WBR0783

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 21 year old man presents to the emergency department for 1 week of severe sore throat with associated odynophagia. The patient also reports significant fatigue that has been keeping him in bed most of the day. The physician does a bed-side rapid strep test that comes out negative. He then asks the patient to visit the lab for a simple blood test. The technologist mixes a drop of the patient’s serum with a 15% suspension of sheep red blood cells in a 5% sodium citrate solution on a glass slide. The mixture is left undisturbed for one minute after which the technologist notices that the sheep red blood cells have agglutinated. Which of the following would bind the organism causing this patient’s disease?]]
Answer A	AnswerA::β2-microglobulin
Answer A Explanation	AnswerAExp::CMV binds β2-microglobulin.
Answer B	AnswerB::Sialic acid
Answer B Explanation	AnswerBExp::Influenza virus hemagglutinin binds to sialic acid.
Answer C	AnswerC::CD21
Answer C Explanation	AnswerCExp::CD21 binding of EBV determines its tropism to B-cells
Answer D	AnswerD::Acetylcholine recptors
Answer D Explanation	AnswerDExp::Acetylcholine receptors are used by rabies virus to bind and enter neuronal cells.
Answer E	AnswerE::CD14
Answer E Explanation	AnswerEExp::CD14 is a macrophage bound receptor that binds to the LPS endotoxin causing an immune reaction.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Infectious mononucleosis is clinical syndrome characterized by fever, pharyngitis, and lymphadenopathy usually caused by Ebstein-Barr virus (EBV) although several other infectious etiologies can give a mononucleosis-like syndrome including toxoplasma, and CMV. The diagnosis is usually clinical supported by serologies and by peripheral smear showing atypical lymphocytes. Another test used to detect EBV mononucleosis vs. other mononucleosis-like syndromes is the heterophile antibody test. The test check for agglutination of horse (Monospot test) or sheep (Paul-Bunnell test) red blood cells when mixed with the patient's serum that would contain the heterophile antibodies produced by EBV infected plasma cells. EBV binds to CD21 on the surface of B-cells allowing them to fuse and enter. EBV mononucleosis is easily mistaken for streptococcal pharyngitis, often indicating streptococcal testing. Educational Objective: EBV causes mononucleosis by binding CD21 on the surface of B-cells. EBV infectious mononucleosis can be detected via heterophile antibody testing. Reference: Luzuriaga K, Sullivan JL. Infectious mononucleosis. N Engl J Med. 2010;362(21):1993-2000. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::EBV, WBRKeyword::Mononucleosis, WBRKeyword::Monospot, WBRKeyword::CD21
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::