Entamoeba histolytica (Amebiasis)

A 19-year-old man presents to a rural clinic in Bangladesh for evaluation of abdominal pain that has been ongoing for the past month. The pain is intermittent and most prominent in the right upper quadrant. In addition, he has often noticed bright-red blood in his stool. The patient consumes alcohol and tobacco and has been sexually active with three female partners over the past year. Temperature is 37.7°C (100°F), blood pressure is 101/72 mmHg, and pulse is 78/min. Physical examination reveals right upper quadrant pain elicited by deep palpation. CT imaging is shown below. Via which of the following routes did this patient most likely acquire the infection?
 
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