Zika virus

Classification and Structure

• Family: Flaviviridae

• Genus: Flavivirus

• Genome: Single-stranded positive-sense RNA (~10.8 kb)

• Structure: Enveloped, icosahedral symmetry, ~50 nm in diameter

• Closely related to other flaviviruses such as dengue, yellow fever, and West Nile virus

Transmission

• Primary vector: Aedes aegypti mosquitoes (also Aedes albopictus)

• Other routes:

  • Maternal–fetal (vertical transmission during pregnancy)

  • Sexual contact (virus detectable in semen for prolonged periods)

  • Blood transfusion

  • Laboratory exposure

Epidemiology

• First identified in 1947 in a rhesus monkey in the Zika Forest, Uganda

• Human cases reported since the 1950s; major outbreaks in Yap Island (2007), French Polynesia (2013), and the Americas (2015–2016)

• Strongly linked to increased microcephaly and other neurological disorders during the Brazil outbreak

Pathogenesis

• Virus enters via mosquito bite → infects skin dendritic cells → spreads to lymph nodes and bloodstream

• Crosses the placenta during pregnancy, potentially disrupting fetal brain development

• Neurotropic, infects neural progenitor cells, leading to apoptosis and impaired neurogenesis

Clinical Manifestations

• Incubation period: 3–14 days

• Most cases: Asymptomatic (~80%)

• Symptomatic illness:

  • Mild fever

  • Maculopapular rash

  • Arthralgia (small joints of hands and feet)

  • Non-purulent conjunctivitis

  • Headache and myalgia

• Complications:

  • Microcephaly and congenital Zika syndrome in newborns

  • Guillain–Barré syndrome in adults

  • Ocular and auditory abnormalities in infants

Diagnosis

• Molecular: RT-PCR for viral RNA in serum, urine, saliva, amniotic fluid (most sensitive during first week)

• Serology: Detection of virus-specific IgM and neutralizing antibodies; cross-reactivity with other flaviviruses may occur

• Prenatal: Ultrasound for fetal abnormalities and amniotic fluid testing

Treatment

• No specific antiviral treatment available

• Management is supportive, focusing on symptom relief

• Measures include:

  • Adequate rest and hydration

  • Paracetamol/acetaminophen for fever and pain

  • Antihistamines for rash and itching

  • Avoid NSAIDs and aspirin until dengue infection is ruled out (to reduce risk of hemorrhage)

• For pregnant women:

  • Regular prenatal monitoring with ultrasound

  • Referral to maternal-fetal medicine specialists if fetal abnormalities are suspected

• For neurological complications:

  • Guillain–Barré syndrome: Supportive care, possible intravenous immunoglobulin (IVIG) or plasma exchange

  • Multidisciplinary management for congenital Zika syndrome (neurology, physiotherapy, speech therapy, occupational therapy)

Prevention and Control

• Vector control:

  • Eliminate mosquito breeding sites

  • Apply larvicides in standing water

  • Insecticide spraying in outbreak areas

• Personal protection:

  • Use of repellents containing DEET, picaridin, or IR3535

  • Wearing long sleeves and pants

  • Sleeping under mosquito nets in risk areas

• Sexual transmission prevention:

  • Condom use or abstinence for a recommended period after travel to endemic zones

• Vaccine status:

  • No licensed vaccine; several candidates in clinical trials

• Public health advice:

• Pregnant women should avoid travel to outbreak areas

• Active surveillance and reporting systems in endemic regions