Chikungunya virus (CHIKV) is an alphavirus that causes chronic and incapacitating arthralgia in humans. To date, interactions between the immune system and the different stages of the virus life cycle remain poorly defined. We demonstrated for the first time that CHIKV Ags could be detected in vivo in the monocytes of acutely infected patients. Using in vitro experimental systems, whole blood and purified monocytes, we confirmed that monocytes could be infected and virus growth could be sustained. CHIKV interactions with monocytes, and with other blood leukocytes, induced a robust and rapid innate immune response with the production of specific chemokines and cytokines. In particular, high levels of IFN-α were produced rapidly after CHIKV incubation with monocytes. The identification of monocytes during the early phase of CHIKV infection in vivo is significant as infected monocyte/macrophage cells have been detected in the synovial tissues of chronically CHIKV-infected patients, and these cells may behave as the vehicles for virus dissemination. This may explain the persistence of joint symptoms despite the short duration of viremia. Our results provide a better understanding on the basic mechanisms of infection and early antiviral immune responses and will help in the development of future effective control strategies.

33Understanding the particle size distribution in the air and patterns of environmental 34 contamination of SARS-CoV-2 is essential for infection prevention policies. We aimed to 35 detect SARS-CoV-2 surface and air contamination and study associated patient-level factors. 36 245 surface samples were collected from 30 airborne infection isolation rooms of COVID-19 37 patients, and air sampling was conducted in 3 rooms. 38Air sampling detected SARS-CoV-2 PCR-positive particles of sizes >4 µm and 1-4 µm in 39 two rooms, which warrants further study of the airborne transmission potential of SARS-40 CoV-2. 56.7% of rooms had at least one environmental surface contaminated. High touch 41 surface contamination was shown in ten (66.7%) out of 15 patients in the first week of illness, 42 and three (20%) beyond the first week of illness (p = 0.010). 43All rights reserved. No reuse allowed without permission.