Every time the Olympics come around, it seems there’s a different disease stalking the event. At Rio 2016 it was Zika. At the postponed Tokyo games it was Covid. And at the 2024 Paris Olympics this summer? Take your pick. Authorities have been working to contain both dengue and measles, which have been on the rise in France and many other countries.
During this summer’s Olympics and Paralympics, millions of people from around the world will concentrate in the host city: French authorities are preparing to welcome more than 15 million visitors to the country. Even for a capital used to mass tourism—almost 40 million people visit Paris every year—this is a huge influx of people. Some will bring infectious diseases with them. Others, without sufficient immunity, risk picking something up during their stay. With dengue and measles already a problem in Paris, authorities have been planning how to limit the potential of the Games becoming a superspreader event.
“It is very difficult to limit the epidemic risk when it comes to dengue,” explains Anna-Bella Failloux, a medical entomologist working at the Pasteur Institute in Paris. The virus is transmitted from human to human by mosquitoes, the culprit in France being the invasive tiger mosquito, Aedes albopictus. The insect becomes an increasing problem when the weather warms up, and Europe’s hot summer is creating conditions for the species to thrive. “The eggs are very resistant, and the metabolism of the mosquito speeds up with the heat. The insect becomes an adult earlier, and, therefore, it bites earlier too.”
Tiger mosquitoes aren’t new in France: They arrived as early as 2004 in the south, and have been in Paris since 2015. Originally from Asia, they lay eggs in pockets of still water, which can then hatch weeks later, even after the water has evaporated. This explains how the insect spread to Europe, arriving first in Genoa, Italy, before making its way to France.
Dengue, however, is a more recent problem. With outbreaks of the virus raging in tropical parts of the world—there have been an estimated 10 million cases worldwide this year, with South America and Southeast Asia badly affected—France has seen cases surge. Between January 1 and April 30, 2024, health authorities recorded 2,166 cases, compared to an average of just 128 for the same period in each of the previous five years. Most of this year’s cases were imported from the overseas French departments of Guadeloupe, Martinique, and French Guiana, where epidemics are ongoing, but the European Centre for Disease Control and Prevention has recorded some instances of transmission inside Europe this year, including in France.
This points to the risk of having an event that concentrates people from all over the world at a time when cases are soaring worldwide. If this raises the number of imported cases in Paris, an abundance of tiger mosquitoes then has the potential to spread the virus domestically.
For most, an infection is asymptomatic or results in mild, feverish symptoms, but in some the disease becomes more severe, and it can be fatal. There is no specific treatment for the virus, and few Europeans have any immunity from prior exposure. Vaccines have only become available in the past few years, and are offered only in a small number of high-transmission countries.
“There are two main differences with the 2016 Zika crisis in Rio,” explains Mark Booth, senior lecturer in epidemiology at the University of Newcastle in the UK. “First, it was wintertime in Rio. Second, Zika was not as prevalent as dengue.” Plus, it’s not something that Europeans and visitors from typically unaffected parts of the world will be ready for. “There’s a disconnect between tropical diseases and Paris: Visitors might not think of protecting themselves from mosquitoes when they visit the French capital,” Booth says.
The French authorities have been taking the threat seriously: In May, the Paris regional health agency laid a network of 526 egg-laying traps across the city to monitor the spread of the tiger mosquito, with this information supported by a citizen-reporting program, and a regional mosquito control agency on hand to help eliminate the insects. Health professionals are also mandated to report any dengue cases they encounter so that steps can be taken to minimize the risk of domestic transmission. Authorities have also been working to get rid of places where the mosquitoes can breed—for instance, by instructing people to get rid of any stagnant water in and around their homes, particularly in areas close to where there will be large gatherings of people.
Mosquito-transmitted diseases aren’t the only ones to pose a threat at the 2024 games. Others being monitored closely include measles, which has also seen a surge in cases in France since the beginning of the year, and pertussis, cases of which have been gradually going up since 2017.
There are efficient vaccines for these two diseases; however, coverage is weaker than it used to be, explains Anh Wartel, deputy director general and head of the European regional office for the International Vaccine Institute. For instance, following the disruption of the pandemic, childhood vaccination rates for measles have fallen, and in many countries, including France, measles vaccine coverage is lower than the 95 percent needed for population immunity. As a sign of this, France saw a spike in measles in 2023, as part of a 30-fold increase in cases across Europe. The US too has been hit by rising cases in 2024.
With a great number of people visiting France, there’s an increased risk of imported cases—which poses a threat to both other visitors and the French population, which is underprotected due to a history of low vaccine uptake for measles (though coverage has been improving). Measles can cause major complications in a minority of patients, and even death in severe cases. As a result, the French national public health agency has reminded citizens of the importance of being up to date with their immunizations.
Just like dengue, levels of measles and pertussis are also going to be closely monitored throughout the summer, but there is no reason to be particularly worried, says Wartel: “Surveillance systems of infectious diseases have been greatly reinforced in France after the Covid-19 pandemic.” Parisian hospitals are also on alert to handle potential disease outbreaks, she adds. “It is not the first time that the country organizes a big sporting event. Many people from all over the world came to France for the 2023 Rugby World Cup, and everything went well.”
Dengue and measles will be distant worries for many Parisians, but bedbugs are still a very real one following last year’s wave of infestations. Many Parisians still have them in mind when they sit in a metro, train, or cinema. As tourism is one of the main factors that explains their proliferation, the arrival of millions of people could drive up their numbers.
However, according to Areki Izri, a medical entomologist at the Greater Paris University Hospitals who has studied bedbugs, Parisians and tourists shouldn’t worry too much about this threat—at least not imminently: “To be honest, we are lacking case studies in Paris right now,” he says. “I have two doctoral students working on bedbugs, and we have to ask around to find infected homes to study. Of course, there will be a few cases during the Olympics, but I’m not worried.”
Izri points out that newly built buildings will host the athletes, lessening the chance of the pests already being there, and that hotels are now well prepared in case bugs are found in rooms. Pest control efforts are also generally better than they used to be: Natural methods, such as killing bugs with extreme heat or cold, are now widely used instead of the insecticides that dominated the beginning of the 21st century, and which contributed to the pests becoming resistant.
If an epidemic risk does exist surrounding the Paris 2024 Olympic Games—and it exists during any large-scale event where people from all around the world gather—France seems ready. Athletes might also be heartened by the recent Tour de France that just ended. This edition of the famous cycling race saw a return of Covid cases, with some cyclists having to drop out of the race, others continuing while sick, and masks becoming mandatory again in all the official zones. But the outbreak did not spread out of control. Hopefully, that will be the case with any disease that might invite itself to the biggest sporting event in the world.
