In a recent issue of the Journal of Medical Virology, Khan et al.[2010] presented an ‘‘assessment of in vitro prophylactic and therapeutic efficacy of chloroquine against Chikungunya virus in Vero cells.’’This article mentions the fact that chloroquine, a wellknown drug developed for the treatment of malaria in the 1930s, was considered previously as a potent antiviral drug in a number of viral diseases (HIV, HBV, influenza A virus, SARS, and others) but makes no reference to previous studies of the antiviral activity of chloroquine against alphaviruses (and more specifically Chikungunya virus) suggesting that the authors had identified a new and promising field of investigation. Their presentation deserves significant qualification.

First, the in vitro antiviral effect of chloroquine is not a recent discovery. It was first reported some 40 years ago [Inglot, 1969; Shimizu et al., 1972]. A clinical antiviral application of the molecule has been assessed over time for a number of viral pathogens, and the concrete benefits or risks of such treatment is still debated [Boelaert et al., 1999; Seth et al., 1999; Fredericksen et al., 2002; Savarino et al., 2006]. Regarding alphaviruses, in cellulo inhibition of Sindbis and Semliki Forest virus replication was reported 30 years ago [Coombs et al., 1981; Helenius et al., 1982], but these results were balanced by those obtained from a mouse model, which suggested that chloroquine may enhance viral replication in vivo and aggravate the disease [Maheshwari et al., 1991]. Soon after the beginning of the Chikungunya outbreak in 2005, in the Indian Ocean, the question of the possible use of chloroquine was raised. It is a matter of fact that, in many tropical areas, chloroquine is used as a symptomatic treatment of febrile illnesses and thus, the health authorities had to face its actual—non-evaluated—use during the acute phase of Chikungunya disease. The (confusing) reasons why a part of the local population utilized chloroquine also possibly included the fact that immunomodulatory effects of chloroquine have been used for a long time in autoimmune and rheumatological diseases [Cooper and Magwere, 2008], including chronic Chikungunya arthritis [Brighton, 1984].