Conditions Zika virus infection

The Zika virus is mainly found in tropical and subtropical 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 no symptoms or only mild symptoms. These 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 the mosquitoes have become infected with the Zika virus, they can pass it on to the next person they bite a short time later. People can pass the virus to one another during unprotected sex, as the virus remains in semen and other bodily fluids for an extended period after an infection. It is possible for the virus to be transmitted via a blood infusion but this is rare.

If a pregnant woman becomes infected with the Zika virus, it can be passed to her unborn child. The risk of damage from the virus is highest in the first and second trimesters of pregnancy.

The risk of contracting Zika virus is particularly high in areas known for large outbreaks. Since the major outbreaks between 2015 and 2017 in South and Central America, infection rates have fallen in many regions. Nevertheless, there are still areas with active transmission. For example, Thailand recorded an increase in Zika virus infections in 2023. In the same year, an increased number of infections were detected in Germany among travelers returning from this region. 

Infections with the Zika virus have been subject to mandatory reporting in Germany since 2016. In recent years, an average of 20 infections per year have been reported. 

The actual number of Zika virus infections is likely higher, because the disease often causes only mild symptoms. It is believed that not everyone affected goes to see a doctor.

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

After major outbreaks of infections, it has been observed that certain neurological disorders occurred more frequently in the population than is normally the case. These include Guillain-Barré syndrome. Certain developmental disorders in newborns also occurred more frequently than usual. It is assumed that Zika virus is responsible. 

Guillain-Barré syndrome

Guillain-Barré syndrome is a rare neurological disorder that leads to paralysis throughout the body. It can occur as a complication of a Zika virus infection. 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. Most people recover from it after a few weeks or months. However, in some cases, paralysis persists.

Birth defects in newborns

A Zika virus infection during pregnancy can lead to miscarriages or birth defects in the child. Possible consequences include:

• impaired brain development
• an abnormally small head (microcephaly)
• problems with food intake, such as swallowing difficulties
• hearing or visual impairments
• seizures
• joint stiffness
• stiff muscles that make movement more difficult

Some children do not yet show any abnormalities at birth, but only after several years. Others show signs of illness that disappear later on. On the other hand, defects such as microcephaly last a lifetime and often result in severe impairments.

There is as yet no vaccine against Zika virus. The most important preventive measure is protection against mosquito bites – especially in high-risk areas.

The Aedes mosquitoes, which transmit the Zika virus, are active during the daytime and at dusk and breed in stagnant water. Breeding sites can often be found near houses and residential areas, such as in rain barrels or watering cans. 

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 

The Zika virus can also be transmitted during sexual contact via semen or vaginal fluid. Therefore, to protect the unborn child from an infection during an ongoing or planned pregnancy, the following measures are important in addition to mosquito protection:

• 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. 

The Zika virus can also be transmitted via blood products. Therefore, after staying in high-risk areas, you must wait at least 4 weeks before you are allowed to donate blood again.

If travelers have stayed in high-risk Zika virus areas and develop typical symptoms, doctors can detect the pathogen using a blood or urine sample.

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.

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

• physical 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.