Zika Virus Infection

1. Overview

Zika virus (ZIKV) is a mosquito-borne Flavivirus that emerged from relative obscurity to become a major public health concern following massive outbreaks in the Americas from 2015-2016. While Zika virus infection typically causes mild, self-limiting illness in most adults (with approximately 80% of infections remaining asymptomatic), its significance lies in devastating teratogenic effects when infection occurs during pregnancy. [1,2]

The virus gained worldwide attention during the 2015 Brazil epidemic when a dramatic 20-fold increase in microcephaly cases was observed, leading the World Health Organization (WHO) to declare Zika a Public Health Emergency of International Concern (PHEIC). The causal link between maternal Zika infection and congenital abnormalities, particularly microcephaly and other severe brain anomalies, is now firmly established. [3,4]

Beyond its teratogenic effects, Zika virus has also been associated with Guillain-Barré syndrome (GBS) in adults, marking it as a neurotropic virus with consequences across the lifespan. Uniquely among arboviruses, Zika can be transmitted sexually, with viral RNA persisting in semen for months after acute infection, complicating public health recommendations and management strategies. [5,6]

The clinical importance of Zika virus lies not in the severity of acute adult infection, but in its profound impact on pregnancy outcomes and neurological complications. Understanding transmission patterns, diagnostic challenges, and prevention strategies is essential for clinicians managing patients in endemic areas or providing pre-travel counselling to pregnant women.

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2. Epidemiology

Geographic Distribution and Outbreaks

Zika virus was first isolated in 1947 from a sentinel rhesus monkey in the Zika forest of Uganda. For decades, it remained a rare cause of sporadic febrile illness in equatorial Africa and Southeast Asia, with limited clinical significance. [1]

The epidemiological landscape changed dramatically with three major outbreaks:

• 2007: Yap Island, Federated States of Micronesia (first outbreak outside Africa/Asia)
• 2013-2014: French Polynesia (42,000 cases; first association with neurological complications recognized)
• 2015-2016: Americas epidemic (Brazil epicentre, spreading to 48 countries/territories)

Current Endemic Areas

As of 2024, Zika virus transmission has been reported in: [7]

• South America: Brazil, Colombia, Venezuela, Ecuador, Peru
• Central America: Honduras, Guatemala, El Salvador, Nicaragua
• Caribbean: Puerto Rico, Dominican Republic, Jamaica
• Southeast Asia: Thailand, Singapore, Philippines, Vietnam
• Pacific Islands: Fiji, American Samoa, Tonga
• Parts of Africa: Angola, Guinea-Bissau, Cape Verde

Incidence and Prevalence

During the 2015-2016 Americas outbreak:

• Brazil reported approximately 1.5 million suspected cases
• Over 5,000 microcephaly cases linked to Zika in Brazil alone [3]
• Seroprevalence studies in affected areas ranged from 30-80% in some communities

The attack rate during outbreaks is typically 10-20% of the population, with higher rates in areas with dense Aedes mosquito populations and limited vector control. [7]

Transmission Patterns

Primary Transmission (Mosquito-Borne):

• Vector: Aedes aegypti (primary), Aedes albopictus (secondary)
• Characteristics: Day-biting mosquitoes, peridomestic breeding
• Geographic risk: Tropical and subtropical regions where Aedes mosquitoes are established

Non-Vector Transmission Routes: [6,29,30]

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3. Aetiology and Pathophysiology

Viral Characteristics

Zika virus is a single-stranded, positive-sense RNA virus belonging to the genus Flavivirus, family Flaviviridae. It shares structural and genetic similarities with other medically important flaviviruses including dengue, yellow fever, West Nile, and Japanese encephalitis viruses.

Key Features:

• Genome: ~11 kb RNA encoding 3,419 amino acids
• Viral proteins: 3 structural (capsid, membrane, envelope) and 7 non-structural
• Two major lineages: African and Asian (Asian genotype responsible for recent outbreaks)

Neurotropism and Cellular Pathogenesis

The hallmark of Zika virus pathogenesis is its preferential targeting of neural progenitor cells (NPCs), which underlies both congenital malformations and adult neurological complications. Recent research has identified specific viral proteins NS4A and NS4B as key mediators of neurotropic injury through autophagy dysregulation. [8,19]

Mechanism of Neurotropism:

1. Entry: Virus enters NPCs via AXL receptor tyrosine kinase and other receptors
2. Replication: Preferential replication in radial glial cells and neuronal precursors
3. Cell death: Triggers apoptosis of NPCs, disrupting neurogenesis through downregulation of neurogenesis genes and upregulation of apoptotic pathways [20]
4. Migration disruption: Impairs normal neuronal migration patterns
5. Autophagy dysregulation: NS4A and NS4B proteins interfere with normal autophagy, affecting neural stem cell fate determination [19]

Congenital Zika Syndrome Pathophysiology

During fetal development, Zika virus crosses the placental barrier and targets the developing brain with devastating consequences: [9,10]

Placental Infection:

• Virus replicates in placental trophoblasts
• Causes placental insufficiency and inflammation
• Disrupts blood-brain barrier development

Fetal Brain Effects:

• Microcephaly: Reduced brain growth from NPC destruction
• Cortical thinning: Loss of cortical neurons
• Ventriculomegaly: Compensatory enlargement of ventricles
• Intracranial calcifications: Particularly at gray-white matter junctions
• Corpus callosum abnormalities: Hypoplasia or agenesis
• Cerebellar hypoplasia: Variable severity

Emerging Evidence on Risk Modifiers: Recent studies suggest prior dengue immunity may exacerbate Zika-induced fetal neuropathology through antibody-dependent enhancement mechanisms, potentially increasing severity of congenital abnormalities. [21]

Timing-Dependent Effects:

• First trimester: Highest risk for severe microcephaly and brain malformations; early infection strong predictor of severe neonatal neurological damage [28]
• Second trimester: Brain growth disruption, though brain structure may be less severely affected
• Third trimester: Lowest risk, but neurological damage still possible; maternal-fetal transmission and adverse perinatal outcomes documented at all trimesters [33]

Guillain-Barré Syndrome Pathophysiology

The association between Zika virus and GBS represents immune-mediated neurological injury: [11]

Proposed Mechanisms:

1. Molecular mimicry: Viral epitopes cross-react with peripheral nerve antigens
2. Immune activation: Robust T-cell and B-cell responses to infection
3. Autoantibody production: Antibodies targeting gangliosides (GM1, GD1a)
4. Demyelination: Acute inflammatory demyelinating polyneuropathy (most common)
5. Axonal damage: Acute motor axonal neuropathy variant

Epidemiological Evidence:

• GBS incidence increased 2.0-9.8 fold during Zika outbreaks [11]
• Median onset: 6 days after Zika symptom onset (range 1-12 days)
• More severe and rapid progression compared to post-Campylobacter GBS

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4. Clinical Presentation

Acute Zika Virus Infection (Symptomatic Cases)

Only 20% of infected individuals develop symptomatic disease. When symptoms occur, they are typically mild and self-limiting. [1,2]

Incubation Period

• Range: 3-14 days (median 5-7 days)

Cardinal Symptoms and Signs

Duration: Typically 2-7 days (rarely exceeds 7 days)

Distinguishing Features from Other Arboviruses:

Congenital Zika Syndrome (CZS)

Congenital Zika syndrome encompasses a spectrum of abnormalities resulting from in utero infection. [9,10]

Diagnostic Criteria for CZS

Major Features:

1. Severe microcephaly (head circumference \u003e2-3 SD below mean)
2. Decreased brain tissue with specific pattern of damage
3. Subcortical calcifications
4. Congenital contractures (arthrogryposis)
5. Hypertonia with extrapyramidal involvement

Additional Brain Abnormalities:

• Ventriculomegaly
• Cerebellar hypoplasia
• Corpus callosum abnormalities (hypoplasia/dysgenesis)
• Cortical malformations (polymicrogyria, lissencephaly)
• Hydrocephalus

Ocular Abnormalities (25-55% of cases):

• Focal pigmentary retinal mottling
• Chorioretinal atrophy
• Optic nerve abnormalities (hypoplasia, pallor)
• Lens subluxation
• Intraocular calcifications

Audiological Abnormalities:

• Sensorineural hearing loss (5-10% of cases)
• May be progressive

The "Collapsed Skull" Phenotype

In severe cases of CZS, a distinctive appearance results from: [9]

• Marked reduction in brain parenchyma
• Normal growth of facial bones
• Skull bones collapse inward
• Redundant scalp skin with prominent rugae
• Depression of anterior fontanelle

This creates a characteristic profile where facial features appear disproportionately large relative to the cranium.

Neurodevelopmental Outcomes

Children with CZS demonstrate severe impairments across multiple developmental domains: [10,22,23]

• Profound developmental delay affecting all domains
• Severe motor impairment (spastic quadriplegia common)
• Intellectual disability (severe in majority)
• Seizure disorders (30-50%)
• Feeding difficulties requiring gastrostomy
• Growth restriction

Long-Term Follow-Up Data (2023-2024): Longitudinal cohort studies of children now reaching 7-8 years of age demonstrate: [22,23]

• Persistent severe functional impairments across all developmental domains at 12 and 24 months
• Progressive neurological deterioration in some cases
• Atypical gross motor development with high risk for cerebral palsy
• Disrupted functional network development on resting-state EEG
• Even children without overt CZS at birth show increased risk of neurodevelopmental delay in early childhood [24]

Prognostic Factors:

• Severity of microcephaly (worse with more severe brain volume loss)
• Presence of cortical malformations
• Timing of maternal infection (first trimester worst)
• Associated anomalies (ocular, auditory)

Neurological Complications in Adults

Guillain-Barré Syndrome

Represents the most significant adult neurological complication. [11]

Clinical Features:

• Onset: Median 6 days after Zika symptoms (range 1-12 days)
• Presentation: Ascending weakness, areflexia
• Severity: Often more severe than GBS from other causes
• Progression: Rapid, with nadir reached in median 4 days
• Respiratory failure: Occurs in 20-30% (higher than typical GBS)
• Sensory involvement: Paraesthesias common, sensory loss less common

Electrophysiological Patterns:

• Acute inflammatory demyelinating polyneuropathy (AIDP): Most common
• Acute motor axonal neuropathy (AMAN): More common than in non-Zika GBS
• Acute motor-sensory axonal neuropathy (AMSAN): Rare

Diagnostic Criteria:

• Clinical: Progressive symmetric weakness, areflexia
• CSF: Albuminocytologic dissociation (elevated protein, normal cell count)
• Electrophysiology: Demyelinating or axonal pattern
• Serology: Evidence of recent Zika infection (IgM positive)

Other Neurological Manifestations (Rare)

• Meningoencephalitis
• Acute myelitis
• Acute disseminated encephalomyelitis (ADEM)
• Seizures
• Optic neuritis

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5. Differential Diagnosis

In Endemic Areas

The clinical presentation of acute Zika overlaps significantly with other arboviral infections. Differentiation is challenging without laboratory confirmation.

Primary Differentials:

In Travellers Returning from Endemic Areas

Must-Not-Miss Diagnoses:

• Dengue fever (can progress to dengue haemorrhagic fever/shock syndrome)
• Malaria (life-threatening if untreated)
• Typhoid fever (progressive illness if untreated)
• Rickettsial infections (including spotted fever rickettsioses)

Epidemiological Clues:

• Travel itinerary and specific destinations
• Activities (urban vs rural, outdoor exposure)
• Preventive measures (mosquito bite prevention, vaccinations)
• Sexual contacts during or after travel
• Pregnancy status

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6. Investigations

The diagnosis of Zika virus infection requires laboratory confirmation due to the non-specific clinical presentation and extensive overlap with other febrile illnesses, particularly other arboviral infections.

Virus Detection (Direct Methods)

RT-PCR (Nucleic Acid Amplification Testing)

Specimens and Timing: [12]

Clinical Pearls:

• Urine is preferred in the first 2 weeks due to longer viral shedding than serum
• Both serum and urine should be tested simultaneously for maximum sensitivity
• Viral RNA becomes undetectable in serum typically by 7-10 days
• Prolonged viremia (weeks) may occur in immunocompromised individuals

Interpretation:

• Positive PCR: Confirms active or recent Zika infection
• Negative PCR after day 7: Does not exclude Zika; proceed to serology

Serology (Indirect Methods)

Zika IgM and IgG Antibodies

Timing: [12]

• IgM: Detectable from day 4-5, peaks at weeks 2-4, may persist for months (up to 12 weeks)
• IgG: Detectable from day 7-10, persists lifelong

Major Challenge: Flavivirus Cross-Reactivity

This is the most significant limitation of Zika serology. [12]

Cross-Reactivity Occurs With:

• Dengue virus (all 4 serotypes)
• Yellow fever virus (including vaccination)
• Japanese encephalitis virus (including vaccination)
• West Nile virus
• Other flaviviruses (tick-borne encephalitis, etc.)

Why Cross-Reactivity Matters:

1. Shared epitopes: Flaviviruses have highly conserved structural proteins
2. Original antigenic sin: Prior flavivirus exposure results in broader antibody response to subsequent infections
3. Vaccination history: Yellow fever and Japanese encephalitis vaccines generate cross-reactive antibodies

Plaque Reduction Neutralization Test (PRNT)

When serological confirmation is required, PRNT is the gold standard for distinguishing Zika from other flaviviruses. [12]

Method:

• Measures virus-specific neutralizing antibodies
• Tests serum against Zika and other flaviviruses in parallel
• Result interpretation based on titre ratio

Interpretation:

• Zika PRNT titre ≥4-fold higher than dengue: Confirms Zika as recent infection
• Comparable titres: Cannot definitively distinguish; "flavivirus infection, cannot determine specific virus"
• Dengue titre higher: Likely dengue or prior dengue with Zika cross-reaction

Limitations:

• Not widely available (reference laboratories only)
• Requires live virus handling (BSL-2 facilities)
• Labour-intensive, expensive
• Results take 7-14 days

Diagnostic Algorithm for Suspected Zika

Patient with compatible symptoms + epidemiological risk
                    ↓
        ┌───────────┴───────────┐
        |                       |
    ≤7 days since            \u003e7 days since
    symptom onset            symptom onset
        ↓                        ↓
    RT-PCR                  Zika IgM
  (serum + urine)           serology
        |                        |
    ┌───┴───┐              ┌─────┴─────┐
    |       |              |           |
Positive Negative      Positive    Negative
    |       |              |           |
  ZIKA  Perform        Consider     Consider
 CONFIRMED serology     PRNT if    alternative
           ↓          available   diagnoses
       Zika IgM           |
           |          ┌───┴───┐
       ┌───┴───┐      |       |
   Positive Negative Zika   Equivocal
       |       |    confirmed   or
     ZIKA   Unlikely          Dengue
  CONFIRMED  Zika            likely

Investigations in Pregnancy

Maternal Testing [13,14]

Symptomatic Pregnant Women:

• RT-PCR (serum + urine) ASAP, ideally within first week of symptoms
• Zika IgM if presenting \u003e7 days after symptom onset
• PRNT if IgM positive (to confirm vs dengue or other flavivirus)

Asymptomatic Pregnant Women with Exposure:

• Recommendations vary by guideline and level of risk
• CDC 2019 guidance: Testing not routinely recommended for asymptomatic women
• Consider IgM testing if high-risk exposure (e.g., sexual partner with confirmed Zika, prolonged residence in outbreak area)

Fetal Assessment [13,14]

Ultrasound Monitoring:

Key Ultrasound Features of CZS:

• Microcephaly (head circumference \u003c2-3 SD below mean for gestational age)
• Ventriculomegaly
• Intracranial calcifications (periventricular, parenchymal, thalamic)
• Cortical malformations
• Cerebellar abnormalities
• Polyhydramnios or oligohydramnios
• Fetal growth restriction

Fetal MRI:

• Provides superior soft tissue detail compared to ultrasound
• Best performed after 20 weeks gestation
• Useful for detecting subtle cortical malformations
• Helps prognostic counselling

Amniocentesis:

• RT-PCR of amniotic fluid can detect Zika viral RNA
• Positive result confirms fetal infection
• Negative result does not exclude fetal infection (sensitivity ~80%)
• Timing: Consider after 15-18 weeks gestation
• Indications: Abnormal fetal ultrasound findings, strong suspicion of infection

Interpretation Challenges:

• Fetal infection can occur without ultrasound abnormalities
• Abnormalities may not be apparent until later in gestation
• Normal ultrasound does not guarantee normal neurodevelopment

Other Laboratory Findings

Routine Blood Tests (Non-specific):

• Mild leukopenia or normal WBC count
• Mild thrombocytopenia (less pronounced than dengue)
• Mildly elevated liver transaminases (occasional)
• Normal or slightly elevated CRP

Findings Suggestive of Alternative Diagnoses:

• Significant thrombocytopenia (\u003c100,000): Consider dengue
• Severe haemorrhagic manifestations: Unlikely Zika, consider dengue haemorrhagic fever
• Marked leukocytosis: Consider bacterial infection
• Profound anaemia: Consider malaria

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7. Management

There is no specific antiviral treatment for Zika virus infection. Management is entirely supportive for acute illness, with emphasis on prevention and monitoring for complications.

Acute Symptomatic Management

Symptomatic Treatment

Recommended:

• Hydration: Oral fluids encouraged; IV fluids if unable to tolerate oral
• Antipyretics/Analgesics: Paracetamol (acetaminophen) 500-1000 mg every 4-6 hours as needed
• Rest: Adequate rest until symptoms resolve

AVOID (Until Dengue Excluded): [1,2]

• NSAIDs (ibuprofen, aspirin, naproxen): Risk of haemorrhagic complications if dengue
• Aspirin: Additional risk of Reye syndrome (if children/adolescents)

Only use NSAIDs after dengue has been definitively excluded (negative serology or positive Zika confirmation with low dengue probability).

Monitoring

Outpatient Management Suitable if:

• Mild symptoms
• Adequate oral intake
• No warning signs (severe headache, persistent vomiting, abdominal pain, bleeding, altered consciousness)
• Able to return for reassessment if worsening

Consider Hospital Admission if:

• Severe dehydration
• Pregnant
• Neurological symptoms/signs (weakness, altered consciousness, meningism)
• Immunocompromised
• Infants or young children with severe symptoms
• Unable to exclude dengue with warning signs

Management of Pregnant Women

The cornerstone of management in pregnancy is prevention. Once infected, management focuses on surveillance and counselling. [13,14]

Prevention Strategies

Pre-Conception Counselling:

• Travel advice: Defer travel to Zika-endemic areas if pregnancy planned
• Contraception timing after exposure (even if asymptomatic):
  • "Women: Use contraception for 2 months after return from endemic area or after symptoms resolve"
  • "Men: Use condoms or abstain for 3 months after return from endemic area or after symptoms resolve"

During Pregnancy:

• Avoid travel to areas with active Zika transmission (CDC/WHO travel advisories)
• If travel unavoidable: Strict mosquito bite prevention (see below)
• Sexual precautions: Condom use throughout pregnancy if partner has travelled to endemic area

Management After Confirmed or Probable Infection [13,14]

Referral:

• Urgent referral to Maternal-Fetal Medicine specialist or specialist Infectious Diseases service
• Multidisciplinary team approach (obstetrician, neonatologist, geneticist, infectious diseases)

Fetal Surveillance Protocol:

Counselling:

• Risk of congenital abnormalities (estimated 5-15% with first-trimester infection)
• Higher risk with symptomatic vs asymptomatic maternal infection
• Options include continued pregnancy with monitoring, or termination of pregnancy (where legal and acceptable)
• Long-term neurodevelopmental implications of CZS
• Resources for families (genetic counselling, early intervention services)

If Fetal Abnormalities Detected:

• Detailed prognostic counselling
• Discussion of termination of pregnancy vs continuation
• Planning for delivery in tertiary centre with neonatal intensive care
• Preparation for long-term care needs

Delivery Planning

If No Fetal Abnormalities:

• Standard obstetric care
• Mode of delivery based on obstetric indications

If CZS Confirmed:

• Delivery at tertiary centre with Level III/IV NICU
• Multidisciplinary team present at delivery
• Immediate neonatal assessment and supportive care

Management of Guillain-Barré Syndrome

Zika-associated GBS is managed identically to GBS from other causes. [11]

Admission and Monitoring:

• Admit all suspected GBS to hospital (high-dependency or ICU if respiratory compromise)
• Monitor respiratory function: Serial spirometry (FVC), continuous pulse oximetry
• Cardiac monitoring: Autonomic dysfunction common
• Thromboprophylaxis: LMWH unless contraindicated

Specific Treatments:

• IVIg and PLEX equally effective; choice based on availability and patient factors
• No benefit to combining IVIg + PLEX
• Corticosteroids: NOT effective for GBS

Supportive Care:

• Respiratory support: Intubation and mechanical ventilation if FVC \u003c15-20 mL/kg or unable to protect airway
• Pain management: Neuropathic pain common; gabapentin, pregabalin, or opioids
• DVT prophylaxis: Immobility risk
• Physiotherapy: Early mobilization, prevent contractures
• Nutritional support: NG tube or PEG if swallowing compromised

Prognosis in Zika-Associated GBS:

• More severe course than typical GBS
• Higher rate of respiratory failure (20-30% vs 20% in typical GBS)
• Recovery: Most improve with treatment, but residual deficits common (30-40%)
• Time to recovery: Median 3-6 months; some require 12+ months

Prevention Strategies

Mosquito Bite Prevention

Personal Protective Measures:

• Insect repellent: DEET (20-50%), picaridin, IR3535, oil of lemon eucalyptus
  • Apply to exposed skin and clothing
  • Safe in pregnancy (DEET up to 50%)
  • Reapply as per product instructions
• Clothing: Long sleeves, long trousers, light-coloured clothing
• Permethrin-treated clothing: Additional protection (lasts multiple washes)
• Indoor protection:
  • Air conditioning preferred (mosquitoes less active in cool environments)
  • Screens on windows and doors
  • Bed nets (if sleeping during day or in unscreened accommodation)

Environmental Measures:

• Eliminate standing water (breeding sites for Aedes)
• Empty containers, flower pots, tyres weekly
• Community vector control programmes during outbreaks

Prevention of Sexual Transmission

Post-Exposure Recommendations: [6,13]

Rationale:

• Zika RNA detectable in semen up to 188 days post-infection (longest documented)
• Infectious virus isolated from semen up to 69 days
• High infectious viral load documented in semen, confirming sexual transmission as significant pathway [30]
• Asymptomatic infection cannot be excluded without testing

Blood Safety

• Blood donor screening implemented in endemic areas
• Nucleic acid testing (NAT) of donated blood
• Deferral periods for donors who have travelled to endemic areas

Vaccine Development

Current Status (2026):

• No licensed Zika vaccine available
• Multiple candidate vaccines in development (mRNA, DNA, inactivated, live-attenuated, viral vector platforms) [32]
• Phase II/III trials ongoing for several candidates
• Challenges: Declining incidence makes efficacy trials difficult, theoretical risk of antibody-dependent enhancement (as with dengue), need for pregnant women trials

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8. Complications

Maternal Complications

Zika infection in pregnancy is generally not more severe in the mother compared to non-pregnant individuals. Complications include:

• Guillain-Barré syndrome: Same risk as non-pregnant adults
• Miscarriage: Possible increased risk (data limited)
• Stillbirth: Reported but rare
• Preterm birth: May be increased with symptomatic infection

Fetal and Neonatal Complications

Neurological Complications (Adults)

Guillain-Barré Syndrome:

• Incidence: 0.24 per 1,000 Zika infections (2.0-9.8 fold increase during outbreaks) [11]
• Peak onset: 6 days after Zika symptoms
• Severity: Higher rate of respiratory failure (20-30%)
• Recovery: Prolonged; residual deficits in 30-40%

Other Rare Complications:

• Meningoencephalitis
• Acute myelitis
• Chronic arthralgia (weeks to months post-infection)
• Uveitis

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9. Prognosis and Outcomes

Acute Illness

In Non-Pregnant Adults:

• Excellent prognosis
• Self-limiting illness resolving in 2-7 days
• Fatality rate: Extremely rare (case fatality \u003c0.1%)
• Chronic symptoms uncommon (arthralgia may persist weeks in minority)

In Pregnant Women:

• Maternal disease generally mild
• Primary concern is fetal impact, not maternal illness

Congenital Zika Syndrome

Neurodevelopmental Outcomes: [10,22,23,24]

• Severe-profound intellectual disability: Majority of cases
• Cerebral palsy (spastic quadriplegia): Very common, with atypical gross motor development
• Epilepsy: 30-50% develop seizures, including motor abnormalities and epilepsy in infancy [25]
• Feeding difficulties: Often require gastrostomy tube
• Vision impairment: Ranging from mild to bilateral blindness
• Hearing loss: Progressive in some cases

Emerging Evidence on Subtle Neurodevelopmental Impact: Recent data demonstrate children exposed to Zika in utero without overt CZS at birth still show increased risk for multidimensional neurodevelopmental delays, with timing of maternal infection being a significant predictive risk factor. [24,26]

Life Expectancy:

• Limited long-term data (oldest affected children now ~9-10 years old)
• Severe cases at risk for aspiration pneumonia, respiratory failure, status epilepticus
• Lifespan likely reduced, but extent unknown

Prognostic Factors:

• Severity of microcephaly: Most important predictor
• Presence of additional structural brain anomalies: Worse prognosis
• Seizure control: Refractory epilepsy worsens outcome
• Associated malformations: Ocular, cardiac, limb anomalies add morbidity

Subtle CZS:

• Some children with in utero Zika exposure appear normal at birth
• May develop neurodevelopmental delays, autism spectrum features, or seizures later [24,26]
• Risk for neurodevelopmental delay persists even without microcephaly at birth, with timing of infection critical [24]
• Functional network disruption detectable on resting-state EEG even in apparently normal children [27]
• Long-term neurodevelopmental follow-up recommended for all exposed infants

Guillain-Barré Syndrome

Recovery Timeline: [11]

• Nadir reached: Median 7-10 days after onset
• Plateau phase: 2-4 weeks
• Recovery phase: Begins weeks to months after nadir
• Full recovery: 6-12+ months; some have permanent residual deficits

Functional Outcomes:

• 60-70% achieve independent ambulation by 6 months
• 30-40% have residual weakness, sensory deficits, or neuropathic pain
• 3-5% mortality (respiratory failure, sepsis, autonomic dysfunction)

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10. Key Guidelines

International Guidelines

Summary of Key Recommendations

For Pregnant Women: [13,14]

• Avoid travel to areas with active Zika transmission
• If unavoidable, strict mosquito bite prevention measures
• Testing: RT-PCR if symptomatic ≤7 days; serology if \u003e7 days or asymptomatic with high-risk exposure
• Serial ultrasound monitoring every 3-4 weeks if confirmed/probable infection
• Referral to Maternal-Fetal Medicine specialist

For Travellers:

• Use insect repellent (DEET 20-50%) and protective clothing in endemic areas
• Post-travel contraception: Men 3 months, women 2 months

For Clinicians:

• High index of suspicion for travellers from endemic areas with febrile illness + rash
• Test for Zika, dengue, and other relevant pathogens simultaneously
• Careful pregnancy screening for all women of reproductive age with suspected Zika

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11. Examination Focus

Common Exam Questions

MRCOG / Obstetrics:

1. "A pregnant woman at 10 weeks gestation has just returned from Brazil. She is asymptomatic. How would you counsel her?"

   • Answer: Assess risk (duration of stay, mosquito exposure, sexual contacts). Current guidelines do not recommend routine testing for asymptomatic women with travel history alone, but individualized risk assessment is appropriate. Emphasize importance of reporting any symptoms. Offer serial ultrasound monitoring. Discuss sexual precautions (condom use for partner for 3 months). Reassure that most infections do not result in congenital abnormalities, but close monitoring warranted.

2. "What investigations would you arrange for a pregnant woman with confirmed Zika infection in the first trimester?"

   • Answer: Baseline detailed ultrasound immediately, then serial ultrasounds every 3-4 weeks. Fetal biometry with particular attention to head circumference. Assess for intracranial calcifications, ventriculomegaly, cortical malformations. Consider amniocentesis for fetal Zika PCR if abnormalities detected. Fetal MRI if ultrasound abnormalities for detailed brain assessment. Multidisciplinary team referral.

3. "Describe the features of congenital Zika syndrome."

   • Answer: Severe microcephaly with "collapsed skull" appearance, intracranial calcifications (particularly at gray-white junction), ventriculomegaly, corpus callosum abnormalities, cerebellar hypoplasia, congenital contractures (arthrogryposis), hypertonia, ocular abnormalities (focal retinal pigmentary mottling, chorioretinal atrophy), sensorineural hearing loss.

MRCP / Infectious Diseases:

1. "A patient presents with fever, rash, conjunctivitis, and arthralgia 5 days after returning from Colombia. What is your differential diagnosis and how would you investigate?"

   • Answer: Differential: Zika, dengue, chikungunya, malaria, influenza. Investigations: FBC (check for thrombocytopenia suggesting dengue), Zika RT-PCR (serum + urine), dengue serology and NS1 antigen, malaria blood film. Avoid NSAIDs until dengue excluded. Pregnancy test if female of reproductive age.

2. "How long after Zika infection should a man use condoms before attempting conception?"

   • Answer: 3 months after symptom onset (or after return from endemic area if asymptomatic). Rationale: Zika RNA can persist in semen up to 6 months, with infectious virus isolated up to 69 days. Conservative 3-month recommendation balances risk with practicality.

3. "What is the association between Zika virus and Guillain-Barré syndrome?"

   • Answer: Zika is a recognized trigger for GBS. During outbreaks, GBS incidence increased 2-9 fold. Median onset 6 days after Zika symptoms. Pathophysiology likely molecular mimicry and autoimmune response. Zika-associated GBS tends to be more severe, with higher rates of respiratory failure. Treatment identical to GBS from other causes (IVIg or plasma exchange).

MRCPCH / Paediatrics:

1. "You are shown a photograph of a neonate with severe microcephaly, redundant scalp skin, and arthrogryposis. What is the diagnosis and what is the likely underlying cause?"

   • Answer: Diagnosis is congenital Zika syndrome. Features include severe microcephaly with "collapsed skull" and redundant scalp (from brain tissue loss with normal skull bone growth), arthrogryposis (congenital joint contractures). Maternal Zika infection during pregnancy, particularly first trimester, causes infection of fetal neural progenitor cells leading to apoptosis, disrupted neurogenesis, and severe brain malformations.

2. "What long-term complications should you counsel the family about for a child with congenital Zika syndrome?"

   • Answer: Severe developmental delay and intellectual disability, cerebral palsy (spastic quadriplegia), seizures (30-50%), feeding difficulties often requiring gastrostomy, vision impairment (from chorioretinal lesions), progressive hearing loss, growth restriction. Lifelong multidisciplinary care required including neurology, developmental paediatrics, ophthalmology, audiology, physiotherapy, occupational therapy, speech therapy. Prognosis for neurodevelopment is very poor in severe cases.

Viva Points

Opening Statement: "Zika virus is a mosquito-borne Flavivirus that has emerged as a significant public health threat due to its devastating teratogenic effects when infection occurs during pregnancy, causing congenital Zika syndrome characterized by severe microcephaly and brain malformations. While acute illness is typically mild in adults, the virus is also associated with Guillain-Barré syndrome. Uniquely for an arbovirus, Zika can be transmitted sexually, with viral RNA persisting in semen for months."

Key Facts for Viva:

• 80% asymptomatic: Most infections are subclinical, complicating pregnancy counselling
• 5-15% risk of CZS with first-trimester maternal infection (highest risk period)
• 3-month rule for men: Post-exposure sexual precautions (due to prolonged semen shedding)
• 2-month rule for women: Post-exposure contraception recommendation
• Diagnostic challenge: Flavivirus cross-reactivity makes serology interpretation difficult; PRNT required for confirmation
• No specific treatment: Management is entirely supportive; prevention is paramount

Evidence to Quote:

• "During the 2015-2016 Brazil outbreak, over 5,000 cases of microcephaly were reported, representing a 20-fold increase, establishing the causal link between maternal Zika and congenital abnormalities." [3]
• "Zika-associated GBS increases incidence 2-9 fold during outbreaks, with median onset 6 days after symptoms and higher rates of respiratory failure than typical GBS." [11]
• "WHO declared Zika a Public Health Emergency of International Concern in 2016 due to the teratogenic risk." [4]

Common Mistakes

❌ Mistakes that Fail Candidates:

1. Using NSAIDs in acute Zika without excluding dengue

   • Dengue and Zika present identically; NSAIDs increase haemorrhagic risk in dengue
   • Always use paracetamol until dengue excluded

2. Relying on negative PCR after 7 days to exclude Zika

   • Viral RNA becomes undetectable by 7-10 days in serum
   • Must proceed to serology if tested late

3. Interpreting positive Zika IgM as confirmatory without PRNT

   • Flavivirus cross-reactivity is extensive
   • PRNT required to confirm Zika vs dengue/yellow fever

4. Failing to provide sexual transmission counselling

   • Forgetting 3-month condom use recommendation for men returning from endemic areas
   • Critical for preventing congenital infection

5. Not recognizing GBS as a Zika complication

   • Zika is a proven GBS trigger; ask about recent travel/rash illness in any GBS case

6. Recommending routine Zika testing for all asymptomatic pregnant travellers

   • Current CDC/RCOG guidelines: Not routinely recommended for asymptomatic women with travel history alone
   • Individualized risk assessment appropriate

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12. References

1. Petersen LR, Jamieson DJ, Powers AM, Honein MA. Zika Virus. N Engl J Med. 2016;374(16):1552-1563. doi:10.1056/NEJMra1602113

2. Musso D, Gubler DJ. Zika Virus. Clin Microbiol Rev. 2016;29(3):487-524. doi:10.1128/CMR.00072-15

3. Rasmussen SA, Jamieson DJ, Honein MA, Petersen LR. Zika Virus and Birth Defects - Reviewing the Evidence for Causality. N Engl J Med. 2016;374(20):1981-1987. doi:10.1056/NEJMsr1604338

4. Plourde AR, Bloch EM. A Literature Review of Zika Virus. Emerg Infect Dis. 2016;22(7):1185-1192. doi:10.3201/eid2207.151990

5. Hills SL, Fischer M, Petersen LR. Epidemiology of Zika Virus Infection. J Infect Dis. 2017;216(suppl_10):S868-S874. doi:10.1093/infdis/jix434

6. Gregory CJ, Oduyebo T, Brault AC, et al. Modes of Transmission of Zika Virus. J Infect Dis. 2017;216(suppl_10):S875-S883. doi:10.1093/infdis/jix396

7. Rabe IB, Hills SL, Haussig JM, et al. A Review of the Recent Epidemiology of Zika Virus Infection. Am J Trop Med Hyg. 2025;112(5):1026-1035. doi:10.4269/ajtmh.24-0420

8. Shaily S, Upadhya A. Zika virus: Molecular responses and tissue tropism in the mammalian host. Rev Med Virol. 2019;29(4):e2050. doi:10.1002/rmv.2050

9. Freitas DA, Souza-Santos R, Carvalho LMA, et al. Congenital Zika syndrome: A systematic review. PLoS One. 2020;15(12):e0242367. doi:10.1371/journal.pone.0242367

10. Gallo LG, Martinez-Cajas J, Peixoto HM, et al. Another piece of the Zika puzzle: assessing the associated factors to microcephaly in a systematic review and meta-analysis. BMC Public Health. 2020;20(1):827. doi:10.1186/s12889-020-08946-5

11. Leonhard SE, Bresani-Salvi CC, Lyra Batista JD, et al. Guillain-Barre syndrome related to Zika virus infection: A systematic review and meta-analysis of the clinical and electrophysiological phenotype. PLoS Negl Trop Dis. 2020;14(4):e0008264. doi:10.1371/journal.pntd.0008264

12. Song BH, Yun SI, Woolley M, Lee YM. Zika virus: History, epidemiology, transmission, and clinical presentation. J Neuroimmunol. 2017;308:50-64. doi:10.1016/j.jneuroim.2017.03.001

13. American College of Obstetricians and Gynecologists. Management of Patients in the Context of Zika Virus: ACOG Committee Opinion, Number 784. Obstet Gynecol. 2019;134(3):e64-e70. doi:10.1097/AOG.0000000000003399

14. Oladapo OT, Souza JP, De Mucio B, et al. WHO interim guidance on pregnancy management in the context of Zika virus infection. Lancet Glob Health. 2016;4(8):e510-e511. doi:10.1016/S2214-109X(16)30098-5

15. Chibueze EC, Tirado V, Lopes KD, et al. Zika virus infection in pregnancy: a systematic review of disease course and complications. Reprod Health. 2017;14(1):28. doi:10.1186/s12978-017-0285-6

16. Shahrizaila N, Lehmann HC, Kuwabara S. Guillain-Barre syndrome. Lancet. 2021;397(10280):1214-1228. doi:10.1016/S0140-6736(21)00517-1

17. Leonhard SE, Mandarakas MR, Gondim FAA, et al. Diagnosis and management of Guillain-Barre syndrome in ten steps. Nat Rev Neurol. 2019;15(11):671-683. doi:10.1038/s41582-019-0250-9

18. Pielnaa P, Al-Saadawe M, Saro A, et al. Zika virus-spread, epidemiology, genome, transmission cycle, clinical manifestation, associated challenges, vaccine and antiviral drug development. Virology. 2020;543:34-42. doi:10.1016/j.virol.2020.01.015

19. Xie Q, Hu X, Ouyang T, et al. Interplay Between Zika Virus-Induced Autophagy and Neural Stem Cell Fate Determination. Front Microbiol. 2023;14:1274331. doi:10.3389/fmicb.2023.1274331

20. Tang H, Hammack C, Ogden SC, et al. Zika Virus Infects Human Cortical Neural Progenitors and Attenuates Their Growth. Cell Stem Cell. 2016;18(5):587-590. doi:10.1016/j.stem.2016.02.016

21. Zimmerman MG, Quicke KM, O'Neal JT, et al. Cross-Reactive Dengue Virus Antibodies Augment Zika Virus Infection of Human Placental Macrophages. Cell Host Microbe. 2018;24(5):731-742.e6. doi:10.1016/j.chom.2018.10.008

22. Soares FP, Vianna RAO, Fonseca LTM, et al. Neurodevelopmental outcomes in a cohort of children with congenital Zika syndrome at 12 and 24 months of age. Trop Med Int Health. 2022;27(8):743-753. doi:10.1111/tmi.13798

23. Nielsen-Saines K, Brasil P, Kerin T, et al. Long-term developmental outcomes of children with congenital Zika syndrome. Lancet Child Adolesc Health. 2024;8(7):493-501. doi:10.1016/S2352-4642(24)00098-9

24. Mulkey SB, Arroyave-Wessel M, Peyton C, et al. Early and Long-Term Adverse Outcomes of In Utero Zika Exposure. Pediatrics. 2025;155(1):e2024067399. doi:10.1542/peds.2024-067399

25. Del Campo M, Feitosa IM, Ribeiro EM, et al. Motor Abnormalities and Epilepsy in Infants and Children With Evidence of Congenital Zika Virus Infection. Pediatrics. 2017;139(Suppl 2):S32-S36. doi:10.1542/peds.2016-2038E

26. Mulkey SB, Vezina G, Bulas DI, et al. Understanding the multidimensional neurodevelopmental outcomes in children after congenital Zika virus exposure. Front Pediatr. 2024;12:1357417. doi:10.3389/fped.2024.1357417

27. Bulut O, LaMonica-Handa R, Rodriguez-Rivera LA, et al. Disruption of functional network development in children with prenatal Zika virus exposure revealed by resting-state EEG. Sci Rep. 2025;15(1):1458. doi:10.1038/s41598-025-85727-6

28. Coutinho CM, Negrini SFBM, Araujo DJL, et al. Early maternal Zika infection predicts severe neonatal neurological damage: Results from the prospective Natural History of ZIKA Virus Infection in Gestation (NATZIG) cohort study. BJOG. 2021;128(2):317-326. doi:10.1111/1471-0528.16490

29. Baud D, Gubler DJ, Schaub B, Lanteri MC, Musso D. An update on Zika virus infection. Lancet. 2017;390(10107):2099-2109. doi:10.1016/S0140-6736(17)31450-2

30. Mansuy JM, Dutertre M, Mengelle C, et al. Zika virus: high infectious viral load in semen, a new sexually transmitted pathogen? Lancet Infect Dis. 2016;16(4):405. doi:10.1016/S1473-3099(16)00138-9

31. Motta IJF, Spencer BR, Cordeiro da Silva SG, et al. Evidence for Transmission of Zika Virus by Platelet Transfusion. N Engl J Med. 2016;375(11):1101-1103. doi:10.1056/NEJMc1607262

32. Poland GA, Kennedy RB, Ovsyannikova IG, Palacios R, Ho PL, Kalil J. Development of vaccines against Zika virus. Lancet Infect Dis. 2018;18(7):e211-e219. doi:10.1016/S1473-3099(18)30063-X

33. Pomar L, Vouga M, Lambert V, et al. Maternal-fetal transmission and adverse perinatal outcomes in pregnant women infected with Zika virus: prospective cohort study in French Guiana. BMJ. 2018;363:k4431. doi:10.1136/bmj.k4431

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13. Patient and Layperson Explanation

What is Zika?

Zika is a virus spread mainly by mosquitoes in tropical countries. For most adults, it causes a very mild illness - like a mild flu with a rash and red eyes. In fact, 4 out of 5 people infected don't even know they had it. You might have a slight fever, joint aches, and a rash for a few days, and then it goes away on its own.

Why is everyone worried about it?

The problem is what Zika does to unborn babies. If a pregnant woman catches Zika, the virus can attack the baby's developing brain. This can cause the baby's brain to stop growing properly, leading to a condition called microcephaly - where the baby is born with a very small head and severe brain damage. These babies have lifelong disabilities and need constant care.

I'm pregnant. Should I cancel my holiday?

If you're planning to travel to a country where Zika is spreading (like parts of South America, Central America, the Caribbean, or Southeast Asia), yes, you should postpone or cancel. It's not worth the risk. Even if you feel fine, you could catch Zika without knowing it (most people don't get symptoms), and your baby could still be harmed.

If you absolutely must travel:

• Use strong insect repellent (DEET) on your skin
• Wear long sleeves and long trousers
• Stay in air-conditioned or screened rooms
• Your partner should use condoms throughout pregnancy if they travel to these areas

We want to try for a baby after our holiday. How long should we wait?

Zika can hide in sperm for months, even if the person feels perfectly well. To be safe:

• If the man travelled to a Zika area: Wait 3 months before trying to conceive
• If the woman travelled: Wait 2 months before trying to conceive

This gives time for the virus to completely clear from the body.

What if I think I caught Zika while pregnant?

See your doctor immediately. They will:

• Do a blood and urine test to check for Zika
• Arrange regular ultrasound scans to check your baby's development
• Refer you to a specialist who looks after high-risk pregnancies

Most babies exposed to Zika are born healthy, but close monitoring is important.

Is there a cure or vaccine?

No. There's no medicine that kills the Zika virus, and there's no vaccine yet (scientists are working on it). The only treatment is rest, fluids, and paracetamol for aches and pains. Prevention is the only way to avoid Zika.

Can I catch Zika from my partner?

Yes. Zika can spread through sex. If your partner has travelled to a Zika area, use condoms for:

• 3 months if they had symptoms or tested positive
• Even if they felt fine, it's safest to use condoms for 3 months

This is especially important during pregnancy.

What should I watch out for?

Symptoms appear 3-14 days after a mosquito bite. Look for:

• Red, itchy rash
• Mild fever (not very high)
• Joint pain (especially hands and feet)
• Red eyes (but no pus)

If you've been in a Zika area and get these symptoms, see your doctor for testing.

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Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists and follow local/national guidelines for Zika virus management.