July 22, 2016

Zika virus was first detected in the Americas in Brazil during early 2015. The disease has now become present in more than 40 countries in the region. However, overall activity has declined in recent months.

During May-June, transmission has continued to taper off in some areas including Brazil, Colombia, and Venezuela where Zika virus case reports had previously been particularly high. In Colombia, for example, where officials have reported 89,962 suspected cases and 8,826 confirmed Zika virus infections as of July 9, disease activity has steadily decreased every week since early April.

Nevertheless, some countries are still currently experiencing high levels of Zika virus activity. Guadeloupe, Martinique, and Puerto Rico are areas that have reported surging numbers of Zika cases during May-June, but activity in those locations is expected to peak and decrease in coming months, as well. The true incidence of disease in the Americas is likely higher than reported, since Zika virus infections are often mild or difficult to differentiate from other common infections, such as dengue fever.


Given the ongoing concerns in the Western Hemisphere, the US CDC maintains an "Alert - Level 2" travel advisory due to the threat of Zika virus in many countries in the Americas. The CDC's "Alert - Level 2" is the second of three advisory levels. This level notifies individuals of increased health risk at a destination or of health risks associated with specific factors. It also encourages travelers to take specific actions and emphasizes the need for individuals to enhance their usual health precautions predominantly against insect bites, in the case of Zika virus. The CDC recommends that pregnant women consider postponing travel to any area where Zika virus transmission is ongoing, and that they consult their doctor before departing, if travel is unavoidable. Women who are trying to become pregnant should also consult their doctor before departing. On March 8, the WHO similarly recommended that pregnant women avoid travel to areas with ongoing Zika virus transmission, and practice safe sex or abstinence for the duration of the pregnancy.

Zika Virus and the Olympics

With the Rio 2016 Olympic and Paralympic Games beginning Aug. 5, Zika virus continues to be a concern for visitors and participants, although risk is low. According to the Pan American Health Organization (PAHO), reports of new Zika virus cases in Brazil have consistently decreased March-May. As of June 11, health authorities have reported 165,932 probable Zika virus infections in Brazil during 2016. However, because Zika virus was not a reportable disease in Brazil until 2016, total case counts from the beginning of local transmission in 2015 are currently unavailable. Nevertheless, officials estimate that as many as 1.3 million cases occurred during 2015. By these estimates, the state of So Paulo could account for as many as 386,000 infections.

Central western states have reported higher Zika virus activity during 2016, as the virus had mainly remained in northeastern states during 2015. Based on data from the Brazilian Ministry of Health (MOH), cumulative Zika virus rates during 2016 have been highest in the states of Mato Grosso (612 cases per 100,000 people), Baha (305.4 cases per 100,000 people), Rio de Janeiro (278.1 cases per 100,000 people), and Tocantins (184.5 cases per 100,000 people). However, Zika virus rates during May were highest in Rio de Janeiro State (89.2 cases per 100,000 people), followed by Baha, Mato Grosso, and Alagoas states (map). Unfortunately, the latest Zika virus data from the Brazilian MOH is only available through June 11. These reports suggest that many states, including Rio de Janeiro State, did not report Zika virus cases during the previous two weeks (May 28-June 11), which is unlikely. It is possible that during that time, data collection was not appropriate, therefore, assessing the current trend is difficult. Nevertheless, Zika virus rates in Rio de Janeiro are likely low.


An additional concern regarding the Olympics is whether Zika virus may spread internationally as a result of the Games. The International Olympic Committee (IOC) and other organizers of the 2016 Summer Olympics in Rio de Janeiro have asserted that the risk to athletes and spectators will be minimal. On May 28, the WHO published official advice regarding travel to the Olympics and Zika virus. The assessment was that attendance to the event will not significantly affect the international spread of Zika, considering that at least 60 countries in the world have already reported Zika virus cases, and that public health measures for mosquito bite prevention continue to be the best way to reduce the risk of disease.

The following public health measures have been implemented in Brazil, especially in areas surrounding Olympic venues and will continue:

  • Continued spraying with insecticides
  • Education for athletes, participants, and spectators regarding Zika virus prevention
  • Enhanced surveillance for the vector at venue sites
  • Accommodations with air conditioning and protective screens

Zika Virus in Florida

On July 19, health officials in Miami-Dade County, Fla., reported that a Zika virus infection was under investigation as possibly the first locally transmitted case in the US (map). The individual has no history of travel outside of the US. Notably, this is the same location where locally acquired cases of chikungunya (transmitted by the same mosquito that spreads Zika) was identified in 2014. The chikungunya cases did not develop into a larger outbreak due to appropriate and robust mosquito control response from local health authorities.

Travel-related Zika virus cases in the US have been rare since 2007, but they will likely increase in frequency, now that the disease is becoming more common in the Americas. Such imported cases may lead to limited local disease activity in areas where mosquitoes are active, including Florida, Louisiana, and Texas. As of July 13, health officials in the US have identified at least 1,300 imported Zika virus infections 2015-2016. The imported Zika cases have been reported in all but five states (Alaska, Idaho, North Dakota, South Dakota, and Wyoming). All of these infections have been contracted while traveling internationally. However, at least 14 imported cases later led to local cases that were contracted via sexual transmission.

Zika Virus Prevention

Avoiding mosquito bites continues to be the main strategy to prevent Zika virus infection. As more information comes to light, improved prevention, protection, and mitigation measures will become available to fight this disease. For more details on Zika virus and how to prevent infection, please see the WorldAware Health team's Zika Virus Information Sheet.

There is currently no cure or specific treatment for Zika virus. The only treatment options for Zika virus remain rest, fluids, and comfort measures to relieve symptoms. Available treatment for neurologic complications and birth complications that may be related to Zika virus are dependent upon the health capacity of a particular region.

Zika in the future: From Epidemic to Endemic

Before its appearance in the Americas in early 2015, Zika virus was already considered endemic in many countries around the world (map). This means that cases continue to appear because the disease is installed as a regular risk, in most cases along with other mosquito-borne illnesses like chikungunya and dengue fever. In areas where the Aedes mosquito is present and transmission has been confirmed, Zika virus infections will continue to be identified indefinitely, especially in tropical areas of Brazil, and in countries where dengue fever is a recurring risk like Colombia, El Salvador, Honduras, and Venezuela.

Since Zika virus creates immunity after infection, the number of cases will likely never be as high as this past year when the disease was originally introduced. Nevertheless, particularly intense dengue fever seasons, often brought on by an increase in rain or drought, will likely also become high Zika virus seasons in the future.

For additional information about Zika virus impact and other Olympic Games related health threats, join us for an Olympics security and health preparedness update webinar on July 28. We'll broadcast live from Rio and provide ample time for questions and answers with our experts.