A 42-year-old man comes to the physician because of dysuria and blood in his urine at the end of urination. He returned to the United States 2 weeks ago after several months touring Africa. While there, he went spelunking, bathed in the beaches and lakes, and ate the local street food. Physical examination is unremarkable. Ultrasonography reveals mild bilateral hydronephrosis and bladder wall thickening. Which of the following animals is the most likely source of this patient's infection?

Question

A 42-year-old man comes to the physician because of dysuria and blood in his urine at the end of urination.  He returned to the United States 2 weeks ago after several months touring Africa.  While there, he went spelunking, bathed in the beaches and lakes, and ate the local street food.  Physical examination is unremarkable.  Ultrasonography reveals mild bilateral hydronephrosis and bladder wall thickening.  Which of the following animals is the most likely source of this patient's infection?

Quizplus · Accepted Answer

11ec160b_3857_eb97_9249_ffcbe0227ecf_MD0001_00 This patient most likely has schistosomiasis caused by Schistosoma haematobium. Humans acquire schistosomiasis via contact with infected freshwater. Infection is not possible in the United States due to absence of the specific freshwater snails that incubate the infectious larvae. Once released into the environment, the larvae can penetrate intact human skin and subsequently travel to the liver where they mature into adults over a period of several weeks. After maturation, the adult worms migrate to specific destinations: the mesenteric venules of the intestine (S japonicum and S mansoni) or the urinary bladder venous plexus (S haematobium). The adult worms remain in these blood vessels for life (5-30 years), adhering to the vessel wall with suckers and releasing eggs into circulation. Eggs released by S japonicum and S mansoni have a tendency to penetrate the bowel wall and be excreted in the feces. They also frequently traverse the portal venous system and lodge in the liver. S haematobium eggs tend to pierce the vesical and ureteral walls and be expelled in the urine. On exposure to freshwater, these eggs release larvae that can infect snails and perpetuate the life cycle. The clinical manifestations of schistosomiasis result from a T_H2-mediated granulomatous response directed against the eggs that is composed of infiltrating T_H2 cells, eosinophils, and M2 macrophages. This ultimately leads to the development of marked fibrosis and ulceration and scarring of the bowel or bladder/ureters (depending on the species). Eggs that settle into the presinusoidal radicals of the portal vein can cause periportal "pipestem" fibrosis (pathognomonic for hepatic schistosomiasis). (Choice A) Bats are a major reservoir for the rabies virus. (Choices B and E) The dog tapeworm Echinococcus granulosus is the most common cause of hydatid cysts in humans. Disease can occur following ingestion of foods contaminated with dog feces. Sheep are an intermediate host in this parasite's life cycle. (Choice C) Infection with the human tapeworm Diphyllobothrium latum occurs due to the ingestion of larvae from raw freshwater fish. Disease classically results in vitamin B12 deficiency and megaloblastic anemia. (Choice D) Human tapeworm infections caused by Taenia solium occur following consumption of larvae in infected undercooked pork. Cysticercosis is a disease caused by the larval stage of the organism following ingestion of eggs found in the excrement of T solium tapeworm carriers. Educational objective: Humans acquire schistosomiasis via contact with freshwater sources that contain snails infected with Schistosoma larvae. S japonicum and S mansoni cause intestinal and hepatic schistosomiasis, and S haematobium causes urinary schistosomiasis. __________ References: The Schistosoma granuloma: friend or foe? (http://www.ncbi.nlm.nih.gov/pubmed/23596444)

A 42-Year-Old Man Comes to the Physician Because of Dysuria