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.

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.

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.

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.

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.

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.

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.

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.

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.

The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs

The pharmacokinetic disposition of pyrantel after intravenous (i.v.) and oral (p.o.) administration as the citrate and p.o. administration as the pamoate salt was determined in pigs. Following i.v. administration pyrantel was quickly cleared from the bloodstream, exhibiting a terminal half-life of 1.75 +/- 0.19 h and a residence time (MRT) of 2.54 +/- 0.27 h. After p.o. administration as the citrate salt, the absorption time (MAT) of pyrantel was 2.38 +/- 0.25 h and although significant quantities of pyrantel were absorbed (mean bioavailability of 41%) the rapid clearance resulted in a MRT of only 4.92 +/- 0.36 h. By comparison, the significantly extended MAT of the less soluble pamoate salt resulted in reduced circulating concentrations and a significantly lower mean bioavailability of 16%. The poor efficacy of pyrantel citrate against nematodes inhabiting the large intestine of pigs is therefore suggested to result from insufficient quantities of drug passaging to the site of infection. When tested against pyrantel-resistant adult Oesophagostomum dentatum the mean efficacy of pyrantel citrate was only 23%, whereas the efficacy of the lesser absorbed pyrantel pamoate was 75%. These results indicate that for maximum activity pyrantel should be administered to pigs as the pamoate salt.

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.

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.

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.

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.

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.

A questionnaire investigation on factors of importance for the development of anthelmintic resistance of nematodes in sow herds in Denmark

A questionnaire survey on the use of anthelmintics and presence of other potential risk factors for the development of anthelmintic resistance of nematodes in 136 Danish sow herds was carried out between November 1992-February 1993. Twenty one veterinarians who specialize in diseases of pigs administered the questionnaire in personal interviews during their regular visits to the respective pig farmers. In the study population, 91% of the farmers currently treated their sows with anthelmintics, while only 38% and 14% treated their weaners and fatteners, respectively. Most respondents treated their sows either before or after farrowing (40%) or once every 6 months (27%). Benzimidazole and pro-benzimidazole (Class I) anthelmintics were the most used in sows by the farmers (39%, 47%, 49%, 50%, 46%, and 47% during the years 1987, 1988, 1989, 1990, 1991 and 1992, respectively). When sows were treated, fenbendazole was the most frequently used anthelmintic during the period 1987-1992 (30%-39%). The proportion of farmers that used Class II (pyrantel and levamisole) or Class III (ivermectin and piperazine) anthelmintics during the year 1992 were 25% and 13%, respectively. Of the 70 farmers who used anthelmintics from either Class I, II or III during the study period, 44 farmers always used the same class of drugs. Eight herd owners among those 44, had changed the pharmaceutical product within the same class. Sixty nine percent of the farmers did not weight the sows, but used visual appraisal of average body.

Recovery of Oesophagostomum dentatum from pigs by isolation of parasites migrating from large intestinal contents embedded in agar-gel

Four groups with three pigs in each group were inoculated with Oesophagostomum dentatum larvae (L3 larvae). Groups 1 and 3 were inoculated with 20,000 larvae, and Groups 2 and 4 with 200,000 larvae. On Days 11 and 34, respectively, Groups 1 and 2 and Groups 3 and 4 were slaughtered, and the contents from the large intestines collected. Subsamples of intestinal contents were mixed with agar to a final concentration of 1% agar and allowed to set. The worms were allowed to migrate from the agar-gel into 38 degrees C 0.9% saline overnight. Then the worms were collected on a sieve (38 microns mesh) and counted. The worms retained in the agar-gel were counted after pouring the melted agar through a sieve (38 microns mesh). The results showed that more than 95% of the worms migrated out of the agar-gel, and subsequently were available for counting in an almost clean suspension. Additionally the method yielded a high worm recovery; all stages were recovered. The recovery percentage was not significantly affected by either the dose of parasites or the time interval from slaughtering to start of incubation (37-128 min).

A possible influence of diet composition on the establishment of nematodes in the pig

Two groups of 20 pigs weighing approx. 26 kg were offered either ground barley plus protein supplement (GBP) or commercial pelleted feed (CPF), two diets consisting of nearly the same amounts of carbohydrates, proteins and micronutrients. All pigs were experimentally infected with 600 infective Ascaris suum eggs and 6000 infective Oesophagostomum spp. larvae and followed coprologically for approx. 12 weeks post infection, whereafter they were slaughtered. The number of Oesophagostomum spp. and A. suum eggs was significantly higher in the GBP-fed pigs compared with the CPF-fed pigs (P < 0.0001). The mean worm burden of adult Oesophagostomum spp. was higher in the GBP-pigs than in the CPF-pigs (P < 0.05), while the mean worm burden of adult A. suum in the two groups was not significantly different. The results indicate that two diets, both fulfilling the requirements of modern pig raising, may result in different establishment rates of natural adult gastrointestinal helminths in swine.

The efficacy of ivermectin against nodular worms of pigs: the response to treatment using three different dose levels against Oesophagostomum dentatum and Oesophagostomum quadrispinulatum

Anthelmintic efficacies of 3 different doses of ivermectin (IVM) were evaluated in 3 isolates of nodular worms in pigs. An isolate of Oesophagostomum quadrispinulatum (OQ) was recently obtained from a commercial farm where poor efficacy of IVM at the recommended dose (300 micrograms.kg-1 body weight) was detected. On this farm, IVM had been used for treatment of sows twice yearly for 6 years. Two other isolates, an O. dentatum (OD) and a mixed Oesophagostomum dentatum and Oesophagostomum quadrispinulatum isolate (ODQ) were obtained from a farm where anthelmintics had never been used. Efficacies of IVM against adult worms of the OQ-isolate at dose rates of 150, 300 and 600 micrograms.kg-1 body weight ranged from 40.5-78.6%. Efficacies against larval stages (L3 and L4) were superior. Efficacies against the OD-isolate were 88.7, 96.1 and 99.6%, respectively. In the ODQ-isolate the efficacies of IVM against adult stages furnished similar results. In conclusion, the efficacy of IVM against O. dentatum was high but against both isolates of O. quadrispinulatum poorer. This suggests that IVM is intrinsically less effective against O. quadrispinulatum and therefore not indicative of acquisition of anthelmintic resistance in the OQ-isolate.

Experimental Oesophagostomum dentatum infections in the pig: worm populations resulting from trickle infections with three dose levels of larvae

This paper describes the worm populations in pigs experimentally infected by trickle infections with different dose levels of the nodular worm, Oesophagostomum dentatum. Four groups each of 20 helminth naïve pigs, 10-12 weeks old, were inoculated with 0 (group 1), 100 (group 2), 1000 (group 3), or 10,000 (group 4) infective larvae twice weekly, and the pigs were killed after 10-13 weeks. No overt clinical signs were observed, and only group 4 had slightly lower food conversion rate (P < 0.05) than the controls. Faecal egg counts revealed that the nodular worms in pigs of groups 2 and 3 had a short prepatent period (3-4 1/2 weeks) and a fairly stable egg output, while the worms in the pigs of group 4 had prepatent periods of 3-10 weeks and low, unstable egg excretion. The mean worm burdens increased with the dose rate (group 2: 929 worms; group 3: 7467 worms; group 4: 19,847 worms), but detailed analyses of the worm populations from 10 pigs from each of the infected groups revealed a clear dose-dependency in worm recovery, percentage adult worms, worm lengths and female fecundity, as all these measures declined significantly with increasing dose level. The adult worms seemed to be shorter and less fertile when they were located posteriorly to their predilection site, and especially in group 4 many stunted infertile adults measuring only 2-5 mm were found in the posterior half of the colon, but there were no indications of worm expulsion. Superimposed on the main experiment was a cohort study in which 4 pigs of group 3 were given a single dose of 1000 pyrantel resistant larvae at day 56 (all other larvae were pyrantel sensitive), treated with 28 mg pyrantel per kg body weight at day 85 and killed at day 90. Appropriate control groups were included. The mean establishment of the cohort was similar to previously uninfected controls, but between-animal variation was much higher in the trickle infected group.

Experimental transfer of adult Oesophagostomum dentatum from donor to helminth naive recipient pigs: a methodological study

This study was carried out to compare potential methods of transplanting adult Oesophagostomum dentatum from experimentally infected donor pigs to helminth naive recipient pigs. The following methods were each tested in five pigs: A. Transfer of worms by stomach tube to the gastric ventricle of pigs per os pretreated with 0.5 mg/kg cisapride to increase gastrointestinal peristalsis; B. Transfer by stomach tube to the gastric ventricle of pigs per os pre-treated with cisapride (0.5 mg/kg) and omeprazol 20 mg which blocks hydrochloric acid secretion; C. Surgical transfer of worms to caecum of pigs. Worms for transplantation to pigs were obtained after slaughter of experimentally infected donor pigs and following isolation from the contents of the large intestine, using an agar gel migration technique. A mean of 1054 nematodes were transferred into each recipient pig within 2 hours. Procedures A and B resulted in establishment rates corresponding to only 0.5% and 7.6% of the transferred worms. In contrast, surgical transfer allowed 74.2% of the transplanted worms to be established. In all groups the transplanted worms migrated to the normal predilection site, i.e. the middle part of the large intestine. More female than male worms established in all groups. It was concluded from this study that surgical transfer was the most reliable of the methods tested for experimental establishment of adult O. dentatum in helminth naive pigs.

A study on the transmission of Oesophagostomum dentatum and Hyostrongylus rubidus among outdoor reared pigs in Denmark

This study was carried out to obtain basic information on the transmission of Oesophagostomum dentatum and Hyostrongylus rubidus in outdoor reared pigs in Denmark. Eighteen 10 weeks old worm-free pigs were allocated into 3 groups of 6 pigs each. In May, all pigs were turned out on the same parasitologically naive pasture, and after 2 weeks the pigs in groups 2 and 3 were experimentally infected with 10,800 O. dentatum and 8,700 H. rubidus infective larvae, respectively. Pigs in group 1 served as non-infected controls. All pigs were reared together on the experimental pasture for further 134 days until slaughter in October. Strongyle egg counts, differentiation of infective larvae at species level, serum pepsinogen, and herbage larval infectivity were monitored at regular intervals throughout. Both strongyle species established in the originally parasite-free pigs (group 1) and cross infections were established in group 2 and 3. The pigs were exposed to steadily increasing herbage infectivity of both species of strongyles. At the end of the experiment, geometric mean worm burdens of O. dentatum in groups 1, 2 and 3 were 1202, 6136 and 1431 respectively, the burden in group 2 being significantly higher (p < 0.05) than that of the 2 other groups. The geometric mean worm burdens of H. rubidus in groups 1, 2 and 3 were 4907, 3679 and 5246 respectively, showing no significant differences between groups.

The effect of two types of diet on populations of Ascaris suum and Oesophagostomum dentatum in experimentally infected pigs

This investigation compared the effect of two common types of diet on worm burdens and faecal egg counts of pigs inoculated with Ascaris suum and Oesophagostomum dentatum. The diets were both considered nutritionally sufficient for pigs of this age, and gave high and comparable growth rates. Pigs were inoculated with both worm species at 14 weeks of age and slaughtered 3 or 12 weeks later. At 3 weeks, A. suum larvae were numerous in the small intestine of pigs fed ground barley plus protein supplement, but were not detected from pigs fed a commercial full-constituent pelleted feed. At 12 weeks, however, average adult worm burdens were low and similar in both groups. At both slaughter times, O. dentatum worm burdens were significantly higher in pigs fed barley plus protein than in pigs given commercial feed, particularly for female worms, and the commercial diet led to worms being located further along the large intestine, and to reduced worm fecundity. The chemical composition of large intestinal contents differed significantly between pigs fed the two diets.

Development of the free-living stages of Hyostrongylus rubidus and Oesophagostomum spp. at different temperatures and humidities

Faeces containing a mixture of Hyostrongylus rubidus and Oesophagostomum spp. eggs were mixed with vermiculite and water and set up at combinations of different relative humidities (65.5%, 79.5% 90.0%, and 100%) and temperatures (5 degrees C, 10 degrees C, 15 degrees C, 20 degrees C, and 25 degrees C) in order to study the rate of egg hatching and larval development. The study established that the development from egg to infective larva showed similar patterns for the two parasites. Optimum development and survival was in the temperature range from 15 degrees C to 20 degrees C and at humidities from 79.5 to 95.5%.