Characterization and determination of animal reservoirs of a novel animal flavivirus.
Professor Yuen Kwok Yung (Co-Investigator)
flavivirus, virus, infection
Block Grant Earmarked for Research (104)
HKU Project Code
Seed Fund for Basic Research
About 70% of the emerging pathogens infecting humans originate from animals (1). Most of the major outbreaks among humans were caused by RNA viruses as a result of their higher mutation rates compared with other types of microbes and their capability for unique genetic change, either by genetic recombination in positive-sense RNA viruses or genetic reassortment in RNA viruses with segmented genomes (1). As exemplified by the recent emergences of the avian influenza A(H7N9) in China (2-6) and the Middle East respiratory syndrome coronavirus in the Middle East with secondary cases in Europe and Africa (7,8), studies on novel viruses’ zoonotic potential (6,7,9) and development of effective diagnostic (5,10) and therapeutic strategies (11,12) for their associated infections are crucial for the prevention of morbidity, mortality, and economic loss. Recently, we discovered a novel flavivirus by RT-PCR sequencing in an animal species caught during the investigation of three patients with acute encephalitis in Hong Kong, of whom two were subsequently diagnosed with Japanese encephalitis and one remains of undetermined microbial etiology. Sequencing analysis showed that the novel flavivirus was less than 70% homologous (either nucleotide or protein) to other known flaviviruses (Fig. 1). Flaviviruses are enveloped, positive single-stranded RNA viruses within the family Flaviviridae. More than 70 flaviviruses have been reported with many being associated with important human diseases via arthropod transmission (13). Important examples of flaviviruses with particular relevance to Hong Kong and China include Japanese encephalitis virus (14,15) and Dengue virus (16). Studies on the cell and tissue tropism, genomes, and animal reservoirs of these two flaviviruses have been crucial to enhance our understanding on the pathogenesis, transmission, outcome, and design of diagnostic and therapeutic strategies for their corresponding infections. For example, in-vitro data showed that three organ systems, namely the immune system, the liver, and endothelial cell linings of blood vessels, have significant roles in the pathogenesis severe dengue (17). Analysis of the genomes of Dengue virus showed that the virus evolves during an epidemic and may be associated with increased severity (17). MicroRNA targeting to control Japanese encephalitis virus tissue tropism and pathogenesis was shown to be a potentially useful approach for virus attenuation and vaccine development (18). Understanding of the transmission cycles and animal reservoirs of the viruses are crucial for formulating preventive strategies against their associated infections (19). These studies exemplify the practical applications that could be derived from our current study on the characterization of our newly discovered flavivirus using complete genome sequencing and cell culture to understand its zoonotic potential and animal reservoirs. The results would facilitate the future development of diagnostic assays for a previously unknown yet potentially important zoonosis in our region. Objectives: To perform complete genome sequencing of and characterize the differential susceptibility of different human tissue and animal species cell lines to this novel flavivirus to provide insight into its clinical significance. - What are the arrangement and characteristics of the genome of this virus? - Which human tissue and animal species cell line does the virus actively replicate in? - What clinical implications, diagnostic, and therapeutic targets might be extrapolated from the data? References: 1. Chan JF et al. Interspecies transmission and emergence of novel viruses: lessons from bats and birds. Trends Microbiol. 2013 Oct;21(10):544-55. 2. To KK et al. The emergence of influenza A H7N9 in human beings 16 years after influenza A H5N1: a tale of two cities. Lancet Infect Dis. 2013 Sep;13(9):809-21. 3. Chen Y et al. Human infections with the emerging avian influenza A H7N9 virus from wet market poultry: clinical analysis and characterisation of viral genome. Lancet. 2013 Jun 1;381(9881):1916-25. 4. Yu L et al. Clinical, Virological, and Histopathological Manifestations of Fatal Human Infections by Avian Influenza A(H7N9) Virus. Clinical Infect Dis. 2013 Nov;57(10):1449-57. 5. Chan KH et al. Analytical sensitivity of seven point-of-care influenza virus detection tests and two molecular tests for detection of avian origin H7N9 and swine origin H3N2 variant influenza A viruses. J Clin Microbiol. 2013 Sep;51(9):3160-1. 6. Yang S et al. Avian-Origin Influenza A(H7N9) Infection in Influenza A(H7N9)-Affected Areas of China: A Serological Study. J Infect Dis. 2013 Sep 18. 7. Chan JF et al. Differential cell line susceptibility to the emerging novel human betacoronavirus 2c EMC/2012: implications for disease pathogenesis and clinical manifestation. J Infect Dis. 2013 Jun 1;207(11):1743-52. 8. Chan JF et al. Is the discovery of the novel human betacoronavirus 2c EMC/2012 (HCoV-EMC) the beginning of another SARS-like pandemic? J Infect. 2012 Dec;65(6):477-89. 9. Zhou J et al. Active Replication of Middle East Respiratory Syndrome Coronavirus Replication and Aberrant Induction of Inflammatory Cytokines and Chemokines in Human Macrophages: Implications for Pathogenesis. J Infect Dis. 2013 Oct 21. 10. Chan KH et al. Cross-reactive antibodies in convalescent SARS patients' sera against the emerging novel human coronavirus EMC (2012) by both immunofluorescent and neutralizing antibody tests. J Infect. 2013 Aug;67(2):130-40. 11. Chan JF et al. Broad-spectrum antivirals for the emerging Middle East respiratory syndrome coronavirus. J Infect. 2013 Dec;67(6):606-16. 12. Lau SK et al. Delayed induction of proinflammatory cytokines and suppression of innate antiviral response by the novel Middle East respiratory syndrome coronavirus: implications for pathogenesis and treatment. J Gen Virol. 2013 Sep 28. 13. Leyssen P et al. Perspectives for the treatment of infections with Flaviviridae. Clin Microbiol Rev. 2000 Jan;13(1):67-82. 14. Riley S et al. Transmission of Japanese encephalitis virus in Hong Kong. Hong Kong Med J. 2012 Feb;18 Suppl 2:45-6. 15. Ma ES et al. Review of vector-borne diseases in Hong Kong. Travel Med Infect Dis. 2011:95-105. 16. Wu JY et al. Dengue Fever in mainland China. Am J Tropical Med Hygiene. 2010 Sep;83(3):664-71. 17. Martina BE et al. Dengue virus pathogenesis: an integrated view. Clin Microbiol Rev. 2009 Oct;22(4):564-81. 18. Heiss BL et al. Insertion of microRNA targets into the flavivirus genome alters its highly neurovirulent phenotype. J Virol. 2011 Feb;85(4):1464-72. 19. Vasilakis N et al. Fever from the forest: prospects for the continued emergence of sylvatic dengue virus and its impact on public health. Nat Rev Microbiol. 2011 Jul;9(7):532-41.