A man in his 20s reported a 3-week history of headache, confusion, and fever aft

Question

A man in his 20s reported a 3-week history of headache, confusion, and fever after being brought to the ER after a seizure. He reported having a number of health problems in recent years including weight loss, weaknesses and repeated minor infections such as colds. He reported that he had used intravenous drugs in the past and regularly shared needles. A test confirmed he was HIV positive. He had not been treated for HIV infection previously and his CD4+ count was at 10 cells/mm3 He lived in Philadelphia with 2 adult family members, a dog and a cat. He had traveled over the summer to New York City, but reported no international travel. He was a non-smoker A brain CT scan was done. The results are shown below Note circular lesion circled in red. What is the most likely diagnosis? What microbe is causing this infection? (5 points) List 2 possible exposure to the microbe causing the infection? Was the infection necessarily recently acquired? (10 points) Describe the life cycle of the microbe. (10 points)

Explanation / Answer

The most likely diagnosis is Toxoplasmosis.

The microbe causing this infection is Toxoplasma gondii.

Two possible exposures to the microbe causing infection are

            1. Passage of parasites from an infected mother to the fetus through placenta

            2. Ingestion of sporulated oocysts from contaminated soil, food, or water

The infection might not be recently acquired, because acute infection acquired after birth may be asymptomatic but is thought to result in the lifelong chronic persistence of cysts in the host’s tissues. In the immunocompromised host, the immune factors necessary to control the spread of tachyzoite infection are lacking, allows the persistence of tachyzoites and gives rise to progressive focal destruction that results in organ failure.

Lifecycle of Toxoplasma gondii

The cat is the definitive host in which the sexual phase of the cycle is completed. Oocysts shed in cat feces can infect birds, rodents, grazing domestic animals, and humans. The bradyzoites found in the muscle of food animals may infect humans who eat insufficiently cooked meat products, particularly lamb and pork. Congenital infection and encephalitis from reactivation of latent infection in the brains of immunosuppressed persons are the most important manifestations central nervous system.

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