Virology Flashcards
Virology
The study of viruses and viral diseases
Virus
Piece of bad news wrapped up in a protein
Virologist
Someone who studies viruses
Importance of Veterinary Virology
Viral diseases cause high rates of mortality and morbidity in animals and birds
Viral diseases can significantly impact food safety and security
Viral diseases can cause tremendous economic losses and are expensive to control and prevent
Zoonosis: most deadly viruses are animal viruses that transferred to humans
Zoonosis
Viral diseases can be transmitted form animals and birds to humans
Defining Viruses
Non-living entities
Contain nucleic acid genome (DNA or RNA) surrounded by a protein coat (capsid) and in some cases other layers of material, such as lipid envelope
Viruses do not possess standard cellular organelles such as mitochondria, etc.
Cannot make energy or proteins by themselves and have to rely on a host cell
Similar to obligate intracellular parasites. Outside the living cell, viruses are inert or dormant particles, whereas, inside the virus hijacks and utilizes the host cell machinery to produce its proteins and nucleic acid for the next generation of viruses
Do not have genetic capability to multiply by division, such as Binary Fission. The process of viral 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
Virus Structure
DNA or RNA genes inside a capsid. Inside a envelop (bubble of fat) with molecules of protein
Capsid
The protein shell of a virus that encases.envelopes the viral nucleic acid or genome
Made up of capsomeres held together by non-covalent bonds
Nucleocapsid
Capsid + virus nucleic acid
Lipid envelope
Some viruses may have an additional layer known as envelope that covers the capsid
Usually a lipid bilayer derived form host cell
Glycoproteins are present on the surface of the envelope, and often appear as spikes
Pleomorphism
The ability of some virus to alter their shape or size
Ebola Virus
Filament shaped
Rabies Virus
Bullet shaped
Bacterophage
Tadpole shaped
Tobacco-mosaic virus
Rod-shaped
Poxvirus
Brick-shaped
Rotavirus
Spherical
Chemical composition of Viruses
Virus Nucleic acid can be either DNA or RNA and these can both be either double-stranded or single-stranded
Virus Replication
Attachment (lock and key specific)
Penetration (enters cell)
Uncoating ( come out of protein capsid coat)
Synthesis of Viral Nucleic acid and Protein ( hijack cell to get multiple copies)
Assembly and maturation (new capsid will fuse and mature)
Release in large numbers
Impacts of Virus replication in host cell
Cell Death: lysis (spread virus all over), alteration of cell membrane, apoptosis
No apparent changes to the infected cell, latent, persistent, or chronic infection
Transformation of cell to malignant one
Fusion of cells, Multinucleated
Viral Taxonomy: ICTV
International committee on taxonomy of viruses 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
What is considered for classification of viruses
Nature of virus genome and virus genetic diversity
Virus replicating strategies
Virus morphology
Diagnosis/Detection
By gross evaluation and histopathology
By cultivation/isolation: cultivation/isolation of viruses in cells/tissue culture. Inoculation in eggs
Electron Microscopy (to identify and study the morphology of a virus)
Serology ( detection of viral antigen or host antibody against virus ELISA)
Detection of viral nucleic acids.molecular biology (RT-PCR)
Treatment
Antiviral drugs
Immune system stimulation: interferon therapy
Synthesis antibodies or administration of natural antiserum (antibodies)
Prevention of Viral diseases
Vaccination
Proper hygiene and sanitation
Eliminating Arthropod vectors
Quarantine and culling
Pathogenicity
The ability of a virus to cause disease in host (I.e. Harm the host)
Pathogen
Virus which causes disease
Pathogenesis
Manner/mechanism of development of disease
Non-pathogenic
No disease- no clinical signs
Virulence
A quantitative or relative measure if the degree of pathogenicity of the infecting virus
Avirulent
Not virulent (not harmful to the host)
Virulence variables
Factors related to Virus, Host, and other
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 (nutritional status, age, hormonal factors, stage of cell differentiation)
Fever
Factors related to other
Environmental
Dual infections
Measuring virulence: Lethal dose 50
The dose of virus required to cause death in 50% of animals
Lower L50 is more virulent
Routes of entry: Skin
Cannot penetrate intact skin Cut or breach Transcutaneous injection 1. bite of arthropods (ticks, flea, mosquito) 2. Bite of infected animal (rabies) 3. Contaminated objects
Routes of entry: Mucous membrane
Conjuctiva
oropharynx
Genitourinary Tract rectum
Defenses: IgA (antibodies), virucidal proteins
Routes of entry: GI tract
Virus in contaminated food and water
Routes of entry: respiratory tract
…
Virus spread in host: epithelium
Local spread of virus on epithelial surfaces
Causes localized infection
May or may not proceed to subepithelial layer/underlying tissues
Virus spread in host: epithelial surfaces
From local infection of epithelial surfaces
Viruses may reach subepithelial layer/underlying tissues from epithelial surfaces
To do this, viruses should overcome local host defense
Virus spread in host: subepithelial
To subepithelial invasion and lymphatic spread
In subepithelial tissue, viruses get access to lymphatics, phagocytic cells and tissue fluids
These may help carry virus to the blood stream
Virus spread in host: blood
To blood stream and then spread via blood stream
Viremia
Presence of virus in blood
Primary viremia
initial entry of virus into the blood
Secondary viremia
Virus has replicated/multiplied in major organs and once more entered the circulation
Disseminated Infection
Infection spreads beyond the primary site of infection
Systemic infection
If a number of organs or tissues are infected
Spread via nerves
Through peripheral nerves
Through receptor neurons in the nasal olfactory epithelium
Central nervous system
Virus can cross BBB and infect CNS
Neurotropic Virus
Viruses that can infect neural cells.
Infection may occur by neural or hematogenous spread
Neuroinvasive Virus
Viruses that enter the CNS after infection of a peripheral site
Neurovirulent Virus
Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death
Tropism
The specificity/affinity of a virus for a particular host tissue
Pantropic virus
Can replicate in more than one host Organ/tissue
Outcomes of viral injury
Cell lysis Apoptosis Oncovirus Persistant infection Immunosupression
Cell Lysis
following virus replication allowing release of new viruses
Apoptosis
The process of programmed cell death, which is essentially a mechanism of cell suicide that the host activates as a last resort to eliminate viral factories before new virus production is complete
Different from lysis where viral replication is complete, host cell is destroyed and new virions released
Oncoviruses
Some virus can cause cancer and are known as oncoviruses or oncogenic viruses
Persistent infection
Some viruses do not cause immediate death of infected host cells bi cause persistent infection
Shedding
Of infectious virions is crucial to the maintenance of infection in populations
Acute infection
Usually intensive shedding over short time period
Persistent infection (shedding)
Can be shed at low titers for months to years
Skin injury
can be localized (papilloma) or disseminated (lumpy skin disease)
Vesicle: fluid filled sac, small distinct elevation
Ulcer: opening in the skin caused by sloughing of necrotic tissue, extending pass the epidermis
Nodule/tumor: palable, solid, elevated mass nodules with distinct borders. Tumors extending deep into the dermis (nodule is a solid tumorous mass)
Warts: benign skin growths that appear when a virus infects the top layer of skin
Erythema: reddening of skin
Injury to GI tract
Ingestion or from blood, systemic infection
destruction of intestinal enterocytes
GI disease, malabsorption, diarrhea
Pronounced dehydration, acidosis, hemoconcentration
Respiratory Tract injury
gasping, respiratory distress from inflammed nervous tissue
CNS injury
Lytic (destruction/bursting) infections of neurons
Neuronal necrosis (necrosis is death of body tissue)
Neuronophagia (killing/devouring of neuronal cells by phagocytic cells)
Pervascular cuffing (inflammatory cells around blood vessels in CNS)
Progressive demyelination
Neuronal vacuolation in prion disease
Hemopoietic Injury
Hemorrhages: petechiae hemorrhage (pin-point/small spots) Ecchymoses hemorrhage (larger areas of hemorrhage, ill-defined margins) Disseminated intravascular coagulation- clots are formed throughout the body followed by hemorrhages
Viral infection of fetus
Teratogenic viruses: cause developmental defects of embryo of fetus after in-utero infection
