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Stages of viral infection - Coggle Diagram
Stages of viral infection
route/site of entry
skin
defences in skin
physical barrier
keratinised
must be breached by abrasions or bites in order for viral entry into cells underneath
immune system
WBC
macrophages
neurophils
natural killed cells (killed T cells)
example of virus to enter via skin
orf infection (parapox virus)
cause lesions around the mouth and teats of lamb and goat
Rabies
papilloavirus
respiratory tract
defefnces
mucocilliary escalator
mucus and cilia
mucus traps large particles and pathogens and sweep them to pharynx for coughing out or swallowing
innate immune response
WBC
respiratory virus examples
influenza
FMDV (foot-and-mouth-disease virus)
rhinovirus
adenovirus
GIT
defences
pH and pH changes
low pH in stomach
denatures proteins and kills most microorganisms
high pH in intestine due to bile and proteolytic enzymes
rapid pH switch from stomach to intestine help kill virus and microorganisms
innate immune response
secretory IgA (antibody A), found in mucus in intestinal tract
examples of virus that infect GIT
infect oropharynx
classical swine flu
replicate in tonsils
spread systemically (i.e. blood/lymph/nerve)
avoid harder downstream conditions of GIT
unenveloped viruses
survive in the harsh downstream conditions of GIT
norovirus
feline coronavirus
how virus infects cells of GIT
enzyme in GIT cleaves the capsid of viruses-->allow infection
rotavirus
some coronavirus
urogenital tract
how to get infected
via infected semen
bluetongue re-emerged from frozen bull semen
example
equine viral arteritis
shed for months/years
in apparently healthy carriers
mainly via respiratory system
porcine reproductive and respiratory syndrome virus
blood
how to get infected
via blood-biting (haemotophagous) insects
bluetongue
schmallenberg
West Nile virus
via blood products/sex contact
Hepatitis B
HIV
via fighting and hunting (in animals)
most common act btw animals: scavenging
transplacental
mother to foetus
example
pestiviruses
bovine viral diarrhoea virus
classical swine fever
PRRSV
viral replication
lecture 2
viral spreading/dissemination (from cells to cells within host) (summary)
local
systemic
spread by blood
spread by nerves
spread by lymph
shedding (from one host to another)
for transmission to new host
virus titre is highest in the tissue it is shed
often: site of entry=site of shedding
exceptions
Rabies
(muscle cells vs salivary glands)
FMDV
respiratory tract vs vesicular fluid in vesicles
virus entry into host
must overcome innate defences
physical
skin
mucus
immunological
WBC and antibodies
entry mainly via mucus membrane (mucosal surfaces)
multiple entry routes
in one host
virus infection via inhalation or ingestion in one host
multiple hosts
viral infection in birds: faecal oral; in humans: respiratory
in order for virus to infect a cell, a cell must be:
susceptible
corr receptors on cell surface (i.e. corr tropism)
permissive
appropriate host factors to complete viral replication
cells=particular cell types
rapidly dividing cells
differentiated cells
viral spreading and dissemination (detailed)
local infection
def
replication occurs in epithelium at infection site
spread cell-to-cell but within same tissue (i.e. epithelium)
site of entry=site of shedding/exit
usually accute (short incubation period+ short duration)
cleared by innate immune response
examples
influenza
rotavirus--GIT
pox viruses/papillomaviruses--skin
systemic infection
primary replication
replicate at site of infection
spread to other sites via blood, lymph, nerve, immune cell
replication at secondary sites (X site of entry)
systemic spread: viremia
primary viremia
spread from site of entry to other sites
spleen
liver
secondary viremia
spread from secondary sites of replication to other further sites
usually higher viral titres and further dissemination to other sites
medium of transport
free in serum--FMDV
cell-associated
macrophages--canine distemper
lymphocytes--FIV
spread via nerve
Rabies
primary replication site (site of entry)=muscle cells/fibres
transport medium: motor neurones/nerves
secondary replication sites: spinal cord and brain in CNS
spread to salivary gland for shedding/onward transmission via secondary viremia
site of entry diff from site of shedding/exit (muscle cells vs salivary gland)
def
site of entry diff from site of shedding/exit
more severe pathology + longer incubation period
greater involvement by adaptive immune response (WBC/antibodies) (when vs localised infections)