Comparative Study of Diagnostic Serology Tests for Q Fever and Rift Valley Fever in Humans and Animals in Rural Chad : [Preprint]

Q fever (QF) and Rift Valley fever (RVF) are endemic zoonotic diseases in African countries, causing significant health and economic burdens. While the gold standard tests for QF and RVF are indirect immunofluorescence assay (IFA) and virus neutralization test, enzyme-linked immunosorbent assays (ELISA) offer rapid, cost-effective alternatives without stringent biosafety requirements. This study aimed to assess commercial ELISA tests suitable for low- and middle-income countries (LMIC).Blood samples were collected from 966 humans and 1041 livestock in rural Chad. Initially, ELISA was performed in Chad, followed by random selection of 10% of the samples for duplicate testing using IFA (for human QF and RVF) and ELISA (for animal QF and RVF) in Switzerland and Germany, respectively. Agreement between duplicate tests and factors influencing inter-test agreement were analysed, including district, setting, sex, age, and animal species.Concordant results and kappa values varied between diseases and species. In humans, QF concordance was 62.5% (kappa: 0.31), while RVF concordance was 81.1% (kappa: 0.52). In animals, QF concordance was 92.3% (kappa: 0.59) and RVF concordance was 94.0% (kappa: 0.59). Multivariate analysis revealed a significant association between test agreement and setting of origin (village vs. camp) and age for QF in human samples, with agreement being higher in younger individuals.In conclusion, this study evaluated commercially available ELISA tests for QF and RVF in LMIC settings. The findings highlight the importance of considering age and sample quality when interpreting test results. Further research is needed to enhance diagnostic accuracy and facilitate effective disease management.