Virus/host interactions (animal) Flashcards by Helen Finney

what are the main routes of entry of virus infection?

respiratory tract (Influenza)
oral cavity(hepatitis a)
genital tract(herpes,HIV)
skin,from insect bites and cuts (rabies,yellow fever)

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what is interesting about the respiratory tract and different influenza types?

it is a traget organ that has different levels of pathogenesis
Normal flu- TOP of tract,yearly epidemic,easy spread,but already have antibody cross-recognition.
Bird flu- lower down, harder to pass on but more fatalities

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are virus’ target organs the first ones they infect?

not always

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what is the primary viremia?

initial infection site

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what are the principle routes of spread after infection called and give 2 examples.

secondary viremia

nervous system
circulatory system

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define pathogenesis

when damage to a target organ is caused due to a high number of dead cells

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what is viral persistence?

when virus persists for a long time period and has modulated the immune system and itself

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define latency

virus lies dormant within a cell and this is denoted as lysogenic part of life cycle

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Is HiV a persistent virus? if so, why is it not recognized by the immune system?

HIV is a very persistent virus,it is integrated into DNA and downregulates surface proteins so that it is not recognised by the immune system. If there is a deep reservoir–> life infection

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how is a latent virus reactivated? what external factors cause this reactivation?

a change in transcription factors detects 1)UV 2)cell stress 3)immunodeficiency
4)another virus

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what is dissemination and what is required for it?

spread of the virus around the body for example in the blood. From entry portal–> target organ.

NEEDS A LARGE AMOUNT OF REPLICATION ONCE AT TARGET ORGAN TO CAUSE DISEASE

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what is localised spread? give examples

if the target organ=portal of entry 
-Flu
-Polio
Colds
-other alimentary tract infections

*1 Virus may not be enough to infect (NORA-vomiting)

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what are prions and what are their target organ? how is their movement similar to viruses’?

proteins. The target organ is the brain and they are thought to have membrane anchors and use nerve cells to move in a similar way to viruses.

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Describe the rabies viruses’ journey from infection portal–> target organ

1) virus in saliva
2) virus in skin cells after biting (little damage here)
3) moves through CNS
4) moves to salivary glands (target organ)

if enough viral replication, pathogenesis can occur from direct cytopathic effects (if enough cells in target organ are killed)

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what are cytopathic effects?

the effects on cells due to viral infection. structural change can cause host cell lysis or can cause death without lysis due to rendering the cell unable to reproduce.

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what is viral shedding?

the expulsion and release of virus progeny following successful reproduction during a host-cell infection. (if virus now present in bodily fluids can be transmitted on to other people)

what can plant viruses use for dissemination?

insect vectors (some viruses can even replicate inside insects)

what viruses use the nervous system as secondary viremia/for dissemination?

Rabies

Herpes

what is an example of a prion?

Kuru (causes incurable degenerative neurological disorder endemic to tribal regions of Papua New Guinea)

what are systems can viruses infect?

1) iimmune
2) digestive
3) nervous

how do HTLV-1 and 2 (leukemia) avoid immune system?

the yare retroviruses common in japan and are integrated into host genome

how do the Epstein Barr virus avoid detection from immune system?

it is actually mainitined IN the immune system. inside B lymphocytes. It also escapes the immune system by down regiulation of virus and cell gene expression by EBV protein

how does the herpes simplex virus avoid the immune system?

maintained in the immune system
hides in nerve cells in brain
cold sores clear and reappear
cells hidden as they are latent and restricting expression
they are activated by UV and stress
even if they are killed persist in the nervous system due to a pool of viral reservoir in brain ganglion

what are 3 examples of viruses that have evolved to evade the immune system ?

herpes simplex virus
HTLV-1 and 2 LEUKEMIA
Epstein barr virus EBV

how can viruses evade the immune system generally?

1) avoidance of neutralising antibodies by preading directly cell-cell 2) genetic and antigenic variation(QUAISI species) 3) inhibition of immune and nonspecific responses 4) becoming latent 5) budding into cytoplasmic vacuoles

why are RNA viruses difficult to form vaccines for?

they have consatnt genetic variation due to being a quaisi species (polio=exception)

What two tyoes of host defenses are there?

non specific | induced defenses

what are smallpox target organs?

smallpox=respiratory mucosa, spleen, | bone marrow, lymph nodes

what are measles target organs?

lymphatic and respiratory systems, | skin, brain

what are some non-specific host defenses?

1) anatomic barriers skin,mucus 2) non specific inhibitors- Temp (affects viral replication) so fever inflammation 3) phagytosis (works better for bacteria as some viruses have incorporated this inti life cycle as a counter defense)

what are some specific induced host defenses?

NK cells | Interferon production

phagocytosis outcomes wrt viruses?

1) virus disruption (Influenza and HSV) 2) virus survival (HIV) 3) WORST -virus multiplication (high virulence HIV and herpes virus')

How long do T cells take to activate and are they specific?

more specific than NK cells but take a while to activate. They are very effective though if virus has no counter response.

what do interferons cause?

-induction of ‘viral state’ in cells -an increase MHC class I expression and antigen presentation in all cells -activation of NK cells to kill virus-infected cells

what are 2 interferon examples?

IFN alpha | IFN beta

what does NK stand for?

non-specific viral killing cells

To NK cells kill all viruses?

no they do not kill all viruses but keep the viral titre | relatively low

How do NK cells work?

1) increases MHC class 1 conc on normal cells only 2) MHC 1 inhibits the killer receptors,NK does not kill normal cell 3) infected cell will have altered or absent MHC1 so cannot stimulate negative signal. NK cell is triggered by signals for activating receptors 4) activated NK releases granule contents inducing aptosis in target cell.

Further examples of viruses avoiding the highly effective immune system:

1) influenza CAP SNATCHING 2) some viruses try to prevent binding of t-cell (note-sometimes this catually makes them more open to NK cells) 3) some produce deploy antigens e.g ebola that washed deploy antigen through the body to wipe out antibodies.