Viral infection and Pathogenesis 1

Question 1

Methods of breaching the skin to cause infection

Answer 1

Abrasion- pox, papilloma
Bite- rabies
Injection- arbo eg west nile

Question 2

Local skin infection eg

Answer 2

Papilloma virus -DNA, non enveloped, wide host range
Doesn’t breach BM so no blood supply or imm resp so not elim
Rare to spread towards BM usually spread away as it needs the cell in cell cycle to repl and cells mature and go into cell cycle as they move away from the BM

Question 3

Major GI tract barriers and eg viruses

Answer 3

Low pH
Proteases
Bile

Rota, parvo, corona, calici, astro

Question 4

GIT route of transmission

Answer 4

Faeces/diarrhoea eg enteric

Saliva in licking, grooming, biting eg herpes and rabies

Question 5

Local gut infection eg

Answer 5

Rotavirus rna virus nonenveloped
Infects cells at tips of villi in small intestine that absorb fluid and causes diarrhoea
Villi shorten as preferentialy infects the tips and kills the tip cells which grow back post infection

Question 6

Major resp tract barriers and eg viruses

Answer 6

Ciliated epi
Mucous lining
Temp

Influenza, rhino, RSV

Question 7

Local Resp tract infection transmission routes

Answer 7

Saliva
Coughs
Sneezes causing airborne droplets

Question 8

Local Resp tract infection influences

Answer 8

Less than 5mM persist longer and penetrate deep in lung
Over 5mM cleared from lung
Temp influence as rhinovirus infect cooler regions of upper resp tract whereas RSV infect lower regions of resp tract (warmer regions)

Question 9

Entry into blood system

Answer 9

Directly eg via arthropod vector or via lymphatics (common route)

Question 10

Lymphatic spread to blood

Answer 10

Virus traverse epi and exposed to tissue macro can enter lymphatic syst
Carried to local lymph nodes and exposed to further macro at each stage virus may be engulfed, degraded and antigens presented to t cells to initiate imm resp, but some viruses repl inside macrophages eg FIPV, canine distemper, maedi-visna causing incr virus output. Some virions will pass straight through the lymphatics into the blood

Question 11

Viremia

Answer 11

Presence of virus in the blood. Once in blood can localise to any body part in minutes
Either cell free - FMD, flavi, toga, entero
Or cell assoc; mono (maedi-visna), lympho (CDV), neutro (FeLV), macro (african swine fever)

Question 12

Cells encountered by virus in blood that determine pathogenesis

Answer 12

Reticulo-endo cells (eg macro)

Vascular endo cells

Question 13

Virus interaction with RE cells

Answer 13

Maybe phagocyt, sestroyed and presented to imm syst (v efficient so viremia only maintained if virions enter blood as quickly as they are removed)
May res phagocyt causing prolonged viremia
Post phagocyt virus could repl in macro causing incr viremia

Question 14

Virus interaction with endo cells

Answer 14

Vasc endo is blood-tissue interface and so is barrier for particles eg virions
Parenchymal invasion by virus in most organs dep on localisation of birus in capillary and venule endo cells where barrier is thinnest
Virions can passively transfer accross or may infect endo cells to pass through

Question 15

Mouse pox description

Answer 15

Dna virus with several hijacked genes from host cells (key virulence determinants)

Question 16

Mouse pox pathogenesis

Answer 16

Virus enters body
Into lymph node (1d)
Into blood
Into spleen and or liver (3-4d)
2o viraemia back into blood
Into skin (6d)
Mild moderate or sever pox lesions appear after 7-11d

Question 17

Nervous system barriers to infection

Answer 17

Well protected from entry of blood pros by blood brain barrier and choroid plexus

Question 18

Nervous system infectious methods

Answer 18

Infection of endo cells eg some arbo
Dam to bbb allowng virus entry
Entry via leukocytes eg maedi visna
Direct entry into pns and cns via nerves eg rabies, some herpes

Question 19

Rabies infection route

Answer 19

Enveloped -ve ssrna
Bite inserts virus which repl in muscle cells
Enters sensory and motor nerve endings and travel via intra axonal transport to cns
Accends bia connecting nerves to the limbic syst where it can cause furious rabies
Also spreads to various other tissues eg salivary gland at this juncture when virus max in sal gland the animal is most aggressive
Continued spread to neocortex causes dumb rabies leading to depression and coma
Death from resp arrest

Question 20

Viral infection of the foetus

Answer 20

Many viral infect in dam have no negative impact on foetus but some can cross the placenta to reach foetal circ
Infection in first two trimesters is kist dam with severe cytolytic infect can cause abortion and foetal death (parvo) and sone can have teratogenic effects (BVD)
In 2nd half of pregnancy course of infection can be affected by deving imm syst and can cause viral clearance

Question 21

Viral shedding from skin

Answer 21

Only a few shes from skin in a way leadin to transmission
FMD
pox
Some herpes

Question 22

Viral shedding from resp tract

Answer 22

Shes in fluid expelled
Small drops evap and remain airborne as small droplet nuclei
Large droplets may fall to the ground and contam fomites
Eg RSV, IBR, paramyxo and some corona shed from both nasal and oral secr

Question 23

Viral shedding from digestive tract

Answer 23

Enteric viruses shed in faeces and are gen more res to enviro inact

Question 24

Viral shedding from urogen tract

Answer 24

Many shed in urine eg rinderpest, FMD, infectious canine hep

Some shed in semen (STD) eg IBR FMD

Question 25

Viruses shed in milk and colostrum

Answer 25

FMD

Visna maedi

Question 26

Viruses transferred via nlood stream

Answer 26

By arthropods or vet needles
Mechanical transfer
Eg arbo