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Zika fever - questions and answers

The Norwegian Institute of Public Health has prepared a list of questions and answers about the Zika virus, transmission routes and protection. The institute is following the situation closely through our established network of international partners. The advice is based on current knowledge and will be updated when new information becomes available.

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About Zika virus and health effects

How long have we known about Zika virus?

The virus was first discovered in 1947 in a monkey found near Lake Victoria in Uganda and is named after the Zika forest. In 1952, antibodies against the virus were first detected in humans and since then, infection has been detected in several African and Asian countries. In 2007, the virus caused a major outbreak on Yap, an island in the Pacific Ocean. In 2013 and 2014 there was a major outbreak in French Polynesia and since 2015, there have been ongoing outbreaks in several countries on the American continent.

What is the link between Zika virus and birth defects?

Since early 2015 there has been an outbreak of Zika fever in Brazil and many other countries on the American continent. Meanwhile, an increase in the number of cases of babies born with microcephaly has been observed, particularly in Brazil. Microcephaly is a condition where a baby is born with a small head, often due to abnormal brain development during pregnancy.  Infants who are affected can have several other health problems, depending on the severity of the condition. Research is continuing to explain the increase, but in March 2016, the World Health Organization declared that based on several studies there is strong scientific consensus that Zika virus is a cause of microcephaly. Other potential causes are also being investigated.

Which other health risks are linked to Zika virus infection?

In March 2016, the World Health Organization declared that, based on several studies, there is strong scientific consensus that Zika virus is a cause of Guillain-Barré syndrome, microcephaly and other neurological disorders. Microcephaly affects foetal development but Guillain-Barré syndrome affects both sexes and different age groupsGuillain-Barré syndrome is a disease where the immune system attacks the nervous system, resulting in acute onset of weakness and pain in the legs and eventually paralysis that may weaken the respiratory muscles. The paralysis usually resolves after a few months. Several infectious diseases, including infection with common intestinal bacteria, can cause this syndrome. To date, we do not know how great the risk of developing neurological disorders such as Guillain-Barré is but it is assumed to be extremely low for otherwise healthy individuals.

What are the symptoms?

The time from infection to onset of symptoms (incubation period) is usually 3-12 days. The majority of those who are infected display no symptoms but some can have fever, eye inflammation, joint pain and a rash for up to a week. Symptoms are usually mild and may be difficult to distinguish from other mosquito-borne diseases like dengue fever and chikungunya fever.

Are children more susceptible to infection or disease?

Children may be more susceptible to mosquito bites so it is important to prevent mosquito bites when staying in the affected areas. Protect small children with impregnated mosquito nets over beds, prams and playpens. To date there are few data about clinical disease among small children but there is nothing to indicate that they are more likely to develop more serious disease than adults.

Why has the WHO published a risk assessment for the possible spread of Zika virus in Europe?

In May 2016, the World Health Organization (WHO) published a report on the risk of a mosquito-borne Zika virus outbreak in Europe during the summer. This risk assessment is based on knowledge about the distribution of mosquito species capable of transmitting the virus, as well as on the capacity of each country to quickly respond to such a situation. The purpose of the risk assessment is to inform countries at risk of Zika transmission so that necessary measures can be introduced at an early stage. The report is not intended to provide an overview over countries to be avoided by pregnant women. Travel advice will be updated as the situation changes.

Transmission route

How is Zika virus spread?

The virus is spread to humans through bites from mosquitoes, mainly Aedes aegypti which is the same mosquito that spreads dengue fever and yellow fever. There is now strong evidence that foetal transmission can occur in pregnant women who are infected with Zika virus. Some cases of sexual transmission have been reported.The virus is not transmitted between humans through normal social contact, coughing, cooking or touch. Norwegian mosquitoes cannot transmit the virus. If a person with Zika virus infection comes to Norway, they will not pose a risk of infection to others than their sexual partners.

When are the mosquitoes most active?

At dusk and dawn, but they are also active during the daytime. They are mainly inactive at night.

Is there a difference between the "Zika mosquito" and the malaria mosquito?

Malaria mosquitoes bite mainly after sunset, while the mosquitoes that spread Zika virus also bite during the day.

If a disease-carrying mosquito is eaten by another insect or a bird, are they carriers?

No, they are not carriers. There are no indications that the virus can be transmitted via food.

If a person who has been travelling abroad is infected with Zika virus returns to Norway and is bitten by a mosquito, could this mosquito spread the disease to other people in Norway?

No. Many mosquitoes found in Norway are in the same genus as the mosquitoes that spread the virus but they cannot transmit the Zika virus.

Is Zika fever present in Norway?

Several cases of Zika fever has been reported in Norway among people who have been to the affected areas on the American continent. We expect that more will occur among tourists who have been to the affected areas. Since the main transmission route is via a mosquito that is not found in Norway, there is no need for special emergency measures in Norway. 

Detection

Can Zika virus be detected in a blood sample?

Yes, it is possible to detect Zika virus in blood samples among those who have are infected. Antibodies against Zika virus can also be detected in blood samples that will confirm an earlier infection but cannot specify when it occurred.

Who will be prioritised for testing for Zika virus?

A Zika test is an extensive and laborious test that is only available at a few laboratories in the country. Testing should therefore be prioritised for:

  • Pregnant women who may have been exposed* to Zika virus during pregnancy, regardless of whether they have symptoms of Zika virus infection or not.
  • People with suspected Zika infection within 3 weeks of possible exposure* to the virus. Symptoms may include rash, fever, headache, muscle and / or joint pain, eye inflammation (without discharge).
  • People with symptoms of Guillain-Barré syndrome or other neurological complications that may occur with Zika infection.

* Exposure refers to a stay in an area with outbreaks or increasing incidence of Zika fever, or unprotected sexual contact with a person who has stayed in areas with outbreaks or increasing incidence of Zika fever

I belong to one of the prioritised groups, where can I take a Zika test?

If you belong to one of the prioritised groups mentioned above, contact your doctor to arrange a test.

I have been to a Zika area and we want to conceive. Can I take a Zika test?

People who been to the affected areas without showing symptoms and who wish to conceive should wait for 8 weeks. A negative test result is not reliable enough to ignore the time recommendations and therefore this group cannot be prioritised for testing.

I have been to a Zika-affected area but have not become ill and I am not pregnant. I want to know if I have been infected. Can I take a test?

Unfortunately, we cannot prioritise testing in this situation. Follow the recommended precautions upon your return.

Can Zika virus be detected in semen?

Zika virus can be detected in semen but these tests are not yet generally available in Norway.

Prevention and treatment

Is there a vaccine?

There is no vaccine against Zika fever. Protection against mosquito bites is the main preventive measure.

How can Zika fever be prevented?

People who travel to the affected areas should take great care to protect themselves from mosquito bites.Use clothing that covers the body (long-sleeved shirts, long trousers and socks), mosquito repellents, sleeping under mosquito nets and spray the residence with insecticide. Use mosquito repellents in the daytime and reapply after sweating.Staying in an air-conditioned room reduces the risk of being bitten.It is not only pregnant women who should protect themselves from mosquito bites when staying in areas with Zika fever. People with an impaired immune system or severe chronic infections should also be careful. Using condoms will reduce the risk of infection from a Zika-infected person during sexual intercourse.

Travel advice

Which general advice applies for travel to countries with Zika fever?

Pregnant women are advised not to travel to areas with outbreaks or increased incidence of Zika fever. People who are immunodeficient or have serious chronic diseases should always consult their doctor before travelling. There is no reason to advise women who are not pregnant or children against travel to Zika-affected areas but they should be particular about mosquito protection.

Which countries are affected?

The NIPH defines the Zika-affected areas in two ways. These are  

  • areas with ongoing outbreaks or increasing incidence of Zika fever
  • areas with sporadic cases

 The risk of infection differs in each type of area so the advice given to pregnant women depends on the country in question.   

What is meant by areas with ongoing outbreaks of Zika fever and when does the travel advice apply?

These are areas where the disease has recently been introduced with many new cases, such as the current situation on the American continent, in few countries in other regions. This has resulted in a complex outbreak situation with a relatively high risk of infection. The risk of infection is therefore significantly greater in these areas. People travelling to or residing in these areas should be extra careful to protect themselves against mosquito bites. The NIPH is advising pregnant women to avoid travel to areas with ongoing outbreaks or an increased incidence of Zika fever. It is also recommended to take precautions after returning from such areas.

What is meant by areas with sporadic individual cases of Zika fever and when does the travel advice apply?

These are areas where there are only few reported cases of Zika fever or where the Zika virus has been present for many years. Many residents in these countries are therefore immune to the disease. The risk of infection with Zika fever in these countries is regarded as low. It is still important to protect against mosquito bites when staying in these countries because of the risk of other mosquito-borne diseases like dengue fever. Pregnant women who plan to travel to areas with sporadic cases but be extra vigilant about mosquito protection or consider postponing their trip. It is unnecessary to take special precautions after returning from such areas.

Why shouldn’t pregnant women travel to areas with outbreaks or increased incidence of Zika fever? 

In March 2016, the World Health Organization declared that based on several studies there is strong scientific consensus that Zika virus is a cause of microcephaly and other foetal brain damage. The risk of developing microcephaly during pregnancy is unknown. It is uncertain if the risk is greatest if pregnant women display symptoms or not. It is also unknown when the risk of foetal damage is greatest, but much indicates that the risk is greatest during the first or second trimester, before 28 weeks of pregnancy.

What can people who are already living in these areas do?

Both pregnant women and others who reside in the affected areas should be extra careful about using mosquito protection. Women staying in areas with outbreaks or increased incidence of Zika fever should use reliable contraception to avoid becoming pregnant during their stay. Long-term residents should follow the advice from local health authorities. Condoms protect against sexual transmission.

What should pregnant women and women who are trying to conceive do?

We advise pregnant women not to travel to areas with outbreaks or increased incidence. If you still intend to travel, use protection against mosquito bites (clothes and mosquito repellent) and inform your doctor / midwife when you return. If you travel to areas with outbreaks or increased incidence, avoid conception until 8 weeks after your return. If the man has stayed in areas with ongoing outbreaks or increased incidence, the couple should wait 6 months before conceiving. 

Pregnant women who choose to travel to areas with sporadic individual cases of Zika fever should be extra careful about mosquito bite protection. 

How best to protect oneself?

The best protection against Zika virus infection is to avoid being bitten by mosquitoes that may be carrying the virus. Pregnant women should not travel to outbreak areas. People living in affected areas should take care to protect themselves against mosquito bites. Use clothes that cover the body (long-sleeved shirt, long pants and socks), use repellents, sleep under mosquito nets and possibly spray the home with insecticide. Use insect repellents during the day.  Staying in rooms with air conditioning reduces the risk of being bitten by mosquitoes. People other than pregnant women should protect themselves against mosquito bites when they stay in areas with Zika fever, particularly those with immunodeficiency or severe chronic infections. The use of condoms during sexual intercourse reduces the risk of infection.

What advice does the NIPH have for travellers to Southern Europe?

The World Health Organization (WHO) has published a report on the risk of a Zika virus outbreak in Europe.  The risk for Norway is considered to be very low. Only Madeira and areas in the Northeastern coast of the Black Sea are considered to have a higher risk for potential spread (if they do not introduce measures to prevent the spread of infection). Other countries around the Mediterranean Sea are considered to have a moderate risk. The NIPH’s advice to travellers to Zika affected areas concerns pregnant women or those who are trying to conceive, and the advice applies only to countries where there is a known outbreak or increasing incidence of Zika virus. To date, no European countries are affected. However, we recommend that pregnant women follow our travel advice when planning trips to Southern Europe in summer. As the temperature drops in Southern Europe in autumn, the risk will be significantly lower. The NIPH will monitor the situation closely and update travel advice as necessary.

What advice does the NIPH have for travellers to Florida and elsewhere in the USA?

Since spring 2016, the US health authorities have considered the risk of a local spread of Zika virus by mosquitoes, especially in Texas, Florida and Hawaii. Mosquito control measures have already been introduced and surveillance has intensified in these states. In late July, it became clear that there were several cases of Zika fever that are believed to be caused by mosquito-borne infection within the Miami area of Florida. Pregnant women are being advised not to travel to Miami-Dade county, and people who have stayed in Miami-Dade county should take precautions after returning home if they have stayed in Miami since 15th June 2016 and the rest of the county since 14th July 2016. There is no reason for pregnant women to avoid travel to other parts of Florida or other states based on the current situation. Travellers returning home after staying outside the Miami area in Florida or other states in the USA do not need to take extra precautions. The Norwegian Institute of Public Health is monitoring the situation closely and will update their travel advice for other areas if the situation changes. 

Is there a risk of infection with Zika virus in Thailand and other Asian countries?

The situation in these countries is very different to the situation on the American continent. While Zika virus was only recently detected on the American continent and has resulted in a complex outbreak situation with a presumed high risk of infection, these countries are considered as endemic areas, which means that the virus has been present for many years and that many are immune to the disease. Never the less, some countries in Southeast-Asia have eported an increasing number of zika cases. Pregnant women are being advised not to travel to Philippines, Thailand, Vietnam, and Singapore, and people who have stayed in these countries should take precautions after returning home. The NIPH is monitoring the situation in Asia countries closely and will update travel advice if the situation changes.

Advice upon return from affected areas

Pregnant women who have recently returned from the affected areas should contact their doctor or midwife for Zika virus testing. If follow-up is required, they will be referred to a regional foetal diagnostics centre. These centres have experience in handling this situation and pregnant women will benefit from expert advice.It is not considered necessary for pregnant women who have visited areas with sporadic cases and who do not have symptoms to be followed up on their return, this also applies to virus testing.  

What is the advice to healthcare personnel when they are contacted by a pregnant women who has returned?

Blood samples for Zika virus testing can be taken at the primary healthcare service and sent to the Norwegian Institute of Public Health for analysis. If the doctor or midwife believes a woman should undergo further investigation, she should be referred to a regional centre for foetal diagnostics for follow-up and advice.

I've been to a Zika-affected area and have symptoms of Zika fever. Should I see a doctor?

If it has been less than three weeks since you returned home and you have symptoms that could be consistent with Zika fever, you should consider seeing a doctor. Your doctor will determine if there is a need to take a blood sample to test for the Zika virus.

If a woman becomes infected with Zika virus and later becomes pregnant, will the foetus be harmed?

Recovery from Zika fever will not cause birth defects in future pregnancies.

How long should a woman wait to get pregnant after she has been in an affected area?

Women who have stayed in areas with outbreaks or increased incidence of Zika fever should wait 8 weeks after leaving the area before conceiving. If the man has stayed in areas with ongoing outbreaks or increased incidence, the couple should wait 6 months before conceiving.

Not enough is known about sexual infection and how long Zika virus remains in some bodily fluids, so this is preliminary advice that will be updated when new information becomes available.

Should a man use a condom if he has stayed in an affected area and has a partner at home who is pregnant?

Sexual partners of pregnant women, living in or returning from areas with outbreaks or increased incidence of Zika fever, should use safer sexual practices or abstinence from sexual activity for the duration of the pregnancy. Not enough is yet known about sexual transmission and how long Zika virus remains in some bodily fluids, so this is preliminary advice that will be updated when new information becomes available.

Should contraception be used if the man has stayed in an affected area and has a partner at home who is at risk of getting pregnant?

Men who has been in areas with outbreaks or increased incidence of Zika fever and has a partner at home who could conceive should use contraception for six months after returning home. Not enough is known about sexual transmission and how long Zika virus remains in some bodily fluids, so this is preliminary advice that will be updated when new information becomes available.

I stayed in the affected areas and am neither pregnant nor had symptoms of Zika fever. Can I take a test?

No. Unfortunately, we cannot prioritise testing in this situation. A negative test result is not reliable enough to ignore the time recommendations. Since you cannot take a test, please follow the advice about avoiding pregnancy and using condoms after your return.

I stayed in the affected areas. How can I avoid sexual transmission when I return?

Condom use reduces the risk of infection with Zika virus. Men and women who have been in areas with ongoing outbreaks or increased incidence of Zika virus can avoid infecting their partner by using a condom. Use condoms for 6 months.

Is there a risk that Zika virus can be transmitted to Norwegian blood banks, and are measures being introduced to prevent this? 

The risk that Zika virus can spread via Norwegian blood banks is minimal. Blood donors who have stayed in areas with outbreaks or increased incidence of Zika fever area must delay giving blood for at least 28 days after leaving the area. Blood donors who have had sexual contact with someone who has been diagnosed with Zika fever or who been to areas with outbreaks or increased incidence of Zika fever during a six month period prior to sexual contact must delay giving blood for at least 28 days after the last sexual contact. This is the recommendation given by the Norwegian Directorate of Health, and is in line with recommendations from the European Communicable Diseases Centre (ECDC).       

International public health crisis

What is a declaration of public health emergency of international concern?

The Director-General of the World Health Organization (WHO) can declare a public health emergency of international concern (PHEIC) if they believe the international community is in a situation that poses a public health threat and where coordination of interventions may be necessary.

Why was an international public health crisis people declared?

The Director-General of the World Health Organization has declared that the increases in cases of microcephaly and other neurological conditions in Brazil in 2015-2016 and French Polynesia in 2014 is a public health emergency of international concern. WHO declared on 18.11.2016 that the Zika virus no longer constitutes an international emergency, but it stressed a need for a long-term effort to address Zika, which has been linked to birth defects and neurological complications.