Abstract

The need to have a screening tool for onchocerciasis control to compliment parasitological and molecular diagnosis has remained an important goal. A novel Onchocerca volvulus slide flocculation test (Ov-SFT) was developed using tissue homogenates from rat organs (kidney, liver, heart, spleen, muscle, brain, lungs and testes). Liver followed by spleen and then kidney tissue homogenates performed better than others. Flocculation reactions were performed with antigens extracted from female adult worms of O. volvulus using sodium dodecyl sulphate (SDS) and sera from confirmed onchocerciasis infected patients. Negative and assay controls included non-infected serum and phosphate buffered saline (PBS). Results were subjectively graded as no reaction, 0 or negative. Positive reactions were rated 1 to 5 for low, moderate, medium, high and very high flocculation. The grading corresponded to titre levels ranging from 1/2, 1/4, 1/8, 1/16 and 1/32. The liver homogenate had the highest titre of 1/16 (4) followed by that of the kidney 1/8 (3) and heart 1/4 (2) flocculation reaction. The liver homogenate was validated as binding surface for Ov-SFT for screening field samples. Serum was added undiluted to SDS-extract at 1:40 dilution. Result showed that 33 (50.8%) of the sera samples (n= 65) from onchocerciasis endemic communities receiving ivermectin treatment tested positive. Intensity of antibody reactivity were at 1/2, 1 (1.54%); 1/4, 4 (6.15%); 1/8, 6 (9.23%); 1/16, 9 (13.85%) and 1/32, 13 (20%) dilutions. Three out of the five malaria positive cases were Ov-SFT sero-positive compared to 9 (63.5%) of the 14 malaria negative. There is potential field and point of care application of this test for surveillance and monitoring of onchocerciasis. The possibility of using it with other parasitic and bacterial diseases control is discussed.

Key words:  Antibodies, extracted antigens, flocculation test, onchocerciasis, serology, tissue homogenate.