Picture of a mosquito

Zika Virus Update: What You Should Know

By Michael D. Holzer MD, MPH&TM, National Travel Medicine Medical Director | 02/01/2016


Zika virus was first identified in Africa in 1947 and up until 2007, sporadic infections occurred in at least 12 countries in Africa and SE Asia. Given its cross-reaction in commonly used dengue blood  tests, misdiagnosis as mild dengue has most likely led to underreporting of Zika virus infection.  In 2007, there was a large outbreak for the first time outside Africa and Asia, in the Micronesian island of Yap, which then spread to other Pacific Islands and French Polynesia.  Since early 2015, the largest outbreak ever was first discovered in Brazil and subsequently in other countries in Central and South America and the Caribbean. While most Zika infections result in either no or very mild symptoms, there is increasing concern of a possible association of Zika infections during pregnancy and infants with microcephaly and other poor pregnancy outcomes. On February 1, 2016 the World Health Organization (WHO) declared the current Zika outbreak " a public health emergency of international concern".


  • Where is the current outbreak occurring (Local Transmission)?
    • South America
      • Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Suriname, Venezuela
    • Central America/North America
      • Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama
    •  Caribbean
      • Barbados, Dominican Republic, Guadeloupe, Haiti, Martinique, Puerto Rico, Saint Martin, US Virgin Islands
    • Other
      • Samoa, Cape Verde

Travel related cases have been reported in some states in the United States, but no locally transmitted cases have occurred.  However, all countries in the Americas, including the United States, are at risk of local transmission of Zika, except Canada and Chile, due to the presence of the mosquito vector.


  • How is Zika transmitted?  
The virus is transmitted by bite of an infected Aedes mosquito, most commonly Aedes aegypti.  This is the same mosquito that transmits yellow fever, dengue, and chikungunya.  These mosquitos bite during the day, with peak biting times being the first 2-3 hours after dawn and mid-late afternoon. In addition, there are a couple reports of Zika being spread by blood transfusion and through sexual contact.  However, these modes of transmission have not been confirmed.


  • What are the symptoms? Approximately, 1 of 5 people who become infected has symptoms.  The time it takes from being bitten from an infected mosquito to having symptoms( incubation period)  is approximately 2-12 days. The majority of cases are very mild and self-limited and last less than a week. Severe disease resulting in hospitalization is very uncommon. The most common symptoms are:
    • Fever
    • Rash
    • Joint pain and muscle aches
    • Conjunctivitis (red eyes)
    • Headache
  • What are possible complications?
    • Microcephaly and other poor pregnancy outcomes
      • Microcephaly is a birth defect in which the infant's head is significantly smaller than normal and may be associated with seizures, developmental delay and other neurological conditions.  Refer to the CDC site on microcephaly for more information.
      • There have been numerous cases of microcephaly and other poor pregnancy outcomes in mothers in Brazil who were infected with Zika while pregnant. Investigations to determine causal association are ongoing and the situation is very fluid.  In an abundance of caution, most authorities including the CDC recommend:
        • Pregnant women and women trying to become pregnant should consider postponing travel to Zika-affected areas. If they do travel, they should speak to their physician or travel health specialist.
    • Guillain-Barre Syndrome (GBS)
      • GBS is an auto-immune condition which can cause muscle weakness and paralysis.
      • There have been reports of increased rates of GBS in Brazil and other Latin American countries.  The case fatality rate is low.  While a causal association has not been confirmed, GBS is known to be a complication of many different viral and bacterial infections.
  •  Who should seek medical evaluation to determine if they have Zika infection?
    • Pregnant women, who while pregnant, experienced signs/symptoms compatible with Zika infection (fever, maculopapular rash, arthralgia, or conjunctivitis) within 2 weeks of travel to an area with local transmission, regardless of the length of time since travel/illness occurred.
    • If not pregnant, signs or symptoms of Zika infection AND travel to an area with local transmission in the 2 weeks prior to the illness  

It is very important to consider other travel related illnesses that may be more common and associated with greater morbidity and mortality.  Therefore, any fever in a returned travelers should be evaluated to rule out other disease including, but not limited to malaria, typhoid, dengue, and chikungunya depending on the specific itinerary and activities.  The best way to prevent becoming ill during or shortly after travelling is to see a travel health specialist prior to travelling.

  • What is the treatment?

There is no specific treatment for Zika.  Treatment is supportive and includes hydration, rest and analgesics.  NSAIDS and Aspirin should be avoided unless dengue is ruled out (due to possible bleeding complications associated with dengue) as the presentation and area of risk is similar.

While Zika is not spread person to person, it is important that a person suspected to have Zika follow strict insect precautions (see below) This is important in order to prevent a local Aedes mosquito from becoming infected and then infecting another person locally.

  • How can Zika be prevented?

There is no vaccine currently available to prevent Zika.  Avoiding being bitten by mosquitoes is the best way to prevent Zika and other insect borne diseases.  For Zika (as well as dengue, chikungunya and yellow fever) daytime insect precautions and personal protection measures should be followed.  This includes, but not limited to:

  • Using an insect repellant containing DEET (25-50%) or picaridin (20%) which are safe in pregnancy.
  • Long pants/long sleeves during biting times.
  • Staying in air conditioned and/or places with window and door screens.
  • Treat clothing and gear with permethrin, including permethrin treated bed net, if not sleeping in a well screened and/or air conditioned room.


The best way to prevent getting ill while travelling is to  see a travel health specialist ideally 4-6 weeks prior to travel.  Your travel health specialist will provide:

  • Recommended and required vaccines
  • Prescriptions to prevent or self-treat common travel-related illnesses
  • Health and safety counseling tailored to your specific itinerary, activities, and medical history


For more up to date information about Zika, refer to www.cdc.gov/zika