Until recently, diagnosis of filarial infection depended on the direct demonstration of the parasite (almost always microfilariae) in blood using relatively cumbersome techniques and having to take into account the periodicity (nocturnal or diurnal) of microfilariae. Alternative methods based on detection of antibodies by immunodiagnostic tests did not prove satisfactory since they both failed to distinguish between active and past infections and had problems with specificity owing to their cross-reactivity with common gastrointestinal parasites and other organisms.

Antigen detection: Circulating filarial antigen (CFA) detection should now be regarded as the 'gold standard' for diagnosing Wuchereria bancrofti infections. The specificity of these assays is excellent, and the sensitivity is greater than that achievable by the earlier parasite-detection assays. Essentially all individuals with microfilaraemia also have detectable circulating antigen, as well as do a proportion of those amicrofilaraemic individuals with clinical manifestations of filariasis (e.g., lymphoedema or elephantiasis) but no circulating microfilariae. In addition, some individuals who appear normal also have detectable circulating antigen that disappears after effective treatment with DEC for these cryptic infections. Two commercial configurations of this assay are available, one based on ELISA methodology that yields semi-quantitative results, and the other based on a simple card (immunochromatographic) test, yielding only qualitative (positive/negative) answers. Thus, this new diagnostic approach is equally applicable to clinical or field evaluation of bancroftian filariasis infections. Unfortunately, no such test is currently available for brugian filariasis.