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Experiments on use of an agar-gel method for recovery of migrating Ascaris suum larvae from the liver and lungs of pigs were conducted to obtain fast standardized methods. Subsamples of blended tissues of pig liver and lungs were mixed with agar to a final concentration of 1% agar and the larvae allowed to migrate out of the agar-gel into 0.9% NaCl at 38°C. The results showed that within 3 h more than 88% of the recoverable larvae migrated out of the liver agar-gel and more than 83% of the obtained larvae migrated out of the lung agar-gel. The larvae were subsequently available in a very clean suspension which reduced the sample counting time. Blending the liver for 60 sec in a commercial blender showed significantly higher larvae recovery than blending for 30 sec. Addition of gentamycin to reduce bacterial growth during incubation, glucose to increase larval motility during migration or ice to increase sedimentation of migrated larvae did not influence larvae recovery significantly.

In order to monitor the early phases of the development of Ascaris suum from domestic pigs, third-stage larvae, retrieved from the liver and the lungs, were studied by analyzing worm growth and length increase of individual transverse annuli in the cuticle. Material for study using light and scanning electron microscopy was obtained from experimental infections. The results show that the third-stage larva (not the second-stage) after emergence from the egg grows continuously, without an ecdysis in the liver. During growth, each annulus is split into a complex of 2 subannuli, each of which attains a bimodal appearance and is a prominent feature during a late phase of the third-stage larva. The results suggest that the first 2 molts occur inside the egg, a synapomorphic feature of the Ascaridoidea. The third-stage larvae of ascaridoids, with some functional similarities of the dauer-larva stage of Caenorhabditis sp., facilitate transmission of these parasitic worms to the digestive tract of the vertebrate final host (utilizing the tracheal route in A. suum), where the third and the fourth molts take place.

For studying the morphogenesis of the adult stage of Ascaris suum, worms were obtained from experimentally infected domestic pigs. Structural and morphometric features of A. suum are analyzed by light and scanning electron microscopy. It was shown that the increase in length of the worm from days 35 to 56 is based on a region-specific lengthening of individual transverse annuli in the cuticle. An increased worm size also results in an increased diameter of different cuticular sense organs. It is shown that a pair of lateral midbody papillae, the centrids, are prominent sensilla in the adult male and female worm. The centrids have an asymmetric placement, the right centrid being more anterior on the worm than the left.

The difficulties in experimentally establishing patent intestinal infections with the pig large roundworm Ascaris suum make transfer of adult or larval stages a potentially important method of inducing this infection. Adult worms and 10-day-old larvae were transferred by stomach tube to untreated pigs and pigs treated with the gastric acid pump inhibitor omeprazole, as well as surgically directly into the small intestine of pigs. Transfer of adult worms resulted in patent infections with comparable worm survival rates in all 3 recipient groups but with a nonsignificant decrease in egg production after transfer to untreated pigs. Thus, it is possible with oral transfer of adult worms to achieve infections with more or less known numbers and sexes of the parasites, as well as producing patent infections in hosts that have never experienced a hepato-tracheal migration. Whereas the orally transferred 10-day-old L3/L4 larvae did not establish well, surgical transfer of larvae to helminth-naive recipient pigs resulted in high recovery rates 1 wk after transfer in 3 out of 5 pigs.

This study was undertaken to determine whether anthelmintic-resistant Oesophagostomum spp. populations occur in Danish swine herds. A controlled field trial on selected sow herds suggested resistance to pyrantel citrate in a herd where faecal egg count depression in response to treatment was only 28.3%. This was confirmed by subsequent experimental infection of pigs where the suspected resistant Oesophagostomum isolate was compared with a susceptible worm isolate. After treatment with the recommended dose of the drug, worm burdens of the suspected isolate were only reduced by 42.6% (p greater than 0.05) in contrast to the susceptible isolate, which was reduced by 94.6% (p less than 0.01). Differential counts of the resistant isolate suggested that O. dentatum might be more resistant than O. quadrispinulatum. The resistant isolate originated from a herd, where the anthelmintic had been administered four times a year over a period of 7 years. The potential for development of anthelmintic resistance in Oesophagostomum spp. under management practices in our country is discussed in the light of the current views on predisposing factors.

Roepstorff A. and Andreassen J. 1982. Course of heavy primary infections and earlier immunologically mediated rejection of secondary infections of Hymenolepis diminuta in mice. International Journal for Parasitology 12 : 23–28. The worms of heavy (50–100 worms) primary Hymenolepis diminuta infections in inbred C57-mice were 1–2 mm long when growth ceased about day 4. Thereafter the mean length decreased by shrinkage and/or ‘decollation’, the worms moved backwards in the small intestine and were rejected from day 6 to day 10. Heavy secondary infections given 14 days after a heavy primary infection were severely stunted (0.2–0.3 mm) but normally situated in the intestine on day 2 and nearly all were rejected by day 4. Even when the time between the primary and secondary infections was increased to 21 or 42 days, therecovery, position and length of the secondary worms were significantly different from primary infections. These results show that an immunologically mediated memory was involved, and that functional antigens can be released from the scolex and/or the neck alone.

During 1982-1984 the occurrence of helminths in 66 sow herds was determined by examining faecal samples from swine of different age groups. Ascaris suum was found in 88% of the herds, while Oesophagostomum spp. and Trichuris suis were found in 58 and 23% of the herds, respectively. Strongyloides ransomi and Hyostrongylus rubidus was not identified in any of the herds. The occurrence of both A. suum and Oesophagostomum spp. was strongly related to the age of the animals. A. suum was most frequently found in growing pigs (30% of the fatteners and 25% of the gilts), whereas only 11-19% of the animals of the adult stock were excreting eggs. In contrast the prevalence of Oesophagostomum spp. increased with the age of the hosts, from 10% of the fatteners to 35 and 44% of the sows and boars, respectively. T. suis occurred only very sporadically, with the highest prevalence being 3% in the gilts. In comparison to previous Danish surveys the present mean prevalences of A. suum and Oesophagostomum spp. were low. Extremely low herd prevalences were found among large herds with intensive management and housing. In these herds, the pigs were infected at a later stage in life than pigs in more traditionally managed herds.

This study was undertaken to determine the level of resistance against pyrantel citrate in strains of Oesophagostomum quadrispinulatum and Oesphagostomum dentatum which have previously been found resistant to this anthelmintic. Groups of pigs were artificially infected with batches of infective larvae which were previously found either susceptible or resistant to pyrantel citrate. After treatment with 1, 2 and 4 times the recommended dose (14 mg kg −1 ) of pyrantel citrate, the resistant O. quadrispinulatum population was reduced by 51.0, 76.2 and 86.1%, and O. dentatum by 41.2, 47.9 and 78.5%. The results indicated that O. dentatum was slightly more resistant ( P O. quadrispinulatum to pyrantel citrate. Treatment of the susceptible worms with 1 and 2 times the recommended dose caused a reduction in worm numbers by 61.0 and 99.4%, respectively.

Nine groups of 5 pigs were inoculated with Ascaris suum eggs on day 0. Groups 1, 2, and 3 were inoculated with 100 eggs, groups 4, 5, and 6 with 1,000 eggs, and groups 7, 8, and 9 with 10,000 eggs. On day 3, groups 1, 4, and 7 were slaughtered, on day 7 groups 2, 5, and 8, and on day 10 groups 3, 6, and 9. The liver (days 3 and 7) and lungs (days 3, 7, and 10) were removed and 2, 25% samples of both organs were collected. Larvae were recovered from 1 sample by the Baermann method and from the other by an agar-gel method. Overall there were no significant differences in the liver larval recovery between the 2 methods. The use of the agar-gel method resulted in a very clean suspension of larvae and thereby reduced the sample counting time by a factor of 5-10 compared to the Baermann method. With both methods larval recovery from the lungs resulted in a clean larval suspension that was easy to count, and there were overall no significant differences between the 2 methods, although there was a tendency toward the Baermann method recovering more larvae from the lungs than the agar-gel method. The tissue sample dry weight did not significantly influence larval recovery by the agar-gel method, and the time interval from slaughtering to start of incubation on day 3 (interval 51-92 min), day 7 (interval 37-114 min), and day 10 (interval 50-129 min) had no significant effect on recovery by either method.

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.

The aim of the present study was to compare the effect of mixed grazing (MI) by sows and heifers with alternate grazing (AL) or grazing heifers (HN) and sows (SN) alone on animal weight gain, sward structure, herbage quality and composition, and selection during grazing. Mixed or alternate grazing consistently improved the weight gain in both heifers and sows, compared with grazing one species alone, but the positive effect was statistically significant only for heifers. The herbage quality of the MI and AL systems was better compared with the SN system, but not clearly better compared with the HN system. The total animal weight gain (heifers+sows) and estimated herbage intake per hectare were also higher in the MI and AL systems compared with SN and HN systems. The sows grazed selectively as they preferred clover rather than grass and grass leaves rather than grass stem. Only few turnovers of the sward by the sows were observed. Animal behaviour was not systematically surveyed, but no adverse behaviour was observed between the two animal species. Herbage quality, proportion of rejected herbage and the load of gastro-intestinal nematodes in heifers could have positively influenced animal weight gain per day and hectare in the MI and AL systems in this study.

A preliminary epidemiological survey indicated an association between Ascaris infections in Danish patients and contact with pigs or pig manure. In the present study, we compared Ascaris worms collected from humans and Ascaris worms collected from pigs by amplified fragment length polymorphism (AFLP) analysis, a technique for whole-genome fingerprinting, and by PCR-linked restricted fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer region of nuclear rDNA. The AFLP data were analyzed by distance- and model-based clustering methods. These results assigned Ascaris worms from Danish patients to a cluster different from that for worms from humans in other geographic areas. In contrast, worms from humans and pigs in Denmark were assigned to the same cluster. These results were supported by the PCR-RFLP results. Thus, all of the examined Danish patients had acquired Ascaris infections from domestic pigs; ascariasis may therefore be considered a zoonotic disease in Denmark.

Summary A plentity of parasites of great diversity is the rule for all animals in nature. A successful parasite has to be transmitted from one host to the next and this transmission is often the weakest point in the life cycle, as the parasites depend on the surrounding environment for days to months to become infective either as free-living stages or within intermediate hosts. For domestic animals, housing and other factors characterizing the production system thus have a great impact on transmission, the ectoparasites being an exception due to their transmission by physical contact between host animals. In the present paper, the effects of production systems on parasitic infections are discussed with focus on pigs. During the last century pigs have moved from traditional husbandry systems with poor hygiene and access to outdoor areas towards highly intensive, exclusively indoor industries, a process which has gradually reduced the number of endoparasite species. Furthermore, ectoparasitic arthropods are easily eradicated by drug treatment in modern pig enterprises. It is thus only a small number of protozoan parasites that are common across farms. At present, the trend of decreasing parasitism is for the first time reversed. Organic pigs or other free-range pigs make up the best and most extreme example, and these pigs may harbour many more parasites than conventional pigs. Only a small minority of domestic pigs, however, live in organic/freerange herds. It may therefore be more important in the future that conventional pig herds are also changing their housing system due to animal welfare issues; straw bedding is being reintroduced, the pregnant sows are untethered to become free-moving, and facilities may include water sprinkling devices which will increase the humidity and thereby the survival of transmission stages. The future challenge of domestic pigs may therefore, for the first time, be to control an increasing parasite load.