The return of dengue in Guadeloupe: intensifying vector control measures

Dengue fever cases have been increasing in the last few weeks on the island of Guadeloupe. In this Infectious Thoughts interview, we speak with Joel GUSTAVE, Head of Vector Control Department, Patrick SAINT-MARTIN, Head of Health Surveillance Department and Florelle BRADAMANTIS, Head of Public Health Department and hear more about Guadeloupe's strategies to control both the mosquito vector of the disease and the risk of a dengue epidemic.

Guadeloupe's last case of dengue was recorded in April 2016 - in your opinion what are the conditions which led to new dengue cases emerging at the end of 2018?

The spread of dengue will depend on several factors: importantly, the amount of contact between competent vector populations and immunologically naive individuals, and also climatic factors. On average, dengue epidemics occur every two to three years in Guadeloupe. The last dengue epidemic in dengue was in 2013, followed by the last confirmed case in April 2016. The reasons for this unusual situation which follows on from two major epidemics of chikungunya (2013) and Zika (2016) aren't clear.

Currently, the dengue serotype 1 is in circulation in Guadeloupe. This serotype was at the origin of the 2009-2010 epidemic, which was of significant importance. Although we don't know the current proportion of the population with immunity, we can observe that the vector density (of Aedes aegypti) and climatic conditions of recent weeks have favoured an increase in dengue cases, with a chance for an epidemic to develop.

What measures are in place to monitor the evolution of dengue cases? Do you have fears of an epidemic developing?

A network of urban doctors is consulted weekly by the regional health authority the ARS (Agence Régionale de Santé) on patients seen with dengue symptoms. In addition, all diagnostics laboratories declare each week the number of tests positive for dengue. Also, vector control interventions in the field can flag cases which have not been seen by medical staff. These weekly updates offer an objective view of the situation and of the impact of the dengue virus.

As soon as the first cases were detected in early October, vector-control departments were mobilised to alert local populations and encourage the adoption of vector-control measures by individuals. Have you noticed a positive response from local populations and which messages or communication strategies were most successful?

Several types of measures were put in place. Overall, response by local population has been timid, as we are still measuring larval forms of the Aedes aegypti mosquito in about 40% of homes and adult forms in over 80% of homes. Unfortunately, the vector control measures which local populations are well acquainted with only intensify once the risk of an epidemic becomes more of a concrete threat.

In addition to measures targeting the local population in general some strategies are aimed at specific epidemic foci and breeding grounds: municipalities and regional authorities are mobilised to remove waste, information points are mobilised (such as schools, infant and maternal protection services...), etc.

What can we learn from this recent increase in clinically detected cases of dengue?

We still don’t know why these cases are occurring now specifically. This shows that dengue is a permanent threat to the region, which will continue to evolve under an endemo-epidemic mode, and that prevention measures must not diminish. There is a very likely risk that, in future, there will be further dengue epidemics with, unfortunately, a high number of victims and even deaths.

France has recently recorded autochthonous cases of dengue - what lessons could mainland France learn from your expertise in dengue control?

In mainland France, the vector is different: it is Aedes albopictus whose ecology is different and who is spreading very rapidly. The ARS and EID (Interdepartmental Agreements on Mosquito Control) are coordinating with a large number of partners, and municipalities in particular have had to tackle these issues regularly in the last few years, thus rapidly developing a real expertise of their own.

Several lessons however can be learned from the experience of France's Overseas Regions (Régions d’Outre Mer). Firstly, the successful use of management tools such as PSAGE (Programme de Surveillance d’Alerte et de Gestion des Epidémies) which help to structure and organise the epidemiologic surveillance on the one hand, as well as the vector control response, communication and case management. These systems are already in place in mainland France and the response in terms of vector prevalence or actual cases of arboviruses is completely organised at the national level.

With specific reference to mosquito breeding grounds, Guadeloupe undertook some important studies on the impact of buildings and urban environments on larval sites. These documents could be adapted to the context of mainland France.

In terms of communication and community engagement, several original experiments wer