Scope of detectability of circulating antigens of human lymphatic filarial parasite Wuchereria bancrofti with smaller amount of serum by Og4C3 assay: its application in lymphatic filariasis elimination programme

Abstract

Filarial antigen detection is an appropriate epidemiological indicator for mapping lymphatic filariasis and impact evaluation of filariasis elimination programme in view of low sensitivity of parasite detection. Monoclonal antibody-based Og4C3 immunological test requires 100 ll serum, which is difficult to collect by finger prick method during community based surveys. Hence, we tested lesser volume of serum compared to standard volume of 100 ll to compare its sensitivity and specificity in detecting the circulating filarial antigens. Blood samples were collected from individuals who tested positive [with titer groups 4 (border line positives), 6 (medium positives), and 8 (high positives)] and negative (titre group 3) for Og4C3 assay. Different volumes of serum samples were used to make-up required volume (100 ll) with appropriate dilutions and subjected to Og4C3 assay. The results showed that known negative samples tested negative at all the serum volumes tested. All positives (titer groups 6 and 8) showed positivity at all reduced volumes of serum sample. However one of the medium positive sample showed negative reaction in 5 ll volume of serum and two of the border line positives showed negative at all the serum volume tested. The results thus showed as less as 15 ll serum is adequate for use in Og4C3 assay. So the test can be performed without losing its sensitivity even with 5 ll serum samples at high titre of antigen (titre group 8) and 15 ll for other groups and this method has scope in programme evaluation.

Occurrence of Lymphatic Filariasis infection after 15 years of mass drug administration in two hotspot districts in the Upper East Region of Ghana

“…the FTS is more sensitive in detecting residual circulating filarial antigens in the blood since residual target antigens are slowly cleared from circulation, as reported by others [10,11,19,20]. This proposition is further strengthened by the fact that the MF positives were clearly <1% in each district.…”

“…There is the need to do a bigger study to include more if not all infected and non-infected in the MF and Og4C3 CFA assessment. Considering that ≥77% of the FTS positive participants from each district tested negative for the Og4C3 antigen, and the fact that majority (81.1%) of the ELISA positives had low Og4C3 antigen concentrations; it can be deduced that the FTS is more sensitive in detecting residual circulating filarial antigens in the blood since residual target antigens are slowly cleared from circulation, as reported by others [ 10 , 11 , 19 , 20 ]. This proposition is further strengthened by the fact that the MF positives were clearly <1% in each district.…”

Discovery of Specific Antigens That Can Predict Microfilarial Intensity in Loa loa Infection

“…The relatively low mf numbers in tested samples may explain why the correlation (r ϭ 0.54) between levels of the LOAG_14221 protein and the corresponding levels of mf is not higher. Detection of circulating mf-derived antigen in serum has been used with limited success for both B. malayi (26,27) and W. bancrofti (28), but none of these assays examined the relationship between amounts of detected antigen and the number of mf in the blood.…”