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G C Coles

Publications and source records attributed to G C Coles.

At least 19 recordsLinked to original sources
PubMed2000

Structural characterization of the N-glycans of Dictyocaulus viviparus: discovery of the Lewis(x) structure in a nematode.

This paper reports the first rigorous evidence for the existence of N-linked oligosaccharides in Dictyocaulus viviparus, an economically important nematode that parasitises cattle. Structural strategies based upon fast atom bombardment mass spectrometry were employed to examine detergent extracts of homogenised adult D.viviparus for their N-glycan content. These revealed that detergent-soluble material is rich in high mannose, truncated and complex-type families of N-linked oligosaccharides. Importantly, the most abundant antennae in the complex-type structures were shown to carry the Lewis(x)epitope (Galbeta1-4(Fucalpha1-3)GlcNAc). Although the Lewis(x)moiety occurs in other helminths such as schistosomes, nematodes have previously been thought to lack this epitope. The Lewis(x)epitopes in D.viviparus are carried on bi-, tri-, and tetraantennary glycans and are therefore candidates for recognition events requiring multivalent ligands. There is compelling evidence from schistosome research that glycoconjugates containing Lewis(x)structures are immunomodulators. We propose that the Lewis(x)-rich glycans identified in this study might similarly be involved in D.viviparus host interactions.

Animals↗
PubMed1999

The in vitro response of sheep scab mites to pyrethroid insecticides.

The response of sheep scab mites to pyrethroid insecticides and organophosphate compounds was studied in vitro with the objective of finding a simple test for detecting insecticide resistance in scab mites. Psoroptes cuniculi from rabbits or P. ovis from sheep were enclosed in small 'tea bags' made from heat sealable paper prior to dipping in insecticide. Mites failed to die 24 h after a 1 min dip in working concentrations of insecticidal sheep dips. With flumethrin a variety of different conditions were tested but most failed to improve the efficacy of flumethrin. It is suggested with freshly collected mites pyrethroids may be taken up by ingestion.

Animals↗
PubMed1999

Nematode control practices and anthelmintic resistance in dairy calves in the south west of England.

A postal survey of worming practices on West Country dairy farms was undertaken and farmers were requested to send faecal samples for nematode egg counts. The majority of the farmers who responded had a nematode control policy which was based on a mixture of anthelmintics and pasture rotation. Sixty-five per cent turned out calves on to the same paddock each year and 57 per cent treated their stock with anthelmintics during the second year. Ninety farms submitted samples for analysis but only 16 samples contained sufficient eggs to justify repeat egg counts and only eight of these produced enough eggs for in vitro tests. The small number of positive samples, even into the latter part of the year suggests a heavy use of anthelmintics with relatively clean pasture. One Somerset farm had larvae which developed in high concentrations of ivermectin, and eggs were still being passed after two treatments with ivermectin at the manufacturer's recommended dose seven days apart. Of 100 male nematodes isolated from two of the calves, 88 were Cooperia species and 12 were Nematodirus species. A controlled trial with this isolate in eight Friesian male calves showed a 44 per cent reduction in egg counts at day 7 but no significant reduction in worm burden postmortem. This is the first reported case of ivermectin-resistant Cooperia species in cattle in the United Kingdom.

Animals↗
PubMed1999

Evidence for double resistance to permethrin and malathion in head lice.

A rising prevalence of head lice among school children and rising sales of insecticides with anecdotal evidence of their treatment failure, led us to examine whether head lice in Bristol and Bath were resistant to the insecticides available for treating head lice. Ten schools in Bristol and Bath were visited to collect field samples of head lice. A comparison was made of the survival rates of fully sensitive laboratory reared body lice and field samples of head lice on insecticide exposure. To confirm the in vitro relevance of these tests we performed supervised treatments of affected subjects with malathion or permethrin. There were significant differences (P < 10-6 Fishers exact test) between head and body lice survival for malathion and permethrin exposure, but not for carbaryl. There was an 87% failure rate for permethrin and a 64% failure rate for malathion with the topical treatment of a selected number of infested school children. We conclude that there is a high resistance to permethrin and malathion, but head lice remain fully sensitive to carbaryl. This is the first report of doubly resistant head lice. As permethrin, phenothrin (a very similar synthetic pyrethroid) or malathion are the active ingredients in all the over-the-counter head lice treatments in the U.K., then it is likely that head lice prevalence will continue to increase. The resistance against permethrin employed by the head louse is probably the kdr (knockdown resistance) mechanism, and an enzyme-mediated malathion-specific esterase is the likely mechanism against malathion.

Animals↗
PubMed1998

Levamisole binding sites in Haemonchus contortus.

Larval and adult extracts from isolates of Haemonchus contortus were assayed for specific [3H]levamisole binding activity. All of the tissue preparations displayed [3H]levamisole binding sites. The sensitive isolate SE and resistant isolate RJ showed no differences in larval and adult binding data. Larval SE extracts had higher receptor density (Bmax = 648 fmol mg-1) and dissociation constant (Kd = 1.28 microM) for [3H]levamisole than larval extracts of the American isolate RUSA (Bmax = 87 fmol mg-1 and Kd = 0.15 microM). Extracts of adult SE and RUSA isolates contain as much as 327 fmol mg-1 of protein and 205 fmol mg-1 of protein, respectively, and similar dissociation constants (Kd = 0.77 microM and Kd = 0.81 microM, respectively). There was a good correlation between specific binding activity of larval and adult extracts in both SE and RUSA isolates. The nicotinic cholinergic antagonist alpha-bungarotoxin had no effects in either isolate on [3H]levamisole binding activity. The results confirm that levamisole acts at a cholinergic receptor in H. contortus, and suggest that target site modification could be involved in the development of levamisole resistance.

Animals↗
PubMed1997

Nematode control practices and anthelmintic resistance on British sheep farms.

Nearly 23 per cent of 3000 randomly selected sheep farmers returned questionnaires on strategies to control the development of anthelmintic resistance. Twenty-five per cent stated that they regularly checked the accuracy of their drenching gun, and 52 per cent stated that they weighed a few animals and treated the whole flock like the heaviest. The mean annual frequency of dosing lambs was 4.39 compared with 2.43 for ewes. Forty-eight per cent stated that they changed the anthelmintic group annually. Seventeen per cent always treated sheep brought on to their farm with ivermectin. However, only 7 per cent had had their flocks tested for anthelmintic-resistant nematodes. The responses suggest that most sheep farmers are not actively seeking to prevent the development and spread of anthelmintic-resistant nematodes.

Animal Husbandry↗