Zika virus infection

Zika virus occurs in all tropical and sub-tropical countries. It is found, for example, in countries in North, Central and South America, as well as South-East Asia, Africa, the Caribbean and the Pacific.

Most people are infected by a mosquito bite or by sexual transmission during unprotected sex.

The infection generally causes only mild symptoms at most, which clear up within a few days. However, if a pregnant woman is infected, the virus can be transmitted to the unborn baby and cause serious birth defects.

Most infections with Zika virus cause mild symptoms or none at all. The first signs of illness occur between 2 and 14 days after contracting the virus through a mosquito bite.

The most common symptoms are:

• a reddish rash
• headache and limb pain
• slight fever
• conjunctivitis

People sometimes experience pain behind the eyeball. In rare cases, the virus causes nausea, vomiting and abdominal pain.

Most symptoms generally disappear after 2 to 7 days. However, people can still transmit the virus to others at this stage.

Zika virus belongs to the Flavivirus group of viruses, which also includes the viruses that cause yellow fever and dengue fever. Viruses in the Flavivirus group are primarily transmitted by yellow fever mosquitoes (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus) – tropical mosquitoes that are active during the day.

If a mosquito contracts Zika virus when feeding on the blood of an infected person, they can pass it on to the next person they bite a short time later. People can also transmit Zika to one another through unprotected sex, as the virus also remains in sperm and other bodily fluids for a long time after an infection. It is possible for the virus to be transmitted via a blood infusion but this is rare.

If a pregnant woman contracts Zika virus, it can pass through the placenta to her unborn child. Unborn children are particularly susceptible to damage from the virus in the first and second trimesters of pregnancy.

The risk of contracting Zika virus is particularly high in areas known for large outbreaks. This was the case, for example, in Central and South America between 2015 and 2017.

A Zika virus infection has been a legally notifiable disease since 2016. 69 Zika virus infections were registered in Germany in 2017, while 18 were registered in 2018. Almost all of those infected contracted the virus outside of Germany.

The actual number of Zika virus infections is likely to be much higher because, in many cases, there are no symptoms and not all those infected will visit a doctor.

For more information about the transmission of Zika virus, refer to the leaflet published by the German Federal Foreign Office (Auswärtiges Amt).

In general, people recover quickly from an infection with Zika virus and don't suffer any long-term consequences.

An abnormally increased prevalence of Guillain-Barré syndrome (a rare condition affecting the nerves) and of certain developmental disorders in newborns have been observed following large outbreaks of Zika virus infections. It is assumed that Zika virus is responsible. Various nervous system disorders are also known to occur as complications of an infection.

Guillain-Barré syndrome

Guillain-Barré syndrome is a rare neurological disorder that can occur as a complication of a Zika virus infection and can cause full-body paralysis. It is likely to be caused by an auto-immune reaction, whereby the immune system incorrectly identifies the body's own nerve structures as foreign bodies and attacks and damages them. Many people recover after a few weeks.

Birth defects in newborns

A Zika virus infection during pregnancy can cause neurological defects in newborn babies – for example:

• an abnormally small head (microcephaly)
• a thin cerebral cortex with calcifications
• changes in the retina in the eye
• congenital joint deformities (causing limited mobility)
• increased muscle tone affecting movement

It is impossible to predict with certainty how a baby who contracts Zika virus in the womb will develop.

Some children show no developmental abnormalities at birth but do so after a number of years. Others show signs of illness that disappear later on. On the other hand, defects such as microcephaly last a lifetime and cause severe impairments.

There is as yet no vaccine against Zika virus. The most important precaution to take against an infection with Zika virus is to avoid getting mosquito bites, especially in tropical regions.

The Aedes mosquitoes that transmit the virus are active during the daytime and at dusk and breed in stagnant water – for example, in rain barrels or watering cans. Such ideal breeding sites are often found close to buildings and residential area.

Personal protection against mosquito bites includes measures such as:

• wearing clothing with long arms and legs
• spraying clothes with suitable mosquito spray, containing ,for example, the active ingredient permethrin that kills insects
• wearing mosquito repellent on the skin, containing, for example, the active ingredients DEET or icaridin
• staying in air-conditioned rooms
• sleeping under a mosquito net 

Zika virus can also be transmitted during sexual contact via sperm and vaginal fluid. The following measures are important to prevent the unborn baby from an infection in a planned or unplanned pregnancy:

• Use condoms for sexual intercourse when staying in a high-risk region.
• After returning home from a high-risk region, men should avoid having unprotected sex for at least 3 months and women should do so for at least 2 months. It is sometimes recommended that condoms be used as protection for 6 months.

As it’s also possible to transmit the virus via blood products, people who have returned from high-risk regions should avoid donating blood for at least 4 weeks.

If travelers to regions that are high risk for Zika virus develop typical symptoms, doctors can take blood or urine samples to detect the pathogen.

The symptoms may indicate a Zika virus infection even if it is the person's partner who has visited the high-risk area.

Zika virus is detected in the lab using a PCR test or serology testing for antibodies. The first of these methods allows the virus's genetic material to be detected. The second looks specifically for antibodies that the immune system produces to fight Zika virus.

Pregnant women in particular should get tested, even if their symptoms are only mild. If an infection is suspected, regular ultrasound scans of the baby can provide more information. An amniocentesis (testing of the amniotic fluid) is not normally performed.

Treatment of a Zika virus infection with symptoms is largely limited to supportive measures. They include:

• bed rest
• adequate fluid intake
• taking medication to relieve pain or fever

It is recommended that anyone with a Zika virus infection should protect themselves against mosquito bites so that the virus is not transmitted to other people via native mosquitoes.

If a person becomes ill with a fever following a stay in a tropical country, this could also be due to an infection with dengue virus (dengue fever). Until dengue virus is ruled out, the person should avoid taking any medication containing acetylsalicylic acid (ASA) as an active ingredient for the relief of pain and fever. Paracetamol can be used instead.