Transmission, symptoms, after-effects: should we be afraid of chikungunya?

It's a disease that's spreading more and more, and causing more and more cases: the chikungunya virus. Overseas departments are the most affected. In Réunion, some 54,340 cases have been confirmed since the beginning of the year, resulting in 28 deaths, according to the Regional Health Agency (ARS). In Mayotte, also in the epidemic phase, 1,112 confirmed cases of chikungunya have been recorded for the same period, according to the ARS.

France is not immune. At the beginning of the summer, the virus circulated at a level never seen so early in the year. Public Health France reports that as of July 15, twelve indigenous transmission clusters—meaning that the infection occurred in mainland France—had been identified in France. This represents a total of 30 cases.

How is this disease transmitted? What are the symptoms? Is it dangerous? And how can you protect yourself? BFMTV.com answers 5 questions about the chikungunya virus.

Chikungunya is a viral disease transmitted to humans through the bite of two Aedes mosquitoes - Aedes albopictus and Aedes aegypti - both recognizable by their black and white stripes, hence the common name tiger mosquito.

As the Ministry of Labor, Health, Solidarity and Families explains, the tiger mosquito is native to Asia but appeared in mainland France in 2004. Since then, it has established itself in 81 departments. "Once established in a town or department, it is practically impossible to get rid of it."

Infection occurs when an uninfected mosquito bites a person infected with the virus, explains the Pasteur Institute. The mosquito then ingests the virus, which replicates and is then transmitted to another person through a new bite. Unlike the common mosquito, the tiger mosquito bites mainly during the day (mainly in the morning and evening) and is silent,as ANSES points out.

Only female mosquitoes bite to reproduce. "After biting, they seek out stagnant water in their environment to lay their eggs," says the Île-de-France prefecture. The eggs cling to the dry walls of containers that could fill with water, while the larvae can survive for several months in their eggs. Once in contact with water, the larvae develop. Within a week, they become adults.

The tiger mosquito's reproduction rate is exponential: a female lays eggs on average five times during her lifetime, every 12 days, around 150 eggs per clutch. That's 750 eggs per female, according to the ARS Auvergne-Rhône-Alpes.

The incubation period for the disease is two to ten days. The infection causes joint damage (wrists, fingers, ankles, feet, knees, and more rarely, hips or shoulders), which is often very disabling, continues the Pasteur Institute.

The word chikungunya means "walking bent forward" in the Makonde language, a language spoken in the south-east of Tanzania, referring to the posture of patients suffering from joint pain.

In addition to joint pain, the infection causes headaches accompanied by fever, severe muscle pain, a rash on the trunk and limbs, conjunctivitis, and inflammation of one or more cervical lymph nodes, the research institute adds. Some patients have also reported bleeding from the gums or nose.

Inserm explains that the acute phase of chikungunya is defined as the 21st day after the onset of symptoms, the post-acute phase is defined as the 90th day after the onset of symptoms, and the chronic phase is defined as the 3rd month after the onset of symptoms. However, the reasons for the persistence of symptoms remain unknown.

"In some cases, severe neurological forms can occur, including meningoencephalitis and peripheral nerve damage," the Pasteur Institute further explains. These complications have primarily been encountered in elderly people or those with weakened immune systems, as well as in newborns infected in utero at the same time as their mother.

But the research institute points out that the disease is rarely fatal. Most of the patients who died from it also had other illnesses. Furthermore, once a person has contracted the chikungunya virus and recovered, "they develop lasting immunity against future infections," assures the Regional Health Agency of Réunion.

"So she can't contract the virus a second time."

The infection can, however, progress to a chronic phase, "marked by persistent joint pain," adds Inserm. Two studies conducted after the 2005–2006 and 2013 epidemics showed that more than half of patients are not completely cured one to two years after the onset of the infection, with a degraded quality of life.

This chronic phase of the disease is particularly observed in people over 40, those with a history of joint disease, or those who have had a high fever for more than seven days. The risk of chronicity is also more common in women.

There is no specific treatment available; only symptomatic treatments (painkillers and anti-inflammatories) can be offered to patients. However, remission of symptoms is generally quite rapid, with fever and rash disappearing within a few days.

A vaccine, Ixchiq, was also authorized for use in 2024. However, following serious adverse events in people over 80 with comorbidities, health authorities decided last spring to revise their vaccination recommendations, limiting the vaccine to people under 65.

However, the European Medicines Agency considered in mid-July that the vaccine could indeed be administered to people over 65, although with the usual precautions.

The Pasteur Institute recommends wearing long clothing, applying skin repellents, and also using insecticides. But the most important thing to limit the spread of the tiger mosquito is to eliminate stagnant water where the larvae develop.

Because these mosquitoes don't move much on their own and only live within a 150-meter radius of their birthplace. "If you notice a tiger mosquito in your home, it's because it was born nearby: on a balcony of your building, in your garden, or at your neighbor's," warns the ARS Auvergne-Rhône-Alpes.

Among these water reservoirs: bowl and flower pot, used tire, child's toy, rainwater collector, garden furniture, folded tarpaulin, wheelbarrow or ashtray... Sometimes very small objects are enough: the tiger mosquito does not necessarily need a lot of water, "the equivalent of a cap can sometimes be enough for its larvae to develop."

This ARS thus reminds us that the fight against tiger mosquitoes is "all year round." "Their eggs can survive and wait all winter for the good weather to return." It recommends covering rainwater collectors, cleaning equipment such as gutters or drain grates to facilitate proper water flow, and emptying containers after each rainfall and after an absence of several days from home. "No water = no tiger mosquito."