Glory Ngongeh Amambo1,2, Raphael Awah Abong1,2, Fanny Fri Fombad1,2, Abdel Jelil Njouendou1,3, Franck Nietcho1, Amuam Andrew Beng1,2, Ritter Manuel4, Mathias Eyong Esum1,2, Kebede Deribe5,6, Jerome Fru Cho1,2, Peter Ivo Enyong1,2, Catherine Poole7, Achim Hoerauf4,8, Clotilde Carlow7, Samuel Wanji9,10. 1. Parasites and Vector Research Unit (PAVRU), Department of Microbiology and Parasitology, University of Buea, P.O. Box 63, Buea, Cameroon. 2. Research Foundation in Tropical Diseases and Environment (REFOTDE), P.O. Box 474, Buea, Cameroon. 3. Department of Biomedical science, Faculty of Health Sciences, University of Buea, P.O. Box 63, Buea, Cameroon. 4. Institute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany. 5. Global Health and Infection Department, Brighton and Sussex Medical School, Brighton, BN1 9PX, UK. 6. School of Public Health, Addis Ababa University, Addis Ababa, Ethiopia. 7. New England Biolabs, Ipswich, MA, USA. 8. German Center for Infection Research (DZIF), Partner Site Bonn-Cologne, Bonn, Germany. 9. Parasites and Vector Research Unit (PAVRU), Department of Microbiology and Parasitology, University of Buea, P.O. Box 63, Buea, Cameroon. swanji@yahoo.fr. 10. Research Foundation in Tropical Diseases and Environment (REFOTDE), P.O. Box 474, Buea, Cameroon. swanji@yahoo.fr.
Abstract
BACKGROUND: The mass drug administration of ivermectin for onchocerciasis control has contributed to a significant drop in Loa loa microfilaria loads in humans that has, in turn, led to reduction of infection levels in Chrysops vectors. Accurate parasite detection is essential for assessing loiasis transmission as it provides a potential alternative or indirect strategy for addressing the problem of co-endemic loiasis and lymphatic filariasis through the Onchocerciasis Elimination Programme and it further reflects the true magnitude of the loiasis problem as excess human mortality has been reported to be associated with the disease. Although microscopy is the gold standard for detecting the infection, the sensitivity of this method is compromised when the intensity of infection is low. The loop-mediated isothermal amplification (LAMP) assay of parasite DNA is an alternative method for detecting infection which offers operational simplicity, rapidity and versatility of visual readout options. The aim of this study was to validate the Loa loa LAMP assay for the detection of infected Chrysops spp. under experimental and natural field conditions. METHODS: Two sets of 18 flies were fed on volunteers with either a low (< 10 mf/ml) or high (> 30,000mf/ml) microfilarial load. The fed flies were maintained under laboratory conditions for 14 days and then analysed using LAMP for the detection of L. loa infection. In addition, a total of 9270 flies were collected from the north-west, east, and south-west regions (SW 1 and 2) of Cameroon using sweep nets and subjected to microscopy (7841 flies) and LAMP (1291 flies plus 138 nulliparous flies) analyses. RESULTS: The LAMP assay successfully detected parasites in Chrysops fed on volunteers with both low and high microfilariaemic loads. Field validation and surveillance studies revealed LAMP-based infection rates ranging from 0.5 to 31.6%, with the lowest levels in SW 2 and the highest infection rates in SW 1. The LAMP assay detected significantly higher infection rates than microscopy in four of the five study sites. CONCLUSION: This study demonstrated the potential of LAMP as a simple surveillance tool. It was found to be more sensitive than microscopy for the detection of experimental and natural L. loa infections in Chrysops vectors.
BACKGROUND: The mass drug administration of ivermectin for onchocerciasis control has contributed to a significant drop in Loa loa microfilaria loads in humans that has, in turn, led to reduction of infection levels in Chrysops vectors. Accurate parasite detection is essential for assessing loiasis transmission as it provides a potential alternative or indirect strategy for addressing the problem of co-endemic loiasis and lymphatic filariasis through the Onchocerciasis Elimination Programme and it further reflects the true magnitude of the loiasis problem as excess humanmortality has been reported to be associated with the disease. Although microscopy is the gold standard for detecting the infection, the sensitivity of this method is compromised when the intensity of infection is low. The loop-mediated isothermal amplification (LAMP) assay of parasite DNA is an alternative method for detecting infection which offers operational simplicity, rapidity and versatility of visual readout options. The aim of this study was to validate the Loa loa LAMP assay for the detection of infected Chrysops spp. under experimental and natural field conditions. METHODS: Two sets of 18 flies were fed on volunteers with either a low (< 10 mf/ml) or high (> 30,000mf/ml) microfilarial load. The fed flies were maintained under laboratory conditions for 14 days and then analysed using LAMP for the detection of L. loa infection. In addition, a total of 9270 flies were collected from the north-west, east, and south-west regions (SW 1 and 2) of Cameroon using sweep nets and subjected to microscopy (7841 flies) and LAMP (1291 flies plus 138 nulliparous flies) analyses. RESULTS: The LAMP assay successfully detected parasites in Chrysops fed on volunteers with both low and high microfilariaemic loads. Field validation and surveillance studies revealed LAMP-based infection rates ranging from 0.5 to 31.6%, with the lowest levels in SW 2 and the highest infection rates in SW 1. The LAMP assay detected significantly higher infection rates than microscopy in four of the five study sites. CONCLUSION: This study demonstrated the potential of LAMP as a simple surveillance tool. It was found to be more sensitive than microscopy for the detection of experimental and natural L. loa infections in Chrysops vectors.
Entities:
Keywords:
Chrysops; Ivermectin; Loa loa; Microscopy; RF4-based LAMP
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