Dermatology MCQ - Viral Infections - Parechovirus infection

A 3-week-old infant is brought to the emergency department with fever, irritability, and a diffuse, erythematous rash. The infant is tachycardic and hypotensive. Laboratory studies reveal leukocytosis and elevated inflammatory markers. Cerebrospinal fluid (CSF) analysis shows pleocytosis with a predominance of monocytes. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Human parechovirus; fecal-oral route
B) Herpes simplex virus; vertical transmission during delivery
C) Enterovirus; respiratory droplets
D) Group B Streptococcus; vertical transmission during delivery
E) Staphylococcus aureus; skin contact

Correct Answer: A) Human parechovirus; fecal-oral route

Explanation

This presentation is classic for human parechovirus (HPeV) infection, particularly HPeV type 3, which causes severe disease in young infants.

Key Clinical Features of HPeV Infection in Infants:

• Fever: Often high-grade and abrupt.

• Sepsis-like syndrome: Tachycardia, hypotension, irritability, and lethargy.

• Rash: Diffuse, erythematous, "sandpaper-like" rash that may be maculopapular.

• CNS involvement: Meningoencephalitis, seizures, or sepsis-like picture. CSF may show pleocytosis with monocytic predominance (though CSF can be normal in early infection).

• Age: Most severe in infants <3 months old.

Virologic Features:

• Causative Agent: Human parechovirus (HPeV), a member of the Picornaviridae family. HPeV type 3 is most associated with severe neonatal disease.

• Transmission: Fecal-oral route is primary; also respiratory droplets.

• Seasonality: Summer and fall.

Why Not the Other Options?

• (B) Herpes simplex virus: Causes neonatal HSV infection (sepsis, seizures, vesicular rash) but is acquired vertically during delivery. CSF typically shows lymphocytic pleocytosis.

• (C) Enterovirus: Causes similar sepsis-like illness in infants but often has CSF with neutrophilic pleocytosis initially. Rash is common but not always "sandpaper-like."

• (D) Group B Streptococcus: Causes early-onset neonatal sepsis (within first week of life) with respiratory distress, but rash is not typical. Acquired vertically during delivery.

• (E) Staphylococcus aureus: Causes bacterial sepsis or scalded skin syndrome (exfoliative rash) but is not common in young infants without risk factors.

Diagnosis

• PCR testing of CSF, blood, or stool for HPeV.

• CSF may show pleocytosis, but HPeV can cause meningitis with normal CSF parameters.

Management

• Supportive care: IV fluids, pressors for shock, antipyretics.

• No specific antiviral treatment; IVIG may be considered in severe cases.

• Empirical antibiotics until bacterial infection is ruled out.

Prognosis:
Most recover fully, but severe cases may have neurodevelopmental sequelae (e.g., white matter injury).

Note: HPeV is a common mimic of bacterial sepsis in infants. The "sandpaper" rash and monocytic CSF pleocytosis are clues. Always consider HPeV in febrile infants <3 months with sepsis-like illness.