Summary / Overview
- Zika virus is a mosquito-borne flavivirus that typically produces a mild, self-limited illness.
- The main public-health importance of ZIKV lies in its ability to cause congenital Zika syndrome (microcephaly and other fetal defects) when infection occurs during pregnancy.
Etiology
- Zika virus (ZIKV) is an RNA virus belonging to the Flaviviridae family and genus Flavivirus.
Pathogenesis
- Zika virus enters the body primarily through the skin following an Aedes mosquito bite.
Symptoms
- Most Zika infections are asymptomatic (≈ 70–80%).
- 1) Common symptomatic presentation
- - Low-grade fever (usually < 38.5°C)
- - Maculopapular rash (often starts on face → trunk → limbs)
- - Mild non-purulent conjunctivitis (red eyes)
- 2) Neurological symptoms
- - Mild sensory neuropathy
- - Paraesthesias
- 3) Gastrointestinal symptoms (less common)
Signs
- Usually mild or non-specific signs.
- - Maculopapular rash (often diffuse, blanching)
- - Conjunctival injection
- - Mild cervical lymphadenopathy
- - Tender small joints (hands, wrists, ankles)
- - Mild synovitis without effusion
- - Mild sensory hypoesthesia may be present
Clinical Features
- Self-limited viral illness; symptoms last 2–7 days.
- Rare but important manifestations
- Risk of congenital Zika syndrome (CZS)
Investigations
- Diagnosis relies on molecular tests during acute phase; serology in later stage.
- If mother tested positive or symptomatic:
Differential Diagnosis
- DDx focuses on distinguishing Zika from other febrile arboviral illnesses and exanthem-type viral infections.
Complications
- Most complications are neurological or pregnancy-related.
Treatment
- No specific antiviral therapy exists for Zika virus.
Prevention
- No vaccine is currently available for Zika virus.
Serotypes / Subtypes
- Zika virus has two major genetic lineages.
- No distinct serotypes like dengue. Only these two lineages are recognized.
Pathology
- Neurotropic virus — strong affinity for neural progenitor cells.
- Pathology mainly results from viral neurotropism + immune-mediated damage.
Radiology / Imaging
- Neuroimaging is the key component — especially in congenital cases.
- Most sensitive modality for congenital Zika syndrome
- Key radiological signature: intracranial calcifications + cortical maldevelopment + microcephaly.
Notes / Teaching points
- Zika virus is mild in most adults — so why is it important?
- Why does Zika cause microcephaly?
- How is Zika different from dengue and chikungunya?
- Why is Guillain-Barré syndrome associated with Zika?
- Why is diagnosis often difficult?
- Teaching Pearls
Self-limited viral illness; symptoms last 2–7 days.
1) Prodromal features
- Low-grade fever (often <38.5°C)
- Malaise, fatigue, mild headache
- Photophobia in some patients
2) Dermatologic
- Diffuse maculopapular rash, often the earliest and most prominent feature
- Rash begins on the face or trunk and spreads rapidly
- Mild pruritus is common
3) Ocular
- Non-purulent conjunctivitis
- Pain, burning, or gritty sensation may occur
- Mild peri-orbital swelling
4) Musculoskeletal
- Arthralgia (especially small joints of hands, wrists, ankles, and feet)
- Myalgia, often mild
- Joint swelling is uncommon
5) Neurological
Rare but important manifestations
- Guillain–Barré syndrome (GBS) association documented
- Mild paresthesias
- Facial palsy occasionally reported
6) Gastrointestinal
- Mild nausea, vomiting, or abdominal discomfort (not very common)
7) In pregnancy
Risk of congenital Zika syndrome (CZS)
- Microcephaly
- CNS malformations
- Visual & auditory defects
Most complications are neurological or pregnancy-related.
1) **Congenital Zika Syndrome (CZS)**
- Severe microcephaly with partially collapsed skull
- Thin cerebral cortices with subcortical calcifications
- Ocular abnormalities (macular scarring, focal pigment mottling)
- Joint deformities (arthrogryposis)
- Intrauterine growth restriction (IUGR)
- Hearing loss
2) **Guillain–Barré Syndrome (GBS)**
- Post-infectious autoimmune neuropathy
- Ascending weakness ± respiratory involvement
- Strong epidemiological association with Zika outbreaks
3) **Myelitis**
- Acute flaccid paralysis
- Sensory deficits below the lesion
- Bladder/bowel dysfunction
4) **Meningoencephalitis**
- Altered sensorium, seizures
- Fever, neck stiffness
- Possible long-term neurological deficits
5) **Ocular Complications (adults)**
- Uveitis
- Optic neuritis
- Retinal vasculitis
6) **Thrombocytopenia / Immune-mediated cytopenias**
- Petechiae, mucosal bleeding (rare compared to dengue)
7) **Hepatitis (mild)**
- Elevated transaminases occasionally observed
8) **Perinatal transmission complications**
- Neonatal Zika infection → rash, irritability, seizures
DDx focuses on distinguishing Zika from other febrile arboviral illnesses and exanthem-type viral infections.
1) **Dengue Fever**
- High fever, severe myalgia, retro-orbital pain
- Thrombocytopenia + hemoconcentration common
- Rash may be similar; however, dengue has higher bleeding risk
2) **Chikungunya**
- More intense joint pains and stiffness
- Chronic arthralgia persists for months
- High fever more abrupt; rash less common than Zika
3) **Rubella**
- Maculopapular rash similar to Zika
- Tender post-auricular and suboccipital lymph nodes
- Usually mild fever and less conjunctivitis
4) **Measles (Rubeola)**
- High-grade fever, cough, coryza, conjunctivitis
- Koplik spots present (glossary: Koplik’s spots)
- Rash starts at hairline and spreads downward
5) **Other Viral Exanthems**
- Enteroviruses (e.g., echovirus, Coxsackie)
- Parvovirus B19
- Adenovirus infections
- EBV/CMV (with rash following antibiotics)
6) **COVID-19 (mild forms)**
- Fever, myalgia, rash, conjunctivitis possible
- PCR testing required to differentiate
7) **Other Arboviruses**
- West Nile virus (more neuroinvasive features)
- Japanese Encephalitis (encephalopathy, seizures)
- Yellow fever (jaundice, bleeding tendencies)
8) **Allergic Dermatitis / Drug Rash**
- Itching more prominent
- No conjunctivitis or arthralgia
- No epidemiological link to mosquito exposure
Zika virus (ZIKV) is an RNA virus belonging to the Flaviviridae family and genus Flavivirus.
ZIKV is closely related to dengue virus, yellow fever virus, West Nile virus, and Japanese encephalitis virus.
Genome:
- Single-stranded, positive-sense RNA (~10.7 kb)
- Enveloped, icosahedral virion
- Encodes structural proteins (C, prM/M, E) and non-structural proteins (NS1–NS5)
Lineages:
- **African lineage**
- **Asian lineage** (responsible for major outbreaks in the Pacific and the Americas, including the congenital microcephaly clusters)
Natural reservoir:
- Primarily **non-human primates**
- Human-mosquito-human cycle occurs in outbreaks
Vectors:
- Mainly **Aedes aegypti**
- Also **Aedes albopictus**, and other Aedes species
Transmission routes:
- Mosquito bite (primary)
- **Vertical transmission (transplacental)**
- **Sexual transmission**
- **Blood transfusion**
- Rare **laboratory exposure**
No other definitive animal reservoirs apart from primates and possibly some small mammals have been confirmed.
Diagnosis relies on molecular tests during acute phase; serology in later stage.
1) RT-PCR (NAT testing) – **gold standard**
- Detects Zika viral RNA
- Best within first 0–7 days of symptom onset
- Performed on serum, plasma, whole blood, or urine
- Urine may remain PCR-positive longer than serum
2) Serology (IgM + PRNT)
- Zika IgM detectable after day 4–5 of illness
- Cross-reactivity common with dengue, yellow fever, Japanese encephalitis
- PRNT (Plaque Reduction Neutralization Test) used to confirm Zika vs dengue
3) CBC
- May show mild leukopenia
- Platelets usually normal (helps differentiate from dengue)
4) LFT
- Mild elevation of AST/ALT may be present
5) CRP/ESR
- Usually normal or mildly elevated
6) Urine PCR
- Viral RNA detectable for >14 days in urine in many cases
- Useful when serum PCR is negative but suspicion remains
7) Pregnancy-specific investigations
If mother tested positive or symptomatic:
- Serial fetal ultrasonography every 3–4 weeks
- Look for: microcephaly, intracranial calcifications, ventriculomegaly, corpus callosum defects, growth restriction
8) CSF testing (rare, neuro cases)
- Zika PCR or IgM in CSF when neurological complications (e.g., GBS) suspected
Zika virus is mild in most adults — so why is it important?
Because its unique danger lies in **pregnancy**, where maternal infection can cause **Congenital Zika Syndrome (CZS)** including microcephaly, brain malformations, ocular defects, and severe developmental disability. This makes it a major public-health concern despite mild symptoms in adults.
Why does Zika cause microcephaly?
Zika shows **tropism for neural progenitor cells**. It destroys these cells during fetal development → reduced brain growth, calcifications, cortical malformation → microcephaly.
How is Zika different from dengue and chikungunya?
- Dengue → hemoconcentration, thrombocytopenia, shock.
- Chikungunya → severe arthralgia, chronic joint pain.
- **Zika → mild rash + conjunctivitis + severe neurological risk in fetus**.
Why is Guillain-Barré syndrome associated with Zika?
Thought to be due to an **immune-mediated response** (molecular mimicry). Occurs after the viral illness, similar to post-Campylobacter GBS.
Why is diagnosis often difficult?
- Symptoms overlap with dengue/chikungunya.
- Cross-reactivity of IgM serology among flaviviruses.
- PCR helpful only in early viremia window (first 7 days).
Teaching Pearls
● Zika is the *only arbovirus* strongly linked to congenital brain malformations.
● Conjunctivitis is more prominent than in dengue or chikungunya.
● Aedes mosquito bites during early pregnancy → highest fetal risk.
● Microcephaly + intracranial calcifications = red flag for congenital Zika syndrome.
● Most adult infections are asymptomatic → surveillance relies on public health tracking.
● Prevention is mainly vector control + pregnancy travel restriction.
● No vaccine yet (clinical trials ongoing).
Zika virus enters the body primarily through the skin following an Aedes mosquito bite.
1) Local infection
- Virus infects **keratinocytes**, **skin fibroblasts**, and **Langerhans cells**.
- Early replication occurs in local dendritic cells.
- ZIKV spreads to regional lymph nodes → bloodstream.
2) Viremia
- Short-lived viremia (usually < 1 week).
- Virus disseminates to multiple organs including brain, placenta, testes, and eyes.
3) Immune evasion
- NS proteins inhibit interferon (IFN) signaling.
- Suppression of innate immunity allows viral spread.
- Increased cytokine release contributes to fever, rash, and arthralgia.
4) Neurotropism
- ZIKV shows strong **tropism for neural progenitor cells**.
- Causes apoptosis, impaired neurogenesis, and microcephaly in fetuses.
- Viral entry via AXL receptor (highly expressed in neural tissues).
5) Placental transmission
- Virus crosses the placenta via trophoblast infection.
- Persistent infection of fetal neural progenitor cells causes congenital Zika syndrome.
6) Guillain–Barré Syndrome mechanism (proposed)
- Immune-mediated demyelination triggered by molecular mimicry.
- No direct neuronal infection in adults is proven.
7) Sexual transmission pathogenesis
- Virus replicates in testes and persists in semen for months.
- Immune-privileged environment allows long-term viral survival.
8) Ocular involvement
- Infection of retinal pigment epithelial cells.
- Causes conjunctivitis, uveitis, and in infants → chorioretinal atrophy.
Neurotropic virus — strong affinity for neural progenitor cells.
Zika virus shows marked **tropism for neural tissue**, particularly fetal neural progenitor cells, leading to impaired neuronal proliferation and apoptosis.
• **Central Nervous System (CNS)**
- Infection of neural stem cells → reduced neurogenesis
- Cortical thinning and microcephaly in congenital infections
- Neuronal apoptosis, calcifications (subcortical, periventricular), astrocyte activation
- White matter hypoplasia and ventriculomegaly in severe cases
• **Placental Pathology**
- Viral replication in trophoblasts
- Placental insufficiency → impaired fetal perfusion
- Chronic villitis and inflammation
- Viral RNA detectable in placental tissues
• **Peripheral Nervous System**
- Immune-mediated demyelination (basis for Guillain–Barré syndrome)
- Lymphohistiocytic infiltration around peripheral nerves
• **Eye Pathology (Congenital Zika syndrome)**
- Optic nerve hypoplasia
- Chorioretinal atrophy
- Pigment mottling of macula
• **Other Tissues**
- Mild involvement of spleen, lymph nodes, liver
- Lymphocytic infiltration and mild hepatitis in some cases
Pathology mainly results from viral neurotropism + immune-mediated damage.
No vaccine is currently available for Zika virus.
1) **Mosquito control (primary prevention)**
- Eliminate standing water (Aedes breeding sites)
- Use indoor residual spraying
- Use larvicides in water storage containers
- Community-wide vector control programs
2) **Personal protection**
- Wear long-sleeved clothing
- Use EPA-approved repellents (DEET, picaridin, IR3535, lemon-eucalyptus oil)
- Use bed nets in high-risk areas
- Keep windows/doors screened
3) **Protection for pregnant women**
- *Strongly avoid travel* to Zika-affected regions
- Strict mosquito bite prevention
- Avoid unprotected sexual contact with partners who traveled to or live in Zika-endemic areas
4) **Sexual transmission prevention**
- Men returning from Zika areas: **Use condoms for 3 months**
- Women returning from Zika areas: **Use condoms for 2 months**
- Couples planning pregnancy: delay conception according to above timelines
5) **Blood and tissue safety**
- Blood donation deferred for travelers returning from endemic zones
- Screening for organ/tissue donation when required
6) **Community & public health measures**
- Early detection and reporting of outbreaks
- Public education on mosquito control and travel advisories
- Prenatal screening & fetal monitoring for pregnant women in affected areas
Neuroimaging is the key component — especially in congenital cases.
● **Cranial Ultrasound (neonate)**
- Ventriculomegaly
- Periventricular calcifications
- Cortical atrophy and enlarged subarachnoid spaces
- Simplified gyral pattern (lissencephaly-like changes in severe cases)
● **CT Brain**
- **Calcifications**: subcortical, periventricular, basal ganglia
- Ventricular enlargement
- Cortical thinning
- Scattered intracranial calcifications (distinct from CMV pattern)
● **MRI Brain**
Most sensitive modality for congenital Zika syndrome
- Reduced brain volume
- Delayed or abnormal cortical formation
- Pachygyria / polymicrogyria
- Hypomyelination
- Corpus callosum hypoplasia
- Brainstem and cerebellar hypoplasia (in severe cases)
● **Spinal Imaging**
- Occasionally shows nerve-root enhancement in Guillain-Barré syndrome
● **Ophthalmologic Imaging**
- OCT / fundus imaging:
- Chorioretinal atrophy
- Optic nerve hypoplasia
- Pigment mottling across macula
● **Chest X-ray**
- Usually normal
- Mild viral pneumonitis only if co-infection or pregnancy-related complications
Key radiological signature: intracranial calcifications + cortical maldevelopment + microcephaly.
Zika virus has two major genetic lineages.
1) **African lineage**
- The ancestral and historically predominant lineage.
- Mainly associated with mild disease.
- Considered the origin of early enzootic circulation.
2) **Asian lineage**
- Responsible for the large outbreaks in the Pacific and the Americas (2013–2016).
- More strongly associated with congenital Zika syndrome and Guillain–Barré syndrome.
- Shows genetic adaptations enhancing human and Aedes mosquito transmission.
No distinct serotypes like dengue. Only these two lineages are recognized.
Usually mild or non-specific signs.
1) Skin
- Maculopapular rash (often diffuse, blanching)
- Rash may be itchy but not always
- Rare petechiae or mild bleeding manifestations
2) Eyes
- Non-purulent conjunctivitis (no discharge)
- Conjunctival injection
- Mild peri-orbital edema
3) Lymphatic system
- Mild cervical lymphadenopathy
- Occasionally retroauricular nodes enlarged
4) Musculoskeletal
- Tender small joints (hands, wrists, ankles)
- Mild synovitis without effusion
5) Neurological
- Normal in most patients
- Mild sensory hypoesthesia may be present
- Rare: lower motor neuron facial palsy
6) General physical signs
- Low-grade fever
- Normal respiratory and cardiovascular findings
Zika virus is a mosquito-borne flavivirus that typically produces a mild, self-limited illness.
The main public-health importance of ZIKV lies in its ability to cause congenital Zika syndrome (microcephaly and other fetal defects) when infection occurs during pregnancy.
Zika virus infection is transmitted primarily through **Aedes mosquitoes** (A. aegypti, A. albopictus), but additional routes include **sexual transmission**, **blood transfusion**, and **vertical (transplacental) transmission**.
Clinically, most infections are **asymptomatic** (≈70–80%). Symptomatic cases present with mild fever, maculopapular rash, arthralgia, non-purulent conjunctivitis, headache, and malaise.
Neurological complications include **Guillain-Barré syndrome (GBS)** in adults, although uncommon.
Major outbreaks occurred in the Pacific Islands (2013–2014) and the Americas (2015–2016), revealing the strong association between **maternal infection and fetal microcephaly**, making ZIKV a major global health concern.
There is **no specific antiviral treatment**; management is supportive. Prevention relies on mosquito-control strategies and personal protection measures.
Most Zika infections are asymptomatic (≈ 70–80%).
1) Common symptomatic presentation
- Low-grade fever (usually < 38.5°C)
- Maculopapular rash (often starts on face → trunk → limbs)
- Mild non-purulent conjunctivitis (red eyes)
- Headache (usually frontal)
- Retro-orbital pain
- Myalgia and arthralgia (notably small joints of hands/feet)
2) Neurological symptoms
- Mild sensory neuropathy
- Paraesthesias
- Rare involvement: facial palsy, peripheral neuropathies
3) Gastrointestinal symptoms (less common)
- Nausea
- Mild abdominal discomfort
4) Genitourinary symptoms
- Hematospermia (rarely reported)
- Persistent viral shedding in semen, but usually asymptomatic
5) Symptoms in pregnancy
- Symptoms same as general population
- Fetal abnormalities occur even if maternal symptoms are mild or absent
6) Duration
- Symptoms typically last 2–7 days
- Fatigue may persist for weeks
No specific antiviral therapy exists for Zika virus.
1) **Supportive care**
- Adequate hydration
- Rest
- Antipyretics (Paracetamol preferred)
2) **Avoid NSAIDs until dengue is excluded**
- NSAIDs/aspirin increase bleeding risk if the illness is actually dengue
- Use **only paracetamol** in the first 48–72 hrs until platelets and dengue tests are confirmed
3) **Symptomatic management**
- Analgesics for arthralgia
- Antihistamines for itching
- Cold compresses for joint swelling
4) **Monitoring**
- Neurological symptoms (GBS risk)
- Pregnant women → ultrasound monitoring of fetal growth and brain development
- If neurological symptoms appear → urgent referral
5) **Management of complications**
- *Guillain–Barré Syndrome →* IVIG or plasmapheresis
- *Meningoencephalitis / Myelitis →* supportive ICU care
- *Ocular involvement →* ophthalmology evaluation
6) **Pregnancy considerations**
- No antiviral therapy
- Serial fetal ultrasounds every 3–4 weeks
- Counseling regarding fetal risks and options
7) **Sexual transmission precautions**
- Recommend condom use for **3 months (men)** and **2 months (women)** after infection
- Avoid conception during this period
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