A record number of Dutch people contracted dengue abroad this year. One of the vectors of the virus is also increasingly common in the Netherlands. Five questions about this infectious disease.
1. What is dengue?
Dengue, or breakbone fever, is a viral disease that you get through mosquito bites. The culprits are the mosquitoes Aedes aegypti (yellow fever mosquito) and Aedes albopictus (tiger mosquito), which transmit the virus. In addition to dengue, these mosquitoes also spread the viruses that cause yellow fever, chikungunya and zika. These creatures like warm, humid environments, so you will find them mainly in tropical and subtropical regions.
The yellow fever mosquito is only found sporadically in the Netherlands. It is sometimes found at and around Schiphol, as a stowaway in cargo from tropical countries. The tiger mosquito, on the other hand, is steadily advancing from the south. In Mediterranean countries it has already established itself permanently and it is also increasingly being seen in northern Europe. In the Netherlands, the tiger mosquito has been spotted this year in South Limburg to Flevoland.
The disease can have a mild course, comparable to a severe flu. But in some cases it can also get out of hand, with serious forms such as ‘dengue hemorrhagic fever’ and ‘dengue shock syndrome’, conditions that can be life-threatening.
Symptoms usually begin a few days after the bite. Think of high fever, pain in your head, especially behind the eyes, and muscle and joint pain. A rash can also occur. Some people experience nosebleeds or bleeding gums. In the worst cases, dengue leads to serious complications such as breathing problems, heavy bleeding and even organ failure.
2. How do you get dengue, and how does it spread?
Dengue is caused by the dengue virus, a member of the flavivirus family, which also includes West Nile virus. This virus has four variants. Anyone who is infected with one of these variants is then immune to that one variant, but not to the other three. This means that you can get dengue repeatedly.
Reinfection is often even more severe. This is because the immune system reacts to a pathogen that it thinks it recognizes from a previous infection, but which may be of a different subtype. The antibodies that the immune system then produces can actually make the disease worse instead of fighting it.
The dengue virus is spread through the bite of an infected female Aedes mosquito. These mosquitoes like stagnant water. Favorite places are buckets of rainwater, old car tires that collect a little rainwater, and unused flower pots. They are active during the day, so the chance of a bite is greatest then.
Dengue does not spread directly from person to person. You only get it from mosquitoes, and in rare cases from blood transfusions or from mother to child during pregnancy.
3. How common is dengue?
Dengue is a growing problem worldwide. The number of cases has been rising sharply for years. The World Health Organization estimates that between 100 and 400 million people are infected each year, of whom approximately 96 million become seriously ill. Most cases are in Asia, Latin America and Africa.
In Europe, dengue was until recently something you only know from holiday stories. In recent years, that has changed. Countries such as France, Spain and Italy are increasingly reporting cases of dengue that were contracted locally. In the Netherlands, we usually see dengue in people who return from countries where the virus has traditionally been common.
Alarm center Eurocross reported that in the first half of 2024, 112 Dutch people contracted dengue abroadas many as in the whole of 2023. No indigenous cases have yet been reported in the Netherlands, but the presence of the tiger mosquito is a reason for vigilance.
4. What is new about the situation in Europe?
The fact that dengue is now present in Europe is something of recent years and a cause for concern. This is mainly due to the spread of Aedes mosquitoes, in particular the tiger mosquito. These mosquitoes originally only occurred in Southeast Asia. Due to globalization and climate change, they moved to other parts of the world, including Europe. Global warming helps these mosquitoes to establish themselves here: warmer temperatures ensure that they survive better.
In recent years, there have even been outbreaks in Southern Europe where people have contracted dengue without having been abroad. This means that the mosquitoes that can transmit the virus have already established themselves in parts of Europe. And that is worrying, because the risk of dengue spreading further is increasing.
5. What can be done against dengue?
There is no specific treatment for dengue fever yet, so prevention is the best defense. The most important step is to avoid getting bitten by a mosquito. You can do this by wearing long clothing, using mosquito repellent with DEET, and installing screens on windows and doors. Also make sure there is no standing water in and around the house, because that is where mosquitoes lay their eggs.
The British-American company Oxitec has been testing genetically modified mosquitoes for ten years to combat the tiger mosquito. Male mosquitoes are equipped with a gene that is lethal to their offspring. After millions of these laboratory mosquitoes were released into the wild in a trial in the Cayman Islands and mated with wild females, the population fell by 96 percent.
Despite these promising test results, there are still many hurdles to overcome before this technology can be used on a large scale to combat the tiger mosquito worldwide.
There is a vaccine against dengue, intended for a limited groupThis concerns people who had dengue at least a year ago and who were also tested positive.
People who have never had dengue can also get the vaccine. For example, because they are traveling to an area where dengue is common. This does require planning: the vaccine consists of two injections that must be administered at three-month intervals. The cost is around 135 euros.
