Ascaris suum: occurrence, epidemiology and control in Saskatchewan pigs

Ascaris suum Goeze, 1782, the large roundworm, is a common parasite of pigs (Sus scrofa domestica Linnaeus, 1758) throughout the world. It is an important cause of economic loss to the pig industry and control of this parasite is difficult. In addition, A. suum is of zoonotic importance and therefore raises concerns related to manure disposal. There are reports describing the epidemiology of A. suum from other areas of the world but little is known regarding the situation in Saskatchewan. This thesis project examined aspects of the occurrence, epidemiology and control of this parasite in Saskatchewan. The project comprised four inter-related studies. First, two surveys investigating the prevalence and intensity of A. suum were conducted at a Saskatchewan abattoir examining livers and intestines of market pigs. Fifty-three percent of animals examined in these surveys displayed evidence of ascarid infection (adult parasites, hepatic lesions or both). Second, a postal survey to determine anthelmintic use in Saskatchewan during 1995 was sent to 5 80 pig producers selected based on annual pig production. Response rate was 33% and represented 20% of the province's annual market pig output. Of all respondents, 76% treated some animals. Sows were treated most commonly (90%) followed by weanlings (86%), boars (75%) and growers (67%). Determination of a parasite problem was not based on quantitative measures of infection and treatment patterns did not appear to be based on known epidemiological information. Third, a study investigated the effects of seasonal temperature variations on the rate of development to infectivity of A. suum eggs in a Saskatchewan barn. Eggs from experimental egg cultures placed in the barn each month (July, 1997 to July, 1998) were monitored weekly for development to the infective larval stage assessed by bioassay. Development to the infective stage took from three to four weeks in summer to as long as 11-12 weeks in winter. Lastly, two groups of pigs were monitored from weaning to market by regular fecal examinations for A. suum infection. No pigs became definitively patent during the study but 92% of animals examined post-mortem had liver lesions consistent with ascarid larval migration