Images of Memorable Cases: Case 72 Peripheral blood film from a 10-year-old Brazilian boy with Romaña’s sign– painless, unilateral, palpebral edema with conjunctivitis and swelling of regional lymph nodes. 72. Acute Chagas disease (American trypanosomiasis) Shown between red blood cells is a trypomastigote of Trypanosoma cruzi. This form of the parasite is visible in the blood only during the acute stage of the disease and is diagnostic. Romaña’s sign, which often heralds the acute phase, develops when the vector, a reduviid bug, deposits the parasite on or near the conjunctiva.