About a third of recovered birds become carriers. Most outbreaks result from a buildup of organisms through several broods of poults, making exposure of the following brood overwhelming. Indirect transmission may result from fecal material carried from one location to another on shoes or equipment. Free-flying birds also may be carriers. Convulsions due to lowered blood sugar levels shortly precede death.
Affected birds suffer losses in weight and survivors remain stunted for long periods.
Dehydration and emaciation are the principle gross lesions. The intestine usually appears to have lost tone with local bulbous areas of congestions. Intestinal contents usually are thin and watery. Diagnosis depends upon history, symptoms and microscopic examination of intestinal contents. A definite diagnosis cannot be made unless typical flagellates can be demonstrated in intestinal contents taken from the duodenum area.