[Epidemiological surveillance du chikungunya on Reunion Island from 2005 to 2011]. / La surveillance epidémiologique du chikungunya a la Réunion entre 2005 et 2011.

INTRODUCTION: The largest chikungunya epidemic in history hit Reunion Island in 2005/6. At that time, a specific monitoring system was set up. Since the end of the epidemic, this monitoring system has continued to operate and has been enhanced. The main objectives of the system are early detection of any case of chikungunya virus infection and epidemiological monitoring. METHODS: During nonepidemic periods, surveillance is focused on active detection of all cases. During epidemic periods, weekly incidence is estimated using data collected via a sentinel physician network. Occurrence of severe and fatal forms is tracked during all epidemiologic situations. RESULTS: In 2005-2006, the estimated number of symptomatic chikungunya-virus infections diagnosed on Reunion Island was 266 000, i.e., an attack rate of 34%. A total of 222 severe cases and 44 mother-to-child transmissions were recorded. Since the end of the outbreak, two clusters have been detected in the western region of the island in 2010 and 2011. The second cluster was non-negligible since it involved 164 cases including 112 that were biologically confirmed. CONCLUSION: Based on results recorded from 2005 to 2006, the chikungunya monitoring system appears to have good sensitivity and reactivity. Recent detection of two disease clusters confirms the system's efficacy.

[New vector control measures implemented between 2005 and 2011 on Reunion Island: lessons learned from chikungunya epidemic]. / L'evolution de la lutte anti-vectorielle entre 2005 et 2011 a la Réunion: les enseignements de l'epidémie de chikungunya.

A major chikungunya outbreak concerned 38% of people living in Reunion Island in 2005-2006. Chikungunya is an arthropod-born-virus disease conveyed by mosquitoes called Aedes albopictus. The health agency in Indian Ocean is responsible for vector control. Previously, in the early 40s, vector control concerned only malaria prophylaxis in La Réunion. Then, during the chikungunya outbreak, a new vector control team was installed and learned from this epidemic. The lessons drawn from chikungunya outbreak in La Réunion are about global executive management and organization linked the local partners and population. The lessons also concern technical topics such as the need of scientific research about vectors and vector-control methods. Finally, the regional cooperation in Indian Ocean (Réunion, Maurice, Seychelles, Comoros, Madagascar) has to be developed to share epidemiologic and entomologic data in order to prevent new chikungunya or dengue outbreak.

How to explain the re-emergence of chikungunya infection in Reunion Island in 2010?

In March 2010, a new outbreak of chikungunya infection was detected in the west of Reunion Island. An investigation was launched to describe the incident cases occurrence and to raise hypotheses on factors that could explain the occurrence of this outbreak. All probable or confirmed cases detected by the surveillance system in the western area between March 1st and July 2nd, 2010 were included in the investigation. A standardized questionnaire was performed by phone, including sociodemographic, environmental and behaviour data. A total of 74 cases were described (i.e. response rate of 72%). They were mainly women (sex ratio M/F=0.7), all ages were represented. Most of them (76%) resided in a house; 31% had recently moved, including 22% from metropolitan France. They reported to have been more exposed to mosquitoes and to infected patients than during the major epidemic of 2005-2006. In addition, 41% reported to have reduced their protection against mosquitoes. The results suggest that several concomitant factors contributed to this outbreak: the reintroduction of the chikungunya virus in the island, the population characteristics and environmental factors.

Epidemiology of Chikungunya infection on Reunion Island, Mayotte, and neighboring countries.

Since 2004, the frequency of chikungunya virus infections has been increasing in Africa, Indian Ocean islands, and Asia. The epidemic began on the Kenyan coast, and reached the Comoros at the end of 2004 before spreading to the South-western Indian Ocean islands (SWIOI) in 2005 and especially in 2006. The epidemic then spread to Asia where epidemic foci are still active today. This increase also affected temperate zone countries where imported cases were reported, and indigenous transmission was reported in Italy in 2007, and in France (Var) in 2010. This review provides an update on the knowledge gained from monitoring chikungunya infections in SWIOI. Despite significant differences in design and performance, the implementation of surveillance systems has allowed describing the evolution of epidemic waves in the affected areas. Synchronous epidemic waves were observed in SWIOI, despite the differences between the preventive measures locally implemented. Between 2005 and 2007, all SWIOI were in inter-epidemic situation, except for Madagascar where a persistent virus circulation in an endemic-epidemic pattern was observed. In 2009, and in 2010, two moderate indigenous outbreaks were identified on the Reunion Island by the inter-epidemic surveillance system. Strains analyses demonstrated a reintroduction of the virus from Madagascar. These limited outbreaks should be a reminder of the vulnerability of SWIOI to arbovirosis, since the entomological indexes for competent vectors are high and the virus keeps on circulating more or less actively in the area.

[Dengue fever in the Reunion Island and in South Western islands of the Indian Ocean]. / Dengue à la Réunion et dans les îles du sud-ouest de l'océan Indien.

South Western islands of the Indian Ocean are permanently threatened by dengue fever outbreaks. On the Reunion Island, two dengue outbreaks were biologically documented (1977-1978 and 2004). And since July 2004 there has been an inter-epidemic period for the island with sporadic cases and clusters. Between January 1, 2007 and October 5, 2009, the epidemiologic surveillance system detected five confirmed autochthonous cases, five confirmed imported cases (South-East Asia), and 71 probable cases. All the five autochthonous confirmed cases occurred in Saint-Louis during two consecutive clusters. In other South Western islands of the Indian Ocean, several dengue fever outbreaks have been reported. Importation of dengue virus from South-East Asia is a major risk for a new outbreak on the island. The introduction of a new serotype could lead to the emergence of new and severe clinical forms, including dengue hemorrhagic fever.

[The reemergence of the Chikungunya virus in Réunion Island on 2010: evolution of the mosquito control practices]. / La réémergence du chikungunya à La Réunion en 2010: évolution des actions de lutte antivectorielle.

The re-emergence of local transmission of chikungunya virus caused by Aedes albopictus since March 2010 in the Réunion Island, French territory in the southwest Indian Ocean, calls for better epidemiological surveys, vector control, and community-based chikungunya control. This paper describes the strategy and the new ways of vector control applied since the last major chikungunya virus outbreak in 2005-2007, and the high levels of collaboration with mayors and local associations for community involvement. Between March 17, 2010 (first chikungunya case) and July 1, 2010, 313 cases were investigated, 13,036 premises inspected, and 34,393 premises concerned by spatial treatment. The traditional entomologic indices don't explain the distribution map of chikungunya cases, and many other factors have to be measured for evaluating the risk of transmission, such as lifestyle, habitat, and the kind of environment the people live in. A big information campaign was conducted beside the implementation of traditional mosquito control techniques. The two themes of this campaign are environmental management and individual protection, considered as important components of chikungunya prevention. The outcome of the mosquito control strategy demonstrates that community participation is not enough, and more studies are required to define new ways of communication for promoting community-oriented activities to prevent chikungunya epidemics.