Case Studies

Managing Schistosomiasis: A Case Study From Zanzibar




Zanzibar has been endemic for urogenital schistosomiasis since immemorial times, with the first report on schistosomiasis dating back to the 19th century in The Lancet. In the 1960s several studies were undertaken showing the high burden of morbidity due to urogenital schistosomiasis on the islands of Unguja (Zanzibar) and especially on Pemba.

In the early 1980s the Ministry of Health (MoH) of Zanzibar, in collaboration with the World Health Organization (WHO), implemented studies to evaluate the impact of large scale school-based treatment with a single dose of the then newly available praziquantel on morbidity and transmission of Schistosoma haematobium.

In 1986, these studies eventually led to an island wide programme on Pemba to evaluate the impact of large scale chemotherapy with praziquantel on the prevalence of morbidity and transmission of S. haematobium. Given the high cost of praziquantel at the time, individuals were selected for treatment using haematuria as an indirect diagnosis of infection. Only individuals positive for haematuria, as identified either by visual examination of a urine sample or reagent strip, were treated with the drug which cost approximately 10 USD per treatment at the time.

Using a pioneering approach, and after only a short two day training, volunteer teachers and older school children were fully engaged by a small team of five MoH Rural Health Assistants of the Kichocho (Schistosomiasis) Control Team, in the diagnosis and identification of school children eligible for treatment. This large scale programme meant that the study target was achieved in half of the planned time: one year instead of two, as as highlighted in a telex sent by the late Dr Ken Mott of WHO Geneva which stated:

"Congratulations stop third survey results show objectives of 65percent reduction of haematuria and 90percent reduction of visual within one year instead of two years repeat instead of two years stop Regards Mott unisante Geneva 13/4/88"

The telex highlighted a significant reduction of overall haematuria, 65% compared to the original 54.3%, and of visual haematuria, 90% compared to the original 15.8%, in over 25,000 school age children on the whole island. Moreover, urinary tract pathology assessed by ultrasound was also reduced by over 90% only 6 months after a single dose of 40mg/Kg body weight of praziquantel.

This strategic approach anticipated the present WHO Preventive Chemotherapy strategy and was defined as "selective population chemotherapy". This pioneering work documented the proof of principle that it was indeed possible to control morbidity in a high transmission setting with an extremely low cost school based approach delivering regular treatment to school age children, even in spite of continuous transmission.

30 years after this innovative effort, morbidity due to schistosomiasis has now been practically eliminated owing to regular large scale preventive anthelminthic chemotherapy. Overall prevalence rates are now kept consistently at around 2% at the national level, compared to prevalence rates of 54% in 1986. Advanced molecular tools are also being utilised to investigate the impact of these intensive control measures on the parasite populations. Individual miracidia are being isolated from infected individuals and genetically analysed to compare populations of S. haematobium across Zanzibar, understand the effects of the different control strategies on the S. haematobium populations and determine the most effective control efforts for reducing the S. haematobium populations.

The Ministry of Health has now decided to move from morbidity control to transmission control aiming at eliminating schistosomiasis from Zanzibar in the next few years. The booster for elimination is the wide array of supporting partners, such as SCI, SCORE and the National History Museum, as well as the availability of free praziquantel donated by Merck through WHO, and the integrated approach with the aid of behavioural change, snail control and water management, that could make Zanzibar the first country to eliminate “Kichocho” in sub-Saharan Africa.