Transmission and control of the parasite Ascaris suum (large round worm) in Danish organic farms

Summary

Ascaris suum is the most common intestinal worm in pigs irrespective of production system. However, organic farms which promote animal welfare (e.g. by providing pastures and bedding material) may further promote survival of the eggs through which the parasite is dispersed to new hosts. The parasite has a negative effect on production results and possibly impairs vaccines. A one year survey of 5 Danish organic farms therefore aimed at mapping the occurrence of parasite eggs in the farm environment, supplemented with laboratory and field studies, including serial necropsies of different age groups of pigs from 2 farms to monitor infection levels. The combined results showed that eggs were present on farrowing and weaning pastures, ensuring continuous exposure to the parasite outdoors. The farms did not have enough land for effective long-term rotation schemes to allow eggs to die and thus disappear naturally, as they can live for at least 9 years in the soil. Consequently, young infected pigs brought the parasite with them into the stables. Here, large numbers of eggs accumulated in the bedding material, but the majority of eggs died as the result of high temperatures and ammonia levels due to bacterial degradation of fecal matter. Nevertheless, infective eggs were present in the bedding material and pigs continued to be exposed and become infected in weaner/starter and fattening pig pens up to slaughter (22 weeks old). As the eggs may need several weeks or months to develop in the environment depending on season, some of the infective eggs in the pens may have been deposited by previous groups of pigs, as not all pens were cleaned between batches of pigs. In conclusion, exposure to A. suum is currently difficult to prevent outdoors in Denmark. The best approach to reduce overall exposure is thus to improve cleaning and disinfection procedures indoors and to compost and store manure/slurry sufficiently to inactivate eggs.