Chikungunya is an Alphavirus transmitted by mosquitoes (Aedes) and which causes fever, rash, myalgia and arthralgia. The disease (CHIKVD) is transient but severe forms leading to chronic incapacitating arthritis have been reported. The study involved first a prospective cohort study of hospitalized patients from Reunion Island subsequently categorized into ‘recovered’ or ‘chronic arthralgia’ groups at M12 post infection. Clinical and immunological parameters were measured throughout the disease course. In part two, we addressed in vitro the role of apoptosis in the infection process and particularly to ascertain the mechanisms allowing the virus to persist in tissue sanctuaries. We observed that a rapid immune antiviral response was evidenced by the robust dendritic/NK//T cell activation and accompanied by a specific IgM/IgG response and a rather weak Th1/Th2 cytokine response in both groups. The viremia was much more pronounced in the chronic group and, critically, we found that CHIKV was persisting (M18) in perivascular synovial macrophages. Fibroblast hyperplasia, strong angiogenesis and acute cell deaths were observed in the injured synovial tissue. In the second part of the study, we found that CHIKV was able to trigger apoptosis through intrinsic and extrinsic pathways. Bystander apoptosis was also evidenced in neighboring cells in a caspase 8-dependent manner. Remarkably, CHIKV hiding into apoptotic blebs was able to infect neighboring cells and these events were inhibited specifically by inhibitors of caspases, blebbing and engulfment. We herein describe a novel mechanism by which CHIKV invades and escapes the host immune response and contribute to chronic arthralgia/arthritis.
