A high-dose inoculum size results in persistent viral infection and arthritis in mice infected with chikungunya virus

Abstract

Chikungunya virus (CHIKV) is an emerging mosquito-transmitted alphavirus that leads to acute fever and chronic debilitating polyarthralgia. To date, the mechanism underlying chronic recurrent arthralgia is unknown. In the present study, newborn wild-type C57BL/6 mice were infected with CHIKV, and the virological and pathological features of CHIKV infection were analyzed over a period of 50 days. Acute viral infection was readily established by footpad inoculation of CHIKV at doses ranging from 10 plaque forming unit (PFU) to 106 PFU, during which inoculation dose-dependent viral RNA and skeletal muscle damage were detected in the foot tissues. However, persistent CHIKV was observed only when the mice were infected with a high dose of 106 PFU of CHIKV, in which low copy numbers (103−104) of viral positive strand RNA were continuously detectable in the feet from 29 to 50 dpi, along with a low level and progressive reduction in virus-specific CD8+ T cell responses. In contrast, viral negative strand RNA was detected at 50 dpi but not at 29 dpi and was accompanied by significant local skeletal muscle damage at 50 dpi when mild synovial hyperplasia appeared in the foot joints, although the damage was briefly repaired at 29 dpi. These results demonstrated that a high viral inoculation dose leads to viral persistence and progression to chronic tissue damage after recovery from acute infection. Taken together, these results provide a useful tool for elucidating the pathogenesis of persistent CHIKV infection and viral relapse-associated chronic arthritis. Author summary CHIKV infection has caused several outbreaks and affected millions of people in epidemic areas since the virus was originally isolated in 1952. CHIKV is transmitted by mosquitoes, resulting in acute diseases typically characterized by severe and debilitating arthritis, myalgia and fever, followed by persistent or recurrent joint and muscle pain that may last for months to years. The persistence of CHIKV in patients has been validated by clinical evidence, but it remains unclear how chronic and recurrent tissue injury are correlated with persistent viral infection. In this study, we established acute and chronic CHIKV infections in mice with different viral inoculation doses and identified the correlation of infection dose with outcomes resulting from CHIKV infection. We found that a high inoculation dose not only resulted in persistent viral infection but also led to a typical acute-recovery-relapse model of myositis and joint injury in mice. We also found that CHIKV RNA replication was interrupted after the acute phase, which might be related to the low antiviral T cell responses and relapse of histopathological injuries. Our study highlights the key factors involved in the clinical outcomes after CHIKV infection and provides new insights into the interaction between viral persistence and recurrent arthritis.