BSP Parasites Online 2021
Schedule : Back to Mr Yannick NIAMSI EMALIO

Unusual localization of blood-borne Loa loa microfilariae in the skin depends on microfilarial density in the blood: Implications for onchocerciasis diagnosis in co-endemic areas

Fri25  Jun04:00pm(15 mins)
Conference room 1


1 Centre for Research on Filariasis and other Tropical Diseases (CRFilMT), Cameroon


Yannick Niamsi-Emalio1, Hugues C. Nana-Djeunga1, Cédric B. Chesnais2, Sébastien D.S. Pion2, Jules B. Tchatchueng-Mbougua3, Michel Boussinesq2, María-Gloria Basáñez4, Joseph Kamgno1,5


1. Centre for Research on Filariasis and other Tropical Diseases (CRFilMT), Yaoundé, Cameroon

2. Institut de Recherche pour le Développement (IRD), UMI233/ INSERM U1175/ Université de Montpellier, 911 avenue Agropolis, BP 64501, 34394 Montpellier Cedex 5, France

3. Service d’Epidémiologie, Centre Pasteur du Cameroun, Membre du Réseau International des Instituts Pasteur, Yaoundé, Cameroun

4. MRC Centre for Global Infectious Disease Analysis and London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK

5. Faculty of Medicine and Biomedical Sciences, University of Yaoundé I, Cameroon


The diagnostic gold standard for onchocerciasis relies on identification and enumeration of (skin-dwelling) Onchocerca volvulus microfilariae (mf) using the skin snip technique (SST). In a recent study, blood-borne Loa loa mf were found by SST in individuals heavily infected with L. loa, and microscopically misidentified as O. volvulus due to their superficially similar morphology. This study investigates the relationship between L. loa microfilarial density (Loa MFD) and the probability of testing SST positive.



A total of 1,053 participants from the (onchocerciasis and loiasis co-endemic) East Region in Cameroon were tested for: i) Loa MFD in blood samples; ii) O. volvulus presence by SST, and iii) IgG4 antibody positivity to Ov16 by rapid diagnostic test (RDT). A Classification and Regression Tree (CART) model was used to perform a supervised classification of SST status and identify a Loa MFD threshold above which it is highly likely to find L. loa mf in skin snips.



Of 1,011 Ov16-negative individuals, 28 (2.8%) tested SST positive and 150 (14.8%) were L. loa positive. The range of Loa MFD was 0–85200mf/mL. The CART model subdivided the sample into two Loa MFD classes with a discrimination threshold of 4080 (95% CI: 2180–12240) mf/mL. The probability of being SST positive exceeded 27% when Loa MFD was >4080mf/mL.



The probability of finding L. loa mf by SST increases significantly with Loa MFD. Skin-snip polymerase chain reaction (PCR) would be useful when monitoring onchocerciasis prevalence by SST in onchocerciasis–loiasis co-endemic areas.  


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