Dengue, chikungunya, and Zika are classic tropical diseases caused by arboviruses. These viruses are regularly brought into France by travelers (imported cases) and can then be transmitted to new hosts by the Asian tiger mosquito (Aedes albopictus).

West Nile virus is also an arbovirus, but it is transmitted primarily by mosquitoes of the Culex genus. Birds are the main reservoir for West Nile virus, but humans, horses, and other vertebrate species are also susceptible to infection through a mosquito bite.

The active season for mosquitoes carrying these diseases began on May 1, while a sharp increase in imported dengue cases in the region had been observed since 2023.

For all these viruses, a portion of infections is asymptomatic (20 to 80% depending on the virus and the study).

The symptoms of these diseases, when present, are similar (fever and muscle and joint pain), but have some specific characteristics:

• Dengue: the most common symptoms are fever and joint pain; complications are rare but can be severe (organ failure and bleeding).

• Chikungunya: The most common symptoms are fever and joint pain, which can persist for weeks or even months in some patients.

• Zika: symptoms are generally mild, but the virus can cause congenital abnormalities if infection occurs during pregnancy.

• West Nile virus: The most common symptoms are fever and joint pain. However, the virus can cause serious neurological complications (meningitis, encephalitis, and meningoencephalitis) in 1% of infections.

How is arbovirus surveillance organized?

Surveillance is based on mandatory reporting of all cases—whether imported or locally acquired—that are biologically confirmed. Each report is submitted by physicians and laboratories and immediately triggers an epidemiological and entomological investigation.

Epidemiological surveillance helps reduce the risk of transmission clusters or even epidemics caused by these viruses. The detection of an arbovirus case triggers epidemiological and entomological investigations to rapidly implement vector control measures and thus limit the risk of local virus transmission.

When an autochthonous case is identified (a person who has not recently traveled to an area where the virus is circulating and who was infected locally), vector control measures are strengthened.

What steps should you take to protect yourself from mosquitoes?

The best steps to take to protect yourself and avoid mosquito bites in areas where infected mosquitoes may be present are:

• wear loose-fitting, long-sleeved clothing;

• use topical mosquito repellents;

• use fans;

• sleep under a mosquito net;

• plug in electric mosquito repellent diffusers;

• use mosquito coils outdoors.

Upon returning from regions or countries where cases have been reported, it is recommended that you:

• see a doctor if you have symptoms (joint pain, muscle pain, headaches, rash with or without fever, conjunctivitis, etc.);

• avoid being bitten by a mosquito and thus infecting new mosquitoes that could transmit the disease to another person.

Learn more:

• Discover the prevention tools available to healthcare professionals, local authorities, and the general public

• View recommendations for travelers | hcsp.fr