Dermatology MCQ - Viral Infections - Zika virus

A 28-year-old pregnant woman (16 weeks gestation) presents with a low-grade fever, pruritic maculopapular rash, conjunctival injection, and arthralgia. She recently returned from a trip to Brazil. Fetal ultrasound reveals microcephaly and intracranial calcifications. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Rubella virus; respiratory droplets
B) Zika virus; Aedes mosquito bite
C) Cytomegalovirus; contact with bodily fluids
D) Toxoplasma gondii; ingestion of undercooked meat
E) Parvovirus B19; respiratory droplets

Correct Answer: B) Zika virus; Aedes mosquito bite

Explanation

This presentation is classic for Zika virus infection, which gained global attention due to its teratogenic effects during the 2015-2016 outbreak in the Americas.

Key Clinical Features of Zika Virus Infection:

• Maternal Symptoms: Often mild or asymptomatic. Symptomatic cases may include:

  • Low-grade fever

  • Pruritic maculopapular rash (often descending)

  • Non-purulent conjunctivitis (conjunctival injection without discharge)

  • Arthralgia (especially small joints of hands and feet)

• Congenital Zika Syndrome: In utero infection can cause:

  • Microcephaly (severe, with partially collapsed skull)

  • Intracranial calcifications

  • Eye abnormalities (e.g., retinal mottling, optic nerve hypoplasia)

  • Arthrogryposis (joint contractures)

• Other Associations: Guillain-Barré syndrome in adults.

Virologic and Epidemiologic Features:

• Causative Agent: Zika virus (a flavivirus).

• Transmission:

  • Primary: Bite of infected Aedes mosquitoes (e.g., Ae. aegypti, Ae. albopictus).

  • Other routes: Sexual transmission, vertical (mother-to-fetus), blood transfusion.

• Geographic Distribution: Tropical and subtropical regions (e.g., Brazil, Caribbean, Southeast Asia).

Why Not the Other Options?

• (A) Rubella virus: Causes similar maternal symptoms (fever, rash, arthralgia) and congenital defects (e.g., microcephaly, cataracts, heart defects). However, rubella is transmitted via respiratory droplets, not mosquitoes. The presence of conjunctival injection and the travel history to Brazil make Zika more likely.

• (C) Cytomegalovirus (CMV): The most common congenital viral infection, causing microcephaly and calcifications, but maternal symptoms are rare (mononucleosis-like if present). Transmission is via bodily fluids, not mosquitoes.

• (D) Toxoplasma gondii: Causes congenital toxoplasmosis (microcephaly, calcifications), but maternal symptoms are mild (flu-like). Acquired through ingestion of undercooked meat or cat feces, not mosquitoes.

• (E) Parvovirus B19: Causes erythema infectiosum in children and arthralgia in adults. In pregnancy, it can cause fetal hydrops, not microcephaly or calcifications. Transmitted via respiratory droplets.

Management:

• Pregnant women with possible exposure: Serial fetal ultrasounds to monitor for microcephaly and other anomalies.

• No specific antiviral treatment; supportive care only.

• Prevention: Mosquito avoidance, condom use during pregnancy if partner has traveled to endemic areas.

Prognosis:
Congenital Zika syndrome has significant neurodevelopmental sequelae. Lifelong supportive care is often required.

Note: Zika virus is a flavivirus, like dengue and yellow fever, but is unique in its teratogenicity and sexual transmission. Always inquire about travel history in pregnant women with rash and fever.