Zika Virus
Summary
Zika is a mosquito-borne Flavivirus (related to Dengue and Yellow Fever) primarily transmitted by the Aedes mosquito. While the acute illness is typically mild or asymptomatic (80%), Zika is globally significant due to its devastating teratogenic effects. Infection during pregnancy, particularly the first trimester, can cause Congenital Zika Syndrome (Microcephaly, cerebral calcifications, and ocular abnormalities). It is also associated with Guillain-Barré Syndrome (GBS) in adults. Uniquely for an arbovirus, it can be transmitted sexually. There is no specific treatment or vaccine. Focus is on prevention: avoiding travel during pregnancy and barrier contraception post-travel. [1,2]
Key Facts
- Vector: Aedes aegypti (day-biting). Also Aedes albopictus.
- The "Mild Dengue": Symptoms overlap with Dengue and Chikungunya but are generally milder (low-grade fever, rash).
- Asymptomatic Rate: ~80%. This complicates advice for pregnant women (exposure but no symptoms).
- Sexual Transmission: Zika RNA persists in semen for months (longer than in blood/urine). Male-to-female transmission is well documented.
Clinical Pearls
Conjunctivitis: Non-purulent (red eye without pus) is a hallmark feature, helping distinguish it from bacterial causes or pure Influenza.
GBS Spike: During the 2015 Brazil outbreak, GBS cases spiked significantly, confirming the neurotropic nature of the virus even in adults.
The "Collapsed Skull": In severe microcephaly, the brain fails to grow, but the facial bones grow normally. The skull collapses around the small brain, leading to a distinctive phenotype with redundant scalp skin (Rugae).
Travel Advice is Dynamic: Endemic zones change. Always check current CDC/NaTHNaC maps before advising a pregnant patient.
Incidence
- 2015 Epidemic: Massive outbreak in Americas (Brazil). Now sporadic transmission worldwide.
- Endemic Areas: South America, Central America, Caribbean, Southeast Asia, Pacific Islands, Parts of Africa.
Transmission
- Mosquito: Primary route.
- Transplacental: Vertical transmission.
- Sexual: Semen (cases documented up to 6 months post infection).
- Blood Transfusion.
Mechanism
- Neurotropism: The virus specifically targets Neural Progenitor Cells.
- Fetal Brain: It crosses the placenta, infects the developing brain, causing cell death (apoptosis) and disruption of neuronal migration.
- Result: Thin cortices, calcifications, ventriculomegaly, microcephaly.
Acute Infection (The 20%)
Congenital Zika Syndrome
- Skin: Diffuse maculopapular rash.
- Eyes: Redness (Conjunctival injection).
- Joints: Mild synovitis.
- Neuro: Check reflexes (rule out GBS).
Virus Detection
- RT-PCR:
- Blood: Positive for 5-7 days after onset.
- Urine: Positive for up to 14 days (more sensitive).
- Semen: Can be positive for months (not routinely tested).
Serology
- IgM Antibodies: Acceptable from Day 5 to 12 weeks.
- Problem: Massive Cross-Reactivity with other Flaviviruses (Dengue, Yellow Fever, Vaccination). A positive Zika IgM requires confirmation with Plaque Reduction Neutralization Test (PRNT) to be sure it isn't Dengue.
Fetal Imaging
- Ultrasound: Monitor head circumference (HC), intracranial calcifications.
- MRI Fetal: More detailed for cortical malformations.
Management Algorithm
TRAVEL TO ENDEMIC ZONE
↓
┌───────────┴───────────┐
PREGNANT NOT PREGNANT
↓ ↓
SYMPTOMS? AVOID PREGNANCY
↓ ↓ (Wait period)
YES NO ↓
↓ ↓ Men: 3 months
PCR/ Ultrasound Women: 2 months
Serology Monitoring
1. Acute Management
- Supportive: Hydration, Paracetamol.
- Avoid NSAIDs: Do NOT use Ibuprofen/Aspirin until Dengue is ruled out (risk of bleeding).
- Avoid Sexual Transmission: Barrier contraception.
2. Pregnancy Management
- Prevention: The only true management. Pregnant women should AVOID travel to outbreak areas.
- If Exposed:
- Test (PCR/Serology) dependent on timing.
- Serial Ultrasounds (every 4 weeks).
- Amniocentesis (PCR of amniotic fluid) can confirm fetal infection.
- Termination of Pregnancy: Discussed if severe fetal anomalies confirmed.
3. Post-Travel Contraception Advice (CDC/WHO)
To prevent sexual transmission/congenital syndrome:
- Men (returning from endemic area): Use condoms for 3 months (even if asymptomatic).
- Women: Avoid pregnancy (contraception) for 2 months.
- Guillain-Barré Syndrome (GBS):
- Autoimmune demyelination typically 1-3 weeks after infection.
- Ascending paralysis.
- Thrombocytopenia (rare compared to Dengue).
- Acute Illness: Excellent prognosis. Self-limiting.
- Congenital: Poor neurodevelopmental outcome. Lifelong disability.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Zika in Pregnancy | RCOG / CDC | Do not travel to ZF areas if pregnant. Serial scans for returnees. |
| Sexual Transmission | WHO | Wait periods: 3 months (men), 2 months (women). |
| Testing | PHE | Test Urine (PCR) and Blood (PCR) in first 2 weeks. Serology unreliable if prior Dengue. |
Landmark Knowledge
1. The Brazil Microcephaly Spike (2015)
- Event: A 20-fold increase in microcephaly cases in NE Brazil coincided with Zika introduction.
- Proof: Virus isolated from fetal brain tissue.
- Impact: Declared a Public Health Emergency of International Concern (PHEIC).
What is Zika?
It's a virus spread by mosquitoes in hot countries. For most adults, it causes a very mild illness (fever, rash, red eyes) or no symptoms at all. You might not even know you had it.
Why is everyone worried?
If a pregnant woman catches Zika, the virus can attack the baby's developing brain, causing it to stop growing (Microcephaly). This causes severe lifelong disabilities.
I'm pregnant. Should I cancel my holiday?
If the country has active Zika transmission: YES. It is not worth the risk.
We want to try for a baby after our holiday.
You must wait. The virus can hide in sperm for months.
- If the man travelled: Wait 3 months.
- If usually the woman travelled: Wait 2 months.
Primary Sources
- Rasmussen SA, et al. Zika Virus and Birth Defects — Reviewing the Evidence for Causality. N Engl J Med. 2016;374:1981-1987. PMID: 27074377.
- Petersen LR, et al. Zika Virus. N Engl J Med. 2016;374:1552-1563.
- Royal College of Obstetricians and Gynaecologists (RCOG). Zika Virus Infection and Pregnancy. Interm Guideline.
Common Exam Questions
- Obstetrics: "Pregnant woman returns from Brazil. Asymptomatic. Advice?"
- Answer: Serial Ultrasound monitoring (or Serology if available, but limitations apply).
- Public Health: "How long to use condoms after male travel to Zika zone?"
- Answer: 3 months.
- Infectious Disease: "Patient with fever, rash, joint pain, red eyes. Platelets normal. Diagnosis?"
- Answer: Zika (Platelets usually low in Dengue).
- Paediatrics: "Features of Congenital Zika Syndrome?"
- Answer: Microcephaly, Collapsed skull, Arthrogryposis, Retinal calcifications.
Viva Points
- Dengue Cross-Reactivity: Why is it a problem? Both are Flaviviruses. Antibodies look the same. A person who had Dengue in the past might test positive for Zika IgG incorrectly ("Original Antigenic Sin").
- Aedes Mosquito: Day biter? Yes. Bed nets at night are not enough. Need DEET during the day.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.