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Biomedical subjects

J L Duncan

Publications and source records attributed to J L Duncan.

At least 19 recordsLinked to original sources
PubMed1996

Isotype-specific antibody responses to the surface-exposed antigens of adult and larval stages of Dictyocaulus viviparus in infected and vaccinated calves.

The antibody responses to the surface-exposed antigens of living larval and adult Dictyocaulus viviparus were measured by quantitative immunofluorescence using sera from calves infected with, or vaccinated against, the parasite. In infected animals, the surface of the sheath of the third-stage larvae (L3) (retained cuticle of second-stage larvae (L2)) proved highly immunogenic despite the fact that it is thought to be shed prior to parasite penetration of the host intestine. When responses to the surface of exsheathed larvae (L3 cuticle) were measured, a high level of heterophile IgM antibody was detected in the serum of animals that had not been previously exposed to the parasite and, following infection, a specific IgG response was detected against the exsheathed L3 surface. The antibody response, however, was less marked than that observed against the intact L3 sheath. Responses of patently infected animals to the adult surface showed an initial IgM response that was superseded with time by IgG1 and IgG2 responses. Vaccinated animals showed only low level responses to the surfaces of the L3 sheath, L3 cuticle and adult stages following immunisation with two doses of irradiated larvae. The immunised animals produced a strong antibody response to the larval surface antigens following challenge with infective larvae but they failed to produce antibody to the surface of adult parasites. These results show that the surfaces of all the stages of D. viviparus examined are immunogenic in infected calves and, depending on the developmental stage, infection regime, or time of infection, high levels of parasite-specific IgG1 or IgM are stimulated. It has previously been shown that significant levels of protective immunity can be obtained in naive animals following passive transfer of serum from infected calves. Thus, the antibody responses detected in the work reported here may be of relevance in protective immunity against dictyocaulosis.

Animals↗
PubMed1996

Influence of soyabean meal supplementation on the resistance of Scottish blackface lambs to haemonchosis.

Protein supplementation improves the resistance of sheep to haemonchosis. This experiment investigated the Scottish blackface breed to establish whether dietary protein supplementation is still beneficial in a genetically resistant breed. Lambs were given either a basal diet or a diet supplemented with soyabean meal to give an additional 80 g crude protein kg dry matter-1. The lambs were given an initial loading dose of Haemonchus contortus, followed by a trickle infection for 10 weeks. The weight gains of the lambs given the supplemented diet were greater and their carcases were leaner, irrespective of infection status. Infected animals on the basal diet were more anaemic and hypoalbuminaemic than animals receiving the supplemented diet, although there were no statistically significant differences in mean worm burdens or faecal egg counts.

Analysis of Variance↗
PubMed1996

Response of Dorper and red Maasai lambs to trickle Haemonchus contortus infections.

Six-month-old red Maasai lambs were more resistant than Dorper lambs to repeated infections at one to two week intervals with 1000 Haemonchus contortus infective larvae. Resistance after infection was assessed by means of faecal egg counts, packed cell volumes, eosinophil counts, total serum protein concentrations and mortality rates. The weight gains of the infected animals were only marginally lower than those of their uninfected controls, most probably because of their significantly higher feed consumption, and evidently the infected lambs were not utilising all of the extra feed for growth. This absence of anorexia in spite of the infection was probably due to the palatability of the high protein diet fed to the lambs.

Animals↗
PubMed1996

Pacemaker patient-triggered event recording: accuracy, utility, and cost for the pacemaker follow-up clinic.

Many pacemaker patients have vague symptoms following implantation. It is often difficult for the physician to ascertain if they are cardiac in origin. A new pacemaker feature has been introduced, Patient-Triggered Event Records (PTER), to help the physician with this diagnosis. The PTER is a continuously running event record which stores the cardiac rhythm and rate. Brief application of a magnet will transfer the record into the device's memory. The data recorded will be the 97 events prior to the magnet application and the 30 events following magnet removal. The exact state of pacing (atrial and ventricular sensing/pacing, or premature ventricular events) and the rate of the ventricular events will be graphically displayed by the programmer for all 127 events. Thus, the exact pacer and cardiac rhythm can be determined during the period of the symptomatic episode. A total of three PTER's can be stored within the device. If a fourth is recorded, it will replace the oldest record. Three pacemakers with the PTER feature were tested in vitro with five different simulated cardiac rhythms. A beat-by-beat comparison between the PTER and the 15 simulated test rhythms revealed a 100% accurate documentation by PTER. Sixteen pacemaker patients which have the PTER feature were monitored using a King of Hearts for a total of 43 symptomatic events. The PTER records produced clinically relevant information 98% of the time while the King of Hearts produced clinically relevant information 81% of the time. A comparison of costs of the two different methods of monitoring these patients, was $2,432 versus $4,480 for the PTER and loop event monitor respectively. The PTER is an accurate, lower cost method for monitoring and diagnosing symptomatic pacemaker patients. The PTER can be used as the first diagnostic tool in troubleshooting patients with paroxysmal symptoms in the pacemaker clinic population.

Adult↗
PubMed1995

Dictyocaulus viviparus: surface antigens of the L3 cuticle and sheath.

The bovine lungworm Dictyocaulus viviparus induces a highly protective immune response in the bovine host. It is consequently a particularly useful host-parasite system for the study of those antigens and immune responses which can induce protective immunity against a parasitic nematode. We have generated monoclonal antibodies to the L3 cuticle and sheath surfaces in order to define antigens present at the host-parasite interface of infective larvae. Three monoclonal antibodies generated against the surface of the infective L3 cuticle bind to a PC-like hapten, and the presence of such an epitope exposed on the cuticular surface appears to be unique to the D. viviparus L3. Six monoclonal antibodies which bind to the surface of the L3 sheath all detect an antigen which is immunodominant in immunised cattle. The possible basis and implications of such marked antigenicity of a molecule on the L3 sheath surface are discussed.

Animals↗
PubMed1995

The repeatability of faecal egg counts, peripheral eosinophil counts, and plasma pepsinogen concentrations during deliberate infections with Ostertagia circumcincta.

Faecal egg counts, peripheral blood eosinophil counts and plasma pepsinogen concentrations were monitored during 2 successive, deliberate infections in 24 Scottish Blackface sheep. For all 3 techniques, the repeatability of replicate counts or of measurements made at short intervals were high which suggests that all 3 assays were reliable. Within an infection the repeatability of different samples from the same animal decreased as the interval between samples increased. The repeatability between infections was only moderate for faecal egg counts but high for peripheral eosinophil counts and plasma pepsinogen concentrations. Of the 3 variables, faecal egg count was the most strongly associated with the worm burden. Together, the three variables accounted for, in a statistical sense, one half of the variation in worm burden. The three variables, if measured concurrently, should provide a more effective identification of resistant and susceptible lambs.

Animals↗
PubMed1995

Immunisation of guinea pigs against Dictyocaulus viviparus using adult ES products enriched for acetylcholinesterases.

The adult ES products of Dictyocaulus viviparus are a source of protective antigens against challenge in the guinea pig laboratory model. High levels of acetylcholinesterase (AChE) activity are present in these products and these enzymes are immunogenic in infected cattle. Here, the potential role of these enzymes in protective immunity was investigated using a fraction enriched for AChE to immunise guinea pigs. The antibody response stimulated by immunisation with AChE-enriched ES products and the worm burdens obtained following challenge with infective larvae were compared with those in animals immunised with whole ES products and challenge controls. The AChE-enriched preparation stimulated high levels of enzyme-specific antibody in immunised animals, which was not the case for those which received unfractionaed ES products. Worm burdens of guinea pigs which received the AChE-enriched fraction were significantly lower than those obtained in adjuvant controls. The animals which received the unfractionated ES products were not significantly protected against challenge. These results suggest that AChEs may be potential candidates for incorporation in a sub-unit vaccine against D. viviparus.

Acetylcholinesterase↗
PubMed1995

An ovine major histocompatibility complex DRB1 allele is associated with low faecal egg counts following natural, predominantly Ostertagia circumcincta infection.

Infection with Ostertagia circumcincta is a major constraint on sheep production in temperate areas of the world. A potential control strategy is the use of genetically resistant sheep. Therefore we examined the association between MHC-DRB1 alleles and faecal egg counts following natural, predominately O. circumcincta infection in a flock of Scottish Blackface sheep. Nineteen DRB1 alleles were identified by a combination of variation in the length of simple repetitive sequences within the intron between exons 2 and 3 and hybridisation of selected oligonucleotides to polymorphisms within exon 2. Faecal samples were taken from 200 lambs from one to six months of age at intervals of 4 weeks. Genetic effects were strongest at 6 months of age. Least-squares analysis indicated that substitution of the most common allele (I) by allele G2 would result in a 58-fold reduction in faecal egg counts in 6-month-old lambs and a 22-fold reduction in 5-month-old lambs. These results suggest that the major histocompatibility complex plays an important role in the development of resistance to O. circumcincta.

Alleles↗
PubMed1995

Protective immunisation of guinea pigs against Dictyocaulus viviparus using excretory/secretory products of adult parasites.

Parasite preparations were examined for their ability to induce protective immunity against Dictyocaulus viviparus in guinea pigs. Dunkin-Hartley strain guinea pigs were immunised with somatic extracts of adult parasites, somatic extracts of third stage larvae or excretory/secretory (ES) products from adult parasites. The groups were immunised twice with Freund's adjuvant four weeks apart and challenged with 6000 infective L3. Significant levels of protective immunity were observed only in the adult ES-immunised animals. The antibody responses of the different groups were compared following analysis by ELISA and immunoprecipitation. To examine the protective role of antibody, guinea pigs were passively immunised with serum from animals immunised with adult ES products or serum from guinea pigs exposed to experimental D. viviparus infection. Following challenge with infective L3, lung-worm burdens of these groups were significantly lower than in guinea pigs which received normal sera. The results suggest that D. viviparus adult ES products contain protective antigens and that antibody-mediated mechanisms contribute to immune protection.

Animals↗
PubMed1995

Influence of supplementation with dietary soyabean meal on resistance to haemonchosis in Hampshire down lambs.

The influence of dietary protein supplementation on resistance to haemonchosis was examined in Hampshire down lambs fed either a basal diet or a diet supplemented with soyabean. At seven months of age the lambs were challenged with an initial loading dose of Haemonchus contortus, followed by a trickle infection three times a week. Blood and faecal samples were collected three times a week and bodyweights were recorded weekly. After 10 weeks the lambs were slaughtered and their worm burdens and carcase composition determined. Although their mean worm burdens were similar, the lambs given the basal diet had higher faecal egg counts, lower packed red cell volumes and lower concentrations of total plasma protein and plasma albumin than the lambs given the supplemented diet. The dietary supplementation also improved the carcase composition of the lambs.

Animal Feed↗
PubMed1995

Different patterns of faecal egg output following infection of Scottish blackface lambs with Ostertagia circumcincta.

Faecal nematode egg counts were monitored in 184 Scottish Blackface lambs during natural exposure to a mixed, predominantly Ostertagia circumcincta infection and 12 lambs were selected which showed consistently zero (low count group; nine lambs) or consistently positive faecal egg counts (high count group; three lambs). These lambs were then treated with anthelmintic and challenged with 50,000 infective larvae of O. circumcincta and monitored thrice-weekly for 38 weeks; they were then re-challenged with another 50,000 infective larvae of O. circumcincta and monitored for a further 8 weeks. All sheep gave positive egg counts following deliberate infection. However, there was considerable variation among sheep in the size and timing of the peak in egg production. In particular, the pattern of mean values for faecal egg counts was different in the two groups. Egg counts were lower in the later periods of the extended infection in both groups of sheep. During the first half of the extended infection, egg counts were lower in sheep from the low count group, but during the second half of the infection the pattern was reversed and egg counts were lower in sheep from the high count group. There was a weak positive correlation between egg counts following anthelmintic treatment and 28 days exposure to natural infection and egg counts 28 days after a deliberate infection. Egg counts in the later stages of the deliberate infection were strongly but negatively correlated with egg counts following natural infection. The results of these studies show that differences in egg count following natural infection can be reproduced in experimental infections and that there is substantial variation in the pattern of egg production over time in different sheep. They also suggest that naturally resistant lambs are better able to delay worm development than naturally susceptible lambs.

Abomasum↗
PubMed1995

A 4-year study on the effectiveness of alternate grazing of cattle and sheep in the control of bovine parasitic gastro-enteritis.

In many farming enterprises, animal management systems which could provide a practical and effective alternative to chemotherapy for the control of bovine helminthosis would be readily accepted. One system which has been proposed and shown to be effective in the short or medium term involves grazing different host species on a rotational basis. The study described here examined the effect of alternating cattle and sheep annually over an extended period of 4 years. Up to the second grazing season the system appeared to be successful, with a marked reduction in the cattle worm burdens. However, by the end of the study period the parasite burdens in calves grazed on the alternated pasture were equal to, or greater than, those of set-stocked control animals. It was thus clear that the alternate grazing strategy had failed. Data obtained from other parameters measured, i.e. faecal egg counts, pasture larval numbers and plasma pepsinogen levels, confirmed this observation.

Animal Feed↗
PubMed1995

Local and plasma antibody responses to the parasitic larval stages of the abomasal nematode Ostertagia circumcincta.

Ovine isotype-specific antibody responses to the parasitic larval stages of the abomasal nematode Ostertagia circumcincta were measured in a simple, indirect enzyme-linked immunosorbent assay. Analysis of variance of replicate tests showed that the assay was very reliable. There was substantial variation among individual sheep in their IgA and IgG1 responses even though the sheep had been matched for breed, age and sex, were born on the same farm, were reared identically and had the same history of exposure and challenge with O. circumcincta. The local IgA responses to a somatic extract of fourth-stage larvae were very similar to responses to excretory-secretory products of fourth-stage larvae. The responses to third stage larvae were correlated with the responses to fourth stage larvae. There was a negative correlation between parasite-specific plasma IgG1 and parasite-specific plasma IgA responses. There was only a moderate association between IgA responses in the mucus and the plasma. Therefore, antibody responses measured in plasma cannot be easily extrapolated to antibody responses in the abomasal mucus.

Abomasum↗
PubMed1995

A comparison of the responses to repeated experimental infections with Haemonchus contortus among Scottish Blackface lambs.

Twenty helminth-naive Scottish Blackface lambs were given three infections with 10,000 infective larvae of Haemonchus contortus at 8 week intervals. An additional six lambs served as uninfected controls and eight lambs were infectivity controls. The lambs were 7 months old at the start of the infection. Four of the 20 lambs developed severe haemonchosis and were put down during the experiment. The remaining 16 lambs plus uninfected controls were necropsied 8 weeks after the third infection. The mean faecal egg count peaked 6-8 weeks after the first infection, gave a second smaller peak 6-8 weeks after the second infection but produced no peak after the third infection. Mean red blood cell counts fell rapidly during the first infection, then rose gradually during the second and third infections. The mean values suggested that two infections were sufficient to produce effective immunity in the sheep population but they masked considerable individual variation. Eleven animals appeared relatively resistant following the first infection, while two animals were relatively susceptible to even the third infection. The repeatability of mean faecal egg counts or mean red blood cell counts for each animal during the replicate infections were very high, because the rankings of the individual sheep remained remarkably stable. Faecal egg counts were very strongly correlated with red blood cell counts. Multiple regression analysis showed that four factors--faecal egg counts, red blood cell counts, weight and sex--accounted for essentially all of the observed variation in worm burdens among the lambs. Therefore, under these controlled experimental conditions, additional markers appear unnecessary for the detection of resistance status.

Analysis of Variance↗
PubMed1995

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) second edition of guidelines for evaluating the efficacy of anthelmintics in ruminants (bovine, ovine, caprine)

The first edition of the W.A.A.V.P. anthelmintic guidelines for ruminants was published in 1982. Since then improved parasitological procedures have been developed, new therapeutic and prophylactic products have appeared requiring different test methods, and registration authorities are requesting more detailed record keeping and data validation. This second edition addresses these developments and fulfills the original goal of publishing guidelines for high quality, scientifically valid testing standards for trials that would be accepted as proof of efficacy by registration authorities regardless of country of origin. This second edition includes updated guidance on standard parasitological procedures, dose titration, dose confirmation and clinical trials, and provides guidelines for evaluating products for efficacy against anthelmintic resistant parasites, persistence of activity and prophylactic activity. Tests for efficacy against nematodes, trematodes and cestodes are included.

Animals↗
PubMed1995

Platelet count and the outcome of operation for ruptured abdominal aortic aneurysm.

PURPOSE: The purpose of this study was to determine the relationship between admission and postoperative platelet count (PC) and mortality and morbidity rates after emergency surgery for ruptured abdominal aortic aneurysm (AAA). METHODS: We performed a case record review of 65 consecutive patients admitted with ruptured AAA. RESULTS: Five patients did not undergo operation because of poor clinical condition, 12 patients died at operation, 13 patients died after operation, and 35 patients survived (operative mortality rate of 58%). Fifteen patients had an admission PC of less than 150 x 10(9)/L, of whom 14 (93%) died; 27 patients had an admission PC of 150 to 250 x 10(9)/L, of whom 8 (30%) died; and 18 patients had an admission PC of greater than 250 x 10(9)/L of whom 3 (17%) died. At the end of operation 29 patients had a PC of less than 100 x 10(9)/L, of whom 13 (45%) died, 20 (69%) had development of multiorgan failure (MOF), and 6 (21%) required relaparotomy for bleeding complications. By contrast, all 19 patients having a PC of 100 x 10(9)/L or greater at the end of the operation survived, three (16%) had development of MOF, and none required further surgery for bleeding. There was a significant inverse correlation between PC at the end of the operation and the number of postoperative days spent on a ventilator, in the intensive therapy unit, and in hospital. After operation, 15 patients had development of thrombocytosis (PC > 400 x 10(9)/L), of whom 10 had development of deep venous thrombosis and 8 had development of pulmonary embolism. There were no deep venous thromboses or pulmonary embolisms in patients who did not have development of a postoperative thrombocytosis. CONCLUSIONS: There is a direct correlation between PC on admission to the hospital and death after emergency repair of ruptured AAA. Thrombocytopenia at the end of the operation is associated with a high risk of morbidity from continuing hemorrhage or MOF. The development of postoperative thrombocytosis is associated with a high risk of thromboembolic complications. PC provides a simple marker of outcome in patients diagnosed with and undergoing operation for ruptured AAA.

Aged↗