ABSTRACT
This chapter summarizes what is known about the biology of the Isospora species of man, nonhuman primates, and domestic animals. The endogenous life cycle of mammalian Isospora species is somewhat different from what is typical for Eimeria species. Sporozoites enter cells in the intestine but usually do not form rounded uninucleate trophozoites. Extraintestinal stages occur in the tissues of the definitive host in canine and feline Isospora species and Isospora belli of humans. Instead of undergoing the normal developmental cycle in the intestinal tract some sporozoites leave and invade extraintestinal sites in the host. I. belli causes serious and sometimes fatal disease in man. Symptoms of I. belli infection include diarrhea, steatorrhea, headache, fever, malaise, abdominal pain, vomiting, dehydration, and weight loss. Anticoccidial treatment of piglets has generally proven unrewarding. Nursing piglets do not eat or drink enough to make in-feed or in-water treatment useful.
