Antibody responses to a recombinant Onchocerca volvulus antigen (Ov1.9) by onchocerciasis patients before and two months after Ivermectin treatment

Osue HO¹, Edeghere H², Galadima M³, Odama LD⁴ and Engelbrecht F⁵

¹Nigerian Institute for Trypanosomiasis Research (N. I. T. R.), P.M.B. 2077, Kaduna, Nigeria

²National Onchocerciasis Control Programme (NOCP), Race Course Road, Kaduna.

³Formerly of Microbiology Department, Faculty of Science, Ahmadu Bello University (A B. U.), Zaria, Kaduna State, Nigeria

⁴National Pharmaceutical Research and Development, Idun, Abuja, Nigeria

⁵Hygeuine Institue, Abt. Parasitologie Im Neunheimer Feld 32469120 Heiderbeg, Germany.

Corresponding author E-mail: Osueho@yahoo.com

Accepted 23 May, 2012

Abstract

Indirect sandwich enzyme-linked immunosorbent assay (ELISA) was used to measure serum IgG antibody responses to Onchocerca volvulus designated (Ov1.9) recombinant antigen in onchocerciasis patients (n=114) prior to initial ivermectin treatment. Paired sera (n=32) obtained 2months after treatment were also analyzed for changes in antibody levels in a sub-population at pre- and post-treatment. The difference between mean optical density (OD) values of IgG antibody level in proven cases (n=95) and the assumed endemic-normal (EN, n=19) of 0.58±0.23 versus 0.37±0.21, respectively was statistically significant (P<0.05) by the t-test of unpaired data. The non-endemic (NEN, n=7) control had mean OD value of 0.12±0.02. There was no significant difference between the sexes or among age groups and the infection subgroups (with or without presence of nodule and/or skin microfilariae mf). At a cut-off point of mean plus 2 standard deviations of OD value for the NEN control, the sensitivity of 87% in proven cases of onchocerciasis (n=95) and 89% in those with skin mf positive (n=62) proved that Ov1.9 may be suitable not as a single screening test reagent, but when in cocktail with one or more antigens. The higher mean OD value in those with chronic skin disease than those without clinical signs of onchocerciasis (n=39); with papular onchodermatitis (n=20) and optic nerve disease (n=12) subgroups was statistically significant by t-test of unpaired data (P<0.05). The heightened IgG antibody response to Ov1.9 with chronic skin disease is clearly indicative of the possible role parasite-specific antibodies may play in the immunopathology of the disease. There was no significant increase in mean antibody level two month post-ivermectin treatment; hence the antigen will not be useful for drug screening.  

Keywords: Serology, sensitivity, Screening, Diagnosis, Antigens and Antibodies.