A simple dot blot assay adaptable for field use in the diagnosis of onchocerciasis: preparation of an adult worm antigen fraction which enhances sensitivity and specificity.

The lack of a convenient diagnostic method for onchocerciasis has motivated attempts to develop better detection techniques. Preliminary results indicate that a dot blot assay of the total immunoglobulin G (IgG) response to an easily available and simply prepared Tris buffer soluble fraction (TSF) of whole female worms may be applicable in the field as a first screening method. The specificity of the assay is improved by using a partially purified fraction of TSF of which the dominant component is a 23 kDa protein antigen, PakF. The IgG response to PakF was 100% sensitive and at least as specific as the IgG4 response to TSF. Sera from 189 individuals including onchocerciasis patients and apparently uninfected control subjects from an endemic area and from an urban area in Ghana were screened. The specificity of the assay with urban and endemic control sera was 93% and 68% respectively. The dot blot assay has advantages over the existing skin snip and enzyme-linked immunosorbent assay techniques in terms of simplicity, cost, consumption of antigen, risk of spreading other infections, and patient comfort.