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- Title
Generation of Loa loa infective larvae by experimental infection of the vector, Chrysops silacea.
- Authors
Ndzeshang, Lontum B.; Fombad, Fanny F.; Njouendou, Abdel J.; Chunda, Valerine C.; Gandjui, Narcisse V.T.; Akumtoh, Desmond N.; Chounna, Patrick W.N.; Steven, Andrew; Pionnier, Nicolas P.; Layland, Laura E.; Ritter, Manuel; Hoerauf, Achim; Taylor, Mark J.; Turner, Joseph D.; Wanji, Samuel
- Abstract
Basic and translational research on loiasis, a filarial nematode infection of medical importance, is impeded by a lack of suitable Loa loa infection models and techniques of obtaining and culturing life cycle stages. We describe the development of a new method for routine production of infective third-stage larvae (L3) of L. loa from the natural intermediate arthropod vector host, Chrysops silacea, following experimental infection with purified microfilariae. At 14-days post-infection of C. silacea, the fly survival rate was 43%. Survival was significantly higher in flies injected with 50 mf (55.2%) than those that received 100 mf (31.0%). However, yield per surviving fly and total yield of L3 was markedly higher in the group of flies inoculated with 100 mf (3474 vs 2462 L3 produced). The abdominal segment hosted the highest percentage recovery of L3 (47.7%) followed by head (34.5%) and thorax (17.9%). L. loa larval survival was higher than 90% after 30 days of in vitro culture. The in vitro moulting success rate to the L4 larval stage was 59.1%. After experimental infection of RAG2-/-IL-2γc-/—mice, the average L. loa juvenile adult worm recovery rate was 10.5% at 62 dpi. More than 87% of the worms were recovered from the muscles and subcutaneous tissues. Worms recovered measured an average 24.3 mm and 11.4 mm in length for females (n = 5) and males (n = 5), respectively. In conclusion, L. loa mf injected into C. silacea intrathoracically develop into infective larvae that remain viable and infective comparable to L3 obtained through natural feeding on the human host. This technique further advances the development of a full laboratory life cycle of L. loa where mf derived from experimentally-infected animals may be utilized to passage life cycle generations via intrathoracic injections of wild-caught vector hosts. Author summary: The Neglected Tropical Disease, loiasis (tropical eye worm disease) affects 13–15 million individuals in Central Africa. Loiasis has recently been identified as a cause of premature mortality and is a barrier to ivermectin-based elimination of onchocerciasis or lymphatic filariasis where co-infections occur, due to the risk of serious adverse events. Loiasis lacks laboratory preclinical models for drug development, biomarker discovery and inflammatory pathology research. Here we detail the successful development of an experimental technique for the laboratory production of Loa loa infective larvae via injection of purified microfilariae into the thorax of wild-caught tabanid flies that are the natural transmission vector. The high yielding infective larvae produced in the laboratory were validated as biologically viable in culture and in a new mouse infection model whereby adult-stage parasites could be produced. The evidence reported herein is an important step to establishing a full laboratory life cycle of L. loa by passage between animal models and experimental injections of the wild-caught vector, Chrysops.
- Subjects
AFRICA; FILARIASIS; NEMATODE infections; LARVAE; LABORATORY animals; ARTHROPOD vectors
- Publication
PLoS Neglected Tropical Diseases, 2020, Vol 14, Issue 8, p1
- ISSN
1935-2727
- Publication type
Article
- DOI
10.1371/journal.pntd.0008415