Zika virus infection: Description
Zika virus infection causes a febrile infectious disease (Zika fever). The pathogen, the Zika virus, is transmitted to humans mainly by mosquitoes of the genus Aedes.
According to the German Federal Ministry of Health, only about a quarter of those infected develop the typical Zika virus symptoms. The course of the disease is usually mild. However, infected pregnant women can transmit the pathogen to their unborn child.
In 2015, an increasing number of cases were reported, particularly in Brazil, in which newborns of infected mothers had a head that was too small (microcephaly). This maldevelopment is usually accompanied by brain damage and severe mental retardation.
In addition, Zika infection could increase the risk in adults for the otherwise very rare Guillain-Barré syndrome – a disease of the nerve tracts in which severe paralysis can occur.
Zika virus illnesses have been reportable in Germany since 2016.
The Zika virus
Spread of Zika virus infection
Zika viruses occur in all tropical subtropical regions, most notably in Africa, Southeast Asia, and the Pacific Islands. Between 2015 and 2017, major outbreaks also occurred in Central and South America. In the fall of 2019, isolated Zika virus infections even occurred in southern France.
Researchers first discovered Zika virus in 1947 in a rhesus monkey in Uganda’s Zika forest. Evidence of the first Zika virus infections in humans occurred in Uganda and Tanzania in 1952. Then, in 2007, the first major outbreak occurred in the western Pacific Yap Islands (part of Micronesia). Seventy-five percent of the population there contracted Zika virus infection. This was followed in 2013 by a wave of infections in French Polynesia. At that time, around ten percent of the population fell ill.
In the meantime, the virus has spread further and further. However, it was not until the major Zika outbreak in Brazil in 2015 that it attracted international attention, particularly because here scientists were able to establish a link to microcephaly in children infected in the womb for the first time.
Travel warning for regions with Zika virus infection
Due to its widespread nature, Zika virus infection is now considered a travel disease. Travelers become infected in the affected countries and bring the virus back home, where they can infect others, for example during sex. However, if the mosquito species that pass on the virus are absent in the home countries, major outbreaks are ruled out. This is the case in Germany, for example.
Travel warnings for pregnant women are in effect for high-risk regions. In addition, vacationers there should protect themselves more from mosquito bites to prevent a Zika virus infection.
Zika virus infection: symptoms
A Zika virus infection is often asymptomatic, i.e. without symptoms.
If symptoms do occur, the disease usually takes a mild course. The first Zika virus symptoms appear about two to seven, sometimes twelve days after infection (incubation period). The signs are similar to those of other mosquito-borne viral diseases, especially dengue or chikungunya fever. Thus, affected individuals usually suffer from the following symptoms:
- nodular-spotted skin rash (maculopapular exanthema)
- joint pain (arthralgia)
- red eyes due to conjunctivitis (inflammation of the conjunctiva)
Some patients feel very ill and fatigued and also complain of headache and muscle pain. In rare cases, patients also report dizziness, stomach pain, nausea with vomiting, and diarrhea.
Severe courses of the disease, as can occur with dengue (bleeding due to massive drop in blood platelets) or chikungunya (joint pain, bleeding for months), are very rare with a Zika virus infection. However, it can be dangerous for pregnant women or their unborn child. There is also a possible connection with Guillain-Barré syndrome.
Zika virus infection in pregnant women
A Zika virus infection usually heals after a few days without consequences. Only the skin rash persists for about a week. However, it can be dangerous if pregnant women become infected with the Zika virus. The pathogen can then be passed on to the child via the blood – even if the pregnant woman herself does not experience any symptoms.
The virus can remain in the body for weeks to months. After that, there is probably lifelong immunity. Therefore, if a woman becomes pregnant weeks after a cured Zika virus infection, there is probably no longer any risk to the child.
Guillain-Barré syndrome after Zika virus infection
A Zika virus infection can also have dangerous consequences for adult infected persons. In individual cases, it causes Guillain-Barré syndrome. This is a rare neurological disease that manifests itself in symptoms of paralysis, which in the worst case can also affect the respiratory muscles. Around 20 percent of patients remain severely physically disabled, and about five percent die.
Zika virus infection: causes and risk factors
Transmission of the Zika virus
According to current knowledge, only mosquitoes of the Aedes genus transmit the Zika virus to humans. Known representatives are Aedes albopictus (Asian tiger mosquito) and Aedes aegypti (Egyptian tiger mosquito), which can also transmit the yellow fever, chikungunya and dengue viruses, among others.
The viruses circulate in the blood. So if an infected person is bitten again by Aedes mosquitoes, they pick up the pathogens with the blood and can transmit them to other people during the next blood meal. This is how a Zika virus infection can spread through the population.
Besides humans, primates are also considered to be the main carriers of the Zika virus.
Among the dangerous mosquitoes, the Asian tiger mosquito (Aedes albopictus) deserves special attention. It is about five millimeters small, black and silver-white striped and widespread. According to the Federal Environment Agency, the Asian tiger mosquito has so far been detected in 26 countries, and is considered established in 19. It now also occurs regularly in Germany.
Zika virus infection during sex
Through sexual contact, an infected person can transmit the Zika virus to another person – even if the infected person does not experience any symptoms (anymore). Men in particular are carriers, presumably because the viruses manage to hide from immune cells for longer in the shielded area of the testicles.
Zika virus infection via blood products
Theoretically, the Zika virus can also be found in blood transfusions. However, transmission by this route is considered extremely unlikely and has only been proven in a few cases to date. Nevertheless, people returning from affected regions should not donate blood for several weeks.
Risk groups
As with other infectious diseases, the following applies to Zika virus infection: people with pre-existing conditions (such as high blood pressure, diabetes, heart failure), a weakened immune system (e.g. due to HIV infection) and the elderly are particularly at risk.
Given the increased number of newborns with small heads (especially in Brazil), pregnant women form a special risk group. However, research is still needed to determine exactly how Zika virus infection affects unborn children. After birth, Zika virus infection tends to be harmless in both children and adults.
Zika virus infection: examinations and diagnosis
Zika virus symptoms such as fever, joint pain and rash also occur in other travel illnesses that can take a much more severe course (e.g. dengue fever). A visit to the doctor is also advisable for pregnant women, as Zika virus infection can cause damage to the unborn child – especially at the beginning of pregnancy.
Medical history
The doctor will first take your medical history (anamnesis). To do this, he or she will ask about your symptoms and recent travel. Possible questions include:
- How long have you had your symptoms?
- When was the last time you were abroad?
- Where did you travel and how long did you stay there?
- Have you been bitten by mosquitoes?
- Have you recently measured an elevated body temperature?
- Have your symptoms subsided in the meantime and are now increasing again?
- Do you have joint pain, red eyes or skin rashes?
Physical examination
Laboratory tests
To confirm the diagnosis of Zika virus infection, the doctor will need to draw your blood. Some blood values may differ from normal. For example, white blood cell (leukocyte) and platelet (thrombocyte) levels are decreased in Zika virus infection. In contrast, other values such as C-reactive protein (CRP) are elevated.
However, such changes are also found in many other diseases, so they are not evidence of Zika virus infection. The diagnosis can only be made with certainty if the pathogen can be detected – more precisely, if the genetic material of Zika viruses can be detected in the blood and/or urine. This detection is carried out using a special laboratory method, the “reverse transcriptase polymerase chain reaction” (RT-PCR). This allows even small traces of Zika virus RNA to be amplified and determined.
Direct pathogen detection via the virus genome is only possible in the acute stage of infection:
- Up to the 7th day after symptom onset, it is useful to test blood and urine samples from the patient for Zika virus RNA.
- If the onset of symptoms was more than 28 days ago, an infection can only be detected by specific antibodies in the blood.
These laboratory methods sometimes deliver incorrect results, since the substances used also react with other flaviviruses (cross-reactivity). In the so-called neutralization test, on the other hand, a reliable detection of the Zika virus infection is possible. However, this method takes several days and is very time-consuming. Therefore, the faster and less expensive RT-PCR is considered the standard method.
Exclusion of other diseases
When testing for a possible Zika virus infection, the physician must exclude other diseases with similar symptoms (especially other tropical/travel diseases) (differential diagnosis). This is very important, because although a Zika virus infection is usually harmless, severe complications can occur with other diseases – with symptoms that are similar at the beginning.
|
Symptom |
Chikungunya |
Dengue |
Zika virus infection |
|
Fever |
sudden, up to 40 degrees Celsius |
gradually increasing |
if at all, then mostly only slight fever, rarely over 38.5 degrees Celsius |
|
Duration of fever |
usually only a few days, two peaks with fever break in between |
one week |
only a few days |
|
blotchy-knotty skin rash |
frequent |
rarely |
frequently, lasting about six days |
|
Bleeding (hemorrhagic fever) |
Rarely |
almost always |
not known |
|
Joint pain |
almost always and long lasting (sometimes months) |
rarely and if, of clearly shorter duration |
yes, but also only a few days |
|
Conjunctivitis |
rarely |
rarely |
frequently |
In addition, white blood cells are usually more significantly reduced in chikungunya than in Zika virus infection or dengue. Platelets, on the other hand, drop into a critical range, especially in dengue fever.
Always remember: If you have possible Zika virus symptoms or other signs of illness during or after travel, especially to high-risk areas, you should seek medical attention immediately.
Zika virus: Treatment
There is no therapy that works directly against the Zika virus. Only symptomatic Zika virus treatment is possible, that is, treatment of the symptoms:
Especially in unclear cases, NSAIDs should not be taken under any circumstances! This could be dangerous if it is not a Zika virus infection but dengue fever. In this disease, internal bleeding can occur, which would be aggravated by NSAIDs.
If there are other symptoms of Zika virus infection, such as conjunctivitis, the doctor will extend treatment accordingly.
Zika virus infection: course of disease and prognosis
Zika virus infection often progresses without signs of illness. Many infected people therefore do not even notice that they are carrying the virus. If symptoms of the disease appear, they usually last only a few days to a week. The skin rash usually lasts the longest. Hospital treatment is only necessary in exceptional cases.
Possible complications of Zika virus infection are – as mentioned above – maldevelopment in unborn children and Guillain-Barré syndrome in adult patients.
Preventing Zika virus infection
The following measures will protect you from bites:
Use insect repellents
So-called repellents with the active ingredients DEET, icaridin or IR3535 are effective. For herbal products, experts recommend those based on lemon eucalyptus oil (PMD/Citriodiol).
However, health authorities advise against using repellents on babies younger than two months. To also protect newborns from Zika virus infection, cover their bodies completely with clothing and equip strollers and car seats with mosquito nets.
Wear long pants and long-sleeved clothing.
The less bare skin you show, the less surface you provide for bloodsuckers to attack. For added protection against mosquito bites and thus Zika virus infection, you can spray your clothing with the insecticide permethrin.
Use mosquito nets.
Install mosquito nets especially over your sleeping area and on windows. For extra protection, you can spray the mosquito netting with permethrin. Keep in mind that high sunlight will cancel out the permethrin protection.
Avoid and eliminate water spots.
Do not travel to risk areas if you have health problems or are pregnant!
Adhere to the current recommendations of the health authorities. For more information on the current situation regarding Zika virus infections, visit the websites of the World Health Organization, the German Foreign Office and the European or American health authorities (ECDC, CDC).
Advise your doctor of any past travels!
This is especially true for pregnant women returning from a high-risk area. Report your trip to your gynecologist no later than your next checkup. If you become ill, they will test you for Zika virus infection and initiate further testing if necessary. If you feel healthy, your doctor will use the information to look especially for early signs of defective brain and skull development in the child on ultrasound.
Not only in the case of Zika virus infection, but in general:
Zika virus: Vaccination?
A medicinal prevention against a Zika virus infection in the sense of a vaccination is not yet possible. However, studies on this are underway.