Tropism and replication of Middle East respiratory syndrome coronavirus from dromedary camels in the human respiratory tract: an in-vitro and ex-vivo study

Summary Background Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic infection causing severe viral pneumonia, with index cases having resided in or recently travelled to the Arabian peninsula, and is a global concern for public health. Limited human-to-human transmission, leading to some case clusters, has been reported. MERS-CoV has been reported in dromedary camels but phenotypic characterisation of such viruses is limited. We aimed to compare MERS-CoV isolates from dromedaries in Saudi Arabia and Egypt with a prototype human MERS-CoV to assess virus replication competence and cell tropism in ex-vivo cultures of human bronchus and lung. Methods We characterised MERS-CoV viruses from dromedaries in Saudi Arabia and Egypt and compared them with a human MERS-CoV reference strain. We assessed viral replication kinetics and competence in Vero-E6 cells (rhesus monkey), tissue tropism in cultures of ex-vivo human bronchial and lung tissues, and cytokine and chemokine induction, gene expression, and quantification of viral RNA in Calu-3 cells (human respiratory tract). We used mock-infected tissue as negative controls for ex-vivo experiments and influenza A H5N1 as a positive control for cytokine and chemokine induction experiments in Calu-3 cells. Findings We isolated three dromedary strains, two from Saudi Arabia (Dromedary/Al-Hasa-KFU-HKU13/2013 [AH13] and Dromedary/Al-Hasa-KFU-HKU19D/2013 [AH19D]), and one from Egypt (Dromedary/Egypt-NRCE-HKU270/2013 [NRCE-HKU270]). The human and dromedary MERS-CoV strains had similar viral replication competence in Vero-E6 cells and respiratory tropism in ex-vivo cultures of the human respiratory tract, and had similar ability to evade interferon responses in the human-respiratory-tract-derived cell line Calu-3. Interpretation The similarity of virus tropism and replication competence of human and dromedary MERS-CoV from the Arabian peninsula, and genetically diverse dromedary viruses from Egypt, in ex-vivo cultures of the human respiratory tract suggests that dromedary viruses from Saudi Arabia and Egypt are probably infectious to human beings. Exposure to zoonotic MERS-CoV is probably occurring in a wider geographical region beyond the Arabian peninsula. Funding King Faisal University, Egyptian National Research Centre, Hong Kong Food and Health Bureau, National Institute of Allergy and Infectious Diseases, and European Community Seventh Framework Program.