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 these vector control activities.
Ivermectin distribution started in 1990. Community-directed treatment with ivermectin started in 2000.
In 2005, the Simulium yahense Bioko form was eliminated from Bioko Island. Reinforcement of community-directed treatment with ivermectin is expected to lead to rapid elimination of onchocerciasis.