The summer of 2018 in Germany was the second hottest and driest year on record, and while this made for a beautiful season of beach-side fun, it also brought a deadly disease with it. The West Nile Virus (WNV) outbreak of 2018 was a single-introduction event, thought to be from the Czech Republic. The infection was detected in wild and aviary birds such as owls and blackbirds, in addition to horses. This was the first documented occurrence of WNV in these birds in Germany. When the outbreak was declared over, a sigh of relief was felt across the country. But the problem was far from over.
In 2019, the European Centre for Disease Prevention and Control declared another WNV outbreak. The 2019 outbreak was determined to be due to transmission from resident mosquitoes to birds and horses, as is typical of WNV. The difference was in that birds and horses could be infected by being in the same area as an infected animal, even if they didn't directly overlap there in time. This suggested that the virus was living in the environment itself, making it infinitely harder to control. While horses cannot transmit the virus, bird and mosquito transmission that can survive and be spread indirectly in an affected area is a scary concept.
The 2019 outbreak also suggests that the WNV infected mosquitoes managed to overwinter successfully. Many tropical diseases are not a problem for Europe, North America, and other countries with cold winters because they and/or their hosts die in the cold, and must be re-introduced to return to the same area. But these mosquitoes managed to survive the German winter.
This is most likely linked to climate change. Diseases that used to be restricted to hot climates are now spreading globally because they can survive in ever-warmer climates. This could only be the tip of the iceberg, as researchers predict we will see more tropical diseases invade traditionally cooler areas.
As scientists look to the skies to track mosquitoes, birds, and changes in sunlight hours and temperature, we can only wait and see if the prediction will come true.