arboroviruses Flashcards
what is an arborovirus?
an arthropod born RNA virus that is spread from an insect to a vertebrate host
how are arboroviruses usually maintained?
by cycling between insect and vertebrate hosts
what are the only two arboroviruses for which the human is the major vertebrate host?
dengue and urban yellow fever
for most arboroviruses, who is the primary host?
birds or other animals. Man is only an incidental alternate host
what is the major arborovirus causing encephalitis?
West Nile Virus (WNV)
besides WNV, what 10 other arborovirses are encephalitis causing?
- Eastern Equine Encephalitis (EEE)
- Western Equine Encephalitis (WEE)
- St. Louis Encephalitis (SLE)
- Ca encephalitis viruses (North America)
- Powassan virus (North America)
- japanese encephalitis
- murray valley encephalitis (australia)
- venezuaelan equine encephalitis
- tick borne encephaliis (europe)
- Severe Fever with Thrombocytopenia Syndrome (SFTS) virus (china)
West Nile Virus (WNV) is a common cause of encephalitis where?
North and South america
most predominand mode of WNV transmission
WNV is transmitted in cycles involving a variety of Culex mosquito species and birds. Humans and domestic animals are incidental hosts
human to human spread of WNV occurs via (5)
- blood transfusions
- organ transplantation
- transplacental spread
- breast milk
- rarely from percutaneous occupational exposure
clinical manifestations of WNV
vast majority = asymptomatic
- only 25% get symptoms, usually characterized by: fever, headache, backache, muscle aches, vomitting, diarrhea and loss of appetite, transient macular rash —> this is called West Nile Fever
West Nile Fever
symptoms experienced by 25% of people with WNV.
characterized by: fever, headache, backache, muscle aches, vomitting, diarrhea and loss of appetite, transient macular rash
manifestations of neuroinvasive WNV (which happens in pprox 1% of cases)
meningitis, encephalitis, polio-like paralysis, death (death rate = 10%)
neuroinvasive forms of WNV are associated with populations:
> 50yo, immunodeficient (organ transplant, cancers)
How is WNV detected during acute disease?
specific IgM, IgG or RNA (by PCR), or IgM in serum
A diagnosis of WNV can be made retrospectively by
demonstrating a >4 fold rise in serum WNV IgG
txt for WNV
there is no known effective txt– you have to prevent it!
what is Eastern Equine Encephalitis (EEE) caused by?
caused by an alphavirus (EEEV) maintained in bird pops in fresh water swamps in the gulf of mexico
where is eastern equine encephalitis virus (EEEV) maintained and how is it transmitted to humans?
(EEEV) maintained in Cs. melanura and bird pops in fresh water swamps in the gulf of mexico and atlantic coasts and is transmitted to humans by different mosquito species
how many cases of encephalitis does EEEV cause a yr?
5-15 each summer/fall
populations most often affected by EEEV?
young children and elderly
death rate in those with EEEV and neurologic sequelae?
death rate: 50-70%. long term neuro sequelae in survivors might be seizures and mental retardation
daignostic procedures for EEEV, WEEV, WNV, and SLEV
similar to WNV: specific IgM, IgG or RNA (by PCR), or IgM in serum
prevention of EEEV, WNV, SLEV, WEEV?
reducing exposure (draining water from mosquito breeding sites), use of mosquito larvicides or mturation inhibitors, and mosquito repellants (10-50% DEET). Vaccines are in dvpmt
what is Western Equine Encephalitis (WEE) caused by?
an alphavirus- WEEV
where is WEEV distributed?
in the western plains and valleys of the US, Canada and SA
life cycle of WEEV is similar to…
EEEV
which generally causes a more mild disease with a lower death rate, EEEV or WEEV?
WEEV
is there txt or a vaccine for WNV, EEEV, WEEV or SLEV?
nope– you have to prevent it!
St. Louis Encephalitis is caused by a
flavavirus (SLEV) widely distributed throughout the western hemisphere
the primary transmission cycle of St. Louis Encephalitis involves…
Culex mosquitos and wild birds
severity of ifxn with St. Louis Encephalitis increases with…
age (> 60 has highest incidence of encephalitis and fatality rate of 22%)
WEE and EEE are both caused by a ____ virus, whereas SLE is caused by a ____
WEE/EEE: alpha virus
SLE: flavavirus
Dengue virus is what type of virus and has how many serotypes?
flavivirus with 4 serotypes
each serotype of dengue provides what type of immunity? what does this mean about infection?
specific lifetime immunity and short-term cross immunity, so each ind can be infected up to 4 times
what is the most common cause of arbovirus disease in the world today?
dengue– 100 million ifxns annually, 500,000 of which have dengue hemorrhagic fever (DHF)
DHF
Dengue hemorrhagic fever– 500,000 cases annually
which mosquitoes carry dengue?
Aedes mosquitoes
the infectious cycle of dengue
involves aedes mosquitoes, primarily in tropical areas of Asia, Africa and the americas
what has caused the increase of Dengue cases?
- lack of proper vector control
- increased urbanization
- climatic changes
- international travel
epidemics of dengue usually involve how many people? and where has dengue reemerged in the states?
thousands of people. outbreaks have reemerged in the US, primarily in texas and florida due to travel
pathogenesis of dengue
- mosquito bite
- DENV replicates locally and in lymph nodes
- w/in 2-3 days spreads via blood to various tissues including skin (multiple tissues/organs can be involved– liver, skin, rarely the brain)
symptoms of dengue correlate with…
- viremia
- replication in certain tissue (eg muscle)
- cytokine release
Dengue Shock Syndrome (DSS) can occur after
sudden extravasation of plasma into extravascular sites including pleural and abdo cavities
Dengue Shock Syndrome (DSS) is associated with
intense immune activation and the formaion of immune complexes and activation of the complement system
DSS occurs most commonly
in secondary ifxns amongst those with pre-existing partial anti-dengue immunity– heterologous antibodies may enhance viral uptake/replication
most common clinical manifestations of dengue
febrile illness similar to influenza, but often with SEVERE muscle aches (“break-bone fever”), together with a rash, headache and mild hepatitis
break-bone fever is associated with which virus?
dengue– severe muscle aches and fever
clinical manifestations of the most severe form of Dengue– Dengue Hemorrhagic fever (DHF)
bleeding from skin, gums, nasal passages, gi tarct and gu tract. blood platelets= low (thrombocytopenia) evidence of leaky capillaries low BP rapid/weak pulse skin = cold and clammy altered mental status death
most rapid diagnosis of dengue virus (DENV)?
most rapid: PCR amplification from acute serum
other: IgM capture assays, but serologic diagnosis may be problematic bc of extensive cross-reactivity among DENV serotypes with other flaviviruses
txt for DENV
intensive care and monitoring of extremely ill pt with DHF-DSS with anticipitory supportive care, but no specific anti-DENV therapy or vaccine avb
major prevention of DENV?
mosquito control
Yellow Fever Virus (YFV) are what type of virus?
flaviviruses with differing genotypes that have been called East Africa, West African and New World
Yellow Fever Virus (YFV) is localized to
tropical areas of sub-saharan african and SA
how was yellow fever brought to the americas?
aboard slave trade ships
the primary transmission cycle for Yellow Fever (YF) involves
nonhuman primates and Aedes monsquitos
annual YF cases and death rate
200,000 annually with fatality of 20-50%
clinical features of YF
asymptomatic or flu-like symp
severe disease: hepatitis/jaundice and hemorrhagic diatheses with bleeding episodes as described for dengue hemorrhagic fever
multi organ involvement may lead to shock, heart failure, renal failure, coma and death
diagnosis of YFV
PCR detection of virus in clinical specimens or by serology (early virus specific IgM, later IgG abs)
treatment for YF
surrportive– no YF specific antiviral agents avb
is YF preventable?
yes, with an attenuated (17D) vaccine that produces immunity in 95% of recipients with single dose
pitfalls of YF vaccine
rarely assoc with neuro comp (encephalitis) or death, esp in elderly
travelers going where should get YF vaccine once every 10 yrs
at risk areas in african and SA
YF prevention can be done via:
- vaccine
2. mosquito control
Chikungunya viruses (CKV) belongs to what genus/family?
alphavirus genus of the togavirus family
what does chikungunya mean and why was the name given
it means “that which binds up” and is referring to the stooped posture from virus induced arthritis
where is chikugunya virus (CKV) common?
Africa, and recently spread to Indian subcontinent and elsewhere in asia
the chikugunya virus (CKV) mutation allowed it to boraden it’s mosquito host from ____ to ____
from A. aegypti to A albopictus
clinical features of chikugunya viruse (CKV)
fever characterized by influenza-like symp, fevers and joint pain. GI symp, rash, lymphocytopenia and hypocalcemia
diagnosis of CKV
detection of viral RNA or infectious virus from blood, or by detection of IgM and or IgG ab in serum
txt of CKV
supportive– no specific antivirals or vaccine
what is the only arbovirus we studied that has a vaccine?
YF
representative flaviviruses of Japanese encephalitis virus group (4)
- japanese encephalitis virus
- murray valley encephalitis virus
- st. louis encephalitis virus
- west nile virus
the enzootic (maintenance/amplification) cycle of WNV is between
a mosquito and a bird
the epizootic spread of WNV is to? the epidemic spread is to?
- horses
2. people
the spread of WNV continues because most people are…
asymptomatic
WNF lasts how long?
approx 1 week, may be followed by persistent fatigue
two togaviridae viruses
- EEEV and WEEV
4 flaviviridae viruses
- SLEV
- JEV
- WNV
- DENV
1 Bunyaviridae virus
California encephalitis virus (CEV)
the macular rash of WNV usually arises… and is more frequent in… than…
upon clinical improvement, and is more frequent in persons with WNF than with neuroinvasive disease
WNV meningitis manifestations
similar to other viral meningitis:
fever, headache, stiff neck, photophobia. CSF pleocytosis; generally lymphocytic, but may be neutrophilic, severe headache, dehydration
clinical manifestation of WNV encephalitis
alterations of mental status and/or focal neuro findings (+/- meningitis)
severity ranges from mild confusion to coma/death
more frequent in elderly/immunosuppressed
assoc. neur manifestations: movement disorders, cranial nerve palsies)
risk factors for neuroinvasive meningitis:
risk increases 1.5 x/decade
immunodeficiency (organ transplant >40x risk), genetic CCR5 deficiency (increased severity/death)
long term clinical outcomes of WNV encephalitis
persistent difficulties, parkinson like tremors that diminish over time, cognitive complaints… but 70% have at least some functional recovery
is WNV encephalitis more common in men or women? young or elderly?
old men (esp 80-90 yo)
WNV poliomyelitis
anterior horn cells– acute, asymmetric paralysis (but generally no sensory loss), asymmetric weakness, monoplegia, and persistend functional impairment
EEEV ifxn is symptomatic in? asymp in?
symp: humans and horses
asymp: in birds
when does EEE happen?
summer
EEEV family: genus: stranded: north american isolate: south american isolate:
family: togaviridae
genus: alphavirus
stranded: single stranded RNA
north american isolate: 1 variant- most neuropthogenic arbovirus in the USA
south american isolate: 3 variants, less virulent
what is the most neuropathogenic arbovirus in USA?
EEEV
clinical manifestations of EEEV
headache, fever, vomiting, malaise, progressing in 24-48 hours to disorientation and somnolence. Mortality is 50-70%
long term sequelae of EEEV
seizures, spastic paralysis, personality changes, mental retardation
lab findings for EEE
spinal fluid pleocytocis (600-2000/mm3), PMN predom. early, later lymph; increased prot; glucose = normal
diagnosis of EEE
most commonly serological, demonstration of rise in Ab titer btwn acute and convalescent serum. virus can be isolated from brain biopsy and sometimes CSF
WEEV commonly found
west of mississippi in US and western canada
SLEV found
throughout americas, except northeast
culture of CSF with SLEV is usually
negative
SLEV manifestations
fever/headache, meningitis or encephalitis.
encephalitis: altered reflexes, CNS changes 20-30%, seizures (10%)– associated w/poor prognosis, ataxia
fatality is 2 (young) -22 (elderly)%, sequelae = infrequent
California encephalitis refers to a grp of related viruses including (2)
- lacrosse
2. janestown canyon
animal reservoir for CA encephalitis viruses
sylvan mammals maintained in northeast and central forests
clinical manifestations of CA encephalitis viruses
most = asymp
enceph = most common in <15 yo
mortality: 1%, long term morbidity includes seizures and personality changes
what greatly increased the spread of arboviruses?
travel
japanese encephalitis is common in
india, nepal, northern south east asia
important non-encephalitis arbovirus?
DENV
DENV is-
family:
stranded:
serotypes:
DENV is-
family: flavivirus
stranded: ss RNA
serotypes: 4 (DENV 1,2,3,4)
what is unique about Aedes aegypti, which transmits DENV?
primarily a daytime feeder
replications/transmission of DENV
- virus transmitted to human by fm Aedes mosquito
- virus replicates in target organ
- virus infects WBC and lymph tissue
- virus released and circs in blood
- second mosq ingests virus in blood
- virus replicates in mosq midgut and other orgs/infects salivary glands
- virus replicates i salivary glands
- mosq transmits virus…
