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

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 hyperreactive 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.

Analysis of diagnostic test outcomes in a large loiasis cohort from an endemic region: Serological tests are often false negative in hyper-microfilaremic infections

“…The RDT has been assessed under laboratory conditions and showed promising results. Sensitivity and specificity for loiasis-detection was also high, when tested against samples positive for other filarial infections [ 23 , 24 ]. In one study, the RDT was employed in the field, but individual diagnostic features of the test were not described [ 25 ].…”

“…Laboratory-based assessments of the diagnostic accuracy of Ll-SXP-1-RDT using samples positive for L . loa and other filarial diseases have shown promising results with good sensitivity and specificity [ 23 , 24 ]. However, test performance data from endemic regions are still limited [ 25 ].…”

Loa loa in the Vitreous Cavity of the Eye: A Case Report and State of Art

“…All in all, considering the acceptable sensitivity (54%), a serological test can play a more helpful diagnostic role in nonendemic areas and where there is not a significant prevalence of other parasite infections (e.g., Onchocerca, soil-transmitted helminths), although for other filariases the correlation between circulating antigen test and microfilaremia showed good results but poor sensitivity and low reliability for L. loa. 28 In a recent review, Gobbi et al 29 compared the performance of a Loa antibody rapid diagnostic test and a commercial ELISA pan-filarial test on 170 patients with various parasitic infection (L. loa, Mansonella perstans, Brugia spp., soil-transmitted helminths) reporting high sensitivity of both the rapid diagnostic and pan-filarial serology tests for the diagnosis of loiasis. Meanwhile, the detection of antigen from urine samples through the luciferase immunoprecipitation system is an object of ongoing studies that might lead to new diagnostic tools, although is not still validated.…”

“… 28 In a recent review, Gobbi et al. 29 compared the performance of a Loa antibody rapid diagnostic test and a commercial ELISA pan-filarial test on 170 patients with various parasitic infection ( L. loa , Mansonella perstans , Brugia spp., soil-transmitted helminths) reporting high sensitivity of both the rapid diagnostic and pan-filarial serology tests for the diagnosis of loiasis. Meanwhile, the detection of antigen from urine samples through the luciferase immunoprecipitation system is an object of ongoing studies that might lead to new diagnostic tools, although is not still validated.…”

The Human Filaria Loa loa: Update on Diagnostics and Immune Response

“…38 This test is currently undergoing point-of-care evaluation. 39 Circulating antigen tests have also been developed; however, these tests are limited by cross-reactivity with other filarial species. [40][41][42][43] Because of the fatal side effects related to microfilariae, quantification of this larval stage in the blood is necessary, and therefore a test using LOAG-16297 and LOAG-17808 based on a competitive LIPS assay was developed.…”