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Tropical Medicine: “You must not underestimate the capability of these viruses“
Doctor Jonas Schmidt-Chanasit;
Tropical diseases used to appear almost exclusively in remote countries – hence the name. The mosquito bite was annoying, but nevertheless harmless in European regions. But the flying pests keep spreading and spreading. And they carry tiny, but dangerous pathogens. Scientists now found out that these viruses are now settling down in Europe. They are called Sindbis, Batai or Usutu.
But how can the tropical pathogens multiply so much, which dangers do they pose and which prognoses can be derived from this?
MEDICA.de spoke to Doctor Jonas Schmidt-Chanasit, head of the virological diagnostics department of the Bernhard-Nocht-Institute for tropical diseases in Hamburg, Germany.
MEDICA.de: Doctor Schmidt-Chanasit, the importance of infectious diseases that can be transmitted from animals to human beings is increasing worldwide. What causes lie at the root of these developments?
Schmidt-Chanasit: We can actually only look at human beings for the causes. We increasingy penetrate areas where human beings had no access just a few short decades ago. This results in closer contact with exotic animals which would never have been possible in the past. Through measures like rainforest deforestation and industrial-scale livestock farming on large farms, wildlife is also being displaced from its natural habitat. These changes significantly contribute to certain viruses being able to more effectively spread to human beings. The strong increase in population in developing countries and the associated close cohabitation between man and farm animals likewise results in a more frequent transmission of zoonotic viruses to human beings.
MEDICA.de: Time and again and in different intervals there are warnings about the swine and avian flu and other occurring zoonotic viruses around the world. What kind of role does globalization play in this?
Schmidt-Chansit: Globalization is also an important factor in terms of the quick spread of zoonotic viruses or vector-borne diseases, since trade and tourist traffic between continents has significantly increased. Thanks to global transportation of goods for example, exotic mosquitoes were introduced to Europe and now transmit the dengue virus to human beings in France and Croatia.
MEDICA.de: Which viruses have the potential of spreading particularly strongly over the next few weeks and months and become especially dangerous for human beings?
Schmidt-Chanasit: The prime example of course is the influenza (flu) virus, which can spread due to the various contacts of man with farm animals, particularly in Southeast Asia. In Europe zoonotic viruses transmitted by mosquitoes play an increasingly larger role, since the mosquitoes as well as the viruses mosquitoes transmit, are spreading more and more. At the same time it is difficult to precisely control these invasive mosquitoes. This problem isn’t new. We have known since the end of the 70s that the Asian Tiger Mosquito for instance has been in Europe. This started in Albania and the massive spread in the Northern Mediterranean countries could only take place because for decades nobody paid attention to this problem. This laissez-faire attitude then made it possible for the dengue virus to gain a foothold in 2010 in Europe.
That’s why it is important for the future that we tackle this problem globally, because due to lack of mosquito control measures dengue fever and the Asian Tiger Mosquito are also on the rise in the U.S.A., especially in the state of Florida. In Southwestern Germany the German Mosquito Control Association (KABS) has been around for more than 30 years and has gotten a good handle on the mosquito plague along the Rhine River. Now it’s essential to communicate this know-how and the experience of KABS to Germany and Europe to effectively push these invasive mosquitoes and the viruses they transmit back.
Viruses that are highly variable and can very quickly change. It is the so-called reassortants where specific genome segments are being exchanged; © Bernhardt-Nocht-Institut für Tropenmedizin
MEDICA.de: How does a host change by a virus from an animal to a human take place? What characteristics does a virus need to switch over to a human being?
Schmidt-Chanasit: There are different mechanisms. For the most part, initially frequent and intense contact between human beings and animals is the decisive factor; this was the case for the avian influenza type H5N1 for example. A brief contact between man and animal was not enough for an effective transmission. This particularly pertained to people that were in closer contact with animals, for instance in poultry farming. On the other hand, these zoonotic viruses are for the most part RNA viruses that are highly variable and can very quickly change. In the case of influenza viruses it is the so-called reassortants where specific genome segments were being exchanged. Due to the reassortment, a mixing and redistribution of genetic information takes place, which for instance enables an influenza virus to infect humans and bring about disease.
We also know reassortants from other viruses, for example the Orthobunyavirus that is transmitted by mosquitoes. Such a reassortant Orthobunyavirus has already appeared in Africa in the 90s: the Orthobunyavirus that was originally harmless to human beings was able to cause hemorrhagic fever after reassortment, similar to the Ebola virus.
MEDICA.de: If it often difficult to exactly predict the phases or stages of a virus outbreak in advance. In the future how big are the chances to be able to intervene sooner and more specifically to control an often still unknown virus?
Schmidt-Chanasit: This is exactly what we neglected for the longest time in terms of zoonotic pathogens and particularly viruses transmitted by mosquitoes. Globally since the 70s, there barely is any comprehensive monitoring of viruses transmitted by mosquitoes. In fact the focus was on individual zoonotic viruses, for instance the dengue virus, but we lost track of the big picture by doing so. That’s why it is now our job to close this gap. We have to ask ourselves for instance which viruses already exist in German mosquitoes and which will be added in the upcoming years for example from tropical regions. So-called surveillance is crucial here. It is necessary for us to continuously catch mosquitoes over the course of many years to find out what has changed. In doing so for instance, we find new viruses like the Usutu virus. Last year we detected the Usutu virus in just one of 70,000 examined mosquitoes and this year there already has been mass mortality of blackbirds in Southwestern Germany due to the Usutu virus. This is why our conducted surveillance projects are crucial to establish an early warning system for mosquito-transmitted viruses in Germany.
MEDICA.de: Several years ago, evidence of the Usutu virus in different areas of Southern Germany gave cause for concern. By now you were able to show three exotic viruses in animals in Germany, those being the Sindbis, Batai and Usutu virus. What makes these viruses so dangerous for human beings?
Schmidt-Chanasit: These three virus types were the first viruses that could be detected in domestic mosquitoes. Because we have now known since 2010 which mosquito-transmitted viruses can be found in this country, we can initiate further research to be able to assess the medical relevance of these findings for the population in Germany. Patients with corresponding disease symptoms can be more specifically examined for this in the future. The Batai virus for example is very versatile – a reassortment is possible.
In the U.S. all blood donors are already being tested for West Nile virus infection; © panthermedia.net/Christoph Hühnel
MEDICA.de: What significance do the results that you collected have for the German and European population?
Schmidt-Chanasit: For starters it is our job to look for human infections. So far however nothing suggests that infections with the Usutu, Batai or Sindbis viruses have decisively occurred in Germany. However, you must not underestimate the capability of these viruses, because in Scandinavia time and again there is already an increase of human Sindbis virus infection with thousands of incidences in a seven-year-rhythm.
MEDICA.de: What medical measures are used to tackle this possible danger?
Schmidt-Chanasit: We work very closely with neurologists, transfusion physicians and critical care physicians to be able to quickly and positively identify corresponding disease incidences. In continuing education courses we also inform our colleagues who work in these areas, so they are able to prepare in advance for disease incidences with these viruses.
MEDICA.de: The U.S.A. has already gained experience with “exotic“ viruses. What measures have already been implemented there?
Schmidt-Chanasit: The development is very clear in the U.S.: Dengue fever has turned up again in Florida and the West Nile virus has circulated in North America since 1999. That’s why the American Red Cross has thought about checking all blood donors for the dengue virus. This test is especially important for high risk patients for whom a blood transfusion that’s contaminated with the Dengue virus could have fatal consequences. In the U.S. all blood donors are already being tested for West Nile virus infection. The test for the Dengue virus is now newly being added. This is of great importance in the U.S.
MEDICA.de: To what extend are German general practitioners already prepared for a possibly increasing transmission of these new viruses?
Schmidt-Chanasit: The Institute for Tropical Medicine hosts many continuing education courses with which we can get hold of many general practitioners. The same also applies to press work to provide our colleagues with solid information. In doing so, a private medical practitioner in Thuringia, Germany, has clinically diagnosed the first case of autochthonous dengue fever in Europe. The patient resided in Thuringia and had vacationed in Croatia. This is a good example of general practitioners who more often question unusual symptoms in patients, examine them more closely and then – in suspicious cases- send blood samples to us.
The interview was conducted by Diana Posth and translated by Elena O’Meara.