Zika virus is an arbovirus transmitted by the mosquito Aedes aegypti. The infection can also be transmitted transplacentally and sexually. Since 2015, epidemic outbreaks of Zika virus infection have occurred in South America, US territories, and in certain southern US states. The infection is typically asymptomatic or results in mild flu-like symptoms. However, this infection has received a lot of attention because it can result in fetal microcephaly when the virus infects pregnant women. Much about this disease is still unknown and it is currently the subject of much study and research. The diagnosis is usually confirmed by PCR and/or serology. Currently, neither a definitive therapy nor a clinically-approved vaccine exist.
Worldwide geographical distribution
- Outbreaks most commonly occur in tropical and subtropical regions.
- Before 2015, a few cases were reported in Africa, southeast Asia, and in the Pacific islands
- Since 2015, epidemic outbreaks have been reported in South America (especially Brazil).
Epidemiology in the US
- The overwhelming majority of cases (> 25,000) are reported in US territories, most of which occurred in Puerto Rico.
- Approx. 4000 cases were reported in the continental US, most of which occur in New York, Florida, California, and Texas.
Epidemiological data refers to the US, unless otherwise specified.
Pathogen: Zika virus
- Genus: flavivirus, type of arbovirus
- Positive-sense, single-stranded, enveloped RNA
Route of transmission
- Vector-borne transmission by the mosquito Aedes aegypti (common)
- Transplacental transmission from the mother to the fetus
- Sexual transmission
- Incubation time: 2–14 days
- Approx. 80% of cases remain asymptomatic
- In symptomatic patients, the manifestations are usually mild and last for 2–7 days
- Low-grade fever
- Flu-like symptoms: headache, arthralgia, myalgia, non-purulent conjunctivitis, malaise
- Maculopapular, pruritic rash (20% of cases) 
The symptoms of Zika virus infection in adults are usually mild and non-specific, but its complications may be devastating (see “Complications” below).
- ↑ Acute phase reactants (e.g., CRP, ferritin)
- Leukopenia, thrombocytopenia
- ↑ LDH, ↑ γ-GT
- During the first 7 days of the infection: PCR detects Zika virus RNA in blood and/or urine samples
- During days 7–28: RT-PCR and/or serology
- After 28 days: serology confirms Zika virus antibodies
A Zika virus infection should be considered in any patient that recently traveled to a region with an outbreak.
- Guillain-Barre syndrome
Congenital Zika syndrome: growth restriction and significant CNS complications in neonates resulting from intrauterine transmission of the Zika virus
- Microcephaly (craniofacial disproportion)
- Subcortical calcifications
- Spasticity (contractures), hyperreflexia, seizures
- Ocular abnormalities (e.g., pigmentary retinal mottling)
- Sensorineural hearing loss
- Congenital Zika syndrome: growth restriction and significant CNS complications in neonates resulting from intrauterine transmission of the Zika virus
We list the most important complications. The selection is not exhaustive.
- A vaccine against Zika virus does not exist yet.
- Vector control and safe sexual practices are the most important public health measure in endemic regions.
- Individuals traveling to endemic regions should be told to use insect repellents, mosquito nets, and long-sleeved clothing.
- In the case of travel to an endemic region and/or a positive Zika test, couples planning to conceive should use a condom or abstain for the following time periods (even if asymptomatic!):
- During pregnancy
Zika virus infection is a notifiable disease!