A large mass in a man's brain turned out to have an unusual cause: a parasitic infection lurking in his body that had "reawakened" in his brain, according to a new report of the case.

The 31-year-old man went the emergency room after he showed signs of confusion and had trouble walking. He also had a headache and a fever. The man had immigrated to the U.S. from El Salvador six years earlier, and had recently been diagnosed with an HIV infection and AIDS, according to the report from doctors at Stanford University.

An MRI of the man's brain showed a large mass, measuring 8 centimeters by 7 cm by 6 cm (3.1 inches by 2.7 inches by 2.3 inches).

When doctors took a sample of fluid from the brain mass and analyzed it under a microscope, they spotted dozens of small organisms inside macrophages — immune cells that gobble up foreign substances.

Genetic sequencing revealed that the man had an infection caused by Trypanosoma cruzi, a parasite that's found mainly in rural areas of Latin America that causes Chagas disease, according to the report, published today (May 9) in the New England Journal of Medicine.

People typically catch the disease when they are bitten by insects called triatomine bugs, also known as "kissing bugs," which carry the parasite, according to the Centers for Disease Control and Prevention (CDC).

Chagas disease has two phases, an acute phase and a chronic phase. During the acute phase — which happens right as a person is infected and lasts a few months — people may have mild symptoms, such as fever, fatigue, body aches and swelling of the eyelids, according to the CDC. During the chronic phase, the parasites may remain "hidden" in the body for decades, or even a lifetime, without causing further symptoms.

But about 30 percent of people with chronic Chagas disease will eventually develop health complications — typically heart problems or digestive problems.

The disease rarely affects the brain or spinal cord, but in patients with weakened immune systems — including patients with AIDS — the disease may "reactivate" in the brain, according to a 2004 report of a similar case of T. cruzi in the brain. When this happens, patients may develop abscesses in the brain, which are collections of pus, immune cells and other substances due to infection, according to the new case.

Doctors treated the man with an anti-parasitic medication called benznidazole and initiated antiviral therapy for his HIV infection. After two weeks of treatment, the man showed improvement in his mental state and walking ability, the report said.

Original article on Live Science.