The CDCs description:

Arthus reactions (type III hypersensitivity reactions) are rarely reported after vaccination and can occur after tetanus toxoid–containing or diphtheria toxoid–containing vaccines. An Arthus reaction is a local vasculitis associated with deposition of immune complexes and activation of complement. Immune complexes form in the setting of high local concentration of vaccine antigens and high circulating antibody concentration. Arthus reactions are characterized by severe pain, swelling, induration, edema, hemorrhage, and occasionally by necrosis. These symptoms and signs usually occur 4–12 hours after vaccination. ACIP has recommended that persons who experienced an Arthus reaction after a dose of tetanus toxoid–containing vaccine should not receive Td more frequently than every 10 years, even for tetanus prophylaxis as part of wound management. See also
Serum sickness

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The cyst form also differs from the trophozoite form because it is non-motile and does not undergo reproduction. Instead, the cyst is the form that the parasite takes when it causes infection. Diagnosis
The diagnosis of balantidiasis can be an intricate process, partly because the related symptoms may or may not be present. However, the diagnosis of balantidiasis can be considered when a patient has diarrhea combined with a probable history of current exposure to pigs (since pigs are the primary reservoir), contact with infected persons, or anal intercourse. In addition, the diagnosis of balantidiasis can be made by microscopic examination of stools in search of trophozoites or cysts, or colonoscopy or sigmoidoscopy to obtain a biopsy from the large intestines which may provide evidence for the presence of trophozoites. Prevention
Preventative measures require effective personal and community hygiene. Some specific safeguards include the following:
Purification of drinking water. Proper handling of food. Careful disposal of human feces. Monitoring the contacts of balantidiasis patients. Treatment
Balantidiasis can be treated with tetracycline, metronidazole or iodoquinol. History
The first study to generate balantidiasis in humans was undertaken by Cassagrandi and Barnagallo in 1896. However, this experiment was not successful in creating an infection and it was unclear whether Balantidium coli was the actual parasite used. The first case of balantidiasis in the Philippines, where it is the most common, was reported in 1904. Currently, Balantidium coli is distributed worldwide but less than 1% of the human population is infected.