• Marianne Comparet (ISNTD)

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 were undertaken at the regional level in the Overseas Territories. The one I would highlight most is the SAPIK tool, an interactive DVD which was developed for primary and secondary school. This tool's originality is that it was not developed by the public health authorities with the support of the education authorities, but rather led by the education authorities and the Department for Education (l'Education Nationale) with support from the ARS. Therefore, this DVD is entirely aligned to education guidelines. Several parts of the curriculum (science, but also literature, arts...) can incorporate the material related to mosquitoes, using thematic learning. The DVD has a wealth of educational resources including tutorials, films, images...

It's also important to highlight local and municipal plans for vector control and also the prevention of vector-borne diseases which are tools which allow a structuring of responses at the local and municipal level, under the guidance of territorial authorities in coordination with the ARS.

Finally, the ARS Guadeloupe teams have been using tablets for several years, which makes it possible to collect data directly in field, and instantly analyse this. This tool has been developed closely with the Ministry of Health, which has improved efficiency and response times.

Are there surveillance, alert and response collaborations with neighbouring islands and countries? Which countries, organisations or partners would you wish to increase your collaboration with?

There have been several trials, particularly with the Dutch part of the bi-national island of Saint-Martin. This resulted in the declaration in 2014, during the chikungunya epidemic, of a memorandum of understanding between France, the Saint-Martin territory and the government of Sint-Maarten for the organisation and control of vector-borne diseases. Joint insecticide treatments and collaborative communications have been developed by the two parts of the island. This is the most successful example of cooperation in this field.

That said, cooperation between Caribbean Islands could be improved. PAHO, Public Health France and the Health Authorities of Guadeloupe, Saint-Martin and Saint-Barthelemy are very much aware of this and working on it.

How could collaboration between water, sanitation, vector-control and public health be improved? Are vector-borne diseases a good platform to accelerate and improve cross-sectoral collaboration?

This is an excellent question as indeed vector-borne diseases would be a good example; however approaches remain too compartmentalised. The health authority is working hard so that the mosquito threat becomes a priority in a wide range of issues for example: water for domestic consumption, sanitation, housing development,... But often, in practice, priorities are very different and it's hard to find convergence. For example, in terms of buildings design, priorities centre around resistance to earthquakes, heat preservation and sound proofing, rather than mosquito proofing homes.

How do your anti-dengue strategies fit into the broader public health agenda in Guadeloupe?

The Vector Control Division is an integral part of the Public Health Division. Prevention measures are a priority and are an integral part of the global disease prevention strategies via two mechanisms:

- Local Health Contracts with municipalities and communes. Vector-control activities are thus on the same level as vaccination, prevention of chronic diseases, access to healthcare and mental health;

- The Education/Health Authority convention: vector control is a prioritised themes alongside nutrition, vaccination, sexual and reproductive health, addiction, psycho-social competencies,...

What would be your message to the international community regarding dengue and the threat of dengue epidemics?

Vector-borne diseases are a major issue in terms of public health for the Guadeloupe region. Aedes aegypti should be without doubt the main focus as it is the vector capable of transmitting the largest number of arboviruses (dengue, chikungunya, Zika, Mayaro, yellow fever, various encephalitis... ). Unfortunately, this mosquito has developed a high level of resistance to chemical insecticides. In addition, community mobilisation and messaging have limits, even though there has been progress in awareness. Finally, the involvement of local authorities has also shown its limits - Guadeloupe, for example, has been facing important financial difficulties and at the same time a rise in demands in environmental issues affecting health (proliferation of algae, water quality...)

It is time to turn to innovative technologies such as the use of endosymbiotic bacteria (Wolbachia) or the Sterile Insect Technique. Guadeloupe is looking to develop this approach with the support of the IRD which has substantial expertise in this field. However, it's important to remember that these solutions will not work individually and will have to sit within a wider integrated framework.

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