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Biomedical subjects

H V Smith

Publications and source records attributed to H V Smith.

At least 55 records · Page 3Linked to original sources
PubMed1996

Snake envenomation in cats and its detection by rapid immunoassay.

OBJECTIVE: To determine the usefulness of a snake venom detection kit (SVDK) in the management of envenomed cats. DESIGN: A clinical study. ANIMALS: Twenty-two cats were investigated. PROCEDURE: Cats injected subcutaneously with approximately 0.25 or 1.0 lethal dose (LD) of tiger snake venom or 1 or 4 LD of brown snake venom were observed for clinical symptoms of envenomation at intervals over the ensuring 24 to 48 hours(h). Blood and urine samples were taken at regular intervals and assayed in a quantitative laboratory assay for snake venoms. Selected samples were assayed in parallel in a rapid, semi-quantitative SVDK. RESULTS: The studies showed that it was important to estimate the elapsed time from envenomation to presentation. If this time was less than 8 h, blood was the most appropriate sample and a negative result should exclude serious envenomation. If the elapsed time exceeded 8 h, it was essential that urine be sampled. Venom levels in urine were high at 8 h and approached the level of test sensitivity over 24 to 48 h; however by this time clinical signs were obvious in endangered cats. CONCLUSIONS: Careful use of the SVDK is a valuable aid in the management of a potentially envenomed cat.

Animals↗
PubMed1995

An epidemiological study of Cryptosporidium parvum in two herds of adult beef cattle.

Prevalences of Cryptosporidium parvum oocysts in faeces and of isotype-specific anti-C. parvum antibodies in serum of apparently healthy adult cattle on two farms were determined. On Farm 1 cryptosporidial diarrhoea had been recorded in more than 80% of calves born over the previous 5 years, whereas on Farm 2 cryptosporidiosis had never been reported. No differences were demonstrated in oocyst excretion or presence of antibodies between the two farms. C. parvum oocysts were detected in 62.4% of faecal smears collected from a total of 553 apparently healthy adult cattle. Sucrose flotation was performed on a proportion of the faecal samples. This proved a more sensitive technique, detecting oocysts in 92% of the samples tested, and highlighting the insensitivity of direct smears for detecting oocysts. More than 90% of the cattle had specific anti-C. parvum IgG, IgG1, IgG2 and IgM antibodies and 58% specific anti-C. parvum IgA antibodies. Results suggest that asymptomatic adults may play an important role in the epidemiology of cryptosporidiosis in calves.

Animals↗
PubMed1995

Prevalence of specific anti-Cryptosporidium IgG, IgM and IgA antibodies in cat sera using an indirect immunofluorescence antibody test.

Sera from 258 healthy and sick domestic and feral cats were screened for specific anti-Cryptosporidium antibodies using an indirect immunofluorescence antibody test (IFA). Sera were positive for IgG, IgM and IgA antibodies in 192 (74%), 84 (32%) and 67 (26%) samples, respectively. Antibody was not detected at dilutions of 1:10 and 1:20 or greater in any of eight specific pathogen-free kittens. IgM and IgA antibody classes were more prevalent in sick than in healthy domestic cats. The presence of IgM and/or IgA antibodies indicated early infection. However, these antibody classes were present in sera from cats either positive or negative for Cryptosporidium infection by faecal examination. Pronounced polar fluorescence was observed in the sporozoites in positive samples under fluorescence microscopy. The higher prevalence of specific anti-Cryptosporidium antibodies and the absence of Cryptosporidium oocysts in faecal samples from some IFA-positive animals suggests that detection of these antibodies in sera from cats could be helpful for the diagnosis of feline cryptosporidiosis.

Animals↗
PubMed1995

Shedding of "virus-like" particles in canine faeces.

Diarrhoeic faeces from about 500 dogs were examined by negative stain electron microscopy. As well as parvovirus, and some of the other recognised viral causes of gastroenteritis, unusual "virus-like" particles were observed in about 8% of the samples. The particles were spherical, 100 nm to 300 nm in diameter, and surrounded by a thick wall penetrated by numerous pores. An additional 74 samples of normal faeces yielded no "virus-like" particles. We do not know the nature of these particles.

Animals↗
PubMed1995

Effect of three concentration techniques on viability of Cryptosporidium parvum oocysts recovered from bovine feces.

Bovine fecal samples (1 g) negative for Cryptosporidium sp. oocysts were seeded with 7 x 10(4) Cryptosporidium parvum oocysts and purified by either water-ether concentration, sucrose density flotation, or zinc sulfate flotation to evaluate oocyst recovery. The effect of these purification techniques on the viability of recovered oocysts was also evaluated. Significantly higher numbers of seeded oocysts were recovered by water-ether concentration (recovery rate, 46 to 75%) than by sucrose density (24 to 65%) or zinc sulfate (22 to 41%) flotation methods. In addition, water-ether concentration did not exert a significant effect on the viability of the population of oocysts recovered, whereas sucrose density flotation and zinc sulfate flotation selectively concentrated viable oocysts. The water-ether concentration procedure is recommended for use in epidemiological studies in which both oocyst enumeration and viability assessment are required.

Animals↗
PubMed1993

External stimuli and intracellular signalling in the modification of the nematode surface during transition to the mammalian host environment.

Previous work has shown that the surface of infective larvae of parasitic nematodes will not bind the fluorescent lipid analogue 5-N-(octadecanoyl)aminofluorescein (AF18) until after exposure of the parasite to mammalian tissue-culture conditions. In this study, culture media which are permissive or non-permissive for the acquisition of lipophilicity for AF18 were altered in order to examine possible stimuli involved. This showed that external alkaline pH and high sodium ion concentration were highly stimulatory. The internal signalling pathways which may be involved in the surface alteration were then examined using agents which are known to affect intracellular signalling in mammalian cells. The results indicated that elevation of cGMP levels was stimulatory whereas inhibition of a putative Na+/H+ antiporter or calcium mobilization was inhibitory, and it is argued that high intracellular levels of cAMP may be inhibitory. Whilst the precise effects of the agents used on nematode cells remain to be established, these results provide a framework for the examination of the processes involved in the modification of the nematode surface which takes place immediately after the infection event.

1-Methyl-3-isobutylxanthine↗
PubMed1993

In vitro excystation of Cryptosporidium parvum.

Protocols for in vitro excystation of oocysts of Cryptosporidium parvum, including different chemical pre-incubation steps, were compared to examine some of the biochemical triggers involved in excystation and to define an in vitro excystation protocol of a reproducibly high efficiency. Pre-incubation steps which increased the permeability of the oocysts were found to enhance excystation dynamics and pre-treatment of oocysts with saliva was found to decrease the permeability and reduce excystation. Although excystation was maximal after incubation for 4 h, sporozoites tended to lyse over this period, and maximum sporozoite recovery occurred after 30 min. The results obtained are discussed in relation to excystation protocols adopted by different research groups and a number of recommendations are given for in vitro excystation of C. parvum oocysts.

Animals↗
PubMed1993

Rapid changes in the surface of parasitic nematodes during transition from pre- to post-parasitic forms.

All mammalian-parasitic stages of a range of nematode species investigated (Brugia pahangi, Acanthocheilonema viteae, Strongyloides ratti, Nippostrongylus brasiliensis, Trichinella spiralis and Ostertagia ostertagi) labelled in a surface-restricted manner with the fluorescent lipid analogues 5-N-(octadecanoyl)aminofluorescein (AF18) or nitrobenzoxadiazole-cholesterol (NBD-chol), but failed to bind other similar probes. In contrast, the surfaces of the 'pre-parasitic' infective stages of these species had affinity for neither AF18 nor NBD-chol. This exclusion of lipid analogues changed rapidly upon exposure of the larvae to tissue culture conditions which mimic the mammalian tissue environment (e.g. RPMI 1640/37 degrees C) such that the above probes could then insert into the surface layer of the larvae. The dauer larva of Caenorhabditis elegans also excluded the probes, but became permissive to labelling upon stimulation to emerge from the dauer state. The time taken for the surface transformation to occur ranged from less than 10 min in the vector-borne parasites to approximately 5 h in those which enter by the oral route, with direct skin-penetrators occupying an intermediate position. In all cases, the alteration proceeded too rapidly for it to have been associated with a moult. Fluorescence Recovery After Photobleaching (FRAP) studies of A. viteae larvae showed that approximately 50% of the AF18 probe was free to diffuse within the plane of the surface immediately after transformation. This is only a transitory state because AF18 was found to be highly restricted in its lateral diffusion on the surface of adult parasites. In the larvae of S. ratti, the change in affinity for AF18 was accompanied by the rapid shedding of an otherwise stable surface coat of polyanionic material, here visualized by labelling with fluorescein-conjugated cationized ferritin. Incubation of larvae in lipid-rich host serum during the induction of transformation inhibited subsequent labelling with AF18. This possibly reflects competition for insertion sites and an in vivo propensity towards the acquisition of host lipid by invading parasites.

Animals↗
PubMed1993

Occurrence of oocysts of Cryptosporidium sp. in Larus spp. gulls.

Between November 1990 and February 1991 101 gull faecal samples, collected in central Scotland, and 50 cloacal lavages, from gulls captured at two refuse tips near Durham, England were examined for the presence of Cryptosporidium sp. oocysts. Five of 101 (c 5%) of faecal samples and 11 of 50 (22%) of cloacal lavages contained oocysts, of which 64% and 83%, respectively were considered viable when examined with propidium iodide and 4'-6-diamidino-2-phenylindole. Since there is insufficient evidence to ascribe these oocysts to a recognized species they are therefore referred to as Cryptosporidium sp. oocysts. There were significant differences in the occurrence of oocysts between gulls captured at the different refuse tips (P < or = 0.01), but no significant difference between the distribution of oocysts in two species of gull, Larus argentatus (Herring Gull) and L. ridibundus (Black-head Gull). The differences may be explained by different food sources and feeding habits. The contribution of gulls to environmental contamination with Cryptosporidium sp. oocysts is probably generally small, but may be more significant when large numbers roost on surface waters.

Animals↗
PubMed1993

Occurrence of Giardia sp. cysts and Cryptosporidium sp. oocysts in faeces from public parks in the west of Scotland.

One hundred faecal specimens, randomly collected from various locations within seven public parks in the west of Scotland, were examined for the presence of Giardia sp. cysts and Cryptosporidium sp. oocysts. Eleven percent of samples contained Giardia sp. cysts and 1% contained Cryptosporidium sp. oocysts. Occurrence data from individual parks varied from 0 to 40% for Giardia and 0 to 2.4% for Cryptosporidium. The occurrence of parasitic organisms in public parks, especially in the vicinity of children's playing areas is a matter of concern for public health officials and regulators of leisure and recreation amenities.

Animals↗
PubMed1993

Evaluation and improvement of an enzyme-linked immunosorbent assay for the detection of isometamidium in bovine serum.

The control of bovine trypanosomiasis in Africa continues to rely heavily on the chemoprophylactic drug isometamidium (ISMM) chloride. However, despite many years of use, no methods are available that are sufficiently sensitive to measure drug levels in treated cattle. An enzyme-linked immunosorbent assay (ELISA) for the detection of ISMM in the serum of treated cattle has been developed and evaluated. Liquid-phase ISMM (sample) competes with solid-phase bound ISMM-protein conjugate for biotinylated sheep anti-ISMM IgG. The specific IgG is detected by streptavidin-peroxidase, using tetramethylbenzidine for colour development. Assay calibration is by four-parameter logistic curve-fitting. Factors contributing to absorbance variance were considered in assay optimization and improvement of precision and the lower limit of detection (approximately 0.1 ng/ml in serum). The ELISA was shown to detect serum ISMM for several months after treatment of cattle in a trypanosomiasis endemic country. The potential uses of this assay include the development of rational prophylactic drug regimens, and the indirect detection of drug-resistant trypanosomes.

Animals↗
PubMed1993

Effects of Preservatives on Viability of Cryptosporidium parvum Oocysts.

Potassium dichromate and formalin reduced the viability of Cryptosporidium parvum oocysts as assessed by inclusion or exclusion of 4',6-diamidino-2-phenylindole (DAPI) and propidium iodide (PI) and excystation. Some formalin-treated oocysts containing dead sporozoites excluded PI; that this fluorogenic assay relies not solely upon exclusion of PI but also upon highlighting of sporozoite nuclei by DAPI is reiterated.

Journal Article↗
PubMed1993

Induction of folds or sutures on the walls of Cryptosporidium parvum oocysts and their importance as a diagnostic feature.

The proportion of oocysts of Cryptosporidium parvum showing a fold on oocyst walls when incubated with either fluorescent monoclonal antibody or a surface-reactive fluorescent dye was increased by incubating suspensions of oocysts with dimethyl sulfoxide, sucrose, or Hanks' balanced salt solution. Further incubation of sucrose-incubated oocysts with water showed this to be a reversible phenomenon. Oocysts demonstrating this fold after incubation in dimethyl sulfoxide were of the same viability as control oocysts and followed the same excystation dynamics. Despite this fold having been previously described as a suture, we were unable to find any evidence that this pattern of fluorescence highlighted the same suture that has been described in ultrastructural studies. Furthermore, oocysts were observed in which this fold was not always continuous with the gape in the oocyst wall through which the sporozoites had emerged. We propose that this fluorescently highlighted region or fold should no longer be described as a suture and question its validity as a diagnostic feature. When environmental and other samples are being examined for the presence of C. parvum oocysts, objects of appropriate size, shape, and fluorescence which do not demonstrate a surface fold should not necessarily be excluded.

Animals↗