The Netherlands Centre for One Health (NCOH) functions as a national coordinating platform for research and partnerships. One of their efforts is combating emerging zoonotic virus infections like MERS-CoV and influenza by understanding these virus host interactions and eventually explore novel solutions.
Infectious diseases form a world-wide threat to human and animal health. To develop global solutions, especially for pathogens that are transmitted from animals to humans, it is important to strengthen knowledge and expertise in the field of One Health research.
The Netherlands Centre for One Health (NCOH) aims for an integrated One Health approach to tackle the global risk of infectious diseases. NCOH commits to create durable solutions for this major challenge by bundling multidisciplinary academic top research in the Netherlands in the area of One Health.
NCOH is an open virtual science-driven network that consists of world-leading academic research groups, across different institutions in the Netherlands that are active in various complementary fields of One Health research. NCOH was initiated by Utrecht University, University Medical Center Utrecht, Wageningen University & Research, Erasmus Medical Center Rotterdam, Academic Medical Center Amsterdam, Leiden University and Leiden University Medical Center.
NCOH aims to perform fundamental, translational, and applied scientific research that integrates human, veterinary, and environmental elements and considerations. It focuses on studying the interactions and connections between human, veterinary, wildlife, and environmental health in pursuit of durable solutions to grand societal challenges requiring a One Health approach.
The NCOH aspires to function as the national coordinating platform for One Health research, strengthen and consolidate the One Health knowledge and research basis in the Netherlands, and provide a trusted and excellent launching platform for public-private partnerships in the international One Health research field. One of these efforts includes the collaboration of the Erasmus Medical Center and the Veterinary faculty at the Utrecht University to combat emerging zoonotic virus infections like the Middle East respiratory syndrome coronavirus (MERS-CoV) and influenza viruses. Through a deeper understanding of the virus host interactions, especially the early interactions between virus and target cell, novel solutions are explored to combat these viruses.
MERS-CoV recently emerged in the human population at the Arabian Peninsula  and continues to cause outbreaks with increasing geographical distribution, five years after its identification. Overall, more than 2000 cases in 27 countries have been reported to the WHO with a 35% case fatality rate. Accumulating serological and molecular evidence indicates that dromedary camels act as the reservoir for MERS-CoV [2,3]. The circulation of the virus in these animals poses a continuous risk of virus spill-over to people in contact with camels, such as those working in slaughter houses and animal farms, evidenced by the presence of MERS-CoV antibodies in sera of those individuals in contact with dromedary camels . Therefore, it is of crucial importance to develop intervention measures at the animal-human interface.
Research groups at the Utrecht University and the Erasmus Medical Center, led by Berend-Jan Bosch and Bart Haagmans, respectively, have worked together to study MERS-CoV and especially the very first step of the infection cycle of this virus; the interaction between the viral particle and the cell surface receptor. This interaction is followed by a series of events that lead to the delivery of the viral genome inside the cytoplasm. Given the fact that the receptor represents the principal determinant of cell, tissue and organ tropism and host range, its identification provided clues on the pathogenesis and mode of transmission, but also may lead to novel clues for intervention strategies.
Early after the identification MERS-CoV at the end of 2012, we identified the MERS-CoV receptor, dipeptidylpeptidase-4 (DPP4), using Fc-tagged fragments of the spike (S) protein in an immunoprecipitation assay followed by mass spectrometry . DPP4 is expressed in the lower respiratory tract of humans (Fig. 1), consistent with the fact that humans succumb to a lower respiratory tract infection . The viral S protein, a type I membrane glycoprotein that is assembled in trimers in the viral envelope, interacts with DPP4 through the S1 subunit, whereas S2 facilitates fusion with cellular membranes. More recent studies have uncovered the crystal structure of the S protein , revealing potential targets for antibodies to block the interaction between the virus and host cells (Fig 2). In fact, neutralizing antibodies are almost solely directed against the S protein, with the receptor binding domain located in the S1 region , being the major immunodominant region. Because S1 is relatively divergent among different human CoVs, specific diagnostic serological assays rely on the use of the recombinant protein as a screening tool for MERS-CoV specific antibodies .
Conversely, induction of neutralizing antibodies can be achieved by administration of recombinant S protein or by delivery using a (viral) vector. We showed that a modified vaccinia virus Ankara virus vaccine expressing the MERS-CoV spike protein confers mucosal immunity in dromedary camels . Significant reduction of excreted infectious virus and viral RNA transcripts was observed in vaccinated animals upon MERS-CoV challenge as compared to controls. The MVA-S vectored vaccine may also be tested for protection of humans at risk, such as healthcare workers and people with camel contacts. In the end, a One Health approach combining different efforts to target both humans and dromedaries may be needed to tackle this zoonotic outbreak.
Influenza A virus (IAV)
IAVs cause seasonal epidemics and occasional pandemics of influenza. While the epidemics are caused by circulating human viruses, the pandemics are caused by animal viruses that managed to cross the host species barrier and became human viruses. All human viruses originate from such animal viruses, but fortunately not every animal virus has managed to become a human virus yet.
Influenza A virus particles contain two glycoproteins that are important determinants of cell and host tropism and main targets of the immune system. The hemagglutinin (HA) protein is a receptor-binding and fusion protein important for virus entry into cells, while the neuraminidase (NA) protein has receptor-destroying activity, which allows virus release after virus assembly and from non-functional decoy receptors found e.g. in mucus. These two glycoproteins work in concert and their activities need to be carefully balanced for the virus to avoid being trapped in mucus and to allow optimal virus replication and transmission. Crossing the host species barrier requires Influenza A viruses to adapt to the novel receptor repertoire of the host by acquisition of mutations in HA and NA. Influenza A viruses bind to sialic acid-containing glycan receptors. Avian viruses prefer binding to α2,3-linked sialic acids, while viruses adapted to humans prefer binding to α2,6-linked sialosides abundantly present on the epithelium of the upper respiratory tract.
Also after animal IAVs have established themselves in the human population they continuously change, which allows them to escape the host immune system. This necessitates a frequent update of the IAV strains to be included in the seasonal vaccines. Mismatches between vaccine and circulating strains may result in vaccine failure. Not every mutation in HA and NA is selected, however, as the two proteins must remain functional and in balance with each other.
Insight into interaction of IAVs with their receptors is key in understanding how IAVs manage to cross the host species barrier and to escape the human immune system and is the topic on which the influenza research groups at the Erasmus Medical Center and the Utrecht University, headed by prof. dr. Ron Fouchier and dr. Xander de Haan, respectively, collaborate.
The group of Ron Fouchier has performed seminal work on the ability of avian IAVs to cross the host species barrier [11,12] and has mapped the antigenic evolution of human IAVs in detail [13,14]. The group of Xander de Haan has developed novel methods to perform in depth analysis of the interaction of HA and NA proteins of human and animal viruses with their sialic acid glycan receptors [15,16].
Within NCOH, these two research groups aim to elucidate the effect of mutations in HA and NA -known to be important for host tropism and antigenic drift- on virus-receptor interactions and virus fitness, with the ultimate aim to not only understand IAV evolution, but possibly also to be able to predict it.
About the Authors
Dr. Bart L. Haagmans is a workgroup leader at the Viroscience department of the Erasmus Medical center in Rotterdam, the Netherlands. His main interest is to further understand the pathogenesis of emerging viral infections including SARS and MERS coronavirus. He was involved in the characterization of the MERS-CoV genome, the receptor used by MERS-CoV to infect cells and the identification of the animal host of MERS-CoV, the dromedary camel. Currently another focus of his research is the development of a MERS-CoV vaccine.
Dr. Berend-Jan Bosch is associate professor at the Virology division of the Faculty of Veterinary Medicine, Utrecht University in Utrecht, the Netherlands. His research focuses on the cell entry mechanism of membrane-enveloped viruses, and has contributed to the identification of several cell surface molecules to which viruses attach to initiate infection, including the dipeptidyl peptidase 4 receptor for the zoonotic MERS coronavirus. He was involved in the elucidation of the first 3D-structure of the coronavirion as well as the first high-resolution structures of the coronavirus spike glycoprotein trimer by advanced cryo-electron microscopy methodologies.
Dr. C.A.M. (Xander) de Haan is associate professor at the Virology Division of the Faculty of Veterinary Medicine of the Utrecht University in Utrecht, the Netherlands. His group particularly focuses on the molecular biology of influenza A viruses, with an emphasis on the interactions of these viruses with sialoside receptors and the consequences thereof for endocytic uptake, tropism and pathogenesis. These virus-receptor interactions are being studied for animal and human viruses among others using recombinant soluble mimics of the envelope glycoproteins HA and NA in combination with glycan array analysis and enzyme-linked lectin assays. In addition, biolayer interferometry is being used to characterize the functional balance between HA and NA in virus particles.
Dr. Ron A.M. Fouchier is a professor in Molecular Virology at the Viroscience Department of Erasmus MC Rotterdam. Achievements of his team include the identification and characterization of several "new" viruses; the human metapneumovirus, human coronavirus NL63, the SARS coronavirus, the MERS coronavirus, and a new influenza A virus subtype, H16. Currently, his research is focused on the evolution and molecular biology of respiratory viruses in humans and animals, with special emphasis on antigenic drift and influenza virus zoonoses, transmission, and pandemics.
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