Treatment for Schistosomiasis
The reason why schistosomiasis is still a world health problem is the difficulty treating it. Effective drugs that have been administered to patients were organic trivalent antimonials, but these were slightly toxic to them and should be given with extra care – in small doses over a period of 2 to 6 weeks, depending on the type of antimonial drug. Mass treatment of infected people using the drug in various countries has not been easy to health workers because a considerable number of people showed side effects.
Because of the side effects associated with the use of organic trivalent antimonials, much effort has been spent by scientists on investigating other less toxic but effective drugs. Luckily, they discovered the drug praziquantel which is now the drug of choice due to its effectiveness against all species of human schistosomes and with little side effects compared to antimonials (Harder 2002). Doenhoff et al. (1985) however reported that some schistosomes show resistance to the drug, so other alternatives are being pursued (Doenhoff et al. 2000). Alternative drugs could be the antimalarial drug artemisin and its derivatives which demonstrated their antischistosomal activity by killing young, developing schistosomes (N’Goran et al. 2003). Another safe and effective antischistosomal drug recently discovered is the plant substance called “myrrh”; although the substance has been known since antiquity, its ability to kill the parasites was only discovered few years ago (Sheir et al 2001). In many cases, appropriate chemotherapy can lead to reversal and even resolution of much fibrosis and urinary pathology (Richter J. 2000). However, heavy infection neglected for a long period of time could lead to irreversible bladder or liver damage (Strickland and Abdel-Wahab 1991).
Preventive Controls for Schistosomiasis
Like many infectious diseases, controlling schistosomiasis involves a multifold effort including (1) educating an affected population on the means of preventing the transmission of the parasites, (2) control of the vectors, (3) treating infected persons through chemotherapy, and (4) vaccinating the populace if vaccines are available.
Educating people is quite hard especially if it involves persuading the uneducated, poor, native people to change some of their customs and traditions in order to prevent the transmission of the parasites.
Prior to the advent of safe and effective antihelminthic drugs, controlling the snails (intermediate hosts of Schistosoma spp.) was the major thrust of control efforts. Until today, it is still a significant support to chemotherapy campaigns and to trim down reinfection (Madsen 1990). Molluscides and other biological agents are being used to control the population of vector snails.
Control by Chemotherapy
Administering effective schistomacidal drugs to an infected population dramatically lowers the prevalence of schistosomiasis. For example, the prevalence of S. mansoni infection to school children in the Nile Delta has decreased from 60.3% to 24.8% one year after treating them (children) with praziquantel and 41.1% three years after the treatment. The statistics was provided by Spencer and colleagues (1990).
Although vaccination is still not a widely used, it offers great potential in controlling schistosomiasis; hence our scientists are now doing extensive research on developing vaccines against Schistosoma parasites.
Doenhoff MJ, Kimani G, and D Cioli. 2000. Praziquantel and the control of schistosomiasis. Parasitology Today 16:364-366.
Doenhoff MJ, Hassounah OA, and SB Lucas. 1985. Does the immunopathology induced by schistosome eggs potentiate parasite survival? Immunolog. Today 6:203-206.
Harder A. 2002. Chemotherapeutic approaches to schistosomes: Current knowledge and outlook. Parasit. Res. 88:395-397.
Madsen H. 1990. Biological methods for the control of freshwater snails. Parasitology Today 6:237-241.
N’Goran EK, Utzinger J, Gnaka H, Yapi A, N’Guessan S, Kigbafori D, Lengeler C, Chollet J, Shuhua X and M Tanner. 2003. Randomnized, double-line, placebo-controlled trial or oral atemether of the prevention of patent Schistosoma haematobium infections. Am. J. Trop. Med. Hyg. 68:24-32.
Richter J. 2000. Evolution of Schitosomiasis-induced pathology after therapy and interruption of exposure to schistosomes: A review of ultrasonoraphic studies. Acta Tropica 77: 111-131.
Sheir Z, Nasr AA, Massoud A, Salama O, Badra GA, El-Shennawy H, Hassan N, and SM Hammad. 2001. A safe effective herbal antichistosomal therapy derived from myrrh. Am. J. Trop. Med. Hyg. 65:700-704.
Spencer HC, Ruiz-Tiben E, Mansour NS, and BL Cline. 1990. Evaluation of UNICEF/Arab Republic of Egypt/WHO Schistosomisis Control Project in Beheira Governorate. Am. J. Trop. Med. Hyg. 42:441-448.
Strickland GT, and MF Abdel-Wahab.1991. Schistosomiasis. In G.T. Strickland (Ed.), Hunter’s tropical medicine, 7th ed. 81 Philadelphia: W.B. Saunders Co., pp. 781-809.