Dobrava hantavirus and coinciding SARS-CoV-2 infection mimicking thrombotic microangiopathy and responding to a single dose of eculizumab

ABSTRACT

The current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has refocused scientific interest on gaining insight into the pathophysiology of systemic viral diseases. Complement activation has been characterized as a driver of endothelial injury and microvascular thrombosis in acute respiratory distress syndrome as well as hantavirus hemorrhagic fever with renal syndrome. On this occasion, we wish to report a case of severe hantavirus disease with coinciding SARS-CoV-2 infection mimicking thrombotic microangiopathy with rapid response of inflammatory markers, hematologic parameters and proteinuria to eculizumab. These findings support a disease model of virus-associated endothelial injury involving alternative pathway complement activation. Future studies are needed to explore whether end organ damage can be mitigated by complement inhibition in life-threatening viral disease.

BACKGROUND

The current severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has refocused scientific interest on understanding the pathophysiology of life-threatening organ failure in systemic viral diseases. Complement dysregulation with alternative pathway activation has been characterized as a driver of endothelial damage and microvascular thrombosis by spike protein–induced disruption of the endothelial glycocalyx in coronavirus disease 2019 (COVID-19) acute respiratory distress syndrome (ARDS) [1]. Additionally, complement consumption has been described as a prognostic factor for COVID-19 severity [2] and treatment with eculizumab reduced ventilator dependence and mortality in clinical intervention trials (as reviewed in [3]). It is now necessary to investigate these advances in other life-threatening viral diseases that are currently on the rise, such as hantavirus hemorrhagic fever with renal syndrome (HFRS) or cardiopulmonary syndrome (HCPS).

Clinical studies on hantavirus infection showed similar correlations between disease severity, SC5b-9 and complement factor C3 levels with alternative pathway complement activation [4, 5]. Alternative pathway activation in hantavirus infection likely results from endothelial cell injury through direct endothelial cell invasion as well as antigen–antibody immune complexes [6]. Deposition of SC5b-9 and complement factor C3 was found in lung tissue of patients with Puumala hantavirus–associated ARDS [4]. These associations hint towards complement-mediated microvascular injury and end organ damage, but clinical proof-of-concept data about response to complement inhibitor therapy are missing in hantavirus infection.

CASE REPORT

A case of severe Dobrava hantavirus and coinciding SARS-CoV-2 infection presenting with thrombotic microangiopathy (TMA)-related features will be reported here. A 38-year-old man presented to the emergency department with acute diarrhea, visual impairment and malaise. Initial SARS-CoV-2 polymerase chain reaction (PCR) was mildly positive (Ct = 30, Delta subvariant). No prior SARS-CoV-2 vaccination and no relevant comorbidities, except for obesity, were reported. Blood chemistry results showed acute kidney injury (creatinine 7.2 mg/dL), hemoglobin 9.8 g/dL, lactate dehydrogenase 700 U/L, bilirubin 2.1 mg/dL, non-detectable haptoglobin, thrombocytopenia (28 G/L) and complement consumption suggesting TMA. C-reactive protein was 10 mg/dL with a ferritin level of 11 200 ng/mL and urinary analysis showed nephrotic-range proteinuria (9 g/g) with normal ADAMTS-13 activity. Eculizumab was administered empirically since atypical hemolytic uremic syndrome (aHUS) was anticipated at this point, potentially triggered by gastrointestinal manifestation of COVID-19. No schistocytes were detected on blood smear and tests for fecal EHEC toxins were negative.

After eculizumab administration, inflammatory markers, platelets, complement activity, haptoglobin levels and proteinuria rapidly returned to normal. Kidney biopsy showed acute tubular damage and interstitial hemorrhage, yet without any evidence of TMA (Fig. 1). In situ hybridization (RNA-scope) for SARS-CoV-2 was negative and no viral structure was identified. Electron microscopy revealed moderate podocyte foot process effacement (Fig. 1). Complement analysis confirmed activation of the alternative pathway without evidence of autoantibodies. Serology was strongly positive for Dobrava hantavirus immunoglobulin M (IgM)/IgG. SARS-CoV-2 PCR turned negative over 1 week followed by seroconversion with positive nucleocapsid-antigen, suggesting recent infection. Particles of murine excretions likely had been inhaled during cleaning of a hen house leading to inoculation with hantavirus 4 weeks prior to presentation. Kidney function returned to normal after 4 months.

Figure 1:

Kidney biopsy was obtained 4 days after administration of eculizumab. (A) Hematoxylin–eosin stain showing normal glomeruli. (B, C) Hematoxylin–eosin and Masson trichrome stains showing subacute tubular injury with tubulointerstitial hemorrhage (arrow). Immunohistochemistry for C3, IgA, IgG and IgM was negative and is not shown here. (D) Electron microscopy showing variable loss of brush border, apical blebs and condensed mitochondria in a swollen tubular cell. (E) Endothelial vacuolar degeneration in a peritubular capillary. (F) Isolated coated vesicle (arrow) without evident viral structure like double membrane vesicles. (G, H) Glomerular morphology included open capillary loops without evidence of electron-dense deposits, slight widening of the subendothelial space and moderate podocytopathy with partial foot process effacement.

DISCUSSION

Despite the fact that hantavirus and SARS-CoV-2 primarily affect renal and respiratory tissue respectively, they share the pathophysiologic commonality of infecting endothelial cells with the ability to activate the alternative complement pathway [3, 6]. In this case, hantavirus inoculation occurred 4 weeks prior to presentation while SARS-CoV-2 Ct-value was increasing with subsequent seroconversion 1 week after presentation, suggesting a temporal overlap of both infections. Concomitant viral replication may have happened during the hantavirus incubation period, but SARS-CoV-2 was likely already subsiding at presentation. We further observed systemic hyperinflammation and activation of the alternative complement pathway with thrombocytopenia, hemolysis and nephrotic proteinuria preceding acute kidney injury, prompting empirical use of eculizumab. Kidney biopsy revealed acute tubular injury with interstitial hemorrhage, peritubular endotheliopathy and unremarkable glomeruli without features of TMA, complement or immune complex deposition, yet moderate podocytopathy on electron microscopy. Additionally, normal ADAMTS-13 level without evidence of schistocytes on blood smear were found. Overall, these findings are most consistent with serologically confirmed, severe Dobrava hantavirus HFRS. Due to the known endotheliopathic effects of both viruses [3, 6], alternative pathway complement activation could theoretically have been aggravated by a synergistic interaction at the vascular endothelium. However, this remains hypothetical.

Remarkably, a rapid response of inflammatory markers, hematologic parameters and proteinuria was observed after a single dose of eculizumab. Hantavirus is known to cause endothelial cell activation and dysfunction by invasion as well as injury from antigen–antibody immune complexes, causing alternative pathway complement activation and release of inflammatory cytokines in HFRS [6]. The rapid decline of C-reactive protein and ferritin levels after eculizumab indicated significant mitigation of systemic inflammation by terminal complement inhibition. Simultaneously, rapid abrogation of platelet consumption, hemolysis and complement consumption pathomechanistically suggested that alternative pathway complement activation may have been a pivot point in sustaining the virus-associated hyperinflammatory response and hematologic manifestations indicative of endothelial injury in this case. Selective overactivation of the alternative pathway was confirmed by detailed complement analysis without detection of any C-nephritic factors. Concerning end organ damage, kidney function did not immediately respond to eculizumab as kidney histology did not reveal any evidence of complement deposition or TMA. However, the rapid response of nephrotic proteinuria is intriguing, as hantavirus is known to cause glomerular barrier dysfunction by inducing loss of endothelial and podocyte cellular adhesion molecules [7]. Therefore, rapid reduction of proteinuria may have been indicative of improved endothelial and podocyte barrier function, or secondary to abrogation of hyperinflammation upon terminal complement inhibition.

Overall, evidence for a pivotal role of alternative pathway complement activation and endothelial cell injury in systemic viral disease has been accumulating from recent research on SARS-CoV-2, but its relevance to end organ damage in other viral diseases is still ill defined. Eculizumab seemed to mitigate signs of virus-associated endothelial injury, including hyperinflammatory response, hematologic manifestations and proteinuria, but did not improve kidney failure in a case of severe hantavirus HFRS. Future studies are warranted to clarify the role of complement activation in virus-associated endothelial injury as it has been implicated by recent research on COVID-19, and whether it may be a potential therapeutic target in certain patients with life-threatening viral diseases.

DATA AVAILABILITY STATEMENT

The data underlying this article are available in the article and in its online Supplementary data.

CONFLICT OF INTEREST STATEMENT

No conflict of interest needs to be declared by the authors.

PATIENT CONSENT

Written patient consent was obtained prior to publication of this manuscript.