Schistosomiasis — artemether

Schistosomiasis is a tropical parasitic disease caused by the blood fluke schistosoma, and ranks second to malaria as an illness of public health and socioeconomic importance. It is caused by contact with a free-swimming form of the parasite, which has a freshwater snail as an intermediate host. It penetrates the skin and matures in the bladder and intestine. The eggs of the parasite cause haematuria, liver ulceration and gastrointestinal disturbance. Treatment of the early stages of the disease is virtually impossible as reinfection is common, and therapy is aimed at killing the mature parasites in the body.

The drug of choice is prazinquantel, a pyrazino-isoquinolone derivative, which is active against most strains of the parasite, but Schistosoma mansoni may not respond fully to prazinquantel, and the possibility of drug-resistance is causing concern. Attempts are being made to find a drug that could attack the immature worms in the body, and so prevent the development of adult female worms and the subsequent development of disease-causing eggs.

A drug of some promise is artemether, a derivative of artemesin, a drug that is altready in use in some areas as an antimalarial.¹ Preliminary studies have shown that artemether has a toxic effect on S. mansoni, and can bring about a worm reduction rate of 97–100%.² The response was at a maximum within 7–28 days after the onset of the infection, a period during which prazinquantel and schistosomicides are generally less effective. A randomised, placebo-controlled trial of artemether has been carried out by Utzinger,³ involving over 300 schoolchildren, some of whom were given artemether in doses of 6mg/kg, repeated every three weeks for a total of six times. The group receiving the active drug had a significantly lower incidence of S. mansoni infection and a lower output of eggs than the group receiving the placebo. From the results of the trial, artemether is considered to have potential value in the control of S. mansoni, and may have prophylactic applications for workers where exposure cannot be avoided, and in flood-relief where previously unexposed individuals may come in contact with infected water supplies.