WBR0548

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Infectious Disease
Prompt	[[Prompt::A 33 year old woman who recently immigrated from Brazil presents for two months of slowly increasing shortness of breath. She reports easy fatigability lately, and several episodes of lower-extremity edema. The patient also complains of two weeks of severe dysphagia and retrosternal chest pain when she eats. She is afraid to eat and has lost 10 pounds. Physical exam shows jugular venous distension, fine basal crackles, and an S3 gallop. Chest X-ray is unremarkable except for minor congestion. Echocardiography reveals dilated left ventricle with EF of 30%. Barium swallow done to evaluate her dysphagia is shown below. If the patient's disease is infectious in origin, which of the following vectors are most likely responsible? ]]
Answer A	AnswerA::Sandfly
Answer A Explanation	AnswerAExp::The sandfly bite is responsible for transmitting Leishmania donovani that causes Kala-azar.
Answer B	AnswerB::Reduviid Bug
Answer B Explanation	AnswerBExp::The Reduviid bug is responsible for transmitting Trypanosoma cruzi the causative agent of Chagas disease whose chronic stage presents similar to our patient.
Answer C	AnswerC::Ixodes tick
Answer C Explanation	AnswerCExp::The Ixodes tick is responsible for causing babesiosis (Babesia microti) and lyme disease (Borrelia burgdorferi).
Answer D	AnswerD::Anophelus mosquito
Answer D Explanation	AnswerDExp::The Anophelus mosquito is responsible for transmitting Plasmodium species the causative agents of malaria.
Answer E	AnswerE::Horse fly
Answer E Explanation	AnswerEExp::The horse fly usually transmits a parasitic filarial worm known as Loa Loa.
Right Answer	RightAnswer::B
Explanation	[[Explanation::Chagas disease is caused by the parasite Trypanosoma cruzi. T. cruzi is commonly transmitted via a painless bite to humans and other mammals by "kissing bugs" of the family Reduviidae or simply Reduviid bugs. Chagas disease has 2 illness stages: acute and chronic. Although the acute stage is usually asymtomatic, the chronic stage affects the nervous system, digestive system and heart. It is characterized by dilation of several hollow organs causing megacolon, megaureter, megaesophagus (Chagas disease also causes secondary achalasia with characteristic bird-beak appearance seen on barium swallow), and dilated cardiomyopathy. Treatment is usually with nifurtimox although of little benefit in the chronic stage. Chagas disease is mostly seen in Central America. Diagnosis is by serologies and by visualizing the parasite amastigotes on blood smear. Educational objective: Chagas disease is caused by the parasite Trypanosoma cruzi transmitted by a painless bite from the Reduviid bug. References: Prata A. Clinical and epidemiological aspects of Chagas disease. Lancet Infect Dis. 2001;1(2):92-100. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Chagas disease, WBRKeyword::Trypanosoma cruzi, WBRKeyword::achalasia, WBRKeyword::dilated cardiomyopathy
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