Virology Flashcards
Virology
Study of viruses and viral disease
Virologist
Someone who studies viruses, they are important because viral diseases can cause high rates of mortality and morbidity in animals and birds
Why are virologist important?
- Can significantly impact food safety and security
- Can cause tremendous economic losses and are expensive to control and prevent
Zoonosis: Viral disease can be transmitted from animals to humans
Defining Viruses
- viruses are non-living entities.
- contain DNA or RNA surrounded by a protein coat (capsid) and, in some cases, other layers of material, such as a lipid envelope.
- Viruses do not possess standard cellular organelles such as mitochondria, chloroplasts, Golgi, and endoplasmic reticulum with associated ribosomes.
- Viruses cannot make energy or proteins by themselves and have to rely on a host cell.
- All Viruses are like obligate intracellular parasites. Outside the living cell, viruses are inert or dormant particles, whereas, inside the cell, the virus hijacks and utilizes the host cell machinery to produce its proteins and nucleic acid for the next generation of virus. Viruses cannot make energy or proteins by themselves and have to rely on a host cell.
- Viruses such as Binary Fission do not have the genetic capability to multiply by division. The process of Virus reproduction resembles an assembly line in which various parts of the virus come together from different parts of the host cell to form new virus particles.
Structure of viruses
DNA and RNA genes
Capsid
Envelope, a bubble of fat
Molecular protein
What is a capsid?
A protein shell of a virus that encases/envelopes the viral nucleic acid or genome
What are capsids made of?
Capsomeres held together by covalent bonds
Nucleocapsid
Capsid + Virus Nucleic acid (DNA or RNA)/Genome
What is the additional layer that some viruses have
Lipid envelop
What is the lipid envelope?
Some Viruses may have an additional layer known as an envelope that covers the capsid.
The envelope is usually a lipid bilayer derived from the host cell.
Glycoproteins are present on the envelope’s surface, often appearing as spikes.
Naked virus
Only protein capsid enclosing nucleic acid
Enveloped viruses
additional layer enclosing the protein capsid enclosing the nucleic acid
Pleomorphism
ability of some virus to alter shape and size
Virus replication
Attachment to the cell
penetration and uncoating: to the cell membrane and injects DNA or RNA into the cell
synthesis of viral nucleic acid and protein replication using cell host machinery
assembly and maturation; release in lg # viral nuclei acid are packaging into viral particles and release from the cell; the host may be destroyed in the process
Impacts of virus replication in host cell
Cell death: Lysis, Alteration Cell Membrane, Apoptosis (Cell Suicide)
No apparent changes to the infected cell. Latent, Persistent or Chronic infection
Fusion of cells: Multi nucleated
Transformation of cell to malignant one
Classification of viruses
The International Committee on Taxonomy of Viruses (ICTV) Classification System is followed by Virologists Worldwide
The ICTV is the only body charged by the International Union of Microbiological Societies with the task of developing, refining, and maintaining a universal virus taxonomy.
Considers the following for Classification of Viruses:
Nature of virus genome and virus genetic diversity
virus replication
virus morphology
Diagnosis/detection of viruses/viral diseases
Gross evaluation and histopathology
Cultivation/Isolation
Electron Microscopy
Serology - ELISA
Molecular Biology (RT-PCR?PCR)
Treatment of viruses disease
Antiviral Drugs
Immune system stimulation: interferon therapy
synthesis antibodies or admission of natural antiserum
Prevention of viral disease
Vaccination
Proper Hygiene and Sanitation
Elimination Arthropod Vectors
Quarantine and Culling
Pathogenecity
ability for virus to cause Disease in HotThe Virus which causes Disease is called a Pathogen
Pathogenesis
is the manner/mechanism of development of a disease
Virulence
is used as a quantitative or relative measure of the degree of pathogenicity of the infecting virus.
Avirulent
Not harmful to the host
Virus pathogenesis and virulence
** tug of war
Virulence is not an absolute property of a virus, but depends on many variable
Factors related to virus:
- Genetic Variation of Virus
- Route of entry of Virus in Host
- Affinity of Virus to Host Organs
- Dose of Infection
- Immuno evasion
Factors related to host
- Host Species
- Host Immunity
- Host Physiological factors (Nutrition status, Age,
- Hormonal Factors, Stage of Cell Differentiation)
- Fever
Other factor in the middle:
- Environment
- Dual Infection
Measuring Virulence
Lethal dose 50 (LD50): The dose of the virus required to cause death in 50% of animals, such as mice.
The lower the LD50 is the more virulent is the virus
Routes of entry of virus into host skin
Cut or Breach
Transcutaneous injection (anthropods)
Bite of infected animals
Contaminated objects
Mucus membrane (conjunctiva, oropharynx, genitourinary tract)
GI tract
Respiratory tract
