Rift valley fever viral load correlates with the human inflammatory response and coagulation pathway abnormalities in humans with hemorrhagic manifestations

Abstract

Rift Valley fever virus is an arbovirus that affects both livestock and humans throughout Africa and in the Middle East. Despite its endemicity throughout Africa, it is a rare event to identify an infected individual during the acute phase of the disease and an even rarer event to collect serial blood samples from the affected patient. Severely affected patients can present with hemorrhagic manifestations of disease. In this study we identified three Ugandan men with RVFV disease that was accompanied by hemorrhagic manifestations. Serial blood samples from these men were analyzed for a series of biomarkers specific for various aspects of human pathophysiology including inflammation, endothelial function and coagulopathy. There were significant differences between biomarker levels in controls and cases both early during the illness and after clearance of viremia. Positive correlation of viral load with markers of inflammation (IP-10, CRP, Eotaxin, MCP-2 and Granzyme B), markers of fibrinolysis (tPA and D-dimer), and markers of endothelial function (sICAM-1) were all noted. However, and perhaps most interesting given the fact that these individuals exhibited hemorrhagic manifestations of disease, was the finding of a negative correlation between viral load and P-selectin, ADAMTS13, and fibrinogen all of which are associated with coagulation pathways occurring on the endothelial surface.

Fig 1. Kinetics of viral RNA load in the blood of patients.

qRT-PCR data from each patient sample was converted to relative TCID₅₀/mL by comparison with a standard curve generated from a virus stock of known titer. Each patient’s relative viral load was plotted as function of days post fever onset.

Fig 2. Kinetics of RVFV specific antibody responses in the blood of patients.

ELISA endpoint titers are shown for each patient for both IgM (dotted line and open shape) and IgG (solid line and solid shape) as function of days post fever onset. The limit of detection of the assay is noted at 100, which is the lowest level at which the assay can accurately detect the presence of antibody.

Fig 3. Statistically significant biomarkers of coagulopathy in RVF cases.

The concentration of each biomarker in each patient is plotted as a function of day post fever onset; Case 1 (square), Case 2 (circle), Case 3 (triangle). The grey area represents the range of the biomarker concentration that was detected in 8 normal healthy individuals. The dotted line is the limit of detection of the assay, which is the lowest level at which the assay can accurately detect the presence of the biomarker.

Fig 4. Statistically significant biomarkers of endothelial function in RVF cases.

The concentration of each biomarker in each patient is plotted as function of day post fever onset; Case 1 (square), Case 2 (circle), Case 3 (triangle). The grey area represents the range of the biomarker concentration that was detected in 8 normal healthy individuals. The dotted line is the limit of detection of the assay, which is the lowest level at which the assay can accurately detect the presence of the biomarker.

Fig 5. Statistically significant cytokines, chemokines and growth factor levels of in RVFV cases.

The concentration of each biomarker in each patient is plotted as function of day post fever onset; Case 1 (square), Case 2 (circle), Case 3 (triangle). The grey area represents the range of the biomarker concentration that was detected in 8 normal healthy individuals. The dotted line is the limit of detection of the assay, which is the lowest level at which the assay can accurately detect the presence of the biomarker. For some of these biomarkers, the shaded area is below the dotted line because the control levels were not detectable above the limit of detection suggesting that these biomarkers are not detectable in healthy individuals.

Fig 6. Statistically significant biomarkers of apoptosis and inflammation in RVF cases.

The concentration of each biomarker in each patient is plotted as function of day post fever onset; Case 1 (square), Case 2 (circle), Case 3 (triangle). The grey area represents the range of the biomarker concentration that was detected in 8 normal healthy individuals. The dotted line is the limit of detection of the assay, which is the lowest level that the assay can accurately detect the presence of the biomarker.