Recent advances in diagnosis of filarial infections

Improved diagnostic methods for human filariasis are needed to facilitate surveillance activities, to monitor control efforts and to evaluate new drugs and vaccines. Currently, diagnosis of filarial infections largely depends upon detection of worms themselves, principally of microfilariae in blood or skin. In many infected people with lymphatic filariae, microfilariae (MF) are not detectable in blood, and removal of skin snips for detection of microfilariae in onchocerciasis seems a rather primitive technique. In addition, because the clinical manifestations of filariae vary greatly between individuals, an ideal diagnostic test would not only reveal individuals that are infected or have been exposed to infection, but would also differentiate between various clinical manifestations that the lymphatic-dwelling parasites, in particular, induce in the infected population. This is important because the pathological reactions induced following treatment with diethylcarbamazine vary with the clinical picture induced by the lymphatic filariae. They are certainly a major problem in onchocerciasis. Recent advances in biotechnology have started revolutionizing the diagnosis of filarial parasites not only in the host but also in their vectors. Monoclonal antibodies have been developed that are specific for detection of circulating antigens in lymphatic filariasis. Species-specific DNA probes have been developed for Brugia malayi, Wuchereria bancrofti, Onchocerca volvulus, and Loa loa. Diagnostic antigens have been obtained by cloning parasite DNA that codes for proteins recognized by infected individuals with only certain species of filariae. Recombinant antigens (rAgs) are available today which detect prepatent infections in onchocerciasis. Several laboratories developing new diagnostic tests for filariasis are currently evaluating these tests in the field with the collaboration of parasitologists, epidemiologists, and vector biologists.