Healthy living Climate change: tropical infectious diseases in Germany?

There are many ticks and mosquitoes native to Germany. Everyone has been bitten by mosquitoes now and then. Although bites from native mosquitoes are irritating they are mostly harmless. However, non-native species of mosquito such as the Asian tiger mosquito have been encountered in Germany from time to time for some years now. These species can spread dangerous pathogens that are relatively unusual in Germany to animals and humans.

Some pathogens and diseases are referred to as “tropical” because they originate in warmer climates. 

Ticks can also pass on pathogens. Well-known examples are native species of ticks such as the castor bean tick (Ixodes ricinus). They mainly transmit tick-borne encephalitis (TBE) virus, which causes tick-borne encephalitis (TBE) and Borrelia burgdorferi bacteria, which cause Lyme disease (borreliosis). Non-native ticks from warmer regions of the world, including the meadow tick (Dermacentor reticulatus) from the south-eastern regions of Europe, are now increasingly being spotted in Germany. Like tropical mosquitoes they can transmit a wide range of new pathogens to humans and animals.

Climate change is a key factor in the spread of a greater number of infectious diseases within Germany. Higher average temperatures, longer summers and milder winters create good conditions for the pathogens and their vectors, i.e. tropical mosquitoes and ticks.

Ticks and mosquitoes often act as vectors by carrying pathogens. These include viruses, bacteria and single-celled parasites. The reason these pathogens can be transmitted to humans is that ticks and mosquitoes need blood to develop and reproduce. They are constantly on the lookout for a new “host” to provide that blood. However pathogens are only passed on by a tick bite or mosquito bite under certain conditions:

• The tick or mosquito must previously have fed on blood from an infected living creature and absorbed pathogens with it.
• The pathogens must have had enough time and the right conditions to reproduce in the tick or mosquito.
• For some pathogens transmitted by ticks, the feeding process must also have persisted for some time. For example, Lyme disease (borreliosis) bacteria are not usually transmitted unless a tick has been attached for at least 12 hours. 

While a tick is sucking blood the pathogens can be transmitted to the person in the tick’s saliva. Most people know that a tick bite can be dangerous. That’s largely because even native species can transmit diseases, particularly Lyme disease (borreliosis) and tick-borne encephalitis (TBE).

However, mosquitoes can also transmit serious diseases. The risk of tropical diseases being spread is largely due to tropical mosquitoes. Despite the spread of these mosquitoes, the risk of becoming infected with tropical pathogens currently remains relatively low in Germany. One reason for this is that the pathogens can only be transmitted at relatively high temperatures. 

Little is known as yet about the capacity of native mosquito species to pass on diseases. However we do know that some native species can also transmit pathogens such as West Nile virus. 

West Nile virus in Germany

Transmission of West Nile virus to human beings was first reported in Germany in 2019. Cases were regularly reported in the following years also. It is suspected that there were other infections which were not detected. That’s because just 20% or so of the people infected actually become ill with West Nile fever and have symptoms that are similar to those of flu. Just under one in every 100 people infected have the severe and sometimes fatal form of the disease. Since West Nile virus now appears to survive the winter in Germany, experts believe it could spread even further in Germany.

The European Centre for Disease Prevention and Control has a map showing where exactly in Germany and in the European Union as a whole cases of infection with West Nile virus have been reported. 

The main reasons for the increase in the spread of tropical pathogens is global trade in goods and travel, as well as climate change. The increase in mobility and international travel mean that tropical pathogens and their vectors are increasingly being introduced into the country. For example, many types of mosquitoes can lay their eggs in even the tiniest of pools of stagnant water. This allows mosquito eggs to be transported long distances.

Some pathogens such as West Nile virus can also be introduced by migratory birds. Transmission from birds to humans via mosquitoes is also possible. But many pathogens can also be transmitted to other animals such as horses, sheep and dogs.

Tropical pathogens would not be able to survive and spread in temperate climates as in Germany if it weren’t for climate change and global warming. The increase in average temperatures means that tropical pathogens and their vectors can reproduce in Germany too. Increasingly mild winters mean that tropical mosquitoes and ticks can now establish themselves permanently in Germany. For example, the meadow tick, which comes from south-eastern Europe, has spread increasingly in Germany in recent years.

Meadow tick

The meadow tick (Dermacentor reticulatus) settled in Germany several decades ago and can now be found throughout the country. They originate in south-eastern regions of Europe. Meadow ticks can transmit a range of pathogens including Babesia and Ehrlichia. However people are rarely bitten by meadow ticks. Horses and dogs are infected more frequently.

Babesia are parasitic pathogens similar to the malaria pathogen. They frequently infect dogs with babesiosis, also known as “canine malaria”. Humans are far less likely to get babesiosis, and even if they do they only have mild symptoms. Typical symptoms of the severe form of the disease in humans are high temperature, anemia and exhaustion.

Ehrlichia are bacteria that reproduce in human and animal cells. Three quarters of people with an Ehrlichia infection (ehrlichiosis) are asymptomatic. However older people and people with immune deficiency can become severely ill from it. Typical symptoms include, for example, high temperature, shivering and other flu-like symptoms.

Brown dog tick

The brown dog tick (Rhipicephalus sanguineus) originally comes from North Africa and southern Europe. It prefers warm, dry regions. It is mostly introduced by people (or their dogs) returning from holiday to Germany. But it has also been found in dogs that have never left Germany. This suggests that it may already have become established in Germany. 

Although the brown dog tick mainly infects dogs there are also rare cases of it biting humans. It transmits a range of pathogens to dogs and humans, again including Babesia and Ehrlichia. However reports of transmission of these pathogens to people continue to be rare in Germany.

Hyalomma ticks

Hyalomma ticks are mainly found in Africa, southern Asia and southern Europe. There have been isolated cases in Germany in recent years and it is assumed that they were introduced by migratory birds. Due to climate change, Germany is also experiencing increasingly longer phases of warm weather, which are favorable to the spread of ticks. Hyalomma ticks can probably spend the winter in Germany. However, it’s unclear whether the few that survive the winter are enough to allow the tick to become established in Germany in large numbers.

Hyalomma ticks can be distinguished from other ticks by their large size and striped legs. This is what a Hyalomma tick looks like:

Hyalomma ticks can also transmit Rickettsia, the pathogens that cause tick-bite fever. These pathogens have already been detected in Hyalomma ticks found in Germany. Crimean-Congo hemorrhagic fever (CCHF) is an infection that can be fatal and is also transmitted by Hyalomma ticks. However the Crimean-Congo hemorrhagic fever virus has not yet been detected in ticks in Germany. 

You can send ticks by mail to the following address:
Robert Koch Institute
ZBS 1 – “Zecke” (“Ticks”)
Seestraße 10
13353 Berlin

The Robert Koch Institute (RKI) provides answers to frequently asked questions about ticks. 

Asian bush mosquito

The Asian bush mosquito (Aedes japonicus) has spread widely around the globe as a result of trade and travel between Asia and other countries. It has also been found in Germany since 2008, mainly in the south of the country. It can theoretically transmit West Nile virus, dengue virus, chikungunya virus and Japanese encephalitis virus.

Asian tiger mosquito

The Asian tiger mosquito also comes, as the name suggests, from Asia. It was first discovered in Italy in the 1980s. It has now become fully native to the country. It has been found in parts of southern Germany since 2007, initially in small numbers but now in larger numbers during the summer. It is also known to survive the winter in southern Germany.

It is believed that this mosquito can act as a vector for over 20 different viruses. Like the Asian bush mosquito, it can transmit dengue virus, West Nile virus and chikungunya virus. Theoretically, it can also transmit Zika virus. However this virus needs rather long periods of very high temperatures to reproduce: at least 14 days of temperatures of 27 degrees Celsius or more.

As far as we know, none of the pathogens listed has been transmitted by the Asian tiger mosquito in Germany. However this cannot be ruled out given the increasingly higher temperatures. Given the sharp rise in the number of cases of dengue and chikungunya in travelers returning from affected countries the Federal Environmental Agency has already classed the Asian tiger mosquito as a potential health risk.

The Friedrich Loeffler Institute (FLI) has a map showing the precise locations in Germany where the Asian tiger mosquito has been detected to date.

In Germany, tropical infectious diseases are usually only detected after people return from traveling outside of the country. The risk of becoming infected with tropical pathogens in Germany currently remains low. If you still want to protect yourself against the pathogens or are spending time in an at-risk area abroad, you need to protect yourself against vectors such as ticks and mosquitoes. It also makes sense to take action to protect yourself against ticks in Germany because native tick species can transmit diseases such as Lyme disease (borreliosis) and tick-borne encephalitis (TBE).

Protection against ticks and the pathogens spread by them

There is no vaccine or any effective treatment for many of the other pathogens spread by ticks. There are no vaccination or effective treatment options for some pathogens such as Crimean-Congo hemorrhagic fever virus. So you should avoid tick bites as far as possible to protect against infection.

The following measures can help:

• Try not to spend time in grass or undergrowth. You’re particularly likely to encounter ticks in these places.
• Wear long clothing and closed shoes when you are out in the countryside, particularly woods and meadows. It can also be helpful to tuck your trousers into your socks. That makes it harder for the ticks to access your skin.
• Use tick repellents such as insect spray before spending time in the countryside. It’s best to apply the spray to your skin and your clothing to get the best effect.

It’s also a good idea to search for ticks after spending time in the countryside. Sometime ticks can be discovered before they attach themselves. Ticks do not usually attach themselves immediately, but look for a suitable site first.

Removing ticks immediately after they bite can protect against transmission of some pathogens such as borrelia. It generally takes 12 to 24 hours for the Lyme disease (borreliosis) bacteria to be transmitted.

However transmission of viruses is mostly quicker and often cannot be prevented by removing the tick. Many tropical species of tick, unlike native species, leave their hosts very quickly after biting them.

Protection against mosquitoes and the pathogens spread by them

Vaccination against dengue virus is possible. A vaccine has been approved in Germany since 2022. The Standing Committee on Vaccination in Germany (STIKO) recommends the vaccine for certain groups, such as people over the age of 4 who are planning to travel to a region where there is a high incidence of dengue virus. However, this recommendation only applies to people who have already had an infection with dengue virus in the past. 

Since 2024, a vaccine against chikungunya virus has been approved in Germany for adults over the age of 18.

As yet, there are no vaccines against West Nile virus or Zika virus. So the best way to protect yourself against infection is to protect yourself from the mosquitoes. Anti-mosquito sprays are an option here. The most effective deterrent is DEET (diethyl toluamide). Wearing long clothing also makes it more difficult for mosquitoes to bite you. In the evenings in particular, you should stay indoors in sealed or air-conditioned rooms.

If you want to protect yourself against mosquitoes indoors, mosquito nets in front of windows or over beds are a good option. To stop mosquitoes from reproducing, avoiding leaving standing water in containers – which mosquitoes can use as breeding sites – or empty the containers completely at least once a week. These include, for example, bird baths or barrels for collecting rainwater.