WBR0052

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics, MainCategory::Immunology, MainCategory::Microbiology
Sub Category	SubCategory::Vascular, SubCategory::General Principles, SubCategory::Infectious Disease
Prompt	[[Prompt::A 6-year-old African American male is brought to the emergency room for severe abdominal pain. On examination, his abdomen is stiff and bloated with diffuse pain, but most severe in the upper left quadrant. This is the second such episode for this patient and one of his older sisters suffered a similar disease. After supportive treatment, this patient must receive a vaccine for a certain encapsulated, catalase-positive gram negative rod. What moiety is used in this vaccine?]]
Answer A	AnswerA::Polyribosylribitol phosphate
Answer A Explanation	AnswerAExp::Correct – See explanation
Answer B	AnswerB::Peptidoglycan
Answer B Explanation	AnswerBExp::Peptidoglycan composes the membrane of most bacteria. It is not used in the Haemophilus Influenza Type B vaccine.
Answer C	AnswerC::Protein A
Answer C Explanation	AnswerCExp::Protein A is a virulence factor of S. Aureus which binds to the Fc portion of Ig and helps to prevent opsonization and phagocytosis. It is not used in the Haemophilus Influenza Type B vaccine.
Answer D	AnswerD::Lipid A
Answer D Explanation	AnswerDExp::Lipid A is a part of endotoxin, a lipopolysaccharide which is a highly immunogenic component of the cell wall of Gram-negative bacteria. It is not used in the Haemophilus Influenza Type B vaccine.
Answer E	AnswerE::M protein
Answer E Explanation	AnswerEExp::M protein is a virulence factor of Strep Pyogenes that helps prevent phagocytosis. It is not used in the Haemophilus Influenza Type B vaccine.
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient in this vignette suffers from sickle-cell anemia. Sickle-cell anemia is an autosomal recessive condition mainly affecting patients of African American and Middle-Eastern ancestry. Patients with sickle-cell anemia suffer from vaso-occlusive crisis, splenic sequestration crisis, aplastic crisis and hemolytic crisis. All of these clinical scenarios are caused by aggregation of sickled red cells and tend to be brought on by conditions of stress or infection. In this vignette, the patient is suffering from a splenic sequestration crisis. Because of its narrow vessels and function in clearing defective red blood cells, the spleen is frequently affected. It is usually infarcted before the end of childhood in individuals suffering from sickle-cell anemia. Splenic sequestration crises are acute, painful enlargements of the spleen. The sinusoids and gates would open at the same time resulting in sudden pooling of the blood into the spleen and circulatory defect leading to sudden hypovolaemia. The abdomen becomes bloated and very hard. Splenic sequestration crises are considered an emergency. After splenectomy, sickle cell patients must receive vaccines to prevent infection with encapsulated organisms including Strep pneumoniae, Neisseria meningitidis and Haemophilus influenza type B. H. influenza type B is an encapsulated, gram negative rod which can cause severe meningitis in infants and children. The vaccine for this organism is a conjugate vaccine, using the bacterial capsular polysaccharide, polyribosylribitol phosphate conjugated with a protein to stimulate long term humoral immunity. Educational Objective: The vaccine for this Haemophilus influenza B is a conjugate vaccine, using the bacterial capsular polysaccharide, polyribosylribitol phosphate conjugated with a protein to stimulate long term humoral immunity. References: First Aid 2014 page 137 First Aid 2012 page 150]]
Approved	Approved::Yes
Keyword	WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Vaccine, WBRKeyword::Sickle, WBRKeyword::Sickle cell, WBRKeyword::Sickle cell anemia, WBRKeyword::Sickle cell disease
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