West Nile fever, caused by a virus, is common worldwide. It often causes no symptoms, but in rare cases can lead to death. More and more people in Europe are falling ill with what is known as West Nile fever. Some of those affected have even died from the disease. In Germany, the virus responsible for the disease was first detected in birds. In the meantime, cases of people falling ill are also becoming known again and again. We explain what is behind the West Nile virus and how the symptoms of the fever are expressed in humans.
What is West Nile fever?
West Nile fever is an infectious disease caused by West Nile virus. The virus belongs to the flavivirus family and can be found in both tropical and temperate areas. The virus primarily affects birds, but can also be transmitted to humans and certain mammals such as horses. The infectious disease is a notifiable disease in birds and horses as well as in humans.
Symptoms of West Nile fever
In humans, no symptoms develop in 80 percent of all cases; therefore, West Nile virus infection usually goes unnoticed. Flu-like signs occur in the remaining 20 percent of cases. The incubation period here is two to 14 days. Symptoms typical of West Nile fever may include:
- Sudden onset of fever
- Headache
- Pain in the limbs
- Lymph node swelling
- Chills
- Fatigue
- Pale, blotchy rash
Course of the infectious disease
After the first episode of fever, there may initially be an attenuation of symptoms. However, fever then increases again (biphasic course). Toward the end of the fever phase, slightly less than half of those affected report a rash that lasts approximately one week. In most cases, the disease then heals on its own.
Complications of West Nile fever
West Nile fever can also take a severe course, because the virus is able to cross the blood–brain barrier. This can cause encephalitis (inflammation of the brain), meningitis (inflammation of the meninges), or paralysis (acute paralysis). These complications can result in permanent damage or even death. According to expert findings, the virus can also lead to kidney failure or affect other organs such as the pancreas, heart or eyes. Infection with West Nile virus can have late effects even months after symptoms have subsided. These include symptoms such as fatigue, muscle pain, or difficulty concentrating.
Who is particularly affected by a severe course?
Especially people over 50 years, children and people with a weakened immune system, such as cancer or HIV patients, run the risk of West Nile fever taking a severe course. The older the person affected, the greater the risk of the infectious disease spreading to the brain and nervous system. A severe course of the disease occurs in about one in 150 affected individuals.
Diagnosis of West Nile fever
The disease can be detected by direct detection of the virus in the blood by means of a cultural cultivation or a so-called viral genome detection (RT-PCR; reverse transcriptase-polymerase chain reaction). The latter is a special test procedure for detecting viruses in the blood. This procedure is usually used a few days after the onset of symptoms. If the disease has existed for a longer period of time, the virus can be detected via antibodies in the blood serum or cerebrospinal fluid. Since West Nile virus is very similar to other viruses of the same genus, there is often a risk of confusion, for example with dengue or yellow fever virus. To rule out these diseases, a plaque reduction neutralization test (PRNT) is usually performed.
West Nile fever: what to do?
There is no specific antiviral therapy for the virus. Therefore, treatment of West Nile fever focuses on relieving symptoms, for example, by using antipyretics. If the disease takes a severe course, hospital care is advisable to quickly counteract complications.
How is West Nile virus transmitted?
The virus is transmitted by mosquitoes.To date, it has been detected in over 43 mosquito species, particularly mosquitoes of the Culex genus. In most cases, infected birds are the reservoir host. This means that the birds are infected with the virus on a long-term basis, but do not suffer from any symptoms of disease. Reservoir hosts are therefore a source of dangerous infections for humans and other mammals. When such birds are bitten by a mosquito, the virus is transmitted to the mosquito through the blood. Many mosquito species bite both birds and humans – one example is the Asian tiger mosquito, which has spread throughout Europe. The mosquito then spreads the virus further by biting a human or mammal. West Nile virus can also be passed through direct blood contact. Accordingly, human-to-human transmission cannot be ruled out, for example, during a blood transfusion or organ transplant. In addition, infected mothers can transmit the virus to their infants via breast milk during pregnancy or later during breastfeeding.
Virus areas: Where does West Nile fever occur?
West Nile virus has been detected on five continents to date. This makes it more geographically widespread than any other mosquito-borne virus. In Africa, West Nile fever is most commonly observed in Uganda and Mozambique. However, the infectious disease has also spread to Egypt, India, Southeast Asia and the Middle East. The spread of the virus is also increasing in Europe. Romania, Italy and Greece are particularly affected, but there are also registered cases in some countries in Central Europe, such as Serbia and Hungary.
West Nile fever in Germany
In Germany, West Nile virus was first detected in birds in Saxony-Anhalt in the summer of 2018. In September 2019, West Nile fever sickened a person infected by a mosquito in this country for the first time – previously, the virus had only appeared in Germany as a travel disease. In September 2020, nine more cases were confirmed in Germany. These occurred in Saxony and Berlin. None of those affected had traveled, so in all likelihood the West Nile fever infection must have occurred in Germany.
