Ecology and viability of eggs of the pig round worm (Ascaris suum) – on-farm and laboratory studies

Summary

Ascaris suum is a highly prevalent parasitic helminth in pig production systems worldwide. In most industrialized countries production systems are highly intensive and fully in-doors (low prevalence of parasites) but there is a growing market for pigs produced out-door or under organic pig farming conditions (high prevalence of parasites). In organic pig production there is a number of factors related to housing and management practices that predispose for A. suum infections. These practices include restricted use of anthelmintics, late weaning of piglets (after min seven weeks of age) and access to outdoor runs. Provision of bedding material, which might be conducive for development and survival of free-living stages of helminths, is mandatory in organic production systems but the amount and type of bedding material vary between farm and housing systems.
The differences in A. suum egg development in different housing systems have been poorly described. Biodegradation of organic matter in deep litter housing systems produces physico-chemical conditions which may affect the development and survival of A. suum eggs, but little is known about such effects. Understanding the ecology and transmission dynamics of A. suum may help prevent infections in organic farming. Pig slurry is used to fertilize crops in organic as well as conventional farming and may be treated to inactivate a variety of pathogens present in it before application. To achieve adequate pathogen inactivation, slurry may need to be stored for around one year which may not be ideal logistically and economically. Chemical treatment of slurry may reduce storage time needed to adequately inactivate pathogens. The eggs of A. suum are commonly used as a conservative indicator in estimating pathogen inactivation during slurry treatment as they are more resistant to environmental stress than bacterial and viral pathogens. The eggs of the poultry ascarid, Ascaridia galli are ubiquitous, resistant and available even in places where the eggs of A. suum cannot be found, e.g., areas without pig keeping, but little is known about the suitability of A. galli eggs as a conservative hygiene indicator. Currently, viability of A. suum eggs is estimated by their ability to embryonate which takes up to six weeks depending on temperature. There is a need to develop more rapid viability tests and in addition, embryonation cannot be used as a viability criterion for already embryonated eggs. A quantitative egg hatch test may thus be helpful for already embryonated eggs. The present Ph.D. project therefore addressed the above issues by investigating in six separate studies, the ecology and transmission of A. suum eggs in organic pig farms, including determination of conditions under which A. suum eggs are inactivated.