sera of 16 D. pteronyssinus-sensitive patients with atopic dermatitis. Some 28 components (14-200 kD) were found in the D. pteronyssinus extract, and sera bound between 1 and 13 of them (mean 6.0). At least one of four components (97, 28, 24 and 14 kD) were bound by 14/16 sera. E. maynei had 25 components (14-227 kD), 13 in common with those of D. pteronyssinus by molecular size. Sera bound between 1 and 11 of them (mean 5.2) and 14/16 sera bound 1 of 38 kD (unique to E. maynei) and/or 1 of 175 kD. There were positive correlations between the number of D. pteronyssinus and E. maynei components bound and anti-D. pteronyssinus and E. maynei serum IgE values (p less than 0.001 in both cases) and between the number of D. pteronyssinus and E. maynei components bound and total serum IgE values (p less than 0.01 in both cases). These results demonstrate a very considerable diversity of IgE antibody responses to domestic mite allergens amongst patients with atopic dermatitis.

Adult↗
PubMed1991

Cryptosporidium infection in cats: prevalence of infection in domestic and feral cats in the Glasgow area.

A clinical and post mortem survey of domestic and feral cats in the Glasgow area revealed that 19 of 235 (8.1 per cent) were infected with Cryptosporidium species. More kittens than adults were infected (P less than 0.01), and of 51 of the cats which had diarrhoea, four also had cryptosporidium infection. Of seven domestic cats with cryptosporidium infection, two were also positive for feline immunodeficiency virus. There was no significant difference between the prevalence of cryptosporidium infection in domestic and feral cats. Cryptosporidium oocysts were detected in faecal and mucosal impression smears stained with auramine-phenol and modified Ziehl-Nielsen techniques. Endogenous developmental stages of cryptosporidium were found in the microvillus region of enterocytes of eight of 19 positive cats in sections stained with haematoxylin and eosin. The results suggest that cryptosporidium infection is common among young and newborn kittens, and that the disease is usually asymptomatic.

Age Factors↗
PubMed1991

A Lyme borreliosis human serosurvey of asymptomatic adults in Ireland.

Blood samples were obtained through the Blood Transfusion Service in Ireland in order to obtain information on the prevalence of asymptomatic B. burgdorferi infections and in an attempt to identify the type of habitat that presents the most risk of infection. Areas in the country were rated as low, medium or high risk based on the availability of suitable tick habitat, access to the public and the distribution of deer, the latter parameter being related to both the occurrence of rodent reservoir hosts and woodland recreational areas. Approximately 100 plasma samples from each of four areas were analysed for IgG anti-Borrelia antibodies by indirect immuno-fluorescence with a titre of 1 :80 indicating a positive reaction in asymptomatic individuals. Prevalence figures of 15, 11, 8 and 5% were obtained for high, high/medium, medium/low and low risk areas respectively. No positive samples were detected in blood from an Icelandic population which is not exposed to I. ricinus bites. The overall subclinical prevalence (9.75%) is surprisingly high in view of the apparent rarity of clinical cases in Ireland, though under-diagnosis probably occurs. These results seem to indicate that farmland is less important than woodland as Lyme borreliosis habitat. If this is so, it is probably due to the presence in woodland of Apodemus sylvaticus, a putative reservoir host, and also to the use of such areas for recreation at certain times of the year.

Animals↗
PubMed1990

The surface lipid of parasitic nematodes: organization, and modifications during transition to the mammalian host environment.

The biophysical properties of the surface lipid of a range of nematode species and their developmental stages were examined, using fluorescent lipid probes and fluorescence recovery after photobleaching (FRAP). These methods can be applied to living, intact parasites, and the analysis confined to lipid on the outermost surface. In all cases, surface lipid was unusual in its selectivity for the insertion of the lipid probes. In addition, a polar lipid probe was generally not free to diffuse in the plane of the surface, in contrast to a non-polar lipid probe which was free to diffuse. This is evidence that the surface lipid layer is heterogeneous, and possibly comprises lipid domains. The infective larvae of Acanthocheilonema viteae, Nippostrongylus brasiliensis, Trichinella spiralis and Ostertagia ostertagi were found to exhibit a rapid change in lipophilicity upon exposure to conditions simulating entry into a mammalian host environment. Parasitic nematodes, therefore, present their hosts not only with a highly unusual biological surface, but also one which can be rapidly re-organised upon a change of environment.

Animals↗
PubMed1990

Parasitic protozoa in drinking water.

The importance of treating public water supplies to destroy pathogenic micro-organisms has long been recognized. In the past, emphasis has been laid on bacteria, but the hazard posed by certain protozoan parasites is being increasingly recognized. Some of these present a particularly serious problem in that they can survive chlorination and most purification treatments regarded by international standards, as giving adequate protection to the consumer.

Animals↗
PubMed1990

Waterborne cryptosporidiosis.

Awareness of the importance of Cryptosporidium as a gastrointestinal parasite of developed countries not only stems from its prevalence in AIDS patients but also from its recent recognition as a possible contaminant of drinking water supplies. The importance of Cryptosporidium to public health has recently been revealed by a series of major epidemics of diarrhoeal disease in the USA and UK. In this review, Huw Smith and Joan Rose document what is known of the causes of some of these outbreaks and explain why this parasite can escape the battery of treatment processes normally used for drinking water supplies in these countries.

Journal Article↗
PubMed1989

An analysis of staining methods for the detection of Cryptosporidium spp. oocysts in water-related samples.

The ability of five staining techniques, originally developed for the rapid identification of Cryptosporidium spp. oocysts in faecal samples, to detect oocysts in water and water-related samples was assessed. All the stains used (modified Ziehl Neelsen, auramine-phenol (Lempert), Wright-Giemsa, safranin-methylene blue and FITC-labelled monoclonal antibody) stained oocysts after storage in water for 2 months at 4 degrees C (71-89% of control values). Storage of oocysts below 0 degrees C greatly reduced the staining ability of auramine-phenol. With the exception of oocysts stored in raw and final waters, the histochemical stains proved less useful in detecting oocysts than the monoclonal antibody. Organisms of similar size and shape took up these stains, causing confusion in interpretation. Cold Ziehl Neelsen and the FITC-labelled monoclonal antibody were best at identifying oocysts from a waterborne outbreak. Screening with a fluorescent antibody, followed by confirmation with cold Ziehl Neelsen, where possible, are the currently recommended procedures for the detection of oocysts in water-related samples.

Animals↗
PubMed1989

A comparison of fluorescein diacetate and propidium iodide staining and in vitro excystation for determining Giardia intestinalis cyst viability.

The viability of 4 human isolates of Giardia intestinalis cysts using either the fluorogenic vital dyes fluorescein diacetate (FDA) and propidium iodide (PI) or in vitro excystation was assessed. Whereas viable cysts, as defined by in vitro excystation were present in each of the 4 isolates, cysts from only 3 of the 4 isolates took up the vital dyes. FDA consistently over-estimated cyst viability whilst PI under-estimated non-viable cysts when compared with in vitro excystation. Following in vitro excystation, both FDA and PI stained a proportion of unexcysted cysts indicating that FDA stained cysts which were incapable of excystation, whereas PI did not stain all cysts which were incapable of excystation. One human cyst isolate, which underwent in vitro excystation, could not be stained with either FDA or PI. In the absence of currently more specific fluorescent indicators of viability, PI alone could be used to determine the lower limit of nonviability in positive water-related samples, where small numbers of cysts are to be expected.

Animals↗
PubMed1989

An outbreak of waterborne cryptosporidiosis caused by post-treatment contamination.

An outbreak of waterborne cryptosporidiosis affecting 27 persons, diagnosed stool positive, occurred in Ayrshire in April 1988. Twenty-one in 27 confirmed cases required some form of fluid replacement therapy. Local general practitioners indicated a two- to fivefold increase in diarrhoeal disease during the outbreak, and following enquiries made by Environmental Health Officers it became apparent that many hundreds of people had suffered a diarrhoeal illness at that time. Cryptosporidium spp. oocysts were detected in the treated chlorinated water supply system, in the absence of faecal bacterial indicators. Oocyst contamination of a break-pressure tank containing final water for distribution was the cause of this waterborne outbreak. An irregular seepage of oocyst-containing water, which increased during heavy rains, was the cause of the break-pressure tank contamination, rather than a failure of the water-treatment processes. The waterborne route should be considered when clusters of cryptosporidiosis-associated with potable water occur. Waterborne cryptosporidiosis can occur in the absence of other faecal indicators of contamination.

Adult↗
PubMed1989

Antigenic relationships between the surface-exposed, secreted and somatic materials of the nematode parasites Ascaris lumbricoides, Ascaris suum, and Toxocara canis.

The cosmopolitan nematode parasites Ascaris lumbricoides, Ascaris suum, and Toxocara canis are closely related phylogenetically, and are all pathogenic to man. In the case of the latter, the antigens released by the tissue-invasive parasitic larvae in vitro ('excretory/secretory' or 'ES' antigens) are routinely used for serodiagnostic purposes. Here we have found, using radioimmunoprecipitation with defined rabbit antiserum, and SDS-PAGE, that there is a significant antigenic similarity between the secreted and somatic antigens of the three nematodes, and have characterized cross-reactive components. Among these is a 14 kD internal protein which has a homologue in all three parasites. This molecule is the subject of an IgG antibody response in Ascaris infection, but there is no measurable response to it in toxocariasis. Lastly, using quantitative immunofluorescence, the antigens exposed on the surface of intact, living, larvae were found to be cross-reactive or specific depending on the developmental stage of the parasites. This means that the surface of tissue-invasive Ascaris larvae bears stage-specific epitopes.

Animals↗
PubMed1987

Shared carbohydrate epitopes on distinct surface and secreted antigens of the parasitic nematode Toxocara canis.

The nematode parasite Toxocara canis is found in all dog populations and poses a poorly defined health hazard to humans. We have studied excretory-secretory antigen (ES) and surface antigens of the infective larval stage which is tissue-invasive in mammalian hosts. Antigens were probed with a panel of eight monoclonal antibodies raised in mice to whole ES. Six of eight antibodies reacted with periodate-sensitive carbohydrate epitopes on ES molecules, and the remaining two (Tcn-3 and Tcn-6) recognized either peptide or periodate-resistant sugar determinants. By immunoprecipitation and immunoblotting, the anti-carbohydrate monoclonals each reacted with several distinct ES molecules, known from previously published work to possess contrasting biochemical properties. Tcn-3 and -6 were directed predominantly against 32,000 and 120,000 m.w. molecules, respectively. Iodinated surface antigens of similar m.w. were precipitated by each antibody after detergent solubilization, but only two clones (Tcn-2 and -8) were able to bind exposed sites on the epicuticle of intact Toxocara larvae. Significantly, these antibodies do not bind to newly hatched larvae, and their target antigens are poorly expressed until the second day of in vitro cultivation. The specificities of the monoclonals were further studied by cold antibody inhibition of radiolabeled monoclonal binding, and by a matrix of two-site binding assays. These data show that Tcn-2, -4, -5, and -8 recognize a related group of repetitive carbohydrate epitopes, whereas Tcn-1, -6, and -7 bind discrete determinants on the same molecules. These studies are being continued to define further the structure of antigenic Toxocara carbohydrates and to compare the diagnostic utility of carbohydrate and peptide antigens.

Animals↗