[Development of an antigen detection dot blot assay for the diagnosis of human onchocerciasis based on the biotin-avidin binding system]

Abstract

The development of a highly sensitive and specific diagnostic test is of urgent need for the field assessment of human onchocerciasis and for monitoring the success of control programs. We report here the development and evaluation of a Dot blot Immunobinding Assay (DIA-BA) based on the biotin-avidin binding system, for the detection of O. volvulus specific antigens in body fluids. Specific antibodies were produced by immunizing rabbits with the O. volvulus recombinant antigen Oncho-C71 and labelled with biotin. The biotinylated probes were then used to detect O. volvulus specific antigens initially blotted onto a nitrocellulose membrane. The smallest amount of blotted antigens detectable by the new test is 0.5ng, 1ng, 1ng and 2ng respectively in urine, dermal fluid, tears and serum samples. Out of 456 onchocerciasis endemic subjects examined, 98.4%, 96.5%, 90.8% and 75.0% were positive by the DIA-BA test on urine, dermal fluid, tears and serum respectively The test was most sensitive (100%) when used on urine and least (54.76%) when used on serum from skin snip positive subjects. The specificity of the test, determined amongst non-exposed individuals, was 100% on all but for dermal fluid samples (97.5%). Also, the color intensities on the blot were observed to positively correlate (r = 0.8 on urine) with the skin microfilaria loads on the individuals. We conclude that DIA-BA test could be very useful for mass diagnosis of prepatent, of low and high level infections due to O. volvulus.