Elevated IL-6, IL-10, and IFN-γ levels in fatal elephant endotheliotropic herpesvirus – hemorrhagic disease (EEHV-HD) cases suggest an excessive proinflammatory cytokine response contributes to pathogenesis

Tabitha E Hoornweg^1*Willem Schaftenaar²Jooske Ijzer³Myrna M P Mulder¹Mariska Lugtenburg¹Anne Van Beest¹Cornelis A M De Haan¹Victor PMG Rutten^1,4

• ¹Department of Biomolecular Health Sciences, Division Infectious Diseases and Immunology, Utrecht University, Faculty of Veterinary Medicine, Utrecht, Netherlands
• ²EAZA elephant TAG, Rotterdam Zoo, Rotterdam, Netherlands
• ³Department of Biomolecular Health Sciences, Division Pathology, Utrecht University, Faculty of Veterinary Medicine, Utrecht, Netherlands
• ⁴Faculty of Veterinary Sciences, Department of Veterinary Tropical Diseases, University of Pretoria, Pretoria, South Africa

Hemorrhagic disease developed as a consequence of an EEHV infection (EEHV-HD) is the leading cause of death of young Asian elephants in Zoos worldwide and also affects elephants in range countries. Although a cytokine storm has long been suggested to underlie disease pathogenesis, there is little evidence and the role of cytokines in EEHV-HD pathogenesis remains unclear to date. In the current study, we compared mRNA levels of eight different cytokines between blood and tissue samples of EEHV-HD cases (n=11) and controls (n=12) in order to determine whether cytokines may contribute to EEHV-HD pathogenesis. We show the presence of significantly elevated mRNA levels of IFN-γ, IL-6 and IL-10, cytokines typically associated with cytokine storms, in blood or tissues with high viral loads (heart and liver) of EEHV-HD cases. Comparable cytokine inductions were not observed in tissues with lower viral loads (tongue, lung and kidney), indicating an association between viral replication and cytokine induction, and suggesting damage observed in these tissues is likely collateral. In conjunction with pathological findings, including acute systemic inflammation and multiple organ dysfunction, we propose that a pathogen-induced cytokine storm indeed underlies EEHV-HD pathogenesis, which would support investigation into the use of anti-inflammatory therapies to control disease.