One of the oldest health problems in pigs has staged a revival, according to reports by veterinary investigators. Their surveys have found substantial evidence of worm parasites in virtually all modern production systems, although most clearly associated with bedded pens and extensive units.

"Despite an increasing emphasis on technology and health management in European pig herds, in particular through the use of anthelmintic programmes, pigs are still infested by many endoparasites," said French researchers at the 2006 congress of the International Pig Veterinary Society. It is an enduring difficulty, they noted. An unpublished study in the Brittany region of northern France in 1999 had found pigs infested with one or several types of intestinal worm helminths on half of 47 indoor breeding herds investigated and the infestations had occurred regardless of whether or not the herd was following a deworming programme.

Describing a more recent survey conducted in 2005, involving 33 units in western France, the same team observed a marked difference in the prevalence of Oesophagostomum nodular worms between indoor and outdoor herds. Prevalence, as measured by checking samples of faeces from gestating and lactating sows, ranged from 100% for the extensive units down to under 17% where the sows were housed indoors. What is more, in both outdoor and indoor cases at least half of sows tested on units where infestation was present proved to be infected. But prevalence was most often nil when sows were housed on fully slatted floors during gestation and lactation and also received regular anthelmintic treatment.

Monitoring may look only at one worm species, but co-infection seems to be common. Certainly that was true on these French farms. Faecal analysis demonstrated the Oesphagostomum to be co-existing with the coccidiosis parasite Isospora and the Trichuris whipworm, as well as the Strongyloides threadworm in 3 instances.

A report from Greece to the IPVS congress looked specifically at coccidia in suckling piglets. Contamination was found to vary remarkably between untreated litters on a farm when the presence of the Isospora had previously been confirmed. This might be related to pen factors such as efficiency of cleaning and disinfection, said the investigators. All pens in which trial litters were located had been pressure-cleaned using cold water and left empty for a week to dry before re-stocking. But one piglet became infected, possibly due to insufficient cleaning and disinfection measures for its pen, and passed the infection to most of its littermates.

German research described to the same congress also referred to coccidiosis in suckling piglets and declared it to be underestimated in Germany as a parasitic infection in farrowing houses. Its prevalence was suggested to vary from farm to farm. On 6 herds examined, prevalence ranged from 10% up to 60% despite a level of hygiene assessed as at least moderate and ranging to good and very good on the individual units.

Still the most well-known internationally of the internal parasites is the Ascaris roundworm. The IPVS meeting heard about work in Italy showing an extraordinary rate of infection on a farrow-to-finish unit even today. Checks in the finishing house revealed positive faecal samples from up to 40% of the pigs, even though the sites had been stocked with piglets thought to originate from an Ascaris-free farrowing unit.

Tracing the route of infection took the researchers back to the pattern of excretion of parasite eggs. The unit was a multi-site enterprise in which farrowing, weaning and early growing took place in 3 different areas before the transfer of the pigs to a single unit for finishing. Results suggested that pigs were already harbouring an infection on entry to the finishing site, having ingested eggs containing infective larvae while still at their site of origin. Positive faecal samples at 23 days after arrival at the finishing place supported this hypothesis. The known life cycle of ascarids indicates a period of 6-8 weeks for larvae to emerge from the infective eggs, migrate within the host animal, return to the intestine and establish a clinical infection in which more eggs are shed.

Pig-to-pig infection inevitably follows when this occurs. The Italian team also detected positive faecal samples from pigs at 43-50 days from entry that could represent either the animals' introduction with a pre-patent infection or their exposure to eggs immediately upon entrance to the site. Further evidence of infections at 93 days from entry, particularly with rather high egg values, were thought probably due to exposure to infection after entry. On the enterprise studied, a single administration of an anti-ascarid dewormer to sows before farrowing did not protect finishing pigs from infection. So a follow-up treatment of pigs before entering the finishing unit was proposed, combined with hygiene measures.

Danish studies added more information in that respect by reporting that anthelmintic treatment twice during the finishing period prevented Ascaris egg excretion, but did not reduce the occurrence of liver white spots at slaughter. To improve performance significantly, said the research group in Denmark, repeated treatments over several consecutive rounds may be necessary.