Performance of a RT-PCR for the Diagnostic of Loiasis in an Endemic Area in Gabon

Loa loa infection is a growing public health issue in the endemic area where two-thirds of infected individuals have no detectable circulating microfilaræmia. Conventional microscopic-based diagnosis on the visualisation of the filarial worm is limited. Molecular tests are known to be sensitive, precise and fast. Here we evaluated the performance of a Real Time PCR assay for the diagnostic of Loa loa infection in blood sample from an endemic area of Gabon. Blood samples were analyzed by microscopy. Proven loiasis was defined by a positive conventional parasitological assay and subconjunctival migration of an adult worm. DNA from blood samples was extracted and tested by RT-PCR targeting the gene coding the Loa loa-15 kDa polyprotein antigen. Microscopic analyses identified 25/545 (4.59%) microfilaremic individuals. Thirty (30/545) samples were RT-PCR positive. According to the classification of infection cases, 26 individuals were positive for proven loiase and 4 individuals for non-loiasis; the test showed a sensitivity of 15.90% (95% CI [12.6 - 17.75]) and a specificity of 99.0% (95% CI [97.6 - 99.7]) for the diagnosis of proven loiase. The evaluated RT-PCR targeting the 15 kDa gene protein detected all microfilaremic cases but only a few amicrofilaremic ones. It is specific to Loa loa infection and might be used for the screening of at-risk populations in epidemiological and/or pretreatment surveys.