1. Todd, Betsy MPH, RN, CIC


What we know now about this emerging global threat.


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Until recently, Zika virus was thought to cause only mild to moderate infection, and no serious complications or deaths had been reported.1, 2 However, reports of a dramatic increase in the birth of microcephalic infants during the recent epidemic of Zika virus in Brazil led the World Health Organization (WHO) to declare Zika-associated microcephaly a global health emergency.3 But as with any emerging infection, it may be some time before questions about transmission and the full spectrum of disease are fully answered. This brief overview addresses several common concerns.

Figure 1 - Click to enlarge in new window Countries and territories in the Americas with active Zika virus transmission. Image (C) Centers for Disease Control and Prevention.

Zika is an arbovirus (meaning it is carried by arthropods, an invertebrate that includes insects).4 It is spread by mosquitos of the genus Aedes, the same mosquitos that spread Chikungunya and dengue.1Aedes aegypti is found in the United States as far north as Washington DC.5A. albopictus is probably also capable of transmitting Zika, and its U.S. range can extend as far north as New York City or Chicago.4 These mosquitoes bite during the day as well as at night.1 Infected human and nonhuman primates appear to be the main reservoirs of the virus,6 providing virus-rich blood to the insect vectors.


The virus can spread without its mosquito intermediary in limited ways. It has been identified in amniotic fluid and the placenta,7, 8 and can spread from mother to baby during the early perinatal period.1, 9 Sexual transmission has also been documented.9 The virus has been detected in asymptomatic blood donors, so blood transfusions (and by extension, likely organ transplantation) provide another mode of transmission.9 There have been no reports of infants infected through breastfeeding.9


What are its symptoms? It's estimated that only 20% of people infected with the Zika virus experience symptoms.1 When symptoms do occur they tend to be mild and nonspecific. Fever, maculopapular rash, joint pain, or nonpurulent conjunctivitis usually appears two to seven days after the bite of an infected mosquito.1, 2 (The incubation period can range from three to 12 days.2) Whether symptomatic or asymptomatic, the infection is thought to confer lasting immunity.1 There is no specific antiviral treatment for Zika infection.6


Zika and microcephaly. There are many known causes of microcephaly, including several infections in the womb, maternal malnutrition or exposure to toxins during pregnancy, and genetic abnormalities such as Down syndrome.10 Case-control studies are currently under way in Brazil to delineate the association between the virus and microcephaly, the role of any cofactors, and the true magnitude of the problem. Although the association between Zika and microcephaly is not fully understood, the seriousness of the problem led the Centers for Disease Control and Prevention (CDC) to take the unprecedented step of advising pregnant women to avoid travel to areas in which Zika is being actively transmitted.11 It also advised that men who have traveled to these areas avoid sexual contact or use condoms.12


The virus can be detected using reverse transcriptase-polymerase chain reaction (RT-PCR) testing, which can be performed at the CDC Arbovirus Diagnostic Laboratory and at some state or local health departments.13 Zika tests are not yet commercially available. Clinicians should report suspect cases to their local health department.


Preventing Zika infection. Neither the CDC nor the WHO has recommended isolation safeguards beyond standard precautions. However, the WHO notes that people caring for Zika-infected patients in an environment in which mosquitoes may be present (such as in facilities in the tropics without window screens) should use insect repellent and wear long sleeves and pants.2


Mosquito surveillance and control is the key to preventing Zika infection. Pesticide sprays and larvicides can be used to target high-mosquito-density areas, but the CDC emphasizes that the most effective way to decrease the number of mosquitoes in a community is to reduce larval habitats.4 Any outdoor containers that can hold even small amounts of standing water should be eliminated from both private property and public spaces. Personal protection from any vector-borne virus includes wearing long sleeves and pants and the careful use of insect repellants approved by the Environmental Protection Agency.



Centers for Disease Control and Prevention


For the latest Zika virus information for health care providers:


For up-to-date travel health notices and other health-related travel information:


International Society for Infectious Diseases


ProMED Mail posts real-time information about infectious disease outbreaks (including Zika virus infection) from clinicians and experts all over the world. Its extensive archives are searchable and free of charge:


World Health Organization


For updates on Zika outbreak areas, research and development, and resources:


For an interesting and practical overview of mosquito control:




1. Centers for Disease Control and Prevention. Zika virus: questions and answers. 2016. [Context Link]


2. Pan American Health Organization. Epidemiological alert. Zika virus infection. Washington, DC; 2015 May 7. [Context Link]


3. World Health Organization. WHO director-general summarizes the outcome of the emergency committee regarding clusters of microcephaly and Guillain-Barre syndrome. Geneva; 2016 Feb 1. [Context Link]


4. Centers for Disease Control and Prevention. Chikungunya virus: surveillance and control of Aedes aegypti and Aedes albopictus in the United States. 2015. [Context Link]


5. Lima A, et al. Evidence for an overwintering population of Aedes aegypti in Capitol Hill neighborhood, Washington, DC Am J Trop Med Hyg. 2016;94(1):231-5 [Context Link]


6. Centers for Disease Control and Prevention. Zika virus: clinical evaluation and disease. 2015. [Context Link]


7. Calvet G, et al. Detection and sequencing of Zika virus from amniotic fluid of fetuses with microcephaly in Brazil: a case study Lancet Infect Dis. 2016 Feb 17 [Epub ahead of print]. [Context Link]


8. Martines RB, et al. Notes from the Field: Evidence of Zika virus infection in brain and placental tissues from two congenitally infected newborns and two fetal losses-Brazil, 2015 MMWR Morb Mortal Wkly Rep. 2016;65(06):159-60 [Context Link]


9. Centers for Disease Control and Prevention. Zika virus: transmission. 2015. [Context Link]


10. World Health Organization. Emergencies: microcephaly. 2016. [Context Link]


11. Centers for Disease Control and Prevention. CDC issues interim travel guidance related to Zika virus for 14 countries and territories in Central and South America and the Caribbean [news release]. 2016 Jan 15. [Context Link]


12. Oster AM, et al. Interim guidelines for prevention of sexual transmission of Zika virus-United States, 2016 MMWR Morb Mortal Wkly Rep. 2016;65:120-1 [Context Link]


13. Centers for Disease Control and Prevention. Zika virus: diagnostic testing. 2015. [Context Link]