#56: A novel test for diagnosis and surveillance of Wuchereria bancrofti infection

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Abstract Background Elephantiasis or Lymphatic filariasis (LF) is a parasitic infection that causes significant morbidity and impacts hundreds of millions of people in 73 countries. Most LF is caused by the nematode Wuchereria bancrofti, but Brugia species cause LF in some areas of Southeast Asia. The global program to eliminate LF uses mass drug administration (MDA) of antifilarial drugs in endemic areas to kill the microfilaria (MF) stage of the parasite that is required for ongoing transmission by mosquitos. Better tools are needed for assessing the success of MDA, because of limitations of available diagnostic tests. MF testing is often not feasible, because it requires collection of blood at night in most endemic areas. Existing antibody and antigen tests remain positive long after effective treatment, and their results do not correlate well with current infectivity. The Brugia Rapid test detects antibodies to BmR1, a Brugia protein that is expressed by MF. These antibodies disappear 2–3 years after effective treatment, and that makes the Brugia Rapid test a useful marker for persistent infection in the few countries with brugian filariasis. We set out to develop a novel antibody test for W. bancrofti infection based on a BmR1 homologue in W. bancrofti. Methods We cloned, expressed and purified a Wuchereria bancrofti protein (provisional name WbN1) that is a homologue of the Brugia malayi protein BmR1. Sera from patients infected with Wuchereria bancrofti as well as sera from patients infected with other closely related filarial species were tested for IgG4 antibodies to WbN1 by indirect ELISA. Results The ELISA has a sensitivity of 90.7% for infection with W. bancrofti based on the 80 bancrofti patient samples tested thus far. Specificity was 91.5% with 59 sera samples from patients infected with Onchocerca volvulus or Loa loa, which are filarial parasites that are co-endemic with W. bancrofti in Africa. Specificity was 97.9% with North American control samples. ELISA with sera from a clinical trial in Sri Lanka demonstrated that antibodies to WbN1 decreased significantly faster after treatment than antibodies to the previously described filarial antigen Bm14. Similar declines in antibody to WbN1 occurred after patients in Papua New Guinea received a single dose of triple drug treatment for LF with Ivermectin Diethylcarbamazine and Albendazole, that is effective for clearing MF from the blood without clearing filarial antigenemia. Conclusions While additional studies are needed, this ELISA for IgG4 antibody to the recombinant protein WbN1 could be a promising new surveillance tool for assessing for ongoing transmission of LF following MDA.

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