A 4-year-old girl has a rash that started on her face and sp

Discussion in 'USMLE STEP 1' started by Guest, Feb 27, 2010.

  1. Guest

    Guest Guest

    A 4-year-old girl has a rash that started on her face and spread to her back, chest, arms, and legs. Her palms and soles are involved. The rash is an erythematous maculopapular rash. There are small red spots with a blue center on her buccal mucosa that resemble grains of sand in appearance. Which of the following virulence factors mediates host cell binding in this condition?
    a. Fusion protein
    b. Matrix protein
    c. Hemagglutinin
    d. Edema factor
    e. Neuraminidase
  2. Guest

    Guest Guest

    C. measles. orthomyxo.Heamaglutinin cam bind to host sialic acid recep in resp epi.
  3. Guest

    Guest Guest

    NO ONE?Choice (C) is the answer.
    Measles is a highly contagious infection caused by a paramyxovirus, which are single-stranded RNA viruses with negative polarity and a non-segmented genome. Paramyxoviruses also have a helical nucleocapsid. Two important virulence factors of the measles virus are hemagglutinin (H) protein and fusion (F) protein (Choice A), both of which are glycoproteins that project from the viral envelop. Hemagglutinin mediates receptor binding to host cells. Fusion protein facilitates membrane fusion and penetration of the host cell membrane. A third protein, matrix or M protein (Choice B), is a viral protein involved in viral assembly. Measles virus initially infects upper respiratory tract mucosal cells, then spreads to the lymphatics and finally to the blood stream. A prodromal syndrome develops after a 10-12 day incubation period that is characterized by fevers and malaise. Classically, the fevers increase in a stepwise fashion over the next several days. Next, a cough, coryza, and conjunctivitis develop followed by the appearance of Koplik spots, which are small red spots with a bluish-gray center that resemble grains of sand that occur on the buccal mucosa opposite the second molars. Koplik spots are pathognomonic for measles. Finally, an erythematous maculopapular rash develops initially on the face and spreads to the trunk, back, and extremities. The palms and soles are involved. Measles is spread to unvaccinated individuals via respiratory droplets. Encephalitis can develop in rare cases, and very rarely, subacute sclerosing panencephalitis may develop years after infection. Subacute sclerosing panencephalitis is a progressive neurological condition that leads to gradual neurological deterioration and ultimately results in death. Edema factor (Choice D) is associated with anthrax. Neuraminidase (Choice E) is associated in influenza virus.

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