MicrobiologyTier 2Medical Sciences concept

Zika virus - transmission and prevention

Core concept

Flavivirus (same genus as dengue, yellow fever, JE, West Nile)
Transmission routes - the exam point is that mosquito bite is not the only one
- Aedes aegypti and Aedes albopictus - daytime biters, urban
- Sexual - the only arbovirus with established sexual transmission; persists in semen far longer than in blood (months)
- Vertical / transplacental - congenital Zika syndrome
- Blood transfusion, organ transplant; laboratory exposure
~80% asymptomatic; symptomatic disease is mild - low-grade fever, maculopapular rash, non-purulent conjunctivitis, arthralgia, 2-7 days
- Rash and conjunctivitis favour Zika; severe myalgia and high fever favour dengue; disabling arthralgia favours chikungunya

Congenital Zika syndrome

Microcephaly with a collapsed skull and overlapping sutures, subcortical calcifications, ventriculomegaly, lissencephaly/cortical malformation
Ocular - macular scarring, optic nerve hypoplasia
Congenital contractures (arthrogryposis), early hypertonia, sensorineural deafness
Risk highest with first-trimester infection (~5-15% of infected pregnancies have an adverse outcome)

Neurological

Guillain-Barre syndrome - the association that defined the 2015-16 outbreak; also myelitis and encephalitis

Diagnosis

Zika RNA by RT-PCR in blood (up to ~7 days) and urine (up to ~14 days) - the definitive test in the acute window
Serology cross-reacts extensively with dengue and after yellow fever/JE vaccination -> IgM needs plaque-reduction neutralisation to confirm
In Australia, Zika is a notifiable, imported infection - discuss with an infectious diseases or sexual health service and the reference laboratory

Prevention - this is the whole management

Pregnant women should not travel to areas with current Zika transmission; if travel is unavoidable, rigorous bite avoidance (DEET or picaridin - safe in pregnancy, permethrin-treated clothing, air conditioning, screens)
After possible exposure (travel to an area with transmission), for couples planning pregnancy - condoms or abstinence, and defer conception
- Men: 3 months after exposure or symptom onset
- Women: 2 months
- These intervals reflect prolonged shedding in semen and are the numbers most likely to be tested
No vaccine and no specific antiviral; supportive care
- Avoid aspirin and NSAIDs until dengue is excluded (bleeding risk)
Blood donation deferral after travel to an affected area
Antenatal management of a possible exposure: maternal PCR/serology, serial ultrasound for growth and CNS anatomy, amniocentesis and neonatal assessment as indicated

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