A 28-year-old pregnant woman (22 weeks gestation) from Tamil Nadu presents with a 4-day history of low-grade fever (38.2°C), maculopapular rash over the trunk and extremities, and mild polyarthralgia of the wrists and ankles. She has no thrombocytopenia (platelets 210,000/μL) and no haemoconcentration. Obstetric ultrasound shows normal fetal biometry. What is the most likely diagnosis and what is the primary clinical concern?

Explanation

## Zika Virus in Pregnancy: Diagnosis and Teratogenic Risk ### Clinical Presentation **Key Point:** Zika virus presents with a mild, self-limited febrile illness characterised by low-grade fever, maculopapular rash, and mild arthralgia. The absence of thrombocytopenia and haemoconcentration distinguishes it from dengue. ### Differential Diagnosis in Pregnancy | Feature | Zika | Dengue | Chikungunya | Rubella | |---------|------|--------|-------------|----------| | **Fever grade** | Low (38–38.5°C) | High (39–40°C) | Moderate–high | Low–moderate | | **Rash** | ✓ (maculopapular) | ✓ (petechial/maculopapular) | ✓ (maculopapular) | ✓ (maculopapular) | | **Arthralgia** | ✓ (mild) | ✗ | ✓✓ (severe) | ✓ (mild) | | **Thrombocytopenia** | ✗ | ✓ | ✗ | ✗ | | **Congenital risk** | Microcephaly, CNS abnormalities | Rare | Neonatal arthritis | Cardiac defects, deafness | | **Vertical transmission** | ✓ (1st/2nd trimester) | Rare | ✓ (perinatal) | ✓ (any trimester) | ### Zika Teratogenicity: Congenital Zika Syndrome **High-Yield:** Zika virus infection in pregnancy, especially during the first and second trimesters, is associated with a constellation of fetal abnormalities collectively termed **Congenital Zika Syndrome (CZS)**. ### Manifestations of Congenital Zika Syndrome 1. **Microcephaly** (most common CNS finding) - Severe reduction in head circumference - Associated with cortical abnormalities and developmental delay 2. **Central Nervous System Abnormalities** - Cortical malformations (polymicrogyria, lissencephaly) - Calcifications (especially basal ganglia) - Ventriculomegaly - Cerebellar hypoplasia 3. **Ocular Abnormalities** - Chorioretinitis - Optic nerve hypoplasia - Cataracts 4. **Skeletal Abnormalities** - Arthrogryposis - Talipes equinovarus 5. **Other Features** - Intrauterine growth restriction (IUGR) - Hearing loss - Seizures **Clinical Pearl:** Normal fetal biometry at 22 weeks does NOT exclude Zika infection; microcephaly may manifest later in pregnancy or postnatally. Serial ultrasounds and fetal MRI are recommended. ### Mechanism of Teratogenicity - Zika virus tropism for neural progenitor cells and cortical stem cells - Direct viral cytotoxicity → apoptosis of neuronal precursors - Impaired neurogenesis and cortical development - Viral persistence in amniotic fluid and fetal tissues ### Management in Pregnancy 1. **Serological testing:** IgM and IgG antibodies; RT-PCR from serum/urine (higher sensitivity) 2. **Fetal assessment:** Serial ultrasound every 4 weeks; consider fetal MRI if CNS abnormalities suspected 3. **Counselling:** Discuss risks of CZS; offer detailed fetal anatomy scan and neurosonography 4. **Monitoring:** Close follow-up postnatally for developmental assessment and ophthalmologic evaluation **Mnemonic:** **ZIKA CNS** — **Z**ika causes **I**ntrauterine growth restriction, **K**eratitis/ocular abnormalities, **A**rthrogryposis; **C**ortical malformations, **N**eurodevelopmental delay, **S**evere microcephaly. [cite:Harrison 21e Ch 189; CDC Zika Virus Guidelines]