The number of reported cases of trypanosomiasis, or sleeping sickness, has reduced in sub-Saharan Africa over the past five years, a new report shows, attributing the decline to huge investments in the fight against the disease.

According to the latest World Health Organisation (WHO) report on tropical diseases that have been neglected since 2009, the number of new cases reported annually has been fewer than 10,000.

“Advances in controlling the disease made during the past decade have achieved an important decrease in its burden, but control and research efforts must continue and be based on sustainable public health,” said the report, adding that the decline reflects a drop in the burden of disease.

Sleeping sickness is caused by trypanosoma parasites transmitted by tsetse fly bites. It affects up to 30,000 people a year in 36 countries in sub-Saharan Africa.

The WHO report shows that there were 9,875 new cases in 2009, 7,139 in 2010 and 6,743 in 2011.

This represents a decrease of 72 per cent in the past 10 years. The number of cases reported annually is considered to be a fraction of the real number. The 2011 figures estimate the incidence could be around 20,000 cases a year.

The chronic form of the disease is endemic in 24 African countries, including all the East African countries, and represents 98 per cent of reported cases.

From 2009 to 2011, Uganda reported between 100 and 200 new cases annually, Tanzania reported fewer than 100, and Kenya reported sporadic cases.

The Democratic Republic of Congo is the only country that has reported more than 1,000 new cases annually, and it accounts for 84 per cent of the cases reported in 2011.

“Reaching the roadmap’s targets for eliminating human African trypanosomiasis depends on increasing access to early, accurate diagnosis; delivering safer and more effective treatment; and continuing surveillance,” the report said.

In 2009, WHO set up a specimen bank that is available to researchers to facilitate the development of new and affordable sleeping sickness diagnostic tools.