Do non-pathogenic viruses exist?
What viral process causes damage to the host?
What is the difference between pathogenicity and pathogenesis?
Pathogenicity: ability of a virus to cause disease
Pathogenesis: manner or mechanism of development of a disease
What is virulence?
measure of the degree of pathogenecity of an infecting virus
T/F: Virulence is an absolute property of viruses
Depends on many different factors: viral, host, and environment
What viral factors affect the virulence of a pathogen?
Genetic makeup Portal of entry Tropism to host organs dose of infection immuno evasion capabilities
What is the LD50?
Lethal dose 50 = the dose of virus required to cause death in 50% of animals
What is the ID50?
Infectious dose 50: The dose of virus that will infect 50% of an experimental group of hosts/animals
T/F: If Virus A has an LD50 of 30 and Virus B has an LD50 of 100: Virus B is more virulent
Virus A is more virulent bc it takes less virus to kill 50% of the population
What protective barriers/factors must a virus surpass to enter a host through the skin?
Outer layer of keratin Low pH Presence of fatty acids Baterial flora Dryness Components of innate and adaptive immunity
How do viruses enter through the skin?
Bite of arthropods
Bite of an infected aniaml
Contaminated objections (like needles etc)
**a virus can never enter through healthy, non compromised skin. Must be a breach
What are some examples of MM viruses can enter the host?
What host defenses are present in the GI tract?
MM of oral cavity and esophagus Acidity of the stomach Alkalinity of the intestine Mucus covering the gut Lipolytic activity of the bile proteolytic activity of the pancreatic enzymes Defensins, IgA, Macrophages
What hose defenses are present in the respiratory tract?
Nasal and bronchus associated lymphoid tissue
What is the order of virus spread when entering through the epithelium?
- Spread of virus on the epithelial surface –> localized infection
- Spread to subepithelial– invasion and lymphatic spread
- To the blood stream and spread systemically
What is the difference between a disseminated infection and a systemic infection?
Disseminated infection: Infection that spreads beyond the primary site of infection
Systemic infection: When a number of tissues or organs are infected
Apical release of viral particles from the epithelium facilitates what?
apical surface is in contact with vascular lumen
Basolateral release of viral particles from the epithelium facilitates what?
Basolateral release provides access to underlying tissues
T/F:Viremia is the presence of virus in the blood
What is the difference between PRIMARY and SECONDARY viremia?
Primary: initial entry of virus into the blood after infection
Secondary: Virus has replicated in major organs and re-enters of the blood circulation
How does one get PASSIVE viremia?
Direct inoculation of virus into the blood. Ex: Arthropod bites, contaminated syringe
T/F: Contracting west nile virus from a mosquito is an example of primary viremia
This is PASSIVE viremia
What is active viremia?
Viremia following initial virus replication in epithelial cells –>lymphatics –> then passed into the blood stream
What cell can some viruses use to travel undetected through blood tissue barriers?
What are neurotropic viruses?
Viruses that can infect neural cells. Infection may occur by neural or hematogenous spread
What are neuroinvasive viruses?
Viruses that enter the CNS - AFTER infection of a peripheral site
What are neurovirulent viruses?
Viruses that cause disease of nervous tissue, manifested by neurological symptoms and often death
T/F: Herpes simplex virus exhibits low neuroinvasiveness and high neurovirulence
It rarely enters the CNS - but when it does the consequences are always severe if not fatal
The rabies virus exhibits _________ neuroinvasiveness and ________ neurovirulence
HIGH and HIGH
If a virus is said to have Retrograde spread, what direction is it spreading in relation to nerve impulse flow?
Opposite direction of nerve impulse flow
Invades axon terminals –> Dendrite or cell body –> crosses synapse to reach the next axon terminal
T/F: If a virus is moving via anterograde spread it is traveling in the direction of nerve impulse flow
Dendrites or cell bodies –> axon terminals –> crosses synaptic contacts to invade the next dendrite or cell body
T/F: Neural spread of viruses to the CNS can occur through olfactory routes
What are three ways viruses can spread to the CNS through the BBB?
- increase permeability of the endothelial cells via secretion of TNF
- Breakdown of endothelial cell junctions through matrix metalloproteinase (MMP)
- Trafficking through monocytes
What kind of viral shedding occurs in an acute infection, and for how long?
Acute infection= intensive shedding over a short period of time
T/F: Persistent infections can be shed at high titers for months to years
shed at LOW titers for months to years
What is viral tropism?
The specificity or affinity of a virus for a particular host tissue
What is special about pantropic viruses?
Can replicate in more than one host organ or tissue
What are some skin injuries of viral infections?
Rash, vesicles, ulcers, nodules, warts, papules, erythema
Viral infection to the GI tract can occur in what two ways?
Ingestion and hematogenous spread/systemic infection
What pathogenesis may occur due to viral infections in the GI tract?
Destruction of enterocytes due to viral replication - hypersecretion
GI dz, malabsorption, diarrhea
pronounced dehydration, acidosis, hemoconcentration
What damage can occur to the villi of the GI tract due to virus replication?
Blunting, fusion of villi, atrophy
What damage may occur in the Respiratory tract due to a viral infection?
Loss of ciliary activity, loss of integrity of the lining mucosal layer, destruction of epithelium, inflammation, exudation, influx of inflammatory cells, airway obstruction - respiratory distress, secondary bacterial infection
When a virus infects the CNS, what injuries would you expect to occur?
Encephalitis or encephalomyelitis characterized by neuronal necrosis, phagocytosis of neurons (neurophagia), and perivascular infiltrations of inflammatory cells (perivascular cuffing)
What neuronal injury does canine distemper cause?
What is a neuronal injury caused by prion diseases that can be observed on histo?
Damage to the endothelium by a virus can be observed grossly by what lesions?
Petechia (pin point hemorrhages) and ecchymoses (larger areas of hemorrhage)
T/F: Viruses of the hemopoietic system can lead to DIC
clots form in small blood vessels all over the body - clotting factors get used up –> that is followed by systemic hemorrhage and multi organ failure
What is teratogenesis?
Abnormal development or arrests in development of an embryo or fetus - due to a viral pathogen
*may result in death or malformations during the antenatal period
A tissue injury mediated by host immune response to a virus infection is called what?
Virus induced immunopathology
*depends on the delicate balance between the protective and destructive effects of the host immune response to viruses
What are some examples of immunopathology due to viral infections?
- tissue damage mediated by hypersensitivity reactions
- Autoimmune dz
- Inflammation-mediated tissue damage (fibrosis)
- Immunodeficiency disorders
What cells play a crucial role in cell mediated lysis and killing of infected host cells?
Cytotoxic T cells (CD8+)
The release of cytokines from what cells can contribute to inflammation associated with viral infections?
CD4+ and CD8+ T cells
Persistent activation of what receptors of innate host cells caused by viruses, will increase the production of pro-inflammatory cytokines and interferons?
T/F: Injury can due to viral infections can be mediated by free radicals such as nitric oxide and superoxide
Can antibody responses to viruses contribute to tissue damage?
Toxicity from antibody response
Feline infectious peritonitis can cause what immune complex dz?
Immune complex-mediated vasculitis
T/F: Viruses can cause immunosuppression
virus induced immunopathology
**Infectious burasal dz - virus replication causes atrophy of the bursa which creates a deficiency of B lymphocytes = immunosuppression
What is an inapparent infection?
When an animal is infected with a virus but shows no clinical signs
- too few cells may be infected
- stimulate host immune response
- possible source of virus spread
T/F: Acute infection or short infection has a rapid clearance from host immune response
Short clinical course and rapid clearance from host immune response
T/F: If an animal has a latent viral infection, they can/will test positive for the infecting virus
Latent infections: infectious virus is not demonstrable except when reactivation occurs. Reactivation is usually stimulated by immunosuppression or cytokines or hormones
T/F: Acute infection followed by latent infection - means that the virus is continuously shed from or is present in infected tissue
Latent should be replaced with CHRONIC to make this correct
What is a slow persistent infection?
Prolonged incubation period lasting months or years
*usually a slow progressive, lethal dz
Which once of the following is NOT usually a feature of persistent viral infection?
- Virus may remain dormant in host cell
- Reactivation (clinical dz) occurs during stress
- Intermittent shedding of virus for long periods
- Rapid clearance from host immunity
Characteristic of acute viral infections
A virus is continuously shed from or is present in infected tissue. What type(s) of infection is this?
T/F: Latent viral infections can evade the immune system
bc they are not active or producing proteins, so they are hidden
Can a chronic infection occupy any part of the body?
No. There are specific organs where chronic viral infections will reside
T/F: Slow persistent infections are characterized by a fast incubation period followed by slow onset of clinical dz.
SLOWWWWWW incubation period