Virus Pathogenesis Flashcards
T/F: Virulence is an absolute property of a virus, regardless of any variables.
FALSE - depends on many things!
The dose of virus needed to cause death or infection in 50% of test subjects is known as:
LD50
ID50
Will a more virulent virus have a higher or lower LD50 or ID50?
Lower - takes less virions to do the same job
Steps in viral infection
Entry and replication Spread, tropism, infection of target organs Virus-cell interactions Tissue and organ injury Shedding
What are the skin’s defenses against infection?
Dense keratin layer Low pH Fatty acids Normal flora Dryness Immune cells
Transcutaneous routes of pathogen entry
Arthropod bite
Bite of infected animal
Contaminated objects (needles)
What are the GI tract’s defenses against infection?
Mucous Stomach acidity Intestinal alkalinity Bile and Pancreatic enzymes Defensins/ IgA/Macrophages
What are the respiratory tract’s defenses against infection?
Mucous
Alveolar macrophages
NALT/BALT
Temperature gradient
What type of infection spreads beyond the primary site?
Disseminated
What direction of viral shedding from cells facilitates systemic spread?
Basolateral release - gives access to underlying tissues
What direction of viral shedding from cells facilitates virus dispersal?
Apical release
________ _______ is the initial entry of the virus into the bloodstream following infection.
Primary viremia
______ ______ happens after the virus has replicated in major organs and once again entered the bloodstream.
Secondary viremia
________ _______ is a direct inoculation of a virus into the blood, such as by arthropod bite or contaminated syringe.
Passive viremia
What are neurotropic viruses?
viruses that can infect neural cells
What kind of viruses are able to enter the central nervous system after infection at a peripheral site?
Neuroinvasive viruses
What kind of viruses cause disease of nervous tissue, manifested as neurological symptoms and often death?
Neurovirulent viruses
If a virus always enters the PNS, but rarely the CNS, and causes severe symptoms/death when it does enter the CNS, it is considered to have ___ _______ but ___ _______.
Low neuroinvasiveness and high neurovirulence
If a virus almost always enters the CNS, but rarely causes neurological disease it is considered to have _______ and ____ _______.
Neuroinvasiveness and low neurovirulence
If a virus readily spreads from the PNS to the CNS and causes death 100% of the time without prompt antiviral medication it is considered to have ____ ______ and ____ ______.
high neuroinvasiveness and high neurovirulence
When a virus travels in the opposite direction of neural impulse flow, from axon terminal to dendrite/cell body, it is called __________ spread.
retrograde
When a virus travels in the direction of neural impulse flow, from dendrite/cell body to axon terminal, it is called ______ spread.
anterograde
What are 2 routes a virus can take to spread to the CNS?
Olfactory
BBB
What type of infection features intensive shedding over a short period of time?
Acute
In what type of infection does a virus spread at low titers for months or years?
Persistent
Definition of pantropic virus
Virus that can replicate in more than one host tissue/organ
Fluid filled sacs or elevations in the skin
Vesicles
An opening in the skin caused by sloughing of necrotic tissue, extending past the epidermis
Ulcer
Palpable, solid, elevated mass. Distinct borders and can be extending deep into the dermis.
Nodule or tumor
Benign skin growths that appear when a virus infects the top layer of skin
Warts
Solid elevations on the skin without fluid
Papules
Reddening of the skin (can be a consequence of systemic viral infection).
Erythema
Gastrointestinal infection can happen via which 2 pathways?
Ingestion
Hematogenous spread/systemic infection
Effects of viral infection on the intestinal tract
Destruction of enterocytes and hyper secretion, leading to GI disease, malabsorption, and diarrhea, causing dehydrating, acidosis, and hemoconcentration.
Effects of viral infection on the respiratory tract
Loss of ciliary activity and integrity of mucus layer
Destruction of epithelium Inflammation Exudation Influx of inflam cells Obstruction of airways Hypoxia/distress Secondary infection
Effects of viral infection on the CNS
Encephalitis Encephalomyelitis Neuronal necrosis Neuronophagia Perivascular cuffing Demyelination Neuronal vacuolation
Effects of viral infection on the hematopoietic system
Damage to endothelium (hemmorrhage)
Disseminated Intravascular Coagulation
Edema
Infarction
What happens during DIC?
A bunch of clots form in the small vessels, restricting blood flow and causing multi-organ failure. After that, coagulation factors are all used up which leads to hemorrhage throughout the body.
The abnormal development or arrest in development of the embryo or fetus.
Teratogenesis
*May lead to death or malformations during the antenatal period.
T/F: During the body’s immune response against infection, tissue injury to the host can occur.
TRUE - Virus-Induced Immunopathology.
*depends on a balance between the protective and destructive effects of the host immune response
What are some manifestations of Immunopathology?
Tissue damage d/t hypersensitivity reactions
Autoimmune diseases (moon blindness)
Inflammation-mediated tissue damage (fibrosis)
Immunodeficiency disorders
The roll of T cells in virus-induced immunopathology
Cytotoxic T cell mediated lysis of infected host cells
Release of cytokines from CD4+ and CD8+, and other cells, that cause inflammation and tissue damage. (Chronic in persistent infections)
Role of TLRs in virus-induced immunopathology
Persistent activation of these receptors leads to production of pro-inflammatory cytokines and interferons (^^ inflammation)
T/F: Production of ROS to combat viral infections will only harm the pathogens.
FALSE - ROS can also injure nearby host cells
How do antibodies contribute to immunopathology?
Binding of Ab to an infected cell activates the complement system and initiates an inflammatory reaction
What’s an example of virus-induced immunopathology leading to immunosuppression?
Infectious Bursal Dz: viral replication causes atrophy of the Bursa of Fabricius in birds, leading to a deficiency in B lymphocytes.
What type of viral infections may not be detected clinically and may lead to spread of the virus?
Inapparent infections
In what type of infection is the virus not demonstrable except in cases of immunosuppression or cytokine activation when it is reactivated?
Latent (persistent) infections
Foot and Mouth Dz in cattle tends to stay in and shed from infected tissue after acute disease. This is an example of what kind of infection?
Chronic (persistent) infection
Prion diseases have a prolonged incubation period that lasts months or years, during which time numbers of infectious particles gradually increase, and eventually cause a progressive lethal disease. This is an example of what kind of infection?
Slow (persistent) infection
What kind if infection is cleared rapidly by the host immune system?
Acute infection
