The Chikungunya outbreak in the Seychelles: implications for vector control
Emma OREFUWA – Kings College, the University of London, London, UK,
The recent Chikungunya outbreak that swept across the Indian Ocean in 2005-2006 was of unprecedented magnitude. This arbovirus reached the small Indian Ocean Islands of the Seychelles
in July 2005, resulting in a two wave epidemic, totalling 9221 suspected cases, with a peak of 3832 cases in February 2006 and an overall estimated attack rate of 11% (cases from July 05-Oct 07)
The presumed vector of this incapacitating disease among the Islands affected was the container breeding mosquito, Ae. albopictus. To more fully understand the timing and development of the epidemic, an epidemiological profile of notified cases was constructed. The highest number of cases was found in the 15-44 age category which reported 13% of cases. A significant difference
was found in the number of cases reported by women compared to men ( χ2=134.106(1), p<0.0005).
With the backdrop of a high incidence of Chikungunya in Seychelles, Mahe, an ovitrap based survey was carried out for a duration of five weeks, from the 29th August to 6th Oct 2008 in residential and communal areas to study the geographical distribution and abundance of Aedes species during the Winter season.
Ovitrap surveillance was conducted for 5 weeks, conventional ovitraps were placed outside randomly selected houses and communal areas to collect outdoor breeding Aedes mosquitoes. It
was found that Aedes albopictus was the most abundant Aedes species even though a small percentage of Culex quinquesfasciatus was found to breed simultaneously in the same ovitrap.
Aedes aegypti was not found. The results from this survey indicate that the dominant mosquito species is Aedes albopictus, and that during the winter season, there are elevated levels of egg
laying. These findings indicate that monitoring and surveillance initiatives need to be ongoing to identify any risks of any future disease outbreaks that can be transmitted by the Asian ‘tiger’
mosquito.