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Summary: Background: Insufficient long-term data are available on antibody kinetics in survivors of Ebola virus disease (EVD). Likewise, few studies, with very small sample sizes, have investigated cross-reactions between Ebolavirus spp. In this study, we aimed to assess the humoral antibody response and its determinants in survivors of EVD and assess cross-reactivity of antibodies between diverse Ebolavirus spp. Methods: In this observational, prospective cohort study, we collected blood samples from patients from three recruitment sites in Guinea included in the Postebogui study, and we assessed IgG antibody binding to recombinant glycoprotein, nucleoprotein, and 40-kDa viral protein (VP40) of Zaire (EBOV), Bundibugyo (BDBV), and Sudan (SUDV) Ebolaviruses. Participants from the PostEbogui study, from whom we had at least one blood sample that could be tested for the presence of antibodies, were eligible for this analysis. Patients in the PostEbogui study were assessed clinically at inclusion, 1 month and 3 months later, and subsequently every 6 months for up to 60 months after discharge from the Ebola treatment centre. We explored predictors of glycoprotein, nucleoprotein, and VP40 antibody concentrations through a linear mixed model. A logistic mixed model was done to estimate the probability of seropositivity and associated determinants. We assessed cross-reactivity by use of hierarchical cluster analysis. Findings: Of the 802 patients included in the Postebogui study, 687 were included in our analyses. 310 (45%) patients were men and 377 (55%) were women, with an overall median age at the time of the first blood sample of 27·3 years (IQR 19·5–38·2). We observed an overall significant decrease over time of EBOV antibodies, with antibodies against nucleoproteins decreasing more rapidly. At 60 months after discharge from the Ebola treatment centre, the probability of having antibodies against glycoproteins was 76·2% (95% CI 67·2–83·3), against nucleoproteins was 59·4% (46·3–71·3), and against VP40 was 60·9% (51·4–69·8). Persistence of EBOV RNA in semen was associated with higher concentrations of IgG antibodies against nucleoprotein EBOV antigens. Individually, we observed in some survivors an antibody wax-and-wane pattern. The proportion of cross-reactions was highest between glycoproteins from Kissidougou and Mayinga EBOV strains (94·5%, 95% CI 92·5–96·1), followed by EBOV VP40 and BDBV VP40 (88·3%, 85·7–90·6), and EBOV VP40 and SUDV VP40 (83·3%, 80·3–86·1). Interpretation: The probability for survivors of EVD to have antibodies against one or more EBOV antigens remained high, although approximately 25% of survivors had undetectable antibodies, which could have implications, such as a possible decreasing population immunity, for future Ebola outbreaks in the same region. Funding: Reacting–Institut National de la Santé et de la Recherche Médicale, Institut de Recherche pour le Developpement, and Montpellier Université d'Excellence.

Background: Q fever is a zoonotic infectious disease characterized by fever, malaise, chills, significant weakness, and muscle pain. In some cases, the disease can become chronic and affect the inner membranes of the heart, such as the valves, leading to endocarditis and a high risk of death. Coxiella burnetii ( C. burnetii ) is the primary causative agent of Q fever in humans. This study aims to monitor the presence of C. burnetii in ticks collected from small mammals and cattle in the Republic of Guinea (RG)., Methods: Rodents were trapped in the Kindia region of RG during 2019-2020, and ticks were collected from cattle in six regions of RG. Total DNA was extracted using a commercial kit (RIBO-prep, InterLabService, Russia) following the manufacturer's instructions. Real-time PCR amplification was conducted using the kit (AmpliSens Coxiella burnetii-FL, InterLabService, Russia) to detect C. burnetii DNA., Results and Conclusions: Bacterial DNA was detected in 11 out of 750 (1.4%) small mammals and 695 out of 9620 (7.2%) tick samples. The high number of infected ticks (7.2%) suggests that they are the main transmitters of C. burnetii in RG. The DNA was detected in the liver and spleen of a Guinea multimammate mouse, Mastomys erythroleucus . These findings demonstrate that C. burnetii is zoonotic in RG, and measures should be taken to monitor the bacteria's dynamics and tick prevalence in the rodent population.