Page last updated: 25 July 2016
Questions and answers: Zika virus disease
What is Zika virus?
Zika is a flavivirus that is mainly 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. Between 2013 and 2015, several outbreaks were documented in islands and archipelagos in the Pacific region, including a large outbreak in French Polynesia. In 2015, Zika virus emerged in South America, with further spread across the Americas.
Where can you get infected with Zika virus?
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. As of July 2016, about 50 countries and territories reported locally transmitted cases of Zika virus infection.
ECDC continuously monitors and publishes updated information regarding areas with current transmission of Zika virus. A list and map of areas with active transmission (sporadic and widespread) can be found here
Weekly epidemiological updates of the Zika outbreak situation.
What are the symptoms of a Zika virus infection?
The most common symptom is a rash – with or without fever – that lasts two to seven days. Patients may also get conjunctivitis (also known as pink eye), as well as muscle and joint pain. Zika virus disease is normally a mild disease and 80 % of infected people do not develop symptoms at all.
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 by getting bitten by a female Aedes aegypti mosquito. These mosquitoes are mostly active during daytime and can also transmit other diseases such as dengue, chikungunya and yellow fever. Aedes aegypti mosquitoes can be found in warm tropical climates and does not survive in cooler climate temperatures. Zika can also be transmitted by the Aedis albopictus mosquito, although it is still contested how effective Aedes albopictus is in transmitting the disease. There is also evidence of transmission through sexual contacts and possibly also through blood donation.
What do we know about the transmission of Zika through substances of human origin such as blood, tissue and cells?
Based on the limited available information, it is assumed that Zika virus can be transmitted by blood and other substances of human origin such as organs and cells. This is why blood donors who have visited Zika-affected areas should not be allowed to give blood until there is no longer a risk that they are carrying the virus.
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
Using a condom when staying in an area with active Zika transmission and continuing to do so for at least eight weeks after returning from this area will reduce the risk of sexual transmission. If symptoms were experienced, condoms should be used for six months following the cessation of symptoms. Travellers returning from Zika-affected areas are not allowed to donate blood until the risk of infection has passed, which is 28 days after returning from a Zika-affected area.
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
Should pregnant women be concerned about Zika?
There is a scientific consensus 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 postpone non-essential travel to areas with widespread transmission.
- Pregnant women and women who are planning to become pregnant should consult their physician or a travel clinic and consider postponing non-essential travel to areas with sporadic transmission.
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.
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
Risk to travellers going to or coming from affected areas
What is the risk to Europe?
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:
1. Pregnant women and women who are planning to become pregnant should:
- postpone non-essential travel to areas with widespread transmission.
- consult their physician or a travel clinic and consider postponing non-essential travel to areas with sporadic transmission.
2. 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. 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.
3. Travellers to areas with active transmission of Zika should be advised that using a condom reduces the risk of sexual transmission.
Why should travellers returning from Zika-affected areas use condom?
Several cases of sexual transmission were reported.
Travellers returning from Zika-affected areas should consider using condoms for at least eight weeks after their return in order to reduce the risk of onward sexual transmission. If symptoms of Zika virus infection occur during that period, a condom should be used for at least six months.
In order to protect the foetus from the risk of infection, male travellers returning from areas with Zika should use a condom with their pregnant partner until the end of pregnancy.
Why should travellers who have returned from Zika-affected areas contact a healthcare provider if they get sick within three 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, it will be necessary to make sure the mosquitoes do not transmit the virus to another person.
Why should travellers who have returned from Zika-affected areas contact a healthcare provider if they get sick within three 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, it will be necessary to make sure the mosquitoes do not transmit the virus to another person.
Risk for Zika-infected people to develop Guillain–Barré syndrome
Does Zika virus infection cause Guillain–Barré syndrome?
An increased number of cases of Guillain–Barré (GBS) syndrome continue to be reported from the countries affected by the current epidemic in the Americas. There is now a strong consensus in the scientific community about the link between Zika infection and developing GBS.
What is Guillain–Barré?
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 Guillain–Barré?
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 of transmission in Europe
What is the risk to Europe?
The main risk to the EU is related to an infected traveller introducing the virus to an area with mosquitoes that are able to transmit Zika virus. In order for this to happen, climatic conditions have to be suitable for the mosquitoes, esp. during spring, summer and autumn, when the mosquitoes are active.
A number of Zika cases imported to the EU by travellers returning from Zika-affected areas were reported, and that number is expected to rise during the summer (see ECDC Zika Surveillance Atlas
The risk of local transmission through mosquito bites is low to moderate.
Other routes of transmission, such as infection through sexual transmission or blood transfusion from infected travellers returning to the EU from Zika-affected areas, cannot be excluded.
Can Zika spread in Europe through mosquitoes? Can I get infected through mosquito bites here 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. Studies of local European mosquito populations have shown a low competence of Aedes albopictus to transmit the disease; the risk of infection is therefore considered to be low to moderate.
The primary vector for Zika, Aedes aegypti, is present in the EU’s outermost regions and territories in the Americas, the Pacific, and on the island of Madeira. Local transmission of Zika was reported from the EU’s outermost regions and territories in the Americas in 2016.
Are there ways that Zika can spread in Europe other than through mosquitoes? Can get I infected in a way other than through mosquito bites?
Sexual transmission of Zika from an infected traveller to other persons is possible, but so far only a few cases of sexual transmission have been detected. There are documented cases of Zika infection transmitted from men to their sexual partners, and recently a suspected case of female-to-male transmission was reported and is being investigated.
To prevent infection, travellers should use a condom for eight weeks after returning from Zika-affected areas, or for six months if they experienced symptoms.
Zika infection is also possible through blood transfusion or organ transplantation. However, this is unlikely in the EU since the relevant national authorities do not allow donations/transplantations from travellers from affected areas until the risk of infection has been ruled out.
How does ECDC keep track of Zika?
ECDC closely monitors the outbreak of Zika and continuously assesses the risks to Europe. ECDC provides frequent updates on the current outbreak and communicates scientific advances regarding Zika and its possible outcomes.
Information on the current spread of Zika worldwide and the number of reported travel-related cases in the EU is updated weekly. ECDC offers options for response and provides guidance for preparedness activities for EU/EEA Member States and the European Commission.
What are the risks regarding the Rio Olympics and Paralympics?
The Rio 2016 Olympics (5–21 August 2016) and the Paralympics Games (7–18 September 2016) will take place during Brazil’s winter. The cooler, drier weather will reduce mosquito populations and significantly lower the risk of infection for visitors. Although the probability of being bitten by an infected mosquito is expected to be low during the events, the risk of infection cannot be excluded. Travellers may become infected and then return to regions of the EU where Aedes vectors are active. ECDC is continuously monitoring the situation regarding the Olympic and Paralympic games.
ECDC published a risk assessment
regarding the 2016 Olympics, which also includes an assessment of the risk of Zika infection.