Laboratory diagnosis of loiasis to support individual patient management: A systematic review

Loiasis is a filarial disease caused by Loa loa, endemic to Central and West Africa. Cases are observed in migrants and occasionally travellers. Its diagnosis may be difficult due to the unspecific clinical picture and the high percentage of people who do not have microscopically detectable circulating microfilariae. We performed a landscape analysis of the laboratory-based diagnostic techniques available for loiasis and of their estimated sensitivity and specificity.

We performed a systematic review of cross-sectional, cohort, case-control, diagnostic accuracy, and clinical trial studies published in PubMed, EMBASE, and CENTRAL (searched on March 26th 2025), applying diagnostic assays for human loiasis. When possible, a proportional meta-analysis was performed by estimating sensitivity and specificity separately against eligible reference tests (direct assays or presence of "eyeworm" or their composite or latent class analysis) for each technique category (microscopy of thick smears or concentrated blood, PCR-based or LAMP-based molecular assay, and ELISA-based or rapid -RDT- serological assays). A random-effects model with the DerSimonian-Laird approach was applied. Study quality was evaluated using the Newcastle-Ottawa Scale.

Ninety-nine publications were included in the landscape analysis and 27 were also eligible for performance assessment. Microscopy was applied in 91/99 (91.9%) studies, PCR-based techniques in 29/99 (29.3%), LAMP in 4/99 (4.0%), and serological assays in 19/99 (19.2%). Within techniques categories, characteristics were highly heterogeneous. Sensitivities ranged from 75.0-98.3% for thick blood smears, 48.2-99.9% for blood concentration techniques, 80.6-98.4% for PCR-based techniques, 88.5-98.1% for LAMP-based techniques, 81.9-90.5% for ELISA seroassays, and 43.6-88.0% for RDTs. Cross-reactivity of L. loa-specific seroassays with M. perstans and other parasitoses was limited (<10%).

Assays for the diagnosis of loiasis are not standardized. ELISA-based serology and possibly PCR-based methods may be appropriate for screening. Microscopy must be performed even in case of negativity on screening when epidemiological or clinical factors suggestive of loiasis are present to plan safe treatment.