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Questions and Answers
What is the primary component that protects the genetic material of a virus?
protein coat (capsid)
What are the two types of RNA viruses?
Double-stranded (ds) RNA and Single-stranded (ss) RNA
What is the function of the H spikes on a virus?
To help the virus enter a cell
What is unique about the cells that a virus can infect?
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What are the two components that make up an enveloped virus?
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What is the primary component of the virus that interacts with the external environment?
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Who first proposed the term 'virus' in the 1890s?
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What is the definition of a virus?
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What is the term for the study of viruses?
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What is the function of the spikes on a virus particle?
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What is the term for the dormant state of a virus inside a host cell?
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What is the main component of a virus particle?
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What is the common name of the disease caused by prions, which affects cattle?
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What is the primary purpose of viral cultivation in clinical specimens?
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What type of organisms are occasionally used in live animal inoculation for viral cultivation?
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Why can't viruses grow in non-living media like nutrient agar or nutrient broth?
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What is the purpose of a plaque assay in virus quantification?
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What type of cells are used in cell culture techniques for viral propagation?
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What is the purpose of cell culture utilization in the study of virus infection?
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How is the concentration of virus determined in research and diagnosis?
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What do clear zones in plaque formation observation signify?
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Why are antibiotics ineffective in treating animal viral infections?
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What is the purpose of antiviral drugs?
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What is the purpose of vaccines in relation to viral infections?
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What is the difference between enveloped and naked viruses in terms of transmission?
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What is the function of glycoproteins in the viral envelope?
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Where do all RNA viruses, except the Influenza virus, replicate within the host cell?
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What is unique about the replication of Retroviruses and some tumour-causing RNA viruses?
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What is the difference between the replication of DNA and RNA viruses?
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Where do Poxviruses replicate within the host cell?
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Study Notes
Introduction to Viruses
- Louis Pasteur first proposed the term "virus" in the 1890s
- Ivanovski and Beijerinck showed that a disease in tobacco was caused by a virus
- Loeffler and Frosch discovered an animal virus that causes Foot-and-Mouth Disease (FMD) in cattle
Definition of a Virus
- A virus is a non-cellular particle made up of genetic material and protein that can invade living cells and reproduce
- Viruses are submicroscopic, obligate intracellular parasites
- They are inert outside of a host cell
Terminology
- Virology: the study of viruses
- Virus particle (virion): the extracellular form of a virus
- Viral Latency: some viruses have the ability to become dormant inside a host cell, e.g. HIV and Herpes viruses
Properties of Viruses
- Non-cellular organisms enclosed in a protective envelope
- Presence of spikes helps in attaching the virus to the host cell
- Do not grow, respire, or metabolize, but reproduce
- Surrounded by a protein coat (capsid) and have a nucleic acid core comprising DNA or RNA
- Considered both living and non-living things
Types of RNA Viruses
- Double-stranded (ds) RNA virus: e.g. Reovirus
- Single-stranded (ss) RNA virus: further classified into two types:
- Positive sense RNA (+RNA): e.g. Poliovirus, Hepatitis A, Rabies virus, Influenza virus
- Negative sense RNA (-RNA)
Diversity of Animal Viruses
- Nonenveloped ssDNA: Parvovirus
- Enveloped ssRNA: partially dsDNA, e.g. Hepadnavirus
- Enveloped dsDNA: e.g. Papovavirus
- ssRNA: e.g. Picornavirus, Rhabdovirus, Togavirus, Orthomyxovirus
- dsDNA: e.g. Poxvirus, Adenovirus, dsRNA, Bunyavirus, Coronavirus, Reovirus
- RNA viruses: e.g. Retrovirus
Structure of the Virus
- A virus is either DNA or RNA, protected by a protein coat called a capsid
- Protein coat (capsid) made of individual protein subunits called capsomeres
- Enveloped or non-enveloped (naked)
- Additional layers: carbohydrates, lipids, other proteins
Viral Glycoproteins
- Reside on the surface of virions and are often the sole component of the virus that interacts with the external environment
- H spikes help a virus enter a cell, and N spikes help it leave
Prions
- Causative agents of Kreutz Feld Jakob disease, scrapie, bovine spongiform encephalopathy (BSE), and kuru
- Incorrectly folded proteins cause normal proteins to fold in such a way as to be non-functional
Techniques in Cultivating and Identifying Animal Viruses
- Primary purposes of viral cultivation: to isolate and identify viruses in clinical specimens, to prepare viruses for vaccines, and to do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells
- Using live animal inoculation: specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits
- Using bird embryos: enclosed in an egg, nearly perfect conditions for viral propagation
- Using cell (tissue) culture techniques: most viruses are propagated in some sort of cell culture
Treatment of Animal Viral Infections
- Antiviral drugs block virus replication by targeting one of the steps in the viral life cycle
- Interferon medication shows potential for treating and preventing viral infections
- Vaccines stimulate immunity
- Antivirals can only be used to treat certain viral infections and do not "kill" or disarm the virus permanently
- Vaccines can only be used to prevent infections (both viral and bacterial) from leading to disease
The Viral Envelope
- Enveloped viruses take a bit of the host cell membrane in the form of an envelope
- In the envelope, some or all of the regular membrane proteins are replaced with viral proteins
- Some proteins form a binding layer between the envelope and the capsid
- Glycoproteins remain exposed as spikes (peplomers) essential for attachment
- Naked: transmitted through feces or orally due to ability to live in the environment
- Enveloped: transmitted only by direct contact (blood, sexually, respiratory, insect/animal bites)
Replication Properties and Site of Replication
- Replication within the cytoplasm of the host cell: e.g. all RNA viruses except Influenza virus
- Replication within the nucleus and the cytoplasm of the host cell: e.g. Influenza virus, Poxvirus
- Replication within the nucleus of the host cell: all DNA viruses except Pox virus
- Replication of the virus through the double-stranded DNA intermediate: e.g. all DNA viruses, Retrovirus, and some tumor-causing RNA viruses
- Replication of the virus through a single-stranded RNA intermediate: e.g. all RNA viruses except Reovirus and tumor-causing RNA viruses
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Description
Test your understanding of viruses, including the concept of a virus, how they infect cells, and the history of virology. Learn about the pioneering work of Louis Pasteur, Ivanovski, Beijerinck, Loeffler, and Frosch, and assess your knowledge of viruses and their effects on living organisms.
