Diagnosis and Treatment of Onchocerciasis

Diagnosis of Onchocerciasis

Demonstrating the presence of O. volvulus in bloodless skin nips is the best diagnostic method. Getting a skin nip from a patient is usually done by raising a small bit of skin using a needle and sliced off with a blade or surgical scissors. The bit of skin is then put into a saline solution on a slide and emerging microfilariae are observed microscopically. Anyone who will do the test should be able to differentiate O. volvulus microfilariae from other species present in the skin sample. If the nodules are to be aspirated, dead worms are present but no microfilariae. Skin-snip biopsies can be obtained anywhere in the body, but if only a single snip is available, it should be obtained from the buttock. The person who will get the skin sample should be careful that the snip is not so deep as to draw blood, the sample might be contaminated with other present filarial species.

Treatment of Onchocerciasis

Surgical excision of nodules around the head can be effective in decreasing both the rate of eye damage and the number of new infections within a community. Administering the drug ivermectin to patients has been a major advance and a modern achievement story. The drug was originally developed and marketed by Merck & Co., Inc for veterinary use but after its effectiveness in treating onchocerciasis, the company charitably donated the drug for mass treatment in poor countries especially in Africa. Prior to the discovery of ivermectin, there has been no satisfactory drug available; the serious side effects of suramin and DEC prevented their use for mass treatment. Ivermectin is now the most acceptable drug available against onchocerciasis because it is well tolerated by patients, and yearly treatment considerably decreases frequency of infection in populations. (Cupp 1992; Taylor et al. 1990) Skin microfilariae are eliminated effectively in a single dose of Ivermectin; the same dosage could inhibit the release of adult females for a year or more (Schulz-Key et al 1992), thus interfering transmission, and appreciably improves skin disease (Burnham 1995). Ivermectin is only considered to be microfilaricidal but repeated doses of it slowly kill adult worms (Duke et al. 1992).

References

Burnham G. 1995. Ivermectin treatment of onchocercal skin lesions: Observations from a placebo-controlled, double-blind trial in Malawi. Am. J. Trop. Med. Hyg. 52:270-276

Schulz-Key H, Soboslay PT and WH Hoffmann. 1992. Ivermectin-facilitated immunity. Parasitology Today 8:152-153.

Cupp EW. 1992. Treatment of Onchocerciasis with ivermectin in Central America. Parasitology Today 8:212-214.

Duke BOL, Zea-Flores G, Castro J, Cupp EW, and B Munoz. 1992. Effects of three-month doses of ivermectin on adult Onchocerca volvulus. Am J. Trop. Med. Hyg.46:189-194

Taylor HR, Pacque M, Munnoz B, and BM Greene. 1990. Impact of mass treatment of onchocerciasis with ivermectin on the transmission of infection. Science 250:116-118.