Human onchocerciasis

The activity of ivermectin against the filarial parasite Dirofilaria immitis in dogs suggested a possible role for the control of filarial parasites of humans (20). It has been extensively tested in human onchocerciasis and is now considered to be the dmg of choice. In a single yearly oral dose, it suppresses microfilariae in the skin and eyes and, in most cases, prevents the progression of the disease to blindness. Table 4 shows the results of a 30-patient double-blind study recorded over one year. 

O. volvulus. This is the causal organism of human onchocerciasis, which is a disease of the skin and eyes. This disease affects between 20 and 40 million people in the world, frequently causing blindness and skin pathology. The tropical zones most affected are Africa, Guatemala and Mexico. A mild form of the disease threatens to spread in tropical South America. The microfilariae circulate in the peripheral blood day and night. Many mosquitoes, such as Culex, Anopheles, Mansonia, Aedes, and Simulium Spp., are vectors for this and other types of filariasis. 

A fortunate fallout of the avermectin work was the finding that Ivermectin has activity against the black fly vector of human onchocerciasis ( river blindness ). It interferes with transmission of the filarial nematode. Onchocerca volvulus, to the human population. Since 40 million people are affected by this disease, the decision by Merck to supply ivermectin free of charge to the World Health Organization, for use in humans in the tropics, was met with great enthusiasm and hope for conquering this parasitic disease. 

Since ivermectin primarily kills the microfilariae of O. volvulus in man, it has been compared with DEC in patients with onchocerciasis [147,161-165]. The drug (single dose of 200 pg/ml) was compared with DEC (a total of 1.3 g as one week s course) in all the trials it was found that ivermectin and DEC were almost equipotent in clearing microfilariae of O. volvulus from the skin. However, the former produced milder and transient Ma2CZotti reaction than DEC. Thus ivermectin may be regarded as a superior drug to DEC in terms of activity, tolerance and safety for the chemotherapy of human onchocerciasis [20]. 

Suramin was till recently the main stay of chemotherapy of human onchocerciasis [3,97,98]. The following dose schedule was used for treating O. volvulus infection [99]. For adults, a test dose of 100-200 mg of the drug was administered intravenously. If this dose was tolerated by the patient, Ig of suramin was injected intravenously at weekly intervals for 5 weeks. For children the test dose is 10-20 mg/kg intravenously, followed by a dose of 20 mg/kg administered intravenously every week for 5 doses. It is essential to inject the test dose first to avoid unpredicted toxicity or fatalities associated with the suramin therapy. 

The efficacy of ivermectin for human onchocerciasis was established in the 1980s and is summarized in this chapter briefly. Clinical study of ivermectin in human strongyloidiasis has not yet been completed. Here we describe the efficacy of ivermectin for human strongyloidiasis as observed in our institution during the past decade. Furthermore, we would like to describe the combination therapy with ivermectin and albendazole for bancroftian filariasis and also the efficacy of ivermectin in the treatment of human scabies. 

Diethylcarbamazine was introduced in the late 1940s and was the drug of choice for human onchocerciasis. Diethylcarbamazine has microfilaricidal effects and rapidly kills microfilariae of O. volvulus in the skin and eye, but also results in cellular cytotoxicity with severe damage to the human host [7]. Ocular complications... 

Awadzi, K., Dadzie, K. Y, Schulz-Key, H., Gilles, H. M., Fulford, A. J., and Aziz, M. A. (1986). The chemotherapy of onchocerciasis XI. A double-blind comparative study of ivermectin, diethylcarbamazine and placebo in human onchocerciasis in northern Ghana. Ann. Trap. Med. Parasitol. 80,433-442. 

Helmby H, Grencis RK 2003 Contrasting roles for IL-10 in protective immunity to different Hfe cycle stages of intestinal nematode parasites. Eur J Immunol 33 2382-2390 Hisaeda H, Maekawa Y, Iwakawa D et al 2004 Escape of malaria parasites from host immunity requires CD4 CD25 regulatory T cells. Nat Med 10 29—30 Hoerauf A, Brattig N 2002 Resistance and susceptibility in human onchocerciasis-beyond Thl vs. Th2. Trends Parasitol 18 25—31... 

Together with the Institute of Tropical Medicine in Tuebingen one of us (J. Schibel) is studying "The epidemiology and molecular biology of Onchocerca volvulus (Nematoda Filarioidea) in North Cameroon (CEC-Project by Dr. A. Renz and G. Wahl). This parasite is causing human onchocerciasis or river blindness, which occurs mainly in the tropical Afiica. 

Duke BOL (1990) Human onchocerciasis disease. Acta Leidensia 59 9-24... 

Brattig NW. Pathr enesis and host responses in human onchocerciasis impact of onchocerca filariae and wolbachia endobacteria. Microbes Infect 2004 6(1) 113-128. 

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