- The Institute
- Travel & Vaccines
It isn't really new. In the past century malaria and severe dengue outbreaks still occurred in Europe, and in 1870, thousands died from yellow fever in Barcelona.
And yet, the threat of presumed tropical infections feels unexpected in our climates. In the past years Chikungunya appeared in Northern Italy, and in Southern France and Croatia people got infected with the Dengue virus. A frightening example was the rapid spread of the West Nile virus across the USA – so far claiming more than a thousand fatalities.
The reason for this development are mosquitoes, first of all the Asian tiger mosquito (<em>Aedes albopictus</em>) and the Japanese bush mosquito (<em>Ochlerotatus japonicus</em>). They are presently spreading worldwide, over long distances by the international exchange of goods – preferred vehicles are used tyres and flower pots – and locally by trucks. The Japanese bush mosquito has meanwhile firmly nationalised in Germany, it is unclear though whether the German representatives bite humans. More importantly, the Asian tiger mosquito is on its way, some specimens have recently been seen in the Upper Rhine valley.
However, mosquitoes on their own don´t make an epidemic. Only if, in addition, an infected human enters the scene, transmission can proceed. For example the Italian Chikungunya outbreak. The tiger mosquitoes had already settled in the Po basin around 1990 when in 2007 a businessman who came from India fell sick with Chikungunya fever in Ravenna and offered Chigungunya viruses in his blood. He was bitten, and the tiger mosquito transmitted the virus to the next human and so on. Nearly 300 Italians came down with Chikungunya fever.
It was not before 1953 that the WHO declared Germany officially malaria-free. In the past decade, the mosquito Anopheles atroparvus was essential for malaria transmission in Germany. As it prefers salty breeding waters, it was particularly widespread in Northern Germany and constituted a large proportion of the mosquito population there.
At over a hundred sites in metropolitan Hamburg, we have collected more than ten thousand mosquitoes and mosquito larvae. For the first time, Culex modestus was among them, which originates from the Mediterranean basin and has never been found this far north.
Using DNA tests, we traced three unusual worm infections. One of them was a dirofilariasis. Dirofilaria are transmitted by mosquitoes and normally affect dogs.
It was in BNITM’s National Reference Centre for Tropical Pathogens where the first case of a Zika infection imported into Europe was diagnosed in 2013. By the end of 2015, there were four. Travellers had been infected in Tahiti, Borneo and more recently, in Brazil.
It started with a failure of our diagnostics department to find the cause of a fatal brain infection of a man from Saxony-Anhalt. Inquiries revealed that the man was a breeder of South American coloured squirrels and that two of his breeder colleagues had also died from unclassified brain infections one and one and a half years ago, respectively.
It is well known that insects transmit many tropical diseases. It is less well known that they themselves can become ill from the infections and even die.
The canine roundworm Dirofilaria repens is transmitted by mosquitoes and occasionally causes skin disease in dogs. If humans are infected, knot-like lesions occur on the skin, and eye infiltration or meningitis may develop worst case.