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Biomedical subjects

C A Hall

Publications and source records attributed to C A Hall.

At least 91 records · Page 5Linked to original sources
PubMed1981

Five generations of selection with benzimidazole and non-benzimidazole anthelmintics against benzimidazole resistant strains of Haemonchus and Ostertagia spp in sheep.

Benzimidazole resistant strains of Haemonchus contortus and Ostertagia spp were subjected to selection pressure over five laboratory generations with the recommended dose rates of either cambendazole, oxfendazole or morantel. A change in response, with larger residual worm burdens remaining after treatment at the fifth generation, was shown for both cambendazole and oxfendazole against both species of nematode. No change in response against either species are shown for morantel. The results are discussed in terms of the problem associated with inefficient removal of the adult parasites after treatment.

Animals↗
PubMed1981

Changes in response of a benzimidazole resistant strain of Haemonchus contortus from sheep after passing through calves.

A benzimidazole resistant strain of Haemonchus contortus was passaged through lambs only or from lambs to calves and back into lambs. Changes in response to thiabendazole were monitored by using an egg hatch test at each animal passage and by a controlled experiment on adult worms at the final passage in lambs. An increased level of resistance was shown for the isolate during its passage through calves by the egg hatch test, although this was not supported on the adult worms in sheep using a single dose rate of 66 mg/kg of thiabendazole.

Animals↗
PubMed1981

Prolonged anthelmintic effect of closantel and disophenol against a thiabendazole selected resistant strain of Haemonchus contortus in sheep.

Two long-acting anthelmintics, closantel and disophenol, were tested by treatment 90, 60 and 30 days before challenge with a thiabendazole selected laboratory strain of Haemonchus contortus. The sheep were slaughtered 28 days after infection for total worm counts. A significant reduction in the number of adults remaining at autopsy was recorded after treatment with both anthelmintics 30 and 60 days before challenge but there was zero efficacy when the animals were treated 90 days before challenge. No significant difference was exhibited between the two compounds. Variability in response was recorded between animals on the 60 day period of treatment, which for disophenol may be dose related because animals receiving the lower volumes showed higher worm counts. For both anthelmintics a variability in the rate of metabolism may be responsible. The possibility offered by both anthelmintics for treating benzimidazole resistant strains of H contortus is discussed.

Animals↗
PubMed1980

Patterns of wool moisture in merino sheep and its associated with blowfly strike.

A method for determining the moisture content of wool with a minimum disturbance to the constituents is described. The method was used to show differences in moisture content according to anatomical site, age, sex, strain of merino and in lesions of fleece rot, bacterial stain and active flystrike. The incidence of natural flystrike was recorded and related to the higher levels of moisture content. The moisture content in proximal wool was found to increase at different rates, following wetting of the fleece with droplets of water falling under gravity to simulate rain. A level of 20 per cent moisture content was reached after different time intervals in different strains of merino sheep, which may explain one of the differences in strain susceptibility to fleece rot

Animals↗
PubMed1980

The effect of a drying agent (B26) on wool moisture and blowfly strike.

A drying agent (B26) was applied as a mist to sheep fleece. A reduction of 30 per cent in wool moisture was recorded, which persisted for 10 to 12 weeks. Reapplication of B26 extended the period of dryness, without adding to the reduction of moisture. Treatment using 100 to 200 ml of the drying agent resulted in reduced fleece moisture content for seven days when exposed to wetting by simulated rain. Treated sheep showed a 60 per cent reduction in the number and severity of fleece rot lesions. Diazinon reduced the incidence of natural flystrike by 50 per cent and the drying agent by 75 per cent over a five week period before shearing compared with untreated animals.

Aluminum↗
PubMed1979

Resistance to thiabendazole in a field population of Ostertagia circumcincta from sheep.

A population of Ostertagia circumcincta from sheep has been found which, in field and laboratory trials, showed a lack of response to the recommended dose (44 mg/kg) of thiabendazole, suggesting that a degree of resistance exists to this anthelmintic. Preliminary experiments indicated a less than expected response to levamisole. This was not confirmed in a laboratory trial and therefore resistance to this anthelmintic has not been shown conclusively.

Animals↗
PubMed1979

Megaloblastic anemia as a result of an abnormal transcobalamin II (Cardeza).

A 34-year-old Black woman had severe megaloblastic anemia in childhood. Initially, and over the years, she responded well to massive doses of parenteral cobalamin (Cbl) or oral folic acid. Metabolic reactions involving Cbl and folate enzymes were normal during both relapse and remission except for the absence of thymidylate synthetase in relapse. Amino acid analyses of urine and plasma showed no significant abnormalities. Neither cystathionine, homocystine, formiminoglutamic acid, nor methylmalonic acid was detected in the urine. The serum Cbl level was repeatedly elevated even when the patient was receiving only folic acid therapy. The elevation of the vitamin in the serum was found to be a result of markedly increased levels of transcobalamin II (TC II), as identified by several physicochemical techniques. The patient's TC II-Cbl shared immunologic properties with normal TC II but did not facilitate or impede the uptake of Cbl or Cbl bound to normal TC II, respectively, by human cells.

Anemia, Macrocytic↗
PubMed1979

The effect of single and divided dose administration on the efficacy of fenbendazole against adult stages of benzimidazole resistant sheep trichostrongylids.

Sheep infected with benzimidazole resistant strains of Haemonchus contortus and Trichostrongylus colubriformis were used to compare the anthelmintic efficacy of fenbendazole given as a single dose or administered in a divided dose regime over five days. Statistical analysis showed no significant difference between the two methods of administration for H contortus. On the other hand, divided dose fenbendazole was significantly less effective than single doses against adult T colubriformis at dose rates of 5 and 7.5 mg/kg. In the case of H contortus a highly significant correlation coefficient between post treatment egg counts and worm counts (r = 0.789) was obtained. This suggests that reduction in faecal egg output following drug treatment would provide a useful field indication of anthelmintic performance of fenbendazole (and possibly related compounds) against benzimidazole resistant strains of this parasite.

Animals↗