Lecture 3 1/31/24 Flashcards
What is adsorption?
the initial interaction between a virus and a cell’s surface
What are the characteristics of adsorption?
-contact only, no entry
-reversible
-initiated at random
-mediated by weak bonds and other factors
How does viral concentration relate to the chance of infection?
higher viral concentration makes infection of the cell more likely
What is viral entry dependent on?
a virus’ ligand interacting with a complementary cell surface receptor
Why is it a misnomer to refer to a cell surface receptor as a viral receptor?
-cells do not have receptors that are specific for viruses
-viruses exploit cell surface molecules to gain entry to the cell
What are the characteristics of viral attachment through receptors?
-some viruses use different receptors based on the cell type
-some viruses can infect many different animal species by adapting to various receptors
-subtle amino acid changes in the receptor affect species susceptibility
What are the two general strategies viruses use to enter the cell?
-endocytosis
-fusion with plasma membrane
What factors impact the route a virus uses to enter the cell?
-cellular receptor functions
-factors such as pH
How can plasma membrane fusion be involved during viral replication?
-single viral-infected cell can fuse with a neighboring cell due to build up of viral fusion proteins during replication
-this fusion allows for the infected cell to spread the virus to the neighboring cell
Why is viral growth not exponential?
one virion is able to make millions of copies
What is the infection period?
period in which the virus attaches to and enters the host cell
What is the eclipse period?
period in which the viral genetic material is uncoated, and viral particles are no longer detected
What is the latent period?
time from the onset of infection to the appearance of virus extracellularly (aka released from the cell)
What is pathogenesis?
process by which disease develops in the host
What is virulence?
measure of pathogenicity of a virus to cause disease in certain species
Does high virulence always indicate high infectivity?
no
How do virulence and pathogenicity differ?
-virulence refers to the severity of a pathogen to cause infection, while pathogenicity is the ability of a pathogen to cause infection
-virulence is quantitative in nature, while pathogenicity is qualitative
-virulence is measured by the ability of the pathogen to cause death, while pathogenicity is measured by virulence factors that enhance pathogen’s evasion mechanisms
What is a localized infection?
infection that remains at the site or system originally affected
What is a disseminated/systemic infection?
infection that spreads beyond the primary site
What is viremia?
presence of virions in the blood
How does a virus enter the bloodstream?
-virus infects epithelial cell and is able to infect the sub-epithelium through cytopathic effects
-virions enter the ECF/lymph, replicate in lymph node, and enter blood through lymphatic ducts
What is passive viremia?
initial wave of viremia in which the virus is introduced into the blood
What is active viremia?
result of viral replication within the bloodstream
What is primary active viremia?
virus released into blood after initial replication in host
What is secondary active viremia?
increased viral replication due to dissemination to other organs
What are the factors involved in chain of infection?
-pathogen
-reservoir
-portal of exit
-mode of transmission
-portal of entry
-susceptible host
What are the potential routes of transmission?
-droplets through conjunctiva
-inhalation into resp. tract
-direct contact
-fomites
-vertical transmission
-sexual transmission
-insect/arthropod vectors
-iatrogenic
How do different body systems shed virus?
-resp. tract: mucus, saliva, aerosols
-GI tract: diarrhea, vomitus
-skin: crusts from lesions, vesicle fluids
-urogenital tract: urine, semen, aborted fetal tissues
-mammary gland: milk
How are enveloped viruses best transmitted, since they do not survive in the environment long?
direct contact
What other factors can impact viral transmission?
-seasonality
-geography
-humidity
-vector availability
What are the characteristics of skin as a barrier/infection site?
-most viruses cannot enter intact skin
-viruses enter through skin defects, such as cuts, bites, via vectors, or iatrogenic means
-infection often seen as a rash
-may infect skin cells directly or cause lesions by infecting underlying blood vessels
What are macules?
localized dilated blood vessels
What are papules?
solid elevations of skin that may be crusty
What are vesicles?
fluid filled popular lesions
What are the characteristics of the eyes as a barrier/infection site?
-tears and eyelid movements can flush viruses
-some viruses infect superficial parts of eye and cause conjunctivitis or keratitis
-trauma or immunosuppression can predispose host
-viral uveitis results from systemic viral infection (CAV-1), but seen in eyes
What are the characteristics of the resp. tract as a barrier/site of infection?
-most common route of exposure
-coughing/sneezing can aerosolize virus
-ciliated epithelium, mucus, and IgA provide protection in URT
-alveolar macrophages inactivate inhaled virions in LRT
-localized and systemic disease possible
What are the characteristics of the GI tract as a barrier/site of infection?
-peristalsis, microbiome, and pH can prevent infection
-GI viruses have evolved to exploit or resist harsh GI environment
-often cause localized disease with vomiting and diarrhea
