Page last updated: 10 March 2016
Questions and answers: Zika virus disease
What is Zika virus?
Zika is a flavivirus that is transmitted by mosquitoes. It belongs to a family that includes the viruses that cause West Nile Fever, dengue, tick-borne encephalitis and yellow fever. Zika virus is not a new virus. It was first discovered in Africa in the 1940s, but prior to 2015 only a few outbreaks had been documented in tropical Africa, Southeast Asia, and the Pacific Islands.
Where can you get infected with Zika virus?
The highest risk is in countries with ongoing outbreaks. Since early 2015, a Zika virus outbreak has been spreading in the Americas. The first cases were reported from Brazil and the disease has since spread to several countries in South America and the Caribbean. It is expected that the epidemic will continue to spread in the Americas during 2016. ECDC publishes regularly updated information regarding affected areas.
Weekly epidemiological updates of the Zika outbreak situation
Is Zika virus disease a severe disease?
Zika virus disease is normally a mild disease. The majority of infected people do not develop symptoms at all.
What are the symptoms of a Zika virus infection?
The most common symptoms are a mild fever and rash that last 2-7 days. Patients may also get conjunctivitis (red eyes), as well as muscle and joint pain.
How long is the incubation period of Zika virus infection?
The time from infection until the first symptoms develop (incubation period) is usually 3 to 12 days after the bite of an infected mosquito.
If Zika is such a mild disease, why is there so much concern about the epidemic?
The concern is that Zika virus can cause severe harm to unborn babies (foetuses) when a woman is infected during pregnancy. It is not yet clear how often infections during pregnancy spread to the baby and cause damage to the brain but what is clear is that the Zika virus is capable of causing such congenital malformations. Nor is it yet well understood when during the pregnancy the risk is highest for malformations. Therefore the entire duration of pregnancy should be considered at risk.
There are also indications that there is an increased risk for people who have recovered from Zika infection to develop an autoimmune neurological disease called Guillain-Barré syndrome.
Knowledge about the risk of congenital brain malformations associated with Zika virus infection during pregnancy is still limited and there are intense efforts to collect and analyse data that can inform the advice about the disease.
How can people get infected with Zika virus?
In most cases Zika virus is caught from a bite by a female Aedes speciesmosquito which is active during daytime. These mosquitos can also transmit other diseases such as dengue, chikungunya and yellow fever. The Aedes aegypti mosquito does not survive in cooler climate temperatures.
Can Zika virus be spread through blood?
Based on the available information, Zika virus can be transmitted by blood. This is why blood donors who have visited Zika-affected areas are deferred until there is no longer a risk that they have the virus in their blood.
Can Zika be spread through sexual contact?
Zika virus has been found in the semen of infected men and sexual transmission has occurred but these events are rare.
Can Zika be spread from mother to foetus?
A foetus can become infected when a woman is infected during pregnancy and the virus can cause damage to the brain of the foetus. It is not yet clear how often this happens or what period of the pregnancy is most vulnerable.
How is Zika virus disease treated?
There is no specific treatment for Zika virus infection.
The symptoms of Zika virus disease can be alleviated by taking plenty of rest and fluids to prevent dehydration and by taking medicine to reduce fever and pain. Infected people should adhere to national recommendations on which fever-reducing medication to use.
Is there a vaccine against Zika virus?
There is currently no vaccine that protects against Zika virus.
How can Zika be prevented?
The best protection from Zika virus is preventing mosquito bites indoors and outdoors, especially from sunrise to sunset when mosquitos are most active.
Such measures include:
- Use mosquito repellent in accordance with the instructions indicated on the product label.
- Wearing long-sleeved shirts and long trousers
- Sleeping or resting in screened or air-conditioned rooms
- Using mosquito nets
How is Zika virus disease diagnosed?
Zika virus infection can be diagnosed using laboratory testing. Healthcare providers may order blood tests to look for Zika if a patient has compatible symptoms with Zika virus disease and has recently travelled in an affected area.
Risk for pregnant women travelling to Zika-affected areas
What is microcephaly?
Microcephaly is a rare condition where a baby has a smaller head than expected when compared with babies of the same age and sex because the brain has not developed properly or has stopped growing. The condition is life-long and can cause a number of problems including seizures, intellectual impairment and difficulties with movement and balance. Microcephaly can be caused by a variety of environmental and genetic factors such as exposure to drugs, alcohol or other toxins, and infections (such as rubella and toxoplasmosis) during pregnancy.
Should pregnant women be concerned about Zika?
There is a growing body of evidence that Zika virus infections during pregnancy can cause brain damage and microcephaly in the foetus. It is not known how frequently this happens or when the risk is highest during the pregnancy.
Pregnant women and women who are planning to become pregnant should consider postponing non-essential travel to areas with ongoing Zika virus outbreaks until after the pregnancy.
Those travelling to and living in Zika-affected areas should consult their healthcare providers for advice and follow strict measures to prevent mosquito bites. Pregnant women that have travelled in areas with Zika virus transmission should mention their travel during antenatal visits in order to be assessed and monitored appropriately.
Sexual transmission & use of condom
Why should male travellers returning from Zika affected areas use condom with their pregnant partner until the end of the pregnancy?
Men who had recent Zika disease may excrete Zika virus in semen for several weeks after infection and there have been occasions of sexual transmission. In order to protect the foetus from the risk of infection, the couple should use condom until the end of pregnancy.
Risk for Zika-infected people to develop GBS
Does Zika virus infection cause Guillain-Barré syndrome (GBS)?
An increased number of cases of Guillain-Barré syndrome continue to be reported from the affected countries during the current epidemic in the Americas but the relationship with the Zika virus epidemic is not yet clear and the investigations into this are ongoing.
Also, during the outbreak of Zika from 2013 to 2014 in French Polynesia, national health authorities reported an unusual increase in Guillain-Barré syndrome. Retrospective investigations are ongoing, including the potential role of Zika virus and other possible factors.
What is GBS?
Guillain-Barré syndrome is a rare condition, where a person’s own immune system damages the nerve cells, causing muscle weakness and sometimes paralysis. These symptoms can last a few weeks or several months. While most people fully recover from GBS, some people have permanent damage and, in rare cases, people have died. People of all ages can be affected, but it is more common in adults and in males.
What causes GBS?
The cause of Guillain-Barré cannot always be determined, but it is often preceded by an infection (such as HIV, dengue, or influenza) and less often by immunisation, surgery or trauma.
Risk for travellers going to/returning from affected areas
Should travel to areas where Zika virus is occurring be avoided?
Travellers are advised to consult local travel advice available in their country prior to travelling to Zika-affected areas.
Based on existing evidence, ECDC advises on the following measures of precaution:
- Pregnant women and women who are planning to become pregnant should postpone non-essential travel to affected areas.
- Travellers with immune disorders and severe chronic illnesses should consult their doctor or seek advice from a travel clinic before travelling, particularly on effective prevention measures.
Why should travellers who have returned from Zika affected areas contact a healthcare provider if they get sick with 3 weeks after their return?
Returning travellers who become ill should contact a healthcare provider so that they can be assessed and, if needed, tested for Zika virus. This is important because if the traveller lives in an area with mosquitoes that can transmit Zika, the it will be necessary to make sure the mosquitoes do not transmit the virus to another person.
See more information in the latest risk assessment
What’s the risk to Europe? Risk of vector transmission in Europe
Due to the presence of the competent mosquito vector (Aedes albopictus) in several places around the Mediterranean, onward transmission from imported cases within the continental EU is possible during the summer season, similar to chikungunya and dengue.
ECDC’s mosquito maps
The Rio Olympics and Paralympics
What are the risks for visitors and athletes?
The Rio 2016 Olympics (5–21 August 2016) and the Paralympics Games (7–18 September 2016) will take place during Brazil’s winter when the cooler, drier weather will reduce mosquito populations and significantly lower the risk of infection for visitors.
ECDC updated rapid risk assessment
ECDC Zika factsheet
WHO Zika website