What is West Nile?

West Nile virus originated in Africa and was first detected in Uganda in 1937. The first cases in Europe occurred in France in the 1960s. Most notably, infections have been reported in horses, birds and also humans in the southern and south-eastern European countries to date. West Nile virus is found on all continents of the world.

How is West Nile virus transmitted?

Bloodsucking mosquitoes are the main carriers of the virus, with birds being the most important hosts. In somewhat rarer cases, the virus is transmitted to horses and humans . For years, the spread of the West Nile virus in Europe has been closely monitored .

How common is West Nile virus?

The virus seems to be able to overwinter in Germany or in other European countries. In 2018, the virus was detected in horses and birds. Then, a year later, the first cases, five diagnosed infections in eastern Germany, were reported. These were presumably transmitted by mosquitoes inland. Thus, the virus was registered for the first time in Saxony, Saxony-Anhalt and Berlin and detected. According to the Robert Koch Institute, another risk area is the warmer region around the Upper Rhine.

In Germany, the pathogen is mainly transmitted by the enormously widespread mosquitoes of the Culex family. In southern European countries the virus has been transmitted for many years and can also overwinter excellently there .

Before 2019, infections had only been detected in travellers returning to Germany . The virus is particularly widespread in Africa, western Turkey, Israel, India, parts of Southeast Asia and between North and Central America. Evidence of seven infected German citizens was found abroad in 2019. No deaths in connection with the virus are known.

What is the morphology of West Nile virus?

The RNA virus, known since 1937, belongs to the family of the Flaviviridae, which is not only widespread in tropical regions, but also in climatic regions. Mainly birds, horses and other mammals are infected by mosquitoes. In very rare cases, the virus can also be transmitted to humans.

What are the symptoms of West Nile virus?

Only a small proportion of infected people show any symptoms at all and only about 1 % of those infected become seriously ill. However, due to the many asymptomatic infections, the Robert Koch Institute assumes that the number of unreported infections is higher . After an infection with the virus , about one fifth of those affected develop symptoms with fever and flu-like symptoms. These can last between three and six days . The course of the disease usually begins with:

• spontaneous onset of fever,
• Headache,
• Backache,
• Chills,
• Swelling of the lymph nodes,
• Fatigue.

 
In very rare cases, an infection with West Nile virus develops into encephalitis.

How is West Nile virus diagnosed?

If there is a suspicion of an infection with West Nile virus , a special laboratory should take over the diagnosis of laboratory material if possible. In the first few days after the symptoms have started , viral RNA can be detected in serum, whole blood or cerebrospinal fluid, predominantly using an RT-PCR test. After the first few days, the detection by means of IgM and IgG determination in serum or cerebrospinal fluid is useful. Since IgM antibodies can be detected for a very long time, it is advisable to make a final diagnosis by examining samples taken during the course of the disease. The West Nile virus can be detected and confirmed beyond doubt on the basis of a fourfold increase in the specific titre .

How is West Nile virus treated?

There is no specific antiviral treatment option for West Nile virus. Therefore, it is treated purely symptomatically. If the course of the disease worsens, the affected person is admitted to a hospital to be kept under observation.

What complications can West Nile virus lead to?

In about one in 100 people, the infection with the West Nile virus turns into a severe neuroinvasive disease. In most cases, some of the people affected develop meningitis, but in most cases this is benign. In somewhat rarer cases, encephalitis occurs , with the following symptoms:

• mental changes,
• flaccid paralysis,
• Weakness of the muscles,
• Ataxia,
• Optic neuritis,
• epileptic seizures due to changes in the cranial nerves.

 
In exceptional cases, inflammation of the liver or heart is observed. As a rule, an infection with West Nile virus heals without complications. If encephalitis develops, up to 50 % of cases must be expected to have late sequelae . About 5-10 % of those affected, who suffer a neuroinvasive illness caused by West Nile virus, die. The elderly and people with immunosuppression and people with previous cardiovascular diseases are particularly affected.

How can you protect yourself from West Nile virus?

Especially in the summer and early autumn, doctors should always keep West Nile virus in mind when corresponding symptoms occur. Transmission of the virus is possible both through blood transfusions, organ transplants and during pregnancy.

So far, there is no vaccination against the virus. Therefore, mosquito protection is considered to be the most efficient means. In places where many mosquitoes gather, you should wear long-sleeved blouses or shirts and also long trousers. At home, you can protect yourself from mosquitoes by using window screens and mosquito nets.

Is there an obligation to report West Nile virus?

In Germany, the presence of West Nile virus in horses or birds is considered a notifiable animal disease. Since 2016, according to German Infection Protection Act, direct or indirect detection of West Nile pathogens in humans is subject to compulsory notification by name. In Austria, on the other hand, only cases of illness or death are subject to mandatory reporting. In Switzerland, even a positive finding by the laboratory must be reported under the Epidemics Act.