Poster Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

Ultrastructural differences observed in viruses of the family Orthomyxoviridae across genera using transmission electron microscopy (TEM). (#210)

Sandra Crameri 1 , Clare Holmes 1 , Andrew Leis 1 , Jenni Harper 1 , Lynette Williams 1 , John Hoad 1 , Ina Smith 1 , Songua Shan 1 , Sue Lowther 1 , Peter Mohr 1 , Nick Moody 1 , Paul Selleck 1 , Alex Hyatt 1
  1. Australian Animal Health Laboratory, CSIRO, Geelong, Vic, Australia

Introduction: Viruses from the family Orthomyxoviridae have produced a significant impact on humans, agricultural and wildlife species. The family comprises six genera. The International Committee on Taxonomy of Viruses (ICTV) describes morphology of the family as either spherical, pleomorphic, or filamentous (1). The ultrastructural determinates are complex; influenza, for example, produces filamentous forms in nature but spherical forms during passage in culture (2). Spherical virions contain a helical genome consisting of 6 to 8 different sized ribonucleoproteins (RNP) surrounded by a thick lipid membrane overlayed by a host cell acquired outer envelope. After cell passage, we compared the progeny virus shape and appearance by thin section TEM.

Methodology: Virus species from different Orthomyxovirus genera were compared:

·         Influenza virus A –  Influenza A virus (IAV )

·         Thogotovirus – Upolo (UPOV)

·         Isavirus – Infectious salmon anaemia virus (ISAV)

·         Quaranjavirus, new genus (3) - Cygnet River virus (CyRV)

·         Putative new genus - Pilchard orthomyxovirus (POMV)

When using comparable methodologies the ultrastructural morphology of viruses can be used to differentiate between the genera of orthomyxoviruses during their morphogenesis. Cell cultures inoculated with virus isolates derived from tissue homogenates of diseased animals or ticks were conventionally prepared for thin section EM. Additionally cell cultures infected with CyRV were also prepared via chemical and high pressure freezing fixation followed by freeze substitution of cultures grown on sapphire discs. Images acquired from the resultant sections were compiled for tomography to examine budding virus shape in 3D.

Results & Conclusion: CyRV particles budding from the plasma membrane after cell passage were predominately spherical in shape, whereas POMV after cell passage assume a ‘peanut’ and spherical shapes.  The viruses infecting avian species had distinct ultrastructure, as did the viruses affecting salmon. These differences can provide indicative criteria in diagnostic EM.

  1. Virus Taxonomy: Classification and Nomenclature of Viruses: Ninth Report of the International Committee on Taxonomy of Viruses. Ed: King, A.M.Q., Adams, M.J., Carstens, E.B. and Lefkowitz, E.J. San Diego: Elsevier, pp 749-761.
  2. Spherical Influenza Viruses Have a Fitness Advantage in Embryonated Eggs, while Filament-Producing Strains Are Selected In Vivo. Seladi-Schulman, J., Steel, J., Lowen, A.C., J Virol. 2013 Dec; 87(24): 13343–13353.doi: 10.1128/JVI.02004-13
  3. Create 2 new species in the proposed new genus Quaranjavirus. McCauley JW, Hongo S, Kaverin NV, Kochs G, Lamb RA et al. (2012), , International Committee on Taxonomy of Viruses, retrieved 12 March 2015