Case 60: St. Louis Encephalitis Virus Flashcards
what type of virus is the St. Louis encephalitis virus? what virus family is it a part of?
it’s an arbovirus = arthropod-borne virus that infects vertebrates = blood sucking like ticks and mosquitos
mainly associated with encephalitis
flaviviridae family = enveloped, icashedral, (+) sense ssRNA
what are the presenting symptoms of the St. Louis encephalitis virus?
- fever
- malaise
- worsening headache
- NVD
- confusion
- tremors of the face and extremities
during what time of the year is St. Louis encephalitis virus more common?
summer
this is when the mosquito population is large and hard to control!
the vector for st. Louis encephalitis virus is mosquitos!
what is the vector and reservoir of St. Louis encephalitis virus?
vector = mosquito
reservoir = birds
what’s the difference between a vector and reservoir?
RESERVOIR: the animal or organism in which the virus or parasite normally resides
VECTOR: any agent, living or otherwise, that carries and transmits parasites and diseases.
what would the CBC of a St. Louis encephalitis virus patient look like?
everything would be normal but WBC would be elevated
which 3 virus families have arboviruses that cause human encephalitis?
- bunyaviridae
- togaviridae
- flaviviridae
what are the characteristics of the bunyaviridae genome?
enveloped, segmented, helical, circular (-) sense ssRNA
what are the characteristics of the togaviridae genome?
enveloped, (+) sense ssRNA viruses
what are the characteristics of the flaviviridae genome?
enveloped, (+) sense ssRNA viruses
which viruses in the flaviviridae family are transmitted by bloodsucking arthropods?
- St. Louis virus
- yellow fever
- dengue fever
in what environment are arboviruses more common?
arboviruses usually exist in woodland habitat, passing between tree hole
mosquitoes and vertebrate hosts (e.g., birds and rodents) in the summer months,
when the mosquito activity is maximal
the vector also uses trash-filled drainage
systems and artificial containers (e.g., dumped tires) in urban areas
through what route are arboviruses transmitted?
mosquitoes
feed on viremic birds (or rodents) then infect humans
vector = mosquito
reservoir = birds
which population is at risk for St. Louis virus?
all age groups are at risk
but severity of disease increases with age
what is the pathogenesis of arboviruses?
arboviruses gain access to humans via the bite of an infective mosquito
viruses
contained in the saliva of mosquitoes are introduced into the capillary bed as the
mosquito’s proboscis penetrates the skin and enters the endothelial cell of the capillary
wall
yhe viruses localize in the vascular endothelium of the reticuloendothelial system,
replicating in the endothelial cells
a primary viremia is induced as the viruses are liberated from these infected cells
after the viruses enter the
circulation, they may localize primarily in the endothelial cells lining the small vessels
of the brain or the choroid plexus
why do arboviruses cause brain damage?
damage to brain or cerebellar tissues is due largely to
vascular involvement because virus-antibody complexes may trigger a complement
activation process, leading to disseminated intravascular coagulation (DIC) in the
brain
what are some of the complications associated with St. Louis viral encephalitis?
- cranial nerve palsies
- hemiparesis
- convulsions
older patients who recover from the virus may have difficulties in concentration and memory, asthenia, and tremor
how do you treat st. Louis virus?
no treatment
supportive treatment only
you just have to wait for the virus to clear on its own
how do you prevent st. louis virus?
there are no vaccines
there is a killed vaccine to protect horses for triple E but nothing for humans
preventative measures include avoidance of mosquito-infested areas, control of vectors, and use
of protective clothes and mosquito repellents
