WBR0153

Author	[[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pathophysiology
Sub Category	SubCategory::Dermatology, SubCategory::General Principles
Prompt	[[Prompt::A mother brings her 2-year-old son into the pediatrician's office for complaints of irritability and poor appetite for the past 3 days. The patient has developed a rash that surrounds his mouth with eruptions on his tongue, palms, and soles. Physical examination is remarkable for a temperature of 38.3 °C (101 °F) and the rash shown below. Which of the following organisms is most likely responsible for the patient's condition? ]]
Answer A	AnswerA::Enveloped ssRNA virus with icosahedral capsid symmetry
Answer A Explanation	[[AnswerAExp::Enveloped ssRNA viruses with icosahedral capsid symmetry encompass several families of RNA viruses including flaviviruses, togavirsuses, and retroviruses. For example, Rubella virus is an enveloped ssRNA virus with icosahedral capsid symmetry. It causes a fine truncal rash and postauricular lymphadenopathy. Rubella virus is not the cause of hand, foot, and mouth disease.]]
Answer B	AnswerB::Enveloped dsDNA virus with icosahedral capsid symmetry
Answer B Explanation	[[AnswerBExp::The herpesviridae family is composed of dsDNA viruses, including HSV1 and VZV. HSV1 can cause an vesicular rash near the mouth similar to the one shown in the vignette but does not typically cause eruptions on the palms of the hands or soles of the feet.]]
Answer C	AnswerC::Nonenveloped dsDNA virus with icosahedral capsid symmetry
Answer C Explanation	AnswerCExp::Nonenveloped dsDNA viruses include adenovirus, papillomavirus, and polyomavirus. Adenovirus is a common cause of bilateral viral conjunctivitis.
Answer D	AnswerD::Nonenveloped ssRNA virus with icosahedral capsid symmetry
Answer D Explanation	[[AnswerDExp::Coxsackievirus A is the etiologic agent of hand, foot, and mouth disease. It is a picornavirus, which is a nonenveloped, single-stranded, positive-sense RNA virus with icosahedral capsid symmetry.]]
Answer E	AnswerE::Spirochete
Answer E Explanation	[[AnswerEExp::While syphilis rash can involve the palms of the hands and soles of the feet, it does not usually cause a rash in the perioral zone. In addition, the clinical presentation of this patient, including his age, prodrome, and features of the rash make HFMD a more likely diagnosis.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Hand, foot, and mouth disease (HFMD) is a common viral infection among children. It is characterized by the presence of a vesicular or a maculopapular a rash in the perioral zone, in the oral cavity, and on palms of the hands and soles of the feet. Patients with HFMD may also have eruptions on their buttocks and the trunk. The disease is caused by Coxsackievirus A virus, a nonenveloped single-stranded positive-sense RNA viruses with icosahedral capsid symmetry that belongs to the picornaviridae family. The incubation period of the disease is 3-6 days with prodrome of low-grade fever, malaise, and sore throat that typically precede the rash. The diagnosis is suspected based on the clinical presentation and the characteristic features of the rash; but it may be confirmed by PCR assay. It is a self-limited disease that self-resolves, and skin lesions last for 1 to 2 weeks with no residual scars. Rarely, HFMD may cause life-threatening complications such as encephalitis, meningitis, pulmonary edema, and myocarditis. Other members of the picornaviridae include poliovirus that causes polio, echovirus that causes aseptic meningitis, rhinovirus that causes the common cold, hepatitis A virus that causes viral hepatitis, and coxsackieviruses B viruses that is much more commonly associated with myocarditis or pericarditis than coxsackievirus A. Educational Objective: Coxsackievirus A virus causes hand, foot, and mouth disease. Coxsackievirus A is a picornavirus, which is a nonenveloped, single-stranded, positive sense RNA virus with icosahedral capsid symmetry. References: Kaminska K, Martinetti G, Lucchini R, et al. Coxsackievirus A6 and hand, foot and mouth disease: three case reports of familial child-to-immunocompetent adult transmission and a literature review. Case Rep Dermatol. 2013;5(2):203–209. First Aid 2014 page 175]]
Approved	Approved::Yes
Keyword	WBRKeyword::Microbiology, WBRKeyword::Virus, WBRKeyword::RNA virus, WBRKeyword::Coxsackie, WBRKeyword::Pediatrics, WBRKeyword::Rash, WBRKeyword::Skin, WBRKeyword::Hand foot and mouth disease
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