Virus/host interactions (animal)

Question 1

what are the main routes of entry of virus infection?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

are virus’ target organs the first ones they infect?

Answer 3

not always

Question 4

what is the primary viremia?

Answer 4

initial infection site

Question 5

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

Answer 5

secondary viremia

• nervous system
• circulatory system

Question 6

define pathogenesis

Answer 6

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

Question 7

what is viral persistence?

Answer 7

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

Question 8

define latency

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

what is dissemination and what is required for it?

Answer 11

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

Question 12

what is localised spread? give examples

Answer 12

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

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

Question 13

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

Answer 13

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.

Question 14

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

Answer 14

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)

Question 15

what are cytopathic effects?

Answer 15

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.

Question 16

what is viral shedding?

Answer 16

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)

Question 17

what can plant viruses use for dissemination?

Answer 17

insect vectors (some viruses can even replicate inside insects)

Question 18

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

Answer 18

Rabies

Herpes

Question 19

what is an example of a prion?

Answer 19

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

Question 20

what are systems can viruses infect?

Answer 20

1) iimmune
2) digestive
3) nervous

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

how does the herpes simplex virus avoid the immune system?

Answer 23

• 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

Question 24

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

Answer 24

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

Question 25

how can viruses evade the immune system generally?

Answer 25

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

Question 26

why are RNA viruses difficult to form vaccines for?

Answer 26

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

Question 27

What two tyoes of host defenses are there?

Answer 27

non specific

induced defenses

Question 28

what are smallpox target organs?

Answer 28

smallpox=respiratory mucosa, spleen,

bone marrow, lymph nodes

Question 29

what are measles target organs?

Answer 29

lymphatic and respiratory systems,

skin, brain

Question 30

what are some non-specific host defenses?

Answer 30

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)

Question 31

what are some specific induced host defenses?

Answer 31

NK cells

Interferon production

Question 32

phagocytosis outcomes wrt viruses?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

what do interferons cause?

Answer 34

-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

Question 35

what are 2 interferon examples?

Answer 35

IFN alpha

IFN beta

Question 36

what does NK stand for?

Answer 36

non-specific viral killing cells

Question 37

To NK cells kill all viruses?

Answer 37

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

relatively low

Question 38

How do NK cells work?

Answer 38

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.

Question 39

Further examples of viruses avoiding the highly effective immune system:

Answer 39

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.