Elsa Balleydier

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.

A226V Strains of Chikungunya Virus, Réunion Island, 2010

To the Editor: Chikungunya virus (CHIKV) first emerged in Indian Ocean islands off the eastern coast of Africa in 2005 and was responsible for large-scale epidemics on the islands of Reunion, Comoros, Mayotte, Mauritius, Madagascar, and Seychelles (1–4). On Reunion Island, a French overseas territory of 810,000 inhabitants, herd immunity reached 38% in October 2006 (5). Molecular epidemiology of the strain responsible for these outbreaks indicated that it had originated in Kenya (6). The epidemic on Reunion Island was associated with a mutation in the envelope protein gene (E1-A226V) that improves replication and transmission efficiency in Aedes albopictus mosquitoes (7). Since 2006, the Regional Office of the French Institute for Public Health Surveillance in the Indian Ocean has conducted epidemiologic and biological surveillance for CHIKV infection. Case definitions have been described (8). During December 2006–July 2009, no confirmed case was detected on Reunion Island and Mayotte, but new outbreaks were reported in Madagascar (9). In August 2009, a cluster of cases was identified on the western coast of Reunion Island (8). We report an outbreak of CHIKV infection that occurred on Reunion Island in 2010. The first case was detected on March 17, 2010. As of July 6, a total of 100 confirmed and 32 probable cases had been identified (Figure A1). Median age of case-patients was 39 years (range 6 months–80 years), and the ratio of male to female case-patients was 0.81:1. In addition to fever (95%), case-patients had arthralgia (95%), headache (78%), and myalgia (75%). Seven (5%) were admitted to hospitals. No severe illness or death was reported. The outbreak remained largely restricted to residents of Saint Paul (75%) on the western coast. Sporadic cases in other cities also were detected. Sequence comparison based on partial envelope gene or complete genome showed a high level (>99.6%) of nucleotide and amino acid identity of 2010 isolates from Reunion Island with the strains of the 2009 sporadic cases on Reunion Island, as well as with the Malagasy strains circulating since 2006. All isolates sequenced bore the A226V substitution within the E1 protein. Altogether, these results support the hypothesis of a continuous circulation of A226V strains in the southwestern Indian Ocean since 2006 and the possible reintroduction of CHIKV on Reunion Island, most probably from Madagascar. Once again, human travel may have contributed to the rapid spread of the virus between islands because imported and autochthonous cases on Reunion Island occurred after a holiday period for residents on Reunion Island who often traveled to Madagascar. Migration and birth rate on Reunion Island might have contributed to a decrease in the immunity of the population. Furthermore, seroprevalence in 2007 was not homogenous throughout the territory. A hypothesis would be that a lower immunity of the population in the Saint Paul area and environmental and vectorial characteristics contributed to the emergence of this CHIKV disease cluster. On Reunion Island, Ae. albopictus mosquitoes have been described as the main vector responsible for transmitting CHIKV (10). The austral winter may contribute to moderate vector activity and transmission. We cannot exclude a continuous transmission until next austral summer, followed by an increase of cases and an extension to the whole island, as occurred in 2005 (1). Epidemiologic and entomologic surveillance has been reorganized to prevent this risk. Medical staff, the general population, and travelers have been informed about the situation through the news media and meetings organized by health authorities, and recommendations have been issued about destroying mosquito breeding sites and preventing mosquito bites. In recent years, the area of circulation and the epidemic potential of CHIKV have increased, and CHIKV has emerged as a major public health problem. This outbreak could be a new warning to Reunion Island health authorities about the need for preparation not only for CHIKV but also for dengue virus (DENV). With the extent of human travel to and from areas with active CHIKV and DENV circulation, viremic returning travelers constitute an ongoing risk for introduction of such viruses on Reunion Island. In May 2010, two locally acquired DENV-3 cases were also detected, illustrating this threat. These cases occurred during an outbreak of DENV-3 in Comoros Island. Public health efforts to control Ae. albopictus mosquitoes have not been completely effective. This outbreak of CHIKV infection, the detection of autochthonous cases of DENV infection, and the influenza season on Reunion Island emphasize the difficulty of making the appropriate clinical diagnosis. Clinicians and biologists should be aware of the cocirculation of CHIKV, DENV, and influenza viruses. The reemergence of CHIKV on Reunion Island illustrates the permanent threat of circulation of exotic pathogens in the Indian Ocean and the need for strong epidemiologic and laboratory surveillance. Human travel and the geographic expansion of Ae. albopictus mosquitoes raise concern for the spread of CHIKV in Europe and North America.

Surveillance épidémiologique de la leptospirose à la Réunion, 2004–2008: possible impact de l’épidémie de chikungunya sur la létalité de la leptospirose

In 2006, increased mortality due to leptospirosis in Reunion Island had alerted the authorities and justified the conduct of this study in order to update knowledge on the epidemiology of leptospirosis, whereas the latest epidemiological data published on the disease dated back to 2003. This study followed the scheme of a descriptive retrospective survey based on data from reporting and investigation of hospitalized cases of leptospirosis that occurred in Reunion between the 1st January 2004 and 31st December 2008. Data from the National Reference Center (NRC) have also been used. The annual number of reported cases (40 to 50) was stable over the period, which contrasted with the historical decreasing trend of incidence reported by the NRC. The circumstances of exposure were those usually associated with the disease on the island: about 80% of cases were infected between January and June, during the wet season; the main exposure factor identified was the practice of agriculture, declared or not; Leptospira icterohaemorrhagiae remained the most frequently isolated serovar, although regressing. Finally, our study has shown that excess mortality observed in 2006 did not result from an increased incidence but from a rise in the case fatality rate. This could be linked to the outbreak of chikungunya, which peaked in February 2006. In endemic areas of leptospirosis, health professionals should remain aware of the risk of occurrence of fatal cases during arbovirosis outbreaks.

Epidemiological surveillance of leptospirosis on Reunion Island in 2004-2008: possible impact of chikungunya infection on the case fatality rate of leptospirosis

In 2006, increased mortality due to leptospirosis in Reunion Island had alerted the authorities and justified the conduct of this study in order to update knowledge on the epidemiology of leptospirosis, whereas the latest epidemiological data published on the disease dated back to 2003. This study followed the scheme of a descriptive retrospective survey based on data from reporting and investigation of hospitalized cases of leptospirosis that occurred in Reunion between the 1st January 2004 and 31st December 2008. Data from the National Reference Center (NRC) have also been used. The annual number of reported cases (40 to 50) was stable over the period, which contrasted with the historical decreasing trend of incidence reported by the NRC. The circumstances of exposure were those usually associated with the disease on the island: about 80% of cases were infected between January and June, during the wet season; the main exposure factor identified was the practice of agriculture, declared or not; Leptospira icterohaemorrhagiae remained the most frequently isolated serovar, although regressing. Finally, our study has shown that excess mortality observed in 2006 did not result from an increased incidence but from a rise in the case fatality rate. This could be linked to the outbreak of chikungunya, which peaked in February 2006. In endemic areas of leptospirosis, health professionals should remain aware of the risk of occurrence of fatal cases during arbovirosis outbreaks.

A major impact of the influenza seasonal epidemic on intensive care units, Réunion, April to August 2016

The 2016 seasonal influenza in Réunion in the southern hemisphere, was dominated by influenza A(H1N1)pdm09 (possibly genogroup 6B.1). An estimated 100,500 patients with acute respiratory infection (ARI) consulted a physician (cumulative attack rate 11.9%). Sixty-six laboratory-confirmed cases (65.7/100,000 ARI consultations) were hospitalised in an intensive care unit, the highest number since 2009. Impact on intensive care units was major. Correlation between severe cases was 0.83 between Réunion and France and good for 2009 to 2015.

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.

Murine Typhus, Reunion, France, 2011–2013

Murine typhus case was initially identified in Reunion, France, in 2012 in a tourist. Our investigation confirmed 8 autochthonous cases that occurred during January 2011–January 2013 in Reunion. Murine typhus should be considered in local patients and in travelers returning from Reunion who have fevers of unknown origin.

Rickettsia and Bartonella Species in Fleas from Reunion Island

Rickettsia felis, Rickettsia typhi, and Bartonella DNA was detected by molecular tools in 12% of Rattus rattus fleas (Xenopsylla species) collected from Reunion Island. One-third of the infested commensal rodents captured during 1 year carried at least one infected flea. As clinical signs of these zoonoses are non-specific, they are often misdiagnosed.

[Epidemic of influenza A(H1N1) 2009 in Reunion Island: epidemiological data].

In Reunion Island, a French subtropical island located in the southern hemisphere, the monitoring of the epidemiological dynamics of the epidemic linked to the emergence of pandemic virus A(H1N1) 2009 was achieved through the regular influenza surveillance system which has been reinforced on that occasion. It was mainly based on a network of sentinel physicians, combined with virologic monitoring, and on surveillance of severe cases and deaths. The data were analyzed and retroinformation was distributed according to a weekly frequency. The first imported case was confirmed on July 5, 2009 in a traveler arriving from Australia, whereas the first autochthonous cases were reported on July 23. The epidemic peak was reached in five weeks and the duration of the whole epidemic episode was 9 weeks. Pandemic virus has quickly supplanted seasonal viruses that had begun to circulate. The estimated attack rate for symptomatic cases of infection with virus influenza A(H1N1) 2009 was 12.85%. The hospitalization rate was 32 per 10,000 estimated cases, and 24 people had a serious form requiring care in ICU. Among death certificates received at the regional office for health and social affairs, 14 mentioned the influenza, including 7 in whom the pandemic virus has been laboratory confirmed. These deaths occurred in patients significantly younger than usually observed in Reunion Island during the seasonal influenza epidemics. Overall, the epidemic intensity and severity have been similar to those of seasonal influenza in Reunion Island.

L’épidémie de grippe à virus A(H1N1) 2009 à la Réunion: données épidémiologiques

In Reunion Island, a French subtropical island located in the southern hemisphere, the monitoring of the epidemiological dynamics of the epidemic linked to the emergence of pandemic virus A(H1N1) 2009 was achieved through the regular influenza surveillance system which has been reinforced on that occasion. It was mainly based on a network of sentinel physicians, combined with virologic monitoring, and on surveillance of severe cases and deaths. The data were analyzed and retroinformation was distributed according to a weekly frequency. The first imported case was confirmed on July 5, 2009 in a traveler arriving from Australia, whereas the first autochthonous cases were reported on July 23. The epidemic peak was reached in five weeks and the duration of the whole epidemic episode was 9 weeks. Pandemic virus has quickly supplanted seasonal viruses that had begun to circulate. The estimated attack rate for symptomatic cases of infection with virus influenza A(H1N1) 2009 was 12.85%. The hospitalization rate was 32 per 10,000 estimated cases, and 24 people had a serious form requiring care in ICU. Among death certificates received at the regional office for health and social affairs, 14 mentioned the influenza, including 7 in whom the pandemic virus has been laboratory confirmed. These deaths occurred in patients significantly younger than usually observed in Reunion Island during the seasonal influenza epidemics. Overall, the epidemic intensity and severity have been similar to those of seasonal influenza in Reunion Island.