Usutu virus in Europe: should we worry?

Daphne van Doorn of Rohde Public Policy discusses the potential threat posed by the Usutu virus, a vector-borne disease relatively new to Europe…

Several exotic mosquitoes have been advancing onto European soil, bringing with them diseases unknown in Europe before their arrival. The latest discovery is the Usutu virus, found in a blood sample from a donor in Hessen, Central Germany during an extensive blood sample test at the end of August 2012.

Mostly found and originating in Africa, the Usutu virus is relatively new to the EU, being extremely rare to be found in the blood sample of a person, as infection in Europe is not common. These kinds of exotic viruses are more often entering the region given the effects of climate change, which is making Europe a more attractive feeding and breeding ground for such mosquitoes.

The virologist who made the discovery at Hamburg’s Bernhard-Nocht-Institut (BNI) for Tropical Medicine, Dr Jonas Schmidt-Chanasit, has stated that more research is needed before any conclusions can be made about the outbreak, and is therefore asking doctors in Germany to send blood samples to the BNI for screening. The Usutu virus can lead, in the worst case scenario, to acute inflammation of the brain. Symptoms such as headache, fever, drowsiness, fatigue and confusion are seemingly innocent, meaning the virus can pass through the body without the person being aware of being infected. Additionally, it is quite important that this virus has been found specifically in a blood sample of a donor, given that these viruses can be transmitted via blood transfusions. As these kinds of viruses are rare and therefore not screened for in a regular blood test, this is a risk to the safety of blood supply.

The Usutu virus is not the first exotic virus to have entered Europe. Over the years there have been several outbreaks of similar viruses; in 2007 a northern region of Italy experienced the Chikugunya virus, which infected a few hundred people. Another, which is increasingly prevalent in Europe, is the West Nile virus, which is now emerging every summer in Eastern Europe, but is slowly moving towards Central Europe. Finally, the Dengue virus has been found in 2010 in regions such as south-east France, as well as Croatia and is also known to show up in Greece. These examples all show the increase of emerging pathogens, which are new to the EU, and provide specific public health challenges. Indeed, during the outbreak of the Chikugunya virus in Italy in 2007, blood donation banks in the region had to be shut down due to the risk of infection, and this protection measure actually caused a temporary shortage in the supply of blood and blood products in the area.

As can be seen by statistics from the European Centre for Disease Protection and Control (ECDC) the prevalence of exotic mosquitoes in Europe has increased in recent years. There have been increased sightings of the yellow fever mosquito (primarily the Aedes aegypti), the Asian tiger mosquito (Aedes albopictus), as well as other potentially dangerous vectors. These exotic mosquitoes can carry certain diseases, such as the aforementioned Dengue fever and others. The Usutu virus is also a vector-borne virus and in the same category, as well as being a zoonosis, a disease that can affect several species – in this case with the possibility to infect humans.

First discovered in South Africa in 1959, the Usutu virus has since been discovered in several other African countries. The first time it was found outside of Africa was in 2001, in Vienna, Austria in blackbirds, with a peak in 2003, most probably due to an exceptionally warm summer. The last two summers there have also been several incidents in the south of Germany where birds have died from the virus. The first time the Usutu virus was discovered in humans was in 2009 in Italy, in two patients who had weakened immune systems. From what has been reported so far, the infection in Germany seems to be a new case, where a person is or has been infected with the virus without having a weakened immune system.

The warm summers are particularly important to mention, given that climate change has been cited as one of the causes for the increase in exotic mosquitoes in Europe. Research has previously been conducted to confirm that the advance of these exotic mosquitoes is linked with the increase in temperature, as well as the increase in international trade. An example shows that stagnant water in truck tyres is an ideal environment for mosquitoes to breed, and they therefore travel with the truck, and similarly, via airplanes or trains.

The areas where the emerging pathogens and mosquitoes have been found in Europe have been quite far towards the west. The discovery of the Usutu virus is an important development, as it shows the entry of yet another potentially dangerous and exotic disease on European territory. The European Union and the World Health Organization (WHO) are both monitoring this situation to make sure appropriate measures are taken, when needed.

Taking into account these developments, and if we assume that climate change will continue, these mosquitoes and their pathogens should be a growing concern for the EU to deal with. The EU has some competence in this field, particularly when dealing with blood policy, such as donor, and recipient, safety as well as the issue with blood supply, via the Blood Directive 2002/98/EC and the Decision on Cross-Border Health Threats, which is a current ongoing legislation to increase cooperation throughout the EU on health threats such as these vector-borne diseases and emerging pathogens.