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Biomedical subjects

G B Mitchell

Publications and source records attributed to G B Mitchell.

35 records · Page 2Linked to original sources
PubMed1985

Epidemiology of Nematodirus battus infection in eastern Scotland.

A field investigation was carried out from 1981 to 1983 on the prevalence of Nematodirus battus under different systems of lowland sheep management. Pasture larval counts, ewe and lamb worm egg counts, and tracer lamb worm counts were carried out. As expected, contamination was generally greater on permanent pasture than on new leys as measured by pasture larval counts and lamb worm egg counts. However significant contamination was also recorded on young grass fields for which alternate grazing with young calves may have been partly responsible. It is suggested that the 1983 hatch was delayed because of a drop in soil temperature in late March which may have increased subsequent scour problems involving N battus seen in May.

Animal Husbandry↗
PubMed1984

Comparative study of gastrointestinal helminthiasis in sheep on 'clean' grazing and permanent pasture under field conditions.

An investigation of sources of helminth infection was carried out on three flocks: a traditional permanent pasture flock (A), one operating a 'clean' grazing system (B), and an East of Scotland College flock (C) which had operated a clean grazing system for nine years. Ewe and lamb worm egg output and pasture larval levels were recorded and tracer lambs were grazed during July and August on each farm. Considerable contamination was present on farm B fields compared with farms A and C, which resulted in higher worm burdens in late summer in farm B tracer lambs and lower weight gains. The main source of this infection was thought to be ewe periparturient egg output, as 21 per cent of ewes had positive worm egg counts over the lambing period. Differences in management practices between farms B and C, eg, earlier stocking of farm B fields, were also considered contributory factors.

Animals↗
PubMed1983

Control of ovine gastrointestinal helminthiasis by the use of 'clean' grazing and strategic dosing in the field.

Despite the widespread adoption of clean grazing systems in lowland sheep flocks, detailed parasitological investigations had not previously been carried out on such flocks. A trial was therefore conducted on two commercial flocks: a traditional permanent pasture flock (A) and one operating a system of clean grazing (B), and on an East of Scotland College flock (C) which had operated a clean grazing system for eight years. Ewe and lamb worm egg output, pasture larval levels and lamb liveweight gains were monitored and tracer lambs were grazed during July and August on each farm. Under clean grazing conditions on farm C all parasitological parameters were lower than on both commercial farms. However, in the commercial flocks comparable contamination was evident from midsummer onwards and tracer lambs grazed during August on farm B had significantly greater worm burdens than on the other two farms. The differences observed between the flocks were thought to be due to greater residual contamination by overwintered larvae in both commercial flocks while the higher worm burdens in August on farm B probably resulted partly from incomplete control of the periparturient rise in ewe faecal egg output and partly to autoinfection of the lamb crop. It was concluded that farm C grazing was the cleanest. Considerable contamination was present on farm A while farm B occupied an intermediate position which resulted in considerable worm burdens in lambs grazing during the latter part of the season.

Animal Husbandry↗
PubMed1981

Successful passive transfer of resistance to Fasciola hepatica infection in rats by immune serum and transfer factor.

Resistance to Fasciola hepatica was shown by a 64 per cent reduction in fluke recovery compared with control rats was recorded in rats inoculated with serum from sheep experimentally infected with F hepatica. A comparable reduction (55.6 per cent) was obtained using transfer factor prepared from lysed leucocytes of infected rats. No significant reduction was obtained using transfer factor prepared from sheep or calves.

Animals↗
PubMed1981

Stimulation of resistance to Fasciola hepatica infection in sheep by a regime involving the use of the immunomodulatory compound L tetramisole (levamisole).

The effect of prior nematode and cestode infection in sheep on the course of experimental Fasciola hepatica was studied. The cross immunising properties of these parasites per se and the modification of any protective effect conferred by the immunomodulatory compound L tetramisole (levamisole) were investigated. It was recorded that no protection was conferred on sheep against F hepatica infection by virtue of prior infection with any helminth species per se, including Cysticercus tenuicollis. However, a degree of immunity to F hepatica was recorded, for only the second time, in sheep primed with helminth infections before treatment with levamisole. This is the first demonstration of a beneficial effect conferred by levamisole by virtue of its immunomodulatory properties in ruminants infected with any helminth species. Resistance was shown by a 47 per cent reduction in flukes recovered from sheep treated in this way (P less than 0.05).

Animals↗
PubMed1980

Failure to protect calves against Taenia saginata using antigens prepared from in vitro cultivation of the larval stage.

Calves were vaccinated intramuscularly against the tapeworm Taenia saginata using excretory/secretory (ES) antigens from short and long term periods of in vitro cultivation of the larval stage of the parasite, four weeks before challenge with 5000 T saginata onchospheres. Neither immunisation regime employed afforded significant protection against challenge. It was considered that this may have been due to a reduction in concentration of, or detrimental effects to, potential immunogens during vaccine production. Elucidation of the nature of the protective ES antigens necessary for standardization of the technique has yet to be achieved in helminths.

Animals↗
PubMedDate not supplied

An adenovirus survey of poultry flocks during the growing and laying periods.

Chicken adenoviruses were isolated from asymptomatic chickens on each of 7 farms tested; a majority of them induced cytopathology by the second serial passage. Although adenoviruses were isolated from chickens ranging in age from 8 to 34 weeks, the highest isolation rate was from those 8 to 14 weeks. Eight serotypes (1, 2, 4, 5, 6, 7, 8, and 9) were identified in a relatively small geographic area; serotypes 1, 4, 7, and 9 were isolated most frequently. Multiple serotypes were found on 6 of 7 farms, with 1 farm having 4 serotypes identified. Repeat isolations of the same serotypes were noted on 2 farms. The pattern of virus isolations was generally related to age but varied according to farm. Although new serotypes kept appearing, even after birds came into lay, no clinical problems were associated with them. The incidence of precipitin reactors tended to be low (10-40%) in immature birds but reached 80% or more after sexual maturity. The "antiserum pool" modification of the VN test was found to be accurate and less cumbersome than the conventional procedure for typing isolants.

Adenoviridae↗