Human IgG Response to Nterm-34KDa Salivary Peptide as a Biomarker to Assess Temporal Exposure to Aedes’ Bites among Individuals Aged ≥ 6 Months in Lower Moshi-Tanzania, 2019

Abstract

Background: Mosquito-borne diseases inflict significant health, economic and social burden on the populations of endemic areas and are a major cause of important morbidity and mortality. Studies have reported several outbreaks occurring worldwide including Tanzania. The levels of human exposure to vector bites remain an indicator of strengthening vector control measures. Currently, the levels of human exposure to vector bites and their association with climatic changes are mainly evaluated based on both pathogen detection in human populations and entomological methods which have some limitations. Recently, serological Aedes salivary biomarkers are most likely reasonable proxies which can offset the limitations. Aedes salivary antigen Nterm-34kDa has been dedicated as a useful candidate suitable proxy to assess the level of human temporal exposure to Aedes mosquitos’ bites ascertained through seroprevalence of IgG. However, these methods have neither been fully evaluated nor attempted to be applied in Tanzania specifically for Aedes. Objective: This study aimed to explored the use of human IgG antibodies to Aedes salivary gland protein (Nterm-34kDa) as a biomarker to assess temporal human exposure against Aedes bites among individuals aged ≥ 6 months living in Lower Moshi, Northern Tanzania 2019. Methods: A cross-sectional laboratory-based study which used archived samples collected from individuals aged ≥ 6 months was conducted. All participants of the previous study consented that their samples could be further analysed for research-related studies. A maximum of 500 ul of whole blood samples were collected from each participant in ethylene diamine tetra-acetic acid (EDTA) capillary tubes, samples were stored and transported as per protocols and processed in the laboratory. Sandwich Enzyme-Linked Immunosorbent Assay test (Sero-Well, Sterilin Appleton Woods Limited-France) was used to analyse a total of 713 plasma samples to detect and quantify the presence of immunoglobulin G (IgG) directed against Nterm-34kDa. Rainfall data was provided by the factory’s meteorological station (TPC Sugar Factory located at the centre of the villages selected for the study) and recorded in millimetres of rain from January 2019 to January 2020. Data were analysed using Stata Version 14 (Stata Corp, TX, USA) and Graph Pad Prism (San Diego, CA, USA) software. Possible associations between Nterm-34kDa seroprevalence and participants’ characteristics were determined. All statistical tests were regarded as significant at p-values < 0.05. Results: The seroprevalence of Nterm-34kDa (measured by IgG responses) to salivary peptide were 34.1% (105/308), 45% (91/201), and 26.5% (54/204) during the dry season (time point 1), rainy season (time point 2), and dry season (time point 3), respectively. The Nterm-34kDa seroprevalences were statistically significantly different during time points 2 and 3 (chi2 =4.1301; p=0.042). The levels of IgG increased as rainfall increases, this was observed during the peak of rainfall, suggesting the temporal association between the two variables. The results indicated heterogeneity of the exposure within a population to Aedes bites which increases during the rainy season (time point 2, p=0.001, Kruskal Wallis test). Logistic regression analysis showed a significant association between IgG response to salivary peptide and exposure level (risk) according to villages, whereby individuals at Mikocheni village had a lower risk of exposure (OR=0.31; 95% CI=0.1-0.9; p=0.038), independently of either age, sex, and educational level. Conclusion: These results confirm that human antibody responses to Nterm-34kDa salivary peptide can be isolated from individuals exposed to Aedes bites, suggesting that the tool can be used to detect both temporal and real-time human exposure to Aedes’s bites. Also, this tool is a sensitive to detect human exposure and is potential in distinguishing seasonal fluctuations in exposure to Aedes bites in both high and low transmission settings thus the risk for arboviral transmission. They can also be used as an indicator for evaluating the efficacy of vector control interventions against Aedes species.