Ascaris suum is the most common intestinal nematode of pigs. Adults in the intestine reduce feed efficiency, and heavy infections cause emaciation. Larval migration incites inflammation in the liver and lungs.
Cryptosporidium sp is a coccidium that attaches to the mucosal epithelium of the intestine of pigs ≥10 days old. It causes villous atrophy in the lower small intestine. Malabsorption and diarrhea may result.
Eimeria spp are common in pigs, but overt disease is seldom seen. Heavy infections may cause significant enterocolitis in young growing pigs.
Hyostrongylus rubidus is the common stomach worm found in pasture-raised pigs. It usually causes little harm.
Isospora suis is a common and important cause of coccidiosis in piglets 6 days to 3 wk old. Infection causes necrosis and villous atrophy of the ileum and jejunum. Secondary bacterial infection of the injured intestinal mucosa is common. Mortality often is 20%–25%, and many pigs are stunted. Diagnosis can be based on identification of immature coccidial forms in the intestinal mucosa by direct mucosal smear (Giemsa stain) or by histologic examination of the affected intestine. Successful prevention most commonly depends on thorough cleaning of farrowing facilities to minimize the number of oocysts. After cleaning, thorough disinfection with 50% bleach has been useful. Coccidiostats are sometimes fed to sows 2 wk before farrowing or administered PO to pigs from birth to 3 wk of age.
Adult nodular worms of Oesophagostomum spp in the large intestine cause little harm, but heavy infection by larvae encysted in the intestinal wall may lead to emaciation.
Strongyloides ransomi (intestinal threadworm) larvae can be transmitted via colostrum or acquired from contaminated skin of the dam. Heavily infected piglets develop severe diarrhea when 10–14 days old, with high mortality. Diagnosis is based on direct microscopical observation of mucosal scrapings.
Trichuris suis (whipworms) penetrate the mucosa of the cecum and colon and cause multifocal inflammation. Heavy infections cause diarrhea and emaciation. The feces are hemorrhagic; therefore, heavy whipworm infections may be confused clinically with swine dysentery or proliferative enteritis. Diagnosis is based on direct observation of whipworms in the large intestine or on fecal flotation.