Virulence and Pathogenicity- Virology Flashcards
Define pathogenicity.
The ability of a virus to cause disease in host
Define pathogen
A virus that causes disease
Define pathogenesis
The manner/mechanism of development of a disease
Define virulence
Quantitative or relative measure of the degree of pathogenicity of the infecting virus
Define avirulent
No virulent (not harmful to the host)
What factors related to the host effect the virulence of a virus?
Species
Immunity
Physiological factors (age, nutrition status, hormones, stage of cell differentiation)
Fever
What factors related to the virus effect its virulence?
Genetic variation of the virus Route of entry into the host Affinity of the virus to host organs Dose of infection Immuno evasion
What factors effect the virulence of a virus unrelated to the host or the virus itself?
Environment
Duel infections
What is used to measure virulence?
Lethal dose 50 (LD50) - the dose of the virus that is required to kill 50% of animals, such as mice
A more virulent virus would have a higher or lower LD50?
Lower - less is needed
What are the routes of entry for a virus?
Skin
Mucous membranes
GI Tract
Respiratory Tract
How does a virus penetrate the skin?
Cut or breach
Transcutaneous injections (bite of arthropods)
Bite of infected animal
Contaminated objects (needles, etc)
How does a virus penetrate the mucous membrane?
Conjunctiva
Oropharynx
Genitourinary Tract and Rectum
How does a virus penetrate the GI Tract?
Contaminated food or water
How do viruses spread in a host?
epithelium –> subepithelial layer/ underlying tissues, lymphatics –> blood streams –> nerves
How is a virus spread in the epithelium?
Local spread, causes localized infection, may or may not proceed to subepithelium
How does a virus spread from the epithelium to the subepithelium?
Overcome local host defense
How does a virus spread from the subepithelium to the blood stream?
The virus get access to lymphatics, phagocytic cells, and tissue fluids in the subepithelium which help carry the virus to the bloodstream.
Define viremia.
Presence of virus in the blood
What is primary viremia?
initial entry of virus into the blood
How does primary viremia happen?
Spread of viral infection to blood from subepithelial tissue/ lymphatics
OR
Direct injection in blood, through bite of mosquitoes or syringes
What is secondary viremia?
When a virus has replicated/multiplied in major organs and once more entered circulation
What is disseminated infection?
Infection spreads beyond the primary site of infection
Whats is systemic infection?
If a number of organs or tissues are infected
How do viruses spread to the nerves?
Through the peripheral nerves
Through receptor neurons in the nasal olfactory epithelium
Viruses can cross blood-brain barrier and infect CNS
Define neurotropic virus
Viruses that can infect neural cells, infection can occue by neural or hematogenous spread
Define neuroinvasive virus
Viruses that enter the central nervous system (spinal cord and brain) after infection of peripheral site
Define neurovirulent virus
Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death
Define tropism
The specificity / affinity of a virus for a particular host tissue
Define pantropic viruses
can replicate in more than one host organ/tissue
What is the mechanism of viral injury and disease?
Virus-cell interactions
What are the outcomes of viral injury?
Cell lysis following virus replication Apoptosis Oncoviruses Persistent Infection - viruses remain latent or dormant in host cell for long periods, escaping detection Immunosupression
What are oncoviruses?
Oncogenic viruses; viruses that cause cancer
Define virus shedding
Shedding of infectious virions is crucial to the maintenance of infection in populations
Define acute infection in terms of shedding
Usually intensive shedding over short period of time
Define persistent infections in terms of shedding
Can be shed at lower titers for months to years
Describe viral injuries that effect the skin.
Can be localized or dissminated.
Ulcer
Nodule
Wart
Erythema
What is a vesicle on the skin?
fluid filled sac
Define ulcer
Opening in the skin caused by sloughing of necrotic tissue, extending past the epidermis
Define nodule
Solid tumorous mass
Define warts
Benign; skin growth that appear when a virus infects the top layer of skin
Define erythema
reddening of the skin
How do viruses get into the GI tract?
Ingestion or from the blood, systemic infection
What happens once a virus enters the GI tract? What are the physical symptoms?
Intestinal enterocytes are destroyed resulting in malaabsorption and diarrhea resulting in dehydration, acidosis, and hemoconcentration
How do viruses effect the respiratory tract?
inflammation
obstruction of air passages
hypoxia and respiratory distress
What is necrosis?
Death of body tissue
What is perivascular cuffing?
Inflammatory cells around blood vessels in CNS
How do viruses effect the hemopoietic system?
damage to epithelium- blood clots form throughout body followed by hemorrhages
viral infection of the fetus- teratogenic viruses
Define teratongenic viruses
Cause developmental defects of embryo or fetus after in-utero infection
