Biomedical subjects

H Bjørn

Publications and source records attributed to H Bjørn.

At least 37 records · Page 2Linked to original sources

PubMed1998

Distinguishing Oesophagostomum dentatum from Oesophagostomum quadrispinulatum developmental stages by a single-strand conformation polymorphism method.

At some life-cycle stages, it is impossible to distinguish between the two species of porcine nodular worm, Oesophagostomum dentatum and Oesophagostomum quadrispinulatum, using morphological features. A PCR-based single-strand conformation polymorphism technique was established to overcome this limitation. The rDNA region spanning the second internal transcribed spacer was amplified by PCR from genomic DNA from morphologically well-defined adult worms. The PCR products were then denatured and subjected to electrophoresis in a non-denaturing gel matrix. Single-strand conformation polymorphism analysis of the products generated characteristic and reproducible patterns for each of the two species and allowed their unequivocal delineation. The single-strand conformation polymorphism was also applied effectively to assess the purity of nine laboratory-maintained cultures of infective third-stage larvae believed to be monospecific for O. dentatum or O. quadrispinulatum. The analysis showed that all six O. dentatum cultures were indeed monospecific, whereas the three cultures believed to be monospecific for O. quadrispinulatum were either a mixture of O. dentatum and O. quadrispinulatum larvae or pure O. dentatum larvae. These findings demonstrated the usefulness of the single-strand conformation polymorphism approach for the routine monitoring of the purity of parasite "lines" and indicated its value for studies on the population biology of porcine nodular worms.

Animals↗

PubMed1998

Evaluation of the infectivity of Trichinella spp. for reptiles (Caiman sclerops).

Experimental inoculation with nine well-characterised Trichinella isolates was performed on caimans (Caiman sclerops) to determine their infectivity for reptiles belonging to the family Crocodilidae. As controls, the same larval batches of Trichinella isolates were inoculated into mice and guinea pigs. It was suggested that Trichinella pseudospiralis was more likely to infect reptiles than encapsulating species, but whereas all Trichinella species established in mice and guinea pigs, the caimans remained negative. The finding that caimans could not be experimentally infected contrasts with a recent report on infections in farmed crocodiles (Crocodylus niloticus).

Alligators and Crocodiles↗

PubMed1998

Survey of anthelmintic resistance on Danish horse farms, using 5 different methods of calculating faecal egg count reduction.

This study reports on the prevalence of anthelmintic resistance in strongyles of horses in Denmark. Of 5 methods used for the calculation of faecal egg count reduction (FECR) the method recommended by the World Association for the Advancement of Veterinary Parasitology, for the detection of resistance in sheep was the most sensitive procedure for detecting resistance. Using this method benzimidazole resistance was detected on 33 of 42 farms (79%) examined. Pyrantel was tested on 15 farms and FECR tests indicate resistance on 3 (30%) farms. On 2 farms on which resistance to pyrantel was detected resistance to benzimidazoles was also detected. On one of 16 farms examined ivermectin resistance was indicated at Day 14 but not at Day 19. On the 15 remaining farms ivermectin was effective. Due to the high prevalence of anthelmintic resistance in Danish horse herds it is recommended that tests of anthelmintic efficacy be conducted routinely to monitor the effectiveness of the strongyle control programmes.

Animals↗

PubMed1997

Worm control practices on sheep farms in Nyandarua District of Kenya.

A questionnaire investigation was used to examine anthelmintic usage and practical worm control for sheep on 50 farms selected randomly in Nyandarua District of Central Kenya. Control of helminths was based primarily on the use of anthelmintics on all 50 farms. On the majority (54%) of these properties, lambs were drenched two times per year. Ewes and rams were drenched three or four times per year on 74% of the farms. Most treatments were given at intervals of approximately 3 months with no specific drenching programmes. Anthelmintic doses for the sheep were based on weights estimated using visual appraisal on 98 and 96% of the properties for lambs and adult sheep, respectively. Only on a small proportion of the farms (22%) was the recommended weight of the heaviest animal used when drenching groups of either lambs or adult sheep. In 1994, the majority (68%) of farmers used levamisole (LEV) in combination with oxyclosanide (OXY) a fasciolicide, 10% used benzimidazoles (BZs), 10% LEV alone and 12% LEV and BZs together. This pattern of anthelmintics use was maintained from 1988 to 1994. Eighty one percent of the farmers had been using only LEV or BZs for three or more consecutive years from 1990 to 1994. The implications of these findings for the development of anthelmintic resistance are discussed.

Animals↗

PubMed1997

Rapid PCR-based delineation of the porcine nodular worms, Oesophagostomum dentatum and O. quadrispinulatum.

At some stages of development, it is impossible to identify the porcine nodular worms Oesophagostomum dentatum and O. quadrispinulatum to the species level using morphological parameters. A molecular approach utilizing genetic markers in the second internal transcribed spacer (ITS-2) of ribosomal (r) DNA was developed to overcome this limitation. The ITS-2 sequence of each species was determined, and specific oligonucleotide primers were designed to regions of greatest sequence difference between the species. Utilizing these primers, rapid PCR procedures were developed for the specific amplification of DNA of O. dentatum or O. quadrispinulatum, which are now used routinely to monitor the purity of larval cultures and to confirm the identity of larvae derived from the intestine or faeces. The application of specific PCR has major implications for studying the population biology of nodular worms in the pig model.

Animals↗

PubMed1997

Prepatent periods of different Oesophagostomum spp. isolates in experimentally infected pigs.

To define prepatent periods of different Oesophagostomum spp. isolates we carried out two separate experiments, one using two monospecific laboratory isolates and another using laboratory isolates as well as isolates obtained from pig herds having different management systems and with different anthelmintic treatment histories. Pigs were inoculated with 1,000-2,000 infective larvae. Fecal samples were collected daily beginning on days 15 and 16 postinoculation (p.i.). Fecal cultures were set up at different times to yield larvae that could be identified by DNA analyses. All pigs started to excrete eggs on days 18-24 p.i. The mean prepatent period was 20.2 +/- 1.4 days, with no significant difference being observed between species and isolates. Prepatent periods of 17-19 days were found for the monospecific laboratory isolates of O. dentatum and O. quadrispinulatum. These findings conflict with parasitology textbooks; therefore, suggestions as to the possible reasons for the observed short prepatent periods are given.

Animals↗

PubMed1997

Use of random amplified polymorphic DNA-polymerase chain reaction for the definition of genetic markers for species and strains of porcine Oesophagostomum.

Nodular worms are common parasites of pigs, and research has recently started to focus on the biology of these nematodes. However, the methods for delineation of species at immature developmental stages and for differentiation of various lines of the same species remain limited. For differentiation of porcine Oesophagostomum species and strains by genomic fingerprinting, random amplified polymorphic DNA-polymerase chain reaction was performed on DNA derived from 20 larval batches of anthelmintic-susceptible and resistant strains and isolates of these nematodes and 2 ruminant Oesophagostomum spp. Polymorphic DNA markers could be amplified with 9 of the 33 primers tested. In all, 13 markers were species-specific and 6 markers could differentiate between strains or groups of strains. With a combination of the latter, artificially selected anthelmintic-resistant strains and the susceptible mother strain of O. dentatum could be delineated. When single adult worms were compared, considerable variations between strains of the same species and between individuals from the same strain could be detected. The differentiation of Oesophagostomum strains and species at all parasitic stages on the basis of genetic markers could greatly facilitate studies on the biology of these parasites.

Animals↗

PubMed1997

In vitro characterization of lines of Oesophagostomum dentatum selected or not selected for resistance to pyrantel, levamisole and ivermectin.

Lines of Oesophagostomum dentatum artificially selected or not selected for resistance to pyrantel, levamisole and ivermectin were used in this study. From the 10th generation of selection eggs were collected from each line and subjected to an in vitro larval development assay (LDA) and an egg hatch assay (EHPA). Significant differences were observed between an unselected line of O. dentatum and the lines selected for resistance to levamisole or pyrantel in both assays. The LDA was more sensitive than EHPA in detecting anthelmintic resistance in O. dentatum. The results obtained from the LDA confirmed side-resistance between levamisole and morantel/pyrantel. The in vitro tests failed to show significant differences between ivermectin-sensitive and resistant lines.

Animals↗

PubMed1997

An in vivo dose-response study of fenbendazole against Oesophagostomum dentatum and Oesophagostomum quadrispinulatum in pigs.

A dose-response study using fenbendazole (FBZ) was carried out in pigs infected with O. dentatum and O. quadrispinulatum to determine the minimum effective dose rate of the drug. Thirty pigs were randomly divided into 6 groups of 5 pigs and infected with 5000 infective larvae each. The animals were re-infected 5 days before treatment (Day 30 after the first infection) with the same number of larvae. On Day 35 the pigs in groups 1-5 were treated with FBZ at the following dose rates: 2.5 mg kg-1 (i.e. 50% of the registered dose level), 1.0 mg kg-1 (20%), 0.25 mg kg-1 (5%), 0.1 mg kg-1 (2%) and 0.05 mg kg-1 (1%), respectively. Pigs in group 6 served as non-treated controls. Seven days after treatment (Day 42 after infection) the pigs were slaughtered, worms recovered from the large intestine and counted. The species and sex of adult worms was determined. A high faecal egg count reduction (FECR) after treatment was observed in groups 1, 2 and 3 (98%, 88% and 91%, respectively), while in groups 4 and 5 the egg counts were not affected by treatment. The mean worm count reduction was high in groups 1, 2 and 3 (100%, 99.9% and 98.6%, respectively), but declined in groups 4 and 5 (77% and 40%, respectively). FBZ showed a high efficacy against immature worms in groups 1 and 2, while in groups 3, 4 and 5 counts were not reduced. Species differentiation revealed a higher effect of FBZ against O. dentatum than against O. quadrispinulatum. Sex differentiation indicated a slightly higher (not significant) efficacy against females than males in both species. This study demonstrated a high efficacy of FBZ against the nodular worms in pigs, even at 5% of the currently registered dose level.

Animals↗

PubMed1997

A new in vitro assay of benzimidazole activity against adult Oesophagostomum dentatum.

A new in vitro assay of benzimidazole activity against adult Oesophagostomum dentatum is described. The method is based on the ability of O. dentatum to migrate through polyamide nets after exposure to various concentrations of benzimidazole. To determine an appropriate mesh size, control worms and worms exposed to 10 microM oxfendazole for 24 h were allowed to migrate through nets with various mesh sizes (300-500 microns) for up to 1 h. A mesh size of 350 microns and migration periods of 10, 20 and 30 min were selected. Exposure to oxfendazole at 10 microM for 24, 48 and 72 h inhibited the migration in a time-dependent manner. After 72 h of exposure and with a 20-min migration period, the EC50 of oxfendazole for O. dentatum was 0.564 microM. In further studies the activities of albendazole sulphoxide, albendazole, cambendazole, fenbendazole, flubendazole, luxabendazole, mebendazole, oxfendazole, oxibendazole, parbendazole and thiabendazole were compared. The worms were exposed to each drug at two concentrations (0.1 and 3.16 microM) for 72 h. At 3.16 microM there were no significant differences in the activity of the drugs. At 0.1 microM significant differences in activity were found. Albendazole sulphoxide and oxfendazole were poor inhibitors of migration compared with their parent compounds, albendazole and fenbendazole.

Animals↗

PubMed1997

The influence of high- and low-fibre diets on the activity of piperazine against Oesophagostomum spp. in pigs.

An in vivo study evaluated the effect of diet on the efficacy of piperazine against nodular worms of pigs. Twenty pigs, later allocated into five groups, were each infected (and 37 days later re-infected) with 3000 infective larvae of a mixed isolate of Oesophagostomum dentatum and Oesophagostomum quadrispinulatum. Beginning on day 23 post infection (p.i.), pigs in groups 1 and 2 were fed a low-fibre diet consisting of 70% barley flour and 30% protein concentrate, while pigs in groups 3, 4 and 5 were fed a high-fibre diet consisting of 55% barley flour, 21% oat-husk meal and 24% protein concentrate. On day 42 p.i., pigs in groups 1 and 3 were orally dosed with 200 mg piperazine dihydrochloride (Ascarex D, 53%) per kg bodyweight, the recommended dose, while pigs in group 4 were given 100 mg kg-1. Groups 2 and 5 served as non-treated controls for the respective dietary regimens. Eight days after treatment, the pigs were slaughtered and worms recovered from the caecum and large intestine (divided into five sections) and counted. The mean worm count reduction (WCR) in group 1 (full-dose piperazine with low-fibre diet) was 89.8%, while the high-fibre diet in group 3 increased the WCR to 99.4%. In group 4, where the pigs were fed the high-fibre diet and treated with only 100 mg piperazine kg-1, the WCR was 90.9%, identical to the "low fibre" group 1 treated with twice this piperazine dose. There was a zero efficacy recorded against immature worms in all three treated groups. The high-fibre diet improved the efficacy of piperazine against more pathogenic and generally more tolerant O. quadrispinulatum to 99.2% compared with 84.3% at the low-fibre diet.

Animals↗

PubMed1997

Faecal egg count reduction percentage calculations to detect anthelmintic resistance in Oesophagostomum spp. in pigs.

The results of four alternative methods of mean faecal egg count reduction percentage (FECR%) calculations were evaluated and compared using data obtained for Oesophagostomum spp. from ten sow herds. The estimates of FECR% and 95% confidence limits obtained using the four methods were different. However, there were few discrepancies in the final decision as to whether a given herd carried drug resistant isolates or not. The methods that used geometric means were more appropriate than those that used the arithmetic mean as the measure of central tendency for eggs per gram of faeces (EPG) values. The use of geometric mean EPG values in calculations has been criticized from several viewpoints, one of which is that its use reduces the comparability of reports between laboratories. If the geometric mean is to be used as we suggest in FECR% calculations, the appropriate references, number of animals in each group, minimum and maximum EPG values and the factor added to zero EPG counts should be reported in order to improve the comparability. The difficulty in obtaining groups with similar pre-treatment EPG values in field situations suggested the inclusion of pre-treatment EPG values in the calculations as an adjustment procedure. The importance of including a non-treated control group in calculations was demonstrated during this study. Therefore, we suggest the use of geometric mean EPG values, to include pre-treatment EPG values and to include the egg counts from the control group in FECR% calculations. The interpretation of the resulting FECR estimate may be different according to the purpose for which the testing procedure is carried out, e.g. survey in detecting anthelmintic resistance, control field tests, etc.

Animals↗

PubMed1997

Use of an agar-gel technique for large scale application to recover Ascaris suum larvae from intestinal contents of pigs.

Four groups each of 3 pigs were inoculated with Ascaris suum eggs. Pigs in groups 1 and 3 were inoculated with 1000 eggs, and pigs in groups 2 and 4 with 10,000 eggs. On day 10 and 21 post-inoculation (p.i.), respectively, groups 1 + 2 and 3 + 4 were slaughtered, and the contents from the small intestines collected. The contents were mixed with agar to a final concentration of 1% agar and allowed to sediment. The larvae were allowed to migrate from the agar-gel into 38 degrees C 0.9% saline overnight, and were then collected on a sieve (20 microns mesh) and counted. The larvae retained in the agar-gel were counted after pouring the melted agar through a sieve (20 microns mesh). The results showed that more than 97% of the larvae migrated out of the agar-gel and were available for counting in an almost clean suspension. The inoculation dose level did not significantly affect the recovery percentage, neither did the larval stage (10 or 21 days old larvae). The variation in the time interval from slaughtering to start of incubation (interval 57-155 min) did not significantly affect the recovery percentage.

Agar↗

PubMed1996

A questionnaire survey of nematode parasite control practices on goat farms in Denmark.

A questionnaire survey to examine worm control practices on angora and other goat farms in Denmark was undertaken in 1993. Questionnaires were inserted in the July, 1993 issue of the official journal of the angora goat farmers in Denmark (Mohair News) and 72 questionnaires posted directly to other goat farms selected from a list of 150 farms registered with the Goat Breeders Association. Data from 51 angora and 41 other goat farms indicated that anthelmintics were used on more than 80% of the farms. On 51% of the farms, no predetermined drenching programmes were followed. On 72% and 64% of the farms, kids (< 1 year of age) and adult goats (> 1 year old) were drenched 1-3, and two or three times per year, respectively. Only 9% of the farmers used the recommended weight of the heaviest animal in a herd to determine anthelmintic doses for groups of both kids and adult goats. Visual perception which may result in underdosing was used to determine weights for drenching on 41% and 69% of the farms for kids and adult goats, respectively. From 1986 to 1993, Class I anthelmintics (benzimidazoles) were the most commonly used. Anthelmintic classes were not alternated annually on the majority of farms, which would enhance selection for resistance. While the majority of farmers (58%) rotated goats regularly between paddocks, only 21% drenched the goats when being moved. Anthelmintic treatment for newly introduced goats was not carried out on 45% of 55 respondent farms, nine of which had imported stock. This increases the likelihood of introducing resistant worms to the farms.

Administration, Oral↗

PubMed1996

Worm control practices on sheep farms in Denmark and implications for the development of anthelmintic resistance.

A questionnaire survey was undertaken on sheep farms in Denmark to obtain information on sheep management and worm control practices. The questionnaires were inserted in the June and July, 1993 issue of the Danish Sheep Breeders Journal, circulated monthly to approximately 1200 sheep breeders nationwide. A total of 183 (11%) questionnaires were returned. A second questionnaire was posted to 50 of the 183 responding farmers to examine the repeatability of responses to the first questionnaire. The majority (97%) of the 183 farmers used anthelmintics. The mean number of doses per year for lambs (< 12 months old) and adult sheep (> 12 months old) were 1.9 and 2.3, respectively. Only 42% of the farms followed predetermined drenching programmes. Live weights were determined by visual appraisal on 45% and 84% of the farms for lambs and adult sheep, respectively. In calculating anthelmintic doses for groups of lambs and adult sheep, the recommended weights of the heaviest animals were only used on only 18% and 27% of the farms respectively. Benzimidazoles were the most commonly used anthelmintics from 1986 to 1993. Eighty one percent of 94 responding farmers had been using the same class of anthelmintic for 3 or more consecutive years. Information from this study indicated lack of knowledge about worm control strategies, anthelmintic use and the problem of anthelmintic resistance among the majority of Danish sheep farmers. The majority of responses to the questionnaire were repeatable at least to a fair degree except when farmers were asked to recall anthelmintics used in past years.

Administration, Oral↗

PubMed1996

A survey of anthelmintic resistance in nematode parasites of goats in Denmark.

The occurrence of anthelmintic resistance in 15 goat herds in Denmark was investigated using the faecal egg count reduction test (FECRT), egg hatch assay (EHA) for thiabendazole (TBZ) and a microlarval development assay (LDA) for TBZ, levamisole (LEV) and ivermectin (IVM). Resistance to both benzimidazole (BZ) and levamisole (LEV) anthelmintics was detected on six farms, and to both BZs and IVM on one farm. Resistance to BZs was also detected on two farms and to LEV on two farms. Ivermectin resistance was present on one farm. Trichostrongylus and Ostertagia spp. were the predominant nematode species in both pre-treatment and post-treatment faecal cultures. In all nine instances where BZ resistance was detected in the FECRT, the LD50 values for TBZ in the EHA were higher than 0.5 microM TBZ (0.1 microgram TBZ/ml), indicating resistance. LD50 values for TBZ in the LDA were also higher than 0.5 microM where resistance to BZs was detected in the FECRT, except two farms where LD50 values of 0.21 and 0.29 microM TBZ were recorded. LD50 values in the LDA for isolates declared resistant to LEV ranged from 0.78 to 5.62 microM LEV. For IVM, the two resistant isolates had LD50 values of 25 and 68 nM IVM. There were disagreements in the declaration of resistance between methods of calculating faecal egg count reduction percentage (FECR%) based on the arithmetic mean and those where geometric mean EPG is used. Similarly, inclusion of pre-treatment EPG or control group EPG in the calculation of FECR% influenced declaration of resistance.

Animal Husbandry↗

PubMed1996

Use of two in vitro methods for the detection of benzimidazole resistance in equine small strongyles (Cyathostoma spp.).

Ten stables were included in a study to evaluate two in vitro methods for the detection of anthelmintic resistance in cyathostomes by comparing a faecal egg count reduction test (FECRT) to a larval development assay (LDA) and an egg hatch assay (EHA). The LDA was used in seven stables and EHA in the last three. On the basis of FECR values, resistance to benzimidazoles was detected in eight of the ten small strongyle populations. Resistance to pyrantel pamoate and ivermectin was not detected. The mean concentrations that inhibited hatching in 50% of the eggs (EC50), using thiabendazole (TBZ) in an EHA, were 1.02 microM in resistant populations and 0.37 microM in susceptible or suspected resistant ones. In the LDA, TBZ concentrations preventing 50% development by first/second stage larvae to the third larval stage (LC50) were 3.8 times lower than EC50 values in resistant worm populations. Mean LC50 for morantel, levamisol, ivermectin monosaccharide and avermectin-B2 in small strongyle populations susceptible to pyrantel and ivermectin was 8.0 microM, 0.99 microM, 15.6 nM and 2.93 nM, respectively. Data on pyrantel and ivermectin resistant populations could not be obtained as no resistant populations were detected. This study concludes that in vitro tests may be useful as a supplement to FECRT for the detection of benzimidazole resistance in cyathostomes, even if reference populations to be used as controls in the assays were not available. It is suggested that EC50 values for TBZ > 0.6 microM in LDA and > 0.5 microM in EHA strongly indicate benzimidazole resistance in equine small strongyles.

Animals↗

PubMed1996

Efficacies of different doses of ivermectin against male, female and L4 Oesophagostomum dentatum in pigs.

Efficacies of ivermectin against larval stages and adult males and females of Oesophagostomum dentatum were investigated in two slaughter assays. In Experiment A, 20 pigs were each infected with 6000 third-stage larvae on Day 0 and Day 24. Pigs were ivermectin treated on Day 28 at dose rates of 0, 75, 150, and 300 micrograms kg-1 bodyweight (bw) and slaughtered 6 days after treatment. In Experiment B, 20 pigs each received 6000 third-stage larvae and were treated 35 days after infection at dose rates of 0, 150, 300 and 600 micrograms kg-1 bw. Pigs were slaughtered 14 days after treatment. In Experiment A, the adult worm burden was reduced by 69.1% at a dose rate of 300 micrograms kg-1 bw and the larval burden was reduced by 68.7 and 90.9% at 150 and 300 micrograms kg-1 bw, respectively. In Experiment B, the adult worm burden was reduced by 88.8, 96.2 and 99.6% at dose rates of 150, 300 and 600 micrograms kg-1 bw, respectively. In the control group of Experiment A, the mean proportion of females among adults worms was 57.6%, but this decreased to 19.7% after ivermectin treatment at 300 micrograms kg-1 bw. In Experiment B, at 300 micrograms kg-1 bw, this proportion was reduced from 46.0% to 0.8%. The fecundity of female worms was reduced at dose rates of 150 and 300 micrograms kg-1 bw in Experiment A, but not in Experiment B. It is concluded that in O. dentatum, ivermectin not only reduces the egg output of female worms, but also is more effective against female than male worms.

Animals↗