IL6 and infection: CHIKV infection of mice deficient in interferon response factors 3 and 7 (IRF3/7−/−) provide a model of CHIKV hemorrhagic shock, with mice showing high viraemia (peaking on day 3 post infection), cytokinemia (high IFNγ, TNF, IL-6, peaking on day 2), fever (day 2), hypothermia (day 4-5), oliguria (day 4-5), thrombocytopenia (day 3-5), raised hematocrits (day 5), hemorrhage and mortality on day 4-6.