Zika
Zika
Editors: Yamilka Díaz, José Antonio Suárez, Laura Naranjo
Key Points
- Zika virus is a Flavivirus transmitted by the mosquito Aedes, but unlike other arboviruses, can also be transmitted via sexual contact.
- Most infections are asymptomatic or mild. Some distinguishing features include aseptic conjunctivitis, and edema of hands and feet.
- Rarely, can be complicated with Guillain Barre syndrome or Congenital Zika syndrome.
- Travelers should be counseled on safe sex practices if recently visited areas of Zika transmission, and to avoid travel if pregnant.
Background
Zika virus (ZIKV) is a Flavivirus, primarily transmitted to humans through the mosquito Aedes. First reports seem to date back to the 1950s in Africa. However, since 2007 in Micronesia, there have been several outbreaks in tropical and subtropical regions of the Americas, Asia, and the Pacific Islands. Lately, a spillover in the Americas occurred in 2015. It is characterized by an acute febrile illness, with potential neurologic complications, and unlike other Flaviviruses, it has the capacity of being sexually or vertically transmitted.
Figure 1. Aedes aegypti
Epidemiology & Transmission
ZIKV is encountered in tropical and subtropical areas across the globe, and it shares similar transmission areas as other arbovirosis. Please check a map of endemic areas for Zika here.
Similar to Yellow Fever, ZIKV exists in two main cycles. Both are more commonly transmitted by Aedes mosquitoes (notably Ae. aegypti):
- A sylvatic cycle - occurs in Africa among non-human primates, and functions as a reservoir for the infection.
- An urban/suburban cycle - occurs between humans.
ZIKV is transmitted via several routes:
- Mosquito-borne (most common).
- Sexual transmission (male to female).
- Vertically transmitted.
- Other possible routes (rare): blood transfusion, organ transplantation, needlestick injuries.
Presentation
Incubation period ranges from 3-14 days. Most infections (~80%) are asymptomatic. When symptomatic, it may present with a self-limiting illness (usual duration 2-7 days) that includes: low-grade fever, headaches, arthralgias, retro-orbital pain, myalgias, malaise, lymphadenopathy, conjunctivitis, and distal edema.
Differentiating this from other arbovirosis is extremely difficult solely based on clinical cues. However, some features might be more suggestive of ZIKV. Look for: non-purulent conjunctivitis, and edema of hands and feet, which are not typical in DENV & CHIKV. A pruritic maculopapular rash has also been described.
Complications (rare):
- Neurologic complications: a rough estimate of 1-2/10,000 cases of Guillain-Barre syndrome may appear following ZIKV infection. Most cases occur within 2 weeks of ZIKV infection, and tend to have neurologic recovery at 2-year follow-up. Less common complications include myelopathy or meningoencephalitis.
- Fetopathy (Congenital Zika syndrome, CZS): the incidence ranges from <1%-13% of neonates born to infected mothers. The clinical spectrum of CZS is variable, and includes: neurological disease (microcephaly, spasticity, seizures), retinal dysfunction, hearing loss, craniofacial abnormalities, joint contractures, among others. Zika during pregnancy is also associated with miscarriage & preterm birth.
Figure 2. Clinical spectrum of Zika virus
Prognosis: Hospitalization or death related to ZIKV is extremely rare, but can happen especially if complications occur.
Diagnosis
Testing is indicated in any symptomatic patients who reside in an area of ZIKV transmission, or those with recent history of travel.
Testing can be considered in asymptomatic pregnant women with recent travel or sexual partners with travel or residence in a location with risk of ZIKV infection, but this practice is not universal.
Testing modalities include:
- Serology:
- IgM → takes ~4-7 days to become positive after the onset of symptoms, and it can remain positive after 3 months of initial infection (sometimes after 1 year of infection), and therefore may not accurately represent acute infection.
- IgG → A four-fold increase between acute and convalescent IgG titers may also help make the diagnosis of acute infection. IgG can remain positive for more than 2 years after infection.
- Pitfalls of serology → it can cross-react with other flaviviruses (most, notably dengue virus infection)
- PCR: can be obtained in blood, urine, or semen. ZIKV RNA can be detected for approximately 2 weeks in blood, 4 weeks in urine and 12 weeks in semen.
Treatment/Management
There is no specific antiviral treatment for ZIKV infection. Treatment is supportive.
Prevention
- Vector avoidance: use insect repellents, permethrin-sprayed clothes, protective clothing (long pants & sleeves), and nets. Avoid traveling to endemic areas while pregnant or soon to be pregnant!
- Vector control: decrease mosquito breeding sites (dump stagnant water), mosquito traps.
- Safe sexual practices: this is SO important and often missed! CDC recommends travelers returning from areas of ZIKV transmission, and those with confirmed infection, to avoid sex or use barrier contraception for 2 months (in women) and 3 months (in men) following last travel or last infection.
Other Media Resources (Optional)
References
This lesson was built in partnership with Infectotrópico and was last updated August 22 2025