Infection

Question 1

virulence

Answer 1

ability of a microbe to cause pathological effects

Question 2

steps in microbial disease

Answer 2

gain entry
invade of cross mucosa/skin
colonise and spread

Question 3

crossing mucosal barriers

Answer 3

adherence - pilli, fimbrae, ligands for cell receptors

crossing -
m- cell trafficking
transcytosis
dendritic cell sampling
lymphocyte trafficking
neuronal transport

Question 4

colonisation and spread

Answer 4

–> systemic disease

cell injury
virulence factors

first to local tissues –> lymph nodes –> organ systems

spread by leukocyte trafficking

Question 5

virulence factors

Answer 5

factors that enable infectivity, colonisation, spread

motility - flagella

adherence -
bind directly to receptors
bind using a pili or fimbrae
invasins - assist invasion

immune evasion -
lipopolysaccharides in cell wall - resists chemical attack and acts as endotoxin
biofilm - resists phagocytosis and antimicrobials
capsule - resists phagocytosis

immune suppression -
toxins - phagocyte destruction

acquisition of nutrients -
siderophores - use iron from blood for nutrition

Question 6

spread mechanisms

Answer 6

passive - free in blood or lymphatics

leukocyte trafficking - macrophages, lymphocytes or dendritic cells take on pathogen for phagocytosis and travel them around
- tb - blocks fusion of phagosome with lysosom
- johnes - blocks action of lysosomal enzymes

Question 7

bacterial toxins

Answer 7

Lipopolysaccharides -
brucella abortus
gram -ves
part of wall, stabilises wall and released when bacteria dies

lipoteichoic acid -
gram +ve - released when they die

exotoxins -
produced by living gram +ve bacteria
clostridia perfingens - direct cytolysis
staph aureus - por forming
crynebacterium - inhibition of protein synthesis
e coli - inhibition of iron pumps

Question 8

e coli

Answer 8

eneterotoxigenic (ETEC) -
fimbrae
toxins - alter secretion of water and electrolyes
alteration of cell membrane electrolyte and fluid transport –> diarrhoea

Enterpathogenic (EPEC) -
intimin - loosens tight junctions between enterocytes
villus atrophy

enterohaemorrhagic (EHEC) -
shiga/verotoxin - cytotoxic
coagulative necrosis –> haemorrhagic diarrhoea

Question 9

anthrax

Answer 9

capsule
spore persist in environment

toxins -
protective antigen - pore forming
oedema - goes through pore - disrupts electrolyte/water transport –> oedema
lethal - goes through pore - causes cytokine production causing cell death

Question 10

atrophic rhinitis - pigs

Answer 10

bortedella bronchiseptica and pasteurella multocida

bortedella phase -
dermonecrotic toxin, lets pasteurella in

pasteurella phase -
pasteurella mutolcida toxin
increases osteoclasts and inhibits osteoblasts –> turbinate atrophy

Question 11

clostridia perfringens

Answer 11

A - alpha toxin
B - alpha, beta and epsilon
C - alpha and beta
D - alpha and epsilon
E - alpha and iota

Alpha toxin - gas gangrene, canine haemorhagic disease, ferret gastroenteritis
Epsilon toxin - pore forming in enterocytes and endothelial cells - pulpy kidney

Question 12

mycobacteria - phagocytosis resistance

Answer 12

TB - blocks fusion of phagosome with lysosome
Johnes - block action of lysosomal enzymes

allows progression to multifocal chronic lesions

Question 13

tropism

Answer 13

specificity in which cells a microbe interacts with

viruses usually quite specific - bing via ligand receptor interactions

Question 14

tropism examples

Answer 14

listeria -
brain tropism
uses catecholamines as food source

canine parvo -
pan-tropic
infects many cell types

Question 15

susceptible cells

Answer 15

cells that allow entry of viruses

Question 16

permissive cells

Answer 16

cells that allow virus to replicate - usually killed by lysis when virus leaves

Question 17

viral virulence factors

Answer 17

antigenic shift - different strains combine to make sudden change in antigenic expression

antigenic drift - gradual change in antigenic expression over time

replication in phagocytic cells - use cells own machinery
outcomes of replication -
cell death by lysis
apoptosis
latency - herpes
cell proliferation - papiloma
malignant transformation - oncogenic viruses

Question 18

gross features of viral infections

Answer 18

lungs - hematogenous spread, interstitial pneumonia

liver - random necrosis

Question 19

histopathologic features of viral infections

Answer 19

cell enlargement
viral inclusion bodies

Question 20

orf

Answer 20

ovine parapox

viral vascular endothelial growth factor - stimulated capillary proliferation, induces vascular permeability and enhances epithelial proliferation

orf virus cytkoine IL10 orthologue - suppresses WBC rectruitment

orf virus interferon resistance gene - inhibits interferon

can initiate apoptosis in antibody producing cells and inhibit apoptosis of infected cells

Question 21

rotavirus

Answer 21

direct damage of enterocytes –> villus atrophy –> malabsorption and osmotic diarrhoea

viral proteins affect enteric nervous system –> secretory diarrhoea and increased motility

NSP4 toxin –> secretory diarrhoea

Question 22

retroviruses

Answer 22

insert copy of DNA into host DNA

Question 23

lentiviruses

Answer 23

infect monocytes/macrophages and CD4 lymphocytes

FIV - immunosuppresion

Maedi-visna - progressive pneumonia

Question 24

oncoretroviruses

Answer 24

strimulate neoplastic transformation - lymphoma

FeLv - 60x risk of mediastinal/thymic T cell lymphoma

FIV - 6x risk of intestinal B cell lymphoma

avian leukosis virus

Bovine leukemia virus - notifiable

enzootic nasal tumour

jaagsiekte sheep retrovirus - pulmonary carcinomas of type 2 pneumocytes

Question 25

viral genes

Answer 25

pol - encodes for reverse transcriptase gag - codes for nucleocapsid glycoproteins - detected in antibody based tests enc - codes for surface glycoprotein that goes recptor binding and cell entry

Question 26

coccidia species

Answer 26

eimeria - gut only eimeria isospora cryptosporidium sarcocystidae - leave git and form cysts in tissues - can cause necrosis and inflammation toxoplasma neospora sarcocystis besnotia

Question 27

coccidia lifecycle

Answer 27

ingestion of oocysts --> sporocysts emerge, invade enterocytes --> asexual reproduction --> formation of sexual stages --> fuse to oocysts --> passed in feces

Question 28

coccia pathogenicity

Answer 28

not all eimeria pathogenic - makes fecal oocyst counts difficult to interpret enterocyte damage when mature schozont rupture villus atrophy --> malabsorption epithelial erosion and ulceration --> exudative enteritis and haemorrhage impaired intestinal barrier --> increased permeability --> diarrhoea alpacas - eimeria predisposes to secondary infection (usually clostridia) crypto - enterotoxin release --> secretory diarrhoea sarcocystidae (usually quite benign outside GIT) - cysts rupture or nervous system infection neospora - abortion in cattle

Question 29

trypanosomes

Answer 29

vector borne 4 forms - amastigotes - intracellular - multiplies incalles, only form without flagella trypomastigotes - blood form - infective, doesnt multiply - flagella and undulating membrane epimastigotes - intermediate form - in midge vector promastigotes - rapid division stage T. cruzi - myocarditis T. evansi - neurological signs - inflammation in brain

Question 30

trypanosomes - virulence factors

Answer 30

proteins on surface bind and assist entry survive in macrophage - rapid movement from lysosome to cytosol antigenic variation in membrane surface glycoproteins

Question 31

fungus

Answer 31

superficial - candida aspergillus systemic - histoplasmosis bastomycosis cocciomycosis cryptomycosis fusarium

Question 32

fungal virulence factors

Answer 32

yeasts - polysaccharide capsule surface antigens constantly shed chronic inflammatory reaction with granulomatous inflammation

Question 33

aspergillosis

Answer 33

inhaled, deposited in mucus layer if phagocytosis disrupted by immunosuppression - change to hyphae enzymes secretion --> damages epithelium --> exposed basal laminae --> colonisation and invasion invasion of underlying bone --> necrosis gliotoxin - anti inflammatory, apopotoses phagocytes fumagillin - antibiotic melanin - antioxidant can cause grey/black pseudomembranous rhinitis granulomas around airawys

Question 34

aspergillosis - species locations

Answer 34

cattle - lungs, placenta, udder horse - guttural pouch cat - lungs

Question 35

helminth immune system modulation

Answer 35

elicits a minimal response - nautralises immune pathways dampens response to other unrelated things - allergens, autoantigens can be beneficial reduces effectiveness of vaccines