Host-Pathogen Interactions Flashcards
________ is the ability of a virus to cause disease in a host
Pathogenicity
_________ refers to the mechanism of development of a disease
Pathogenesis
What is virulence?
Quantitative measure of the degree of pathogenicity of a virus
**not an absolute property of a virus, depends on many variables
What is LD50?
Dose of a virus that causes death in 50% of animals
What is ID50?
Infectious dose 50
dose of a virus that will infect 50% of an experimental group
LD50 of 15 vs LD50 of 45, which is more virulent?
LD50 of 15
What mechanisms of defense does the skin have against viruses?
- Dense keratin layer
- Low pH
- Dryness
- Fatty acids
- Bacterial flora
- Components of innate and adaptive immunity
How can viruses enter through skin?
- Bite of arthropod
- Bite of animal
- Contaminated objects/ needles
What are routes of entry for a virus?
- Skin
- Mucus membranes
- GI tract
- Respiratory tract
What mechanisms of defense does the GI tract have against viruses? (9)
- MM of oral cavity
- Acidity of stomach
- Alkalinity of SI
- Layer of mucus
- Activity of bile
- Pancreatic enzymes
- Macrophages
- IgA
- Defensins
What mechanisms of defense does the resp tract have against viruses?
- Mucociliary blanket
- Alveolar macrophages
- NALT
- BALT
- Temp gradient
What is a disseminated infection?
One that spreads beyond primary site of infection
What is a systemic infection?
If a # of organs are infected
_________ of viruses from the infected epithelium is critical to subepithelial spread
Directional shedding
_______ release provides access to underlying tissues and facilitates systemic spread
Basolateral
________ release facilitates virus dispersal
Apical
What is viremia?
Presence of virus in blood
True or False: A virus may be free in blood or in a cell
TRUE
What is primary viremia?
Initial entry of a virus into the blood after infection
What is secondary viremia?
Virus that replicated in major organs and once more entered circulation
What is passive viremia?
Direct inoculation of virus in host, no initial replication elsewhere in host
Ex: contaminated syringe or bite of arthropod
What is active viremia?
Viremia following initial virus replication in host.
Release of virions from initial site of replication
True or False: Tick bites can transmit some viruses directly into the blood. This is called active viremia
FALSE - passive viremia
What is a neurotropic virus?
Virus that infects neural cells
Infection can occur by neural or hematogenous spread
What is a neuroinvasive virus?
Viruses that enters the CNS after infection of a peripheral site
What is neurovirulent virus?
Viruses that cause disease of nervous disease manifested by neuro symptoms and sometimes death
What does it mean for a virus to have low neuroinvasiveness but high neurovirulence?
Virus always enters peripheral nervous system and rarely enters CNS
when it does enter CNS, consequences are severe/fatal
What does it mean for a virus to have high neuroinvasiveness but low neurovirulence?
Infection invades the CNS but neuro disease is mild
What does it mean for a virus to have high neuroinvasiveness and high neurovirulence?
Virus infects peripheral nervous system and spreads to CNS with 100% lethality unless given antivirals shortly after infection
What is retrograde spread?
Virus travels in opposite direction of nerve impulse
What is anterograde spread?
Virus that travels in the same direction of a nerve impulse
How can viruses spread to the CNS?
- Olfactory routes
- Through the BBB
Secretory IgA is important in ___________ infections
Localized acute
________ infections have a long incubation period
Systemic acute
________ infections can cause pathology at distant sites
Systemic acute
_________ infections have no viremia
Localized acute
__________ is characterized by intensive shedding over a short period of time
Acute infection
What is a persistent infection?
Infection shed at low titers for months to years
What is tropism?
Specificity/ Affinity of a virus for a particular host tissue
What is a pantropic virus?
Virus that can replicate in more than 1 host organ/tissue
A family of viruses may prefer a particular organ for effective replication. The term used to describe this is _________-
Tropism
__________ is a small distinct elevation with fluid
Vesicle
_________ is a solid, palpable, elevated mass with distinct borders, extending deep into the dermis
Nodule / Tumor
What are warts?
Benign skin growths that appear when a virus infects the TOP layer of skin
_________ is an opening of the skin caused by sloughing of necrotic tissue, extending past the epidermis
Ulcer
What is a papule?
Solid elevation WITHOUT fluid, sharp borders
What is erythema?
Reddening of the skin
** consequence of viral infection
How do viruses cause damage to the GI tract?
First enters GI tract via ingestion or hematogenous spread/systemic infection
- Destroys enterocytes due to viral replication
- GI disease, malabsorption, diarrhea
- Dehydration, acidosis, hemoconcentration
What injuries are caused by viruses entering the resp tract?
- Loss of cilia
- Loss of mucus
- Inflammation
- Obstruction of airways
- ***secondary BacT infection (VIRAL-BACTERIAL SYNERGISM)
- Hypoxia
What injuries are caused by viruses entering the CNS?
- Encephalitis or encephalomyelitis characterized by neuronal necrosis
- Neurophagia -Phagocytosis of neurons
- Perivascular cuffing - perivascular infiltrations of inflamm cells
- Progressive demyelination
- Neuronal vacuolation
Which virus enters the CNS and causes progressive demyelination?
Canine distemper virus
What injuries are caused by viruses damaging the endothelium?
- Petechial and ecchymotic hemorrhages
- DIC (blood clots in small vessels)
- Edema
- Infarction / ischemic necrosis
__________ are larger areas of hemorrhage with ill defined margins
Ecchymoses hemorrhage
What does petechiae hemorrhage look like?
small pinpoint lesions
What is teratogenesis?
Abnormal development or arrests in development of the embryo or fetus
results in death or malformations during antenatal period
What is virus induced immunopathology?
tissue injury mediated by host IR to virus infection
depends on balance between protective and destructive effects
________ is the cause of damage with viruses that are non-cytolytic and persistent
Immunopathology
What are results of immunopathology?
- Tissue damage from hypersensitivity rxn
- Autoimmune dz (Ex: moon blindness in horses)
- Inflammation-mediated tissue damage (ex: Fibrosis)
- Immunodeficiency
What are mechanisms of virus induced immunopathology?
- The role of T cells
- cytotoxic killing of host cells
- cytokines from CD4+ and CD8+ cause inflamm. that becomes chronic against persistent infection - TLRs - persistent activation causes production of pro inflamm cytokines
- Injury mediated by free radicals like nitric oxide and superoxide
- Toxicity from Ab response
- Vasculitis mediated by immune complex formation
What is infectious bursal disease?
immunosuppression from viral induced immunopathology
- virus caused atrophy of bursa of fabricius resulting in deficiency of B cells and immunosuppression
What are characteristics of an inapparent infection?
- No CS or symptoms
- Few cells infected
- Stimulates host IR
- Possible source of virus spread
What are characteristics of an acute infection?
= short term infection
- obviously lasts a short time
- rapid clearance from host IR
What are characteristics of a latent infection?
= persistent infection
- infection not detectable until reactivation occurs
-reactivated due to immunosuppression or by the action of a cytokine or hormone
What are characteristics of a chronic infection?
= persistent infection
- continuous shed of virus
-usually limited to a specific infected tissue
What are characteristics of a slow infection?
= persistent infection
- prolonged incubation time, months-years
-slow, progressive, lethal dz
Ex: prions
