During a prenatal screening clinic in Mumbai, a pregnant woman (28 weeks gestation) with a recent febrile illness is found to have serological evidence of recent flavivirus infection. Fetal ultrasound shows microcephaly and ventriculomegaly. Which feature best distinguishes Zika virus from dengue and chikungunya as the causative agent?

Explanation

## Zika Virus: Distinguishing Feature from Dengue and Chikungunya ### The Defining Characteristic **Key Point:** Congenital Zika syndrome — characterized by microcephaly, intracranial calcifications, ventriculomegaly, and other CNS malformations — is the unique and defining feature of Zika virus infection during pregnancy. Neither dengue nor chikungunya are associated with congenital anomalies or fetal microcephaly. ### Comparative Table: Arboviral Infections in Pregnancy | Feature | Dengue | Chikungunya | Zika | |---------|--------|-------------|------| | **Congenital anomalies** | None reported | None reported | **Microcephaly, CNS malformations** | | **Fetal loss risk** | Minimal | Minimal | Increased (especially 1st/2nd trimester) | | **Vertical transmission** | Rare | Rare | Common (especially 1st trimester) | | **Maternal rash** | Maculopapular | Maculopapular | Maculopapular (often pruritic) | | **Arthralgia** | Myalgia, bone pain | Severe, chronic | Mild arthralgia | | **Thrombocytopenia** | Marked | Mild | Mild | | **CNS involvement** | Dengue encephalitis (rare) | Rare GBS | **Congenital microcephaly** | ### Clinical Pearl **Clinical Pearl:** The 2015–2016 Zika epidemic in Brazil established the causal link between maternal Zika infection (especially in the first trimester) and congenital microcephaly. Imaging findings include microcephaly, cortical malformations, intracranial calcifications (particularly at the gray-white matter junction), and ventriculomegaly — a constellation NOT seen with dengue or chikungunya. ### High-Yield Fact **High-Yield:** Zika virus has **tropism for neural progenitor cells**, causing direct fetal CNS damage. This is unique among the three arboviruses. Dengue and chikungunya do not cross the placenta efficiently or cause fetal CNS malformations. ### Mnemonic **Mnemonic:** **ZIKA = CNS** (Central Nervous System in congenital infection). Remember: Dengue and Chikungunya spare the fetus; Zika attacks the developing brain. [cite:Park 26e Ch 10; Harrison 21e Ch 189]