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CNSLF Micro - Viral Infections + Prions in CNS (ii) (Rabies (Tx (wash…
CNSLF Micro - Viral Infections + Prions in CNS (ii)
HSV encephalitis
most common causative agent of encephalitis in N european countries
HSV1>2 (esp in adults + children > 3 months)
human only infection
routes
virus spreads from sites of primary infection
or from latent infection in cranial N ganglia to frontal or temporal lobes of brain
mechanism of reactivation not understood
direct neuronal transmission of virus via the trigeminal or olfactory N to the brain
causes haemorrhagic necrosis + inflamm infiltrates
clinical features - acute neuro syndrome
behavioural disturbance
hemiparesis
aphasia
focal seizures
dx
MRI (temporal lobe changes - though global brain involvement in neonates - brain almost liquified)
EEG
CSF - HSV PCR
antiviral tx NB - IV acyclovir - without tx mortality = 70%
in the neonate
HSV usually acquired from mother's infected genital secretions around time of delivery (trans-vaginal)
tends to disseminate (whereas usually confined to CNS in adults)
high mortality (nearly 100%)
tx = IV acyclovir
guidelines on genital herpes in pregnancy - aim = to prevent neonatal HSV
moreso HSV 1
West nile virus
belongs to a group of viruses called arboviruses (=arthropod borne - transmitted by insects, ticks, etc)
birds = usual host (main reservoir)
transmitted by bite of infected mosquito
can infect humans, birds, horses + some other mammals
temperate countries (e.g. Northern N America): late summer/early autumn
tropical countries: all yr round (temps are higher so mosquitoes active all the time)
global warming: mosquitoes migrating (S Europe)
clinical features
no symptoms in 80%
mild symptoms - ILI
fever
headache
generalised aches + pains
usually make full recovery
severe symptoms in <1%: encephalitis, meningoencephalitis, risk increase with age + immunosuppression
Dx
West bile virus IgM (blood or CSF) - since IgM ab doesn't cross BBB, IgM Ab in CSF strongly suggests CNS infection
Management
usually self-limiting
supportive if severe
hospitalisation
IV fluids
resp support
prevention of secondary infections
Rabies
acute encephalitis
bite or direct contact with the saliva of infected animal
main reservoir = wild + domestic dogs (cause 99% of human cases), wolves, foxes, coyotes, dingoes, bats
virus travels to brain by following peripheral Ns
Incubation period depends on distance virus has to travel to reach the CNS
In Africa, S America, Asia
Once it reaches the CNS symptoms appear - no effective antiviral tx - fatal within days
Prodrome: fever, pain @ bite site, salivation (ANS)
CNS: restless/irritable/aggressive (may also be disorientated + have seizures), then encephalitis/paralysis
Tx
wash wound asap
post exposure prophylaxis asap (within days of exposure)
rabies Ig (around bite site + also IM)
rabies vaccine
prevention
vaccine incl post-exposure
preventative veterinary measures incl vaccination of cats + dogs as well as oral vaccination of wild animal pops
Other causes of viral encephalitis
enteroviruses (incl polio) can cause encephalitis but much more commonly meningitis
the arboviruses (many, in different regions of the world)
Zika virus
infects CNS + PNS
Congenital Zika syndrome
incl severe microcephaly resulting in a partially collapsed skull, decreased brain tissue with brain damage
a/w Guillain Barre syndrome
a post infectious paralysis
patient's own immune cells attack + damage the N cells, causing muscle weakness + sometimes paralysis
Some viruses a/w persistent/chronic infection of the CNS
measles
JC virus
HIV