Part 1: the West Nile virus in human medicine
The West Nile virus belongs to the flaviviruses and occurs in many different regions of the world. The virus is transmitted by different mosquito species. Areas with a high incidence of West Nile virus are mainly located in tropical and subtropical areas. However, now the first human cases of West Nile virus were reported in Germany. Prof. Dr. Jonas Schmidt-Chanasit investigates with his working group at the Bernhard-Nocht-Institute for Tropical Medicine in Hamburg different mosquito-transmitted viruses, called arboviruses. Since the West Nile virus is one of these arboviruses we spoke with Prof. Schmidt-Chanasit about this new disease in Germany.
Note: the interview was translated from German. See the original German version
ZOOP: The name “West Nile virus” sound rather exotic and is nothing you would expect to find in Germany. Where does the virus come from?
Schmidt-Chanasit: The virus was discovered first in a female patient with a fever in the West Nile district of Uganda in 1937. The woman was checked for Yellow fever and in the process, the virus was discovered. In the following years, the virus received little attention. However, when the first cases were reported in the USA and the virus started to spread to Europe the awareness and the interest in the virus increased.
ZOOP: When were the first human infections reported in Germany?
Schmidt-Chanasit: The first reported human case was in Munich in 2018. However, this was caused by a laboratory accident and not by a natural infection. The first natural infection with the virus in Germany was reported in mid-September from Leipzig. It was an infection with a severe course of disease, the neuroinvasive type, which only occurs rarely.
ZOOP: What are typical symptoms of a West Nile virus infection in humans?
Schmidt-Chanasit: The majority of West Nile virus infections in humans are asymptomatic. Only about 20 % develop clinical symptoms, which is referred to as West Nile fever. In most cases, these are flu-like feverish symptoms. Only in about 1 % of the infected we witness a severe cause of disease. This is referred to as the “neuroinvasive type” and affects mostly elderly and patients with pre-existing conditions.
ZOOP: Did the first human infections in Germany occur out of the blue or were you expecting them?
Schmidt-Chanasit: The first infections in humans in Germany did not surprise us. It was already known from our neighbouring countries that the virus circulates in Europe and there were no reasons to suspect that the virus could not spread to Germany. Therefore, we were expecting it eventually. However, what surprised us was the high number of severe cases, which we usually only observe in a small proportion of those actually infected.
ZOOP: So we can assume that the people showing symptoms only make up a very small part of the people actually infected with West Nile virus in Germany? How high are the infection rates estimated for Germany?
Schmidt-Chanasit: Yes, we do assume that most infections are asymptomatic. Therefore, we need to assume that the diagnosed cases are only the tip of the iceberg. Accordingly, hundreds of people in Germany have already be infected whereby that does not cause any symptoms in most people.
ZOOP: What role will the West Nile virus play in Germany in the future?
Schmidt-Chanasit: We need to expect that the West Nile virus is not going to simply vanish again from Germany within the next years. There is a high probability that the spread is even going to increase further. So far, the reported cases have tended to be recorded in regions with relatively low population density. A spread into metropolitan areas like Frankfurt am Main could lead to a sharp increase of case numbers.
However, developments will also strongly depend on climatic conditions in the country. Another mild winter like 2018/2019 will favour the spread of the virus because warm temperatures facilitate the hibernation and the transmission of the virus. In addition, warm temperature in summer speak for a further spread of the virus in Germany.
ZOOP: How well is Germany prepared for the virus? How do you judge the available methods?
Schmidt-Chanasit: Germany has a well-established diagnostic in the reference laboratories. The serology is a bit more complex. However, the required PCRs (polymerase chain reactions) are already established in some routine laboratories. On the positive side, it should also be noted that in Germany there are already some surveillance programs put into place which are a valuable early warning system. In my opinion, we should aim for a continuation of these measures in the future, as they can make a valuable contribution to health protection in Germany.
ZOOP: Is there a routine testing for West Nile Virus in blood donations?
Schmidt-Chanasit: Yes, this is regulated well in Germany by law. Due to the first recorded cases in Germany blood donations need to be tested for West Nile virus in Germany. This way one excludes infections via blood donations.
ZOOP: It is encouraging to hear that some capacities have already been build in Germany to fight the West Nile virus. How well are physicians and public health authorities prepared for the occurrence of the virus?
Schmidt-Chanasit: Honestly, that is quite diverse. Some diagnosis Das ist ehrlich gesagt sehr unterschiedlich. Some diagnoses are due to attentive physicians who have recognized West Nile virus as a potential cause of disease in their patients and have sent the appropriate samples. On the other hand, numerous doctors in hospitals and medical practices have little knowledge of the virus. At this point, further training and close cooperation between reference centres and the public health service is important in order to be able to provide the necessary education. Formats such as the “ÖGD workshops” of the Zoonoses Platform can be helpful at this point.
ZOOP: Is there a vaccine available? How can one prevent an infection?
Schmidt-Chanasit: No, there is no vaccine for humans yet. At the moment the most effective way to protect oneself is to protect from the transmitter meaning the mosquito. Here common protection measures such as nets, long clothes or eventually spray can be named. Furthermore, one should prevent water accumulations in the garden or on the balcony like for example in buckets. Because mosquitoes can lay their eggs in them.
ZOOP: Prof. Schmidt-Chanasit, thank you very much for the interview!
Interview: Dr. Dana Thal for the German Research Platform for Zoonoses (ZOOP)
In the second part of our interview series about the West Nile virus in Germany Dr. Ute Ziegler, veterinarian specialised in viruses and head of the reference laboratory for West Nile virus at the Institute of Novel and Emerging Infectious Diseases at the Friedrich-Loeffler-Institute, answers questions on the health risk of the virus for animals.
In the third part Dr. Helge Kampen of the Friedrich-Loeffler-Institute explains the role of mosquitoes in the transmission of the disease. Which mosquito species are relevant? Is it feasible to take control measures against them? Are there other vectors? What is the future prognosis? These among other questions are answered by our expert in part 3.