Performance of two serodiagnostic tests for loiasis in a Non-Endemic area

Federico Gobbi,Dora Buonfrate,Sebastien D Pion,Marco Biamonte,Paola Rodari,Zeno Bisoffi,Lucia Moro,Ronaldo Silva,Cedric B Chesnais,Francesca Tamarozzi,Michel Boussinesq

doi:10.1371/journal.pntd.0008187

Abstract

Loiasis, caused by the filarial nematode Loa loa, is endemic in Central and West Africa where about 10 million people are infected. There is a scarcity of convenient, commercial diagnostics for L. loa. Microscopy requires trained personnel and has low sensitivity, while the serodiagnosis is currently not standardized. Individual case management is also important in non-endemic countries to treat migrants, expatriates and tourists. We retrospectively compared the performance of a Loa Antibody Rapid Test (RDT) and a commercial ELISA pan-filarial test on 170 patients, 65 with loiasis [8 with eyeworm, 29 with positive microfilaremia, 28 with neither microfilaremia nor history of eyeworm but eosinophilia and history of Calabar swelling (probable loiasis)], 95 with other common parasitic infections and no previous exposure to L. loa (37 with M. perstans, 1 with Brugia sp., 18 with strongyloidiasis, 20 with schistosomiasis, 5 with hookworm, 4 with Ascaris lumbricoides infection, 10 with hyper-reactive malarial splenomegaly), and 10 uninfected controls. The sensitivity of the RDT and of the ELISA were 93.8% (61/65) and 90.8% (59/65), respectively. For the RDT, most of the cross-reactions were observed in patients with M. perstans: 7/37 (18.9%), followed by 1/10 (10%) with hyper-reactive malarial splenomegaly and 1/20 (5%) with schistosomiasis. None of the 27 subjects infected with intestinal nematodes was found positive at this test. The ELISA is meant to be a pan-filarial assay, and reacted extensively with cases of M. perstans (95%), as expected, and also in 11/18 (61.1%) patients with strongyloidiasis and in 3/5 (60%) with hookworm infection. The RDT and the ELISA are both highly sensitive for the diagnosis of loiasis. The main difference lies in the extent of cross-reactivity with other parasites. Considering that the RDT is specifically meant for Loa loa infection, and its high sensitivity, this test could be a useful tool for the diagnosis of occult loiasis.

Highlights

Loiasis, the disease caused by the infection with the filarial nematode Loa loa, is transmitted through the bite of tabanid flies of the genus Chrysops
Loiasis is still regarded as a benign condition even if a recent a study found an association between high L. loa microfilarial density (MFD) and increased mortality risk [4]
The 95 subjects of Group III included 37 with M. perstans microfilaraemia, one with Brugia sp. microfilaraemia, 57 with a different parasitic infection that was tested for possible cross-infection (A. lumbricoides, hookworm, Schistosoma sp., S. stercoralis or hyper-reactive malarial splenomegaly)

Summary

Introduction

The disease caused by the infection with the filarial nematode Loa loa, is transmitted through the bite of tabanid flies of the genus Chrysops. It is endemic in Central and West Africa where, according to the most recent estimates, about 10 million people are infected [1]. The two most specific signs of infection are transient oedemas known as “Calabar swellings”, and the movement of the adult worm under the conjunctiva (“eye worm”) [2]. These manifestations are major reasons for people seeking medical advice in endemic areas [3]. It is mandatory to rule out this infection before treatment with these drugs, or at least to quantify the number of circulating mf

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