In some patients, the trophozoites invade the mucosa and cause
large ulcerative lesions similar to those produced by Entamoeba
histolytica; however, balantidial lesions usually are larger.
As the trophozoites multiply by binary fission in the mucosa and
submucosa, adjacent lesions may anastomose with one another, and
the ulcers often extend deeply into the muscularis. Fortunately,
perforation or extraintestinal invasion rarely ensues.
With invasive disease, patients may have mild to severe diarrhea
that contains mucus and blood, abdominal pain, nausea, vomiting, and
often tenesmus. Secondary infection of the colonic lesions by bacteria
can worsen the clinical picture. The disease may be self-limiting,
with spontaneous eradication and healing, or it can become chronic,
with constipation alternating with diarrhea. Occasionally, cecal
swelling can lead to typhlitis, and rarely the organisms will perforate
the large intestine and affect the small intestine, the appendix,
the vagina, the uterus, and the bladder, and on very rare occasions
may disseminate to the liver and lungs.7,8