Viruses of NS Flashcards
what is the route of entry for viruses into the NS?
via skin or alimentary tract
what are the 2 components of the PNS?
sensory and motor neurones
how do viruses spread into CNS using the PNS? what are names of the two types of transport?
1) infect peripheral NS
- travel up neuron AWAY from cell body to CNS/back to peripheral
- ANTEROGRADE VIRAL TRANSPORT
2) infect peripheral NS
- travel up neuron TOWARDS the cell body
- RETROGRADE VIRAL TRANSPORT
how do viruses use BBB to spread to the CNS?
- tight junctions joining endothelial cells which form BBB
- only small mol & few immune cells can cross
- viruses cross by infecting the endotheliium, or by infecting monocytes that can cross the barrier
what is a neurotropism?
hundreds of viruses that exhibit tropism for CNS or PNS
give an example of a virus that has evolved to enter PNS and exploit neuronal biology?
alphaherpesvirus
give an example of a virus that has no advantage for it to infect the CNS?
- often a ZOONOTIC INF
- eg rabies
give an example of a virus that causes OPPORTUNISTIC infection of CNS?
HIV, human cytomegalovirus
what are the key symptoms of viral inf of CNS?
1) Aseptic meningitis- inflammation of meninges w/ sterile CSF
2) Encephalitis- infection of brain
3) Meningoencephalitis- inflammation of brain AND meninges
4) Myelitis- inflammation of the spinal cord—>long term paralysis
what are the symptoms of meningitis?
- severe headache
- photophobia
- stiff neck
- nausea vom
- fever
- confusion
what are the symptoms of encephalitis?
- hallucinations
- confusion
- seizures
- paralysis (face/body)
- muscle weakness
- speech problems
- loss of consciousness
what can cause meningitis?
- HSV2 (herpes virus type 2)
- mumps
- HIV
what can cause encephalitis?
- HSV1
- measles
- insect borne viruses
- rabies
- polio
what is a lesser known way that viruses can enter the body?
olfactory route- - olfactory cell layer only 1 CELL DEEP before NS
which viruses use motor route to infect?
RABV (rabies) and polio
which viruses use sensory route to infect?
Herpes (HSV)
which human alphaherpesviruses?
HSV1, HSV2, VZV (varicella-zoster virus)
which animal alphaherpesviruses?
- pseudorabies virus (pigs)
- bovine herpesvirus 1
- equine herpesvirus 1
which part of the NS do alphaherpesviruses infect?
in PNS
are alphaviruses species specific or not?
yes- species specific
HSV1 infection comes from where?
describe pathogenesis
where does it lie dormant?
inside AND outside
- once replicated, transmits into neurons that are innervating the initial infection
- travels RETROGRADE into cell body
- lies dormant in TRIGEMINAL NERVE
- becomes REACTIVATED
- travels ANTEROGRADE to initial infection
OR can travel to CNS (rare)
what type of infection do alphaherpesviruses cause?
latent infection O infected for life
what causes reactivation of Herpes?
- sunlight (UV)
- hormonal (menstrual cycle)
primary HSV causes what?
- white coating on tongue, or asymptomatic
reactivated HSV causes what? occurrence is affected by?
cold sores, these are periodic
affected by: genetics
primary VZV causes what?
chickenpox, then transport into the SACRAL GANGLIA causing reactivation
reactivated VZV causes what? how common is this?
shingles (zoster) only occurs ONCE in a lifetime
can HSV cause encephalitis?
yes (HSE)
how is HSE HSV encephalitis caused?
how common is it?
who does this normally affect?
- neural invasion, the virus DOESN’T travel back to skin to cause cold sore, it travels to CNS
- the MOST COMMON non-epidemic viral encephalitis
- mostly affects elderly (immunocompromised)
how dangerous is HSE HSV encephalitis? how is it treated?
VERY dangerous, often fatal
- must have antiviral treatment, this can leave brain damage
rabies virus is part of which family?
rhabdovirus family
the rabies virus has what kind of a genome?
RNA- O can change very easily
how is rabies virus transmitted? who are the common infected animals?
- via SALIVA of infected animals (dogs, bats, foxes)
what is the route of infection of rabies?
bite from infected animal
what is the pathogenesis of rabies?
- bite
- replication of virus in muscle
- travels across neuro musc junction O gets into nerve cells
- travels up axons
- replicates in these neuorns & spinal cord
- enters brain via spinal cord
- spreads back out to skin
what are the symptoms of rabies virus?
- fever
- headache
- nausea/vomiting
- agitation
- anxiety
- confusion
- hyperactivity
- difficulty swallowing, excessive salivation
- fear of water(due to difficulty in swallowing)
- hallucinations, insomnia, partial paralysis
how long is the incubation period for rabies virus? what is the length of the incubation period dependent on?
- can be as long as ONE YEAR O no symptoms for a year
- the further the CNS the initial bite, the longer the incubation period
at what point does rabies become fatal?
once symptoms appear
how many people die a year from rabies?
almost 59000
who does rabies affect most?
poor and disadvantaged
how is rabies treated?
- thorough washing of wound
- then vaccination (~15 million get post bite vaccination)
how is rabies prevented?
vaccinate DOGS
what type of virus is polio?
picornovirus
what is the genus of poliovirus?
enterovirus
is poliovirus a small or large virus?
small
what form of genetic information is used by poliovirus?
RNA genome
can poliovirus surivive for a long time outside the host?
yes
what is the route of transmission for polio? how does it enter the body?
faecal-oral
ingestion of contaminated water
how long is the incubation period for poliovirus?
6-10 days
once ingested, where can polio replicate?
can be TONSILS, but predominantly in the GUT
- transmitted from gut to form PRIMARY VIRAEMIA in bs
- -> then SECONDARY viraemia when it spreads to other tissues (CNS)
what can polio lead to?
meningitis, encephalitis & paralysis
how does polio enter the brain?
- orally ingested
- passes low pH in stomach
- blood circulation
- crosses BBB
- replicates in cell body of motor neurones
- transmitted into skeletal muscle
- causes paralysis (POLIO MYELITIS)
what are the outcomes of polio infection?
95% no illness (asymptomatic, STILL transmittsable)
4% minor illness (ABORTIVE POLIOMYELITIS) - meningitis
1% major illness, paralysis (poliomyelitis) or non paralytic poliomyelitis
how is polio prevented?
oral poliovirus vaccine (OPV)
- attenuated vaccine, combination of 3 serotypes
- for each serotype, there are around 20-50 nt within each attenuated virus
what is used to transmit arboviruses (arthropod-borne) ?
vectors include mosquitos and ticks
where does the problem arise with arboviruses?
when the vector infects HUMANS/HORSE (dead end hosts) etc
organisms that are not normally meant to be infected with this
give 2 examples of new and emerging diseases?
Nipah and Hendra virus
what is the reservoir host for Nipah and Hendra virus?
bat (flying fox)
Nipah and Hendra are what type of virus?
paramyoxovirus
what is the genome like of Nipah and Hendra?
enveloped RNA genome
where did Nipah get transmitted from (spillover hosts)?
pigs –> humans
where was Hendra transmitted from (spillover hosts)?
horses –> humans
subacute sclerosing panencephalitis is caused by what?
measles virus
how long after measles infection does subacute sclerosing panencephalitis occur?
late, 5-15 years after infection
how common is subacute sclerosing panencephalitis?
v rare (2/100,000)
what type of disease is subacute sclerosing panencephalitis?
progressive, degenerative disease of the CNS
what is subacute sclerosing panencephalitis characterised by?
high levels of measles virus ANTIBODIES in serum and CSF
how is subacute sclerosing panencephalitis protected /prevented against?
vaccinate against measles
why is HIV inf in the brain known as ‘Trojan horse’ infection?
- HIV infects macrophages
- goes on to infect microglia, other cell types in brain
what are consequences of HIV in the brain? how quickly do these occur?
- depression
- cognitive disorders
- HIV Associated dementia
very slow to progress
who is most susceptible to infections of the brain?
immunocompromised individuals (transplant, chemotherapy, AIDS, genetic defects)
which viruses can cross BBB?
human cytomegalovirus (hCMV) and HIV
give an example of a genetic defect that leaves people predisposed to primary HSV infection?
- mutation in TLR3 pathway individual (esp children)
- if infected with HSV infection, can lead to ENCEPHALITIS
