Bioko Island, Equatorial Guinea The island of Bioko is a mass of
earth of volcanic origin with a surface area of just over 2000
km2. It is located in the Gulf of Guinea, off the coast of
Cameroon and Gabon. There are two seasons: a dry season
(November to March) and a rainy season (April to October). The
average annual temperature is 25 0C. Rainfall varies from 1930
mm in the north to 10990 mm in the south. About 40% of the
island is inaccessible by land due to the dense tropical forest.
The island is made up of small slow rivers where blackfly
vectors of the Simulium damnosum complex – S. yahense Bioko form
– breed. There are an estimated 90 000 people living on Bioko
Island. The island is the only island known to be endemic with
onchocerciasis. The geographical location of the island protects
it from re-invasion of the blackfly. Large scale aerial and
ground larviciding started in 2003, and aerial spraying
continued in 2005. Environmental assessment surveys showed no
detrimental environmental impact of thes