Chikungunya is a viral disease transmitted from human to human by the bite of infected mosquitoes of the species Aedes albopictus. In 2005/2006, an outbreak of chikungunya occurred on Réunion Island. After the first episode between March and June 2005, the chikungunya outbreak resurged on the island in October 2005, reaching a peak in February 2006. The French Institute for Public Health Surveillance (InVS) estimated that about 266,000 people developed a clinical form of the disease and severe forms of the disease were reported for the first time. During the period from January to December 2006, 246 people were hospitalised in an intensive care unit on Réunion Island.
With no vaccine or treatment for this disease, the primary means of controlling the outbreak of chikungunya has been to control the mosquitoes responsible for the transmission of this disease (vectors) and their larvae in an effort to reduce their density. To be effective, these mosquito control operations should also be accompanied by personal protective measures to prevent mosquito bites in the general public. Recommendations encouraging the use of mosquito nets or insecticide-impregnated clothing have therefore been issued by several organisations (French Health Products Safety Agency [AFSSAPS], InVS, etc.), especially for protecting children under 30 months of age and pregnant women.
Within the framework of managing the chikungunya epidemic on Réunion Island, the Director General for Health (French Ministry of Health) and the Director General for Pollution and Risk Prevention (DPPR) from the Ministry for Ecology made a formal request to the Agency in August 2006 to assess the risks associated with the repeated use of insecticide products for impregnating mosquito nets and clothing in the short, medium and long terms.
In view of the specific skills required to carry out this work, a dedicated group of experts was set up in order to gather the skills of the toxicologists from the Agency’s Expert Committee (CES) on biocides, together with entomologists from the French Development Research Institute (IRD), the World Health Organization (WHO), and French army health services.
The work of the Agency and recommendations
On the basis of existing literature and international recommendations (particularly from the WHO), the Agency identified the products available on the market and associated hazards. Scenarios of use were then proposed and the corresponding exposures assessed.
Permethrin and deltamethrin are the two active substances that are commonly used for impregnating fabrics.
Although the effectiveness of a mosquito net to protect against attacks from mosquitoes that are active during the day—such as the mosquito responsible for the transmission of chikungunya—may be surprising initially, the Agency’s work has shown that this use has been important in terms of suppressing disease transmission.
The isolation, under mosquito nets, of patients suspected of being infected by the chikungunya virus helps to prevent mosquitoes that come to feed on their blood from being contaminated and infecting other people. Mosquito nets also help protect vulnerable populations such as young children who are not yet walking, bedridden people and pregnant women as well.
The Agency therefore recommends the preferential use of long-life industrially impregnated mosquito nets, the assessment of which has not revealed any particular risk.
Lastly, the Agency’s work showed that the use of impregnated clothing could also provide additional protection, particularly for populations whose activity did not allow them to remain under a mosquito net. This scientific expert assessment was accompanied by recommendations for use so as to guarantee the safety of users.
These recommendations could be applicable to epidemic contexts apart from the one on Réunion Island, when the behaviour of the vector mosquito is comparable to that of the mosquito responsible for the transmission of chikungunya.