WBR0052
| Author | [[PageAuthor::William J Gibson (Reviewed by Rim Halaby, M.D. [1] and Yazan Daaboul)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::General Principles, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 6-year-old African American boy is brought to the emergency department for severe abdominal pain. He reports his abdomen is stiff and bloated with diffuse pain, but most severe in the left upper quadrant. This is the second time such episode happens for this patient and one of his older sisters suffered a similar disease. His past medical history is also significant for dactylitis at the age of 18 months. After supportive treatment, this patient is required to receive a vaccine for an encapsulated, catalase-positive, gram-negative rod. What moiety is used in this vaccine?]] |
| Answer A | AnswerA::Polyribosylribitol phosphate |
| Answer A Explanation | [[AnswerAExp::The vaccine for Haemophilus influenzae type B is a conjugate vaccine that uses the bacterial capsular polysaccharide polyribosylribitol phosphate conjugated with a protein to stimulate long term humoral immunity.]] |
| Answer B | AnswerB::Peptidoglycan |
| Answer B Explanation | [[AnswerBExp::Peptidoglycan composes the membrane of most bacteria. It is not used in the Haemophilus influenzae 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 influenzae 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 influenzae type B vaccine.]] |
| Answer E | AnswerE::M protein |
| Answer E Explanation | [[AnswerEExp::M protein is a virulence factor of Streptococcus pyogenes that helps prevent phagocytosis. It is not used in the Haemophilus influenzae 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 hemoglobinopathy that mainly affects 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 episodes that cause congestive splenomegaly and eventual autosplenectomy after repeated episodes. 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 hypovolemia. The abdomen becomes bloated and very hard. Splenic sequestration crises are considered an emergency.
Surgical splenectomy may be required in some cases, while others are closely followed-up. Both cases are still characterized by functional asplenia and must receive vaccines to prevent infection with encapsulated organisms including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type B. Haemophilus influenzae type B is an encapsulated, gram negative rod which can cause severe meningitis in unvaccinated infants and children. The vaccine for this organism is a conjugate vaccine that uses the bacterial capsular polysaccharide polyribosylribitol phosphate (PPRP) conjugated with a protein to stimulate long-term humoral immunity. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Vaccine, WBRKeyword::Sickle, WBRKeyword::Sickle cell, WBRKeyword::Sickle cell anemia, WBRKeyword::african american, WBRKeyword::Sickle cell disease, WBRKeyword::PRP, WBRKeyword::hemophilus, WBRKeyword::infleunzae, WBRKeyword::autosplenectomy, WBRKeyword::splenectomy, WBRKeyword::dactylitis |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |