Human immune response against salivary antigens of Simulium damnosum s.l.: A new epidemiological marker for exposure to blackfly bites in onchocerciasis endemic areas

• Published in: PLoS neglected tropical diseases Vol. 15; no. 6; p. e0009512
• Main Authors: Willen, Laura, Basáñez, Maria-Gloria, Dvorak, Vit, Veriegh, Francis B. D, Aboagye, Frank T, Idun, Bright, Osman, Maha Elhadi, Osei-Atweneboana, Mike Y, Courtenay, Orin, Volf, Petr
• Format: Journal Article
• Language: English
• Published: San Francisco Public Library of Science 01.06.2021; Public Library of Science (PLoS)
• Subjects: Age; Analytical methods; Antibodies; Antigen-antibody reactions; Antigens; Apyrase; Arthropods; Biology and Life Sciences; Bites; Bites and stings; Biting; Black flies; Blood; Collectors; Complications and side effects; Defence mechanisms; Development and progression; Electrophoresis; ELISA; Enzyme-linked immunosorbent assay; Epidemiology; Ethics; Exposure; Feeding; Gel electrophoresis; Gels; Glands; Health aspects; Immune response; Immune response (humoral); Immune system; Immunity; Immunoassay; Immunoassays; Immunogenicity; Immunoglobulin G; Immunoglobulin M; Infections; Insect bites; Labour; Liquid chromatography; Markers; Mass spectrometry; Mass spectroscopy; Medicine and Health Sciences; Nematodes; Nucleotidase; Onchocerciasis; Parasitic diseases; People and Places; Proteins; Proteomes; Rainy season; Research and Analysis Methods; Risk factors; Saliva; Salivary gland; Salivary glands; Samples; Seasonal variations; secretions; Simulium; Tropical diseases; Vector-borne diseases; Wet season; Ghana; Africa
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0009512

Background Simulium damnosum sensu lato (s.l.) blackflies transmit Onchocerca volvulus, a filarial nematode that causes human onchocerciasis. Human landing catches (HLCs) is currently the sole method used to estimate blackfly biting rates but is labour-intensive and questionable on ethical grounds. A potential alternative is to measure host antibodies to vector saliva deposited during bloodfeeding. In this study, immunoassays to quantify human antibody responses to S. damnosum s.l. saliva were developed, and the salivary proteome of S. damnosum s.l. was investigated. Methodology/Principal findings Blood samples from people living in onchocerciasis-endemic areas in Ghana were collected during the wet season; samples from people living in Accra, a blackfly-free area, were considered negative controls and compared to samples from blackfly-free locations in Sudan. Blackflies were collected by HLCs and dissected to extract their salivary glands. An ELISA measuring anti-S. damnosum s.l. salivary IgG and IgM was optimized and used to quantify the humoral immune response of 958 individuals. Both immunoassays differentiated negative controls from endemic participants. Salivary proteins were separated by gel-electrophoresis, and antigenic proteins visualized by immunoblot. Liquid chromatography mass spectrometry (LC-MS/MS) was performed to characterize the proteome of S. damnosum s.l. salivary glands. Several antigenic proteins were recognized, with the major ones located around 15 and 40 kDa. LC-MS/MS identified the presence of antigen 5-related protein, apyrase/nucleotidase, and hyaluronidase. Conclusions/Significance This study validated for the first time human immunoassays that quantify humoral immune responses as potential markers of exposure to blackfly bites. These assays have the potential to facilitate understanding patterns of exposure as well as evaluating the impact of vector control on biting rates. Future studies need to investigate seasonal fluctuations of these antibody responses, potential cross-reactions with other bloodsucking arthropods, and thoroughly identify the most immunogenic proteins.