Pathogenesis of Crimean-Congo Haemorrhagic Fever (CCHF) - interaction of immune response, viral load and clinical course

Introduction Crimean-Congo haemorrhagic fever a potentially fatal acute viral disease that is geographically widespread across southern areas of Africa and Eastern Europe, Russia and the Middle East. It is a major emerging infectious diseases threat, but limited data exist on the clinical course, host immune response, viral dynamics and associated coagulopathy. Aims A cohort of adults with PCR positive CCHF in Turkey was recruited to determine the viral load dynamics and coagulopathy over the course of clinical infection and to investigate the host immune response through serial measurement of cytokine/chemokine levels and quantitative serological response, related to disease severity and clinical outcomes. Methods Prospective observational cohort study. Demographic, clinical and laboratory data were collected from patients admitted with confirmed CCHF in Turkey, between May 2014 and August 2015. Diagnosis was confirmed on admission by a positive CCHF polymerase chain reaction (PCR) or IgM enzyme-linked immunosorbent assay. Quantitative RT-PCR, serology, luminex flow cytometry and rotational thromboelastometry (ROTEM) was undertaken at admission, during acute illness and in convalescence. Results During the study period 104/144 patients recruited were confirmed to have CCHF. The majority were male (66/104) and had mild disease (63/104), with a median age of 50 years. Median temperature at admission was 37.50C with fever, headache, myalgia, lethargy and vomiting the most frequent symptoms reported. 23% of participants had an episode of bleeding and 37% received blood product transfusion. Higher CCHF viral load at admission was associated with increased disease severity (p=0.02), lower platelet counts (p=0.02) and fatal outcome (p=0.01). APTT, PT, LDH, CK and creatinine correlated with CCHF viral load. Median clearance of CCHFV from plasma was 5 days, occurring more rapidly in mild disease. Urine is rarely PCR positive in acute infection (8/578 samples) or in convalescence (0/101 samples). At admission 43/102 (42.2%) participants had a positive CCHFV IgM and 51/102 (50.0%) had a positive CCHFV IgG. 13/61 (21%) participants remained IgM positive at 1 year after infection. IL-10, IP-10, GM-CSF, IL-12, IL-17A and IL-8 were significantly elevated in moderate/severe cases, with IL-10, IL-6, IL-8, TNF-α and MCP-1 higher in fatal cases. TNF-α, IL-6, IFN-Α2, IL-15, IL-8 and MIP-1β correlated with CCHF viral load. At admission, EXTEM S clotting time (CT), amplitude 10 minutes (A10), clot formation time (CFT) and maximum clot firmness (MCF) were significantly different between mild and moderate/severe cases. EXTEM S MCF and A10 were lowest on days 4-6 of illness. There were no significant differences in FIBTEM A10/MCF by severity and no hyperfibrinolysis. Conclusions CCHF frequently occurs in remote resource-limited settings and has been designated a priority for research development by WHO. CCHF viral load at baseline is an important prognostic indicator that is associated with more severe disease and prolonged viraemia, whilst urine is rarely RT-PCR positive. CCHF is characterised by a pro-inflammatory and early adaptive host immune response. ROTEM analysis has demonstrated that the coagulopathy in CCHF is predominantly in clot development/stabilisation suggesting platelet dysfunction