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63 Cards in this Set

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Why are arboviruses so named?
Arthropod-borne viruses = Arbovirus
All arboviruses are transmitted how?
Bits of arthropod vectors: mosquitoes, fleas, ticks
Arboviruses include what virus families?
They're no specific to a family or genus, but include viruses in togaviridae, flaviviridae, and bunyaviridae, and reoviridae
Analogous to Endemic but with animals (low but constant rate)
Enzootic
What are the primary diseases caused by arboviruses?
Fever, Encephalitis.
Mneumonic for remembering arboviruses:
paul BUNYan, about to chop down an ARBOL, wearing a TOGA, with a rich FLAVor attractive to mosquitos
In incidental host model, How do humans Represent a “dead end” for the virus life cycle in arboviruses?
although they become ill they do not develop enough viremia to infect new vectors
When humans are primary vertebrate hosts for the virus, what happens?
Infection achieves high viremia in human.

vector bites human, moves to another human to vit.

Basic cycle is human-vector-human.
Eastern Equine Encephalitis (EEE)
Western Equine Encephalitis (WEE
St. Louis Encephalitis (SLE)
La Crosse Encephalitis (California group)
West Nile Encephalitis (WNE)
Colorado Tick Fever (CTF)
Powassan Fever (POW)

Are all examples of what?
Arbovirus-caused encephalities in North America
Most severe and potentially fatal of the North American arboviral encephalitides
Eastern Equine Encephalitis
Main togaviridae alpha viruses
Western Equine Encephalitis
Eastern Equine Encephalitis
Venezuelan Equine Encephalitis
Two diseases caused by bunyaviridae
La Crosse/California Encephalitis, Rift Valley Fever
West Nile Encephalitis: What family
Flaviviridae
West Nile Vector
Vector: primarily Culex species mosquitoes
West Nile Virus is most lethal in what species?
Birds, horses
Clinical Manifestations of West Nile
Most people are asymptomatic.

Some get headache, maculopapular rash. May be followed by fatigue, weakness, difficulty concentrating.

Very serious disease may be neuroinvasive (aseptic meningitis, frank encephalitis, weakness, paralysis)
Colorado Tick Fever: caused by what?
Virs that's RNA virus in Reoviridae family
Primary vector and reservoirs of colorado tick fever
Vector: Wood tick
Reservoir: Squirrels, chipmunks
Powassan Virus: vector, transmission, disease
Virus: RNA virus in Flaviviridae family
Vector: ticks, 3 Ixodid species and D. andersoni
Epidemiology
Range is eastern Canada and northeastern US
Infection mostly occurs June to September
Rare cause of encephalitis, but with high incidence of neurologic sequelae
Arboviral Encephalitis:Clinical Features/Symptoms
With the exception of EEE, all produce similar symptoms of encephalitis
Typical early symptoms include fever, headache, anorexia, nausea/vomiting, myalgias
Progression to features of encephalitis – photophobia, severe headache, altered mental status (confusion, disorientation, lethargy),
May progress to seizures and coma
Arboviral Encephalitis: Diagnosis
1) Suggested by symptoms and exposure to endemic areas or vectors

2) Mainly serologic: detection of IgM antibody, or 4x rise in IgG antibody on convalescent serum

3) Detection of viral genome sequences in CSF by RT-PCR
Arboviral Encephalitis: Treatment
Mainly supportive. No specific anti-viral agents.
Eastern Equine Encephalitis: What %age of adults and children develop encephalitis and what is mortality rate?
2% of infected adults and 6% of children develop encephalitis
Outcome: mortality is 30% with frequent neurologic sequelae in survivors
Complete recovery is uncommon
Venezuelan Equine Encephalitis (VEE)
Japanese Encephalitis (JE)
Tick-Borne Encephalitis (TBE)
West Nile Virus (WNV)
Murray Valley Encephalitis (MVE)

What do they have in common?
They're arboviral encephalites outside of N America
Most important global cause of arboviral encephalitis
Japanese Encephalitis Virus
Where is Japanese Encephalitis Virus found?
Across Asia, north Japan, Korea, China, Taiwan, Philippines, Indonesia
T/F Japanese Encephalitis Virus more severe in adults
F. More severe in children
Clinical features of infection
with Japanese Encephalitis Virus
Only about 1 in 250 infections result in illness
Causes mild febrile illness to frank encephalitis
Can also cause acute flaccid paralysis primarily in children
T/F Acute flaccid paralysis caused by Japanese Encephalitis virus rarely recovers
T
Japanese Encephalitis Virus: Diagnosis and treatment
Diagnosis is primarily serology.

Treatment is supportive.

Mortality in hospitalized patients is 30%
Japanese Encephalitis Virus: Prevention
Formalin-inactivated vaccine is used internationally
A live attenuated vaccine is available in China
Vaccine recommended for travelers to endemic countries staying >1month in rural areas or during periods of endemic transmission
Tick-Borne Encephalitis: Characteristics
Virus: RNA virus in Flaviviridae family
Vector: Ixodid (hard) ticks
Three geographic subtypes:
A benign syndrome caused by several arthropod-borne viruses characterized by biphasic fever, myalgia or arthralgia, rash, leukopenia and lymphadenopathy
Dengue fever
Severe, often fatal febrile disease characterized by capillary permeability, abnormal hemostasis and in severe cases, a protein-losing shock syndrome (dengue shock syndrome)
Dengue hemorrhagic fever
Arguably most important arthropod-borne viruses from a medical and public health perspective with >100 million human infections year and 2.5 billion at risk
Dengue viruses
Dengue virus characteristics
4 antigenic types (1-4)
RNA Viruses in flaviviridae family
Why is Dengue also called Break-bone fever?
Causes pain backache, muscle and joint pain, and severe headache
Repeat infection with what serotype predisposes to Dengue Hemorrhagic fever?
Serotype 2?
"Dengue takes you down in the 2nd round"
What is the Dengue virus transmission cycle?
Human-mosquito-human cycle.

Mosquitos primary vectors. Bite humans.
Most dengue disease occurs in what population groups?
Older children and adults
What is hyperendemic dengue?
Continuous circulation of multiple dengue virus serotypes in the same area
What is the mosquito vector of dengue?
Aedes aegypti
Results from introduction of a single virus strain into a region with large population of susceptible hosts and mosquitoes
Epidemic dengue
Dengue Fever: Course of Illness
Incubation period of 1-7 days
Sudden onset of high fever often with frontal or retro-orbital pain
Severe back pain may precede fever: “back-break fever”
Transient macular generalized rash may be seen in the first 24-48 hours
Fever remits after about 6 days, then recurs in 1-2 days with a morbilliform rash
Biphasic fever pattern
Most patients recover uneventfully
Dengue Hemorrhagic Fever: Course of Illness
Initial phase similar to dengue fever, followed in 2-5 days by rapid clinical deterioration.

Cold extremities, flushed face, diaphoresis, mid-epigastric pain.

Coagulopathy: petechiae, ecchymosis (bruise), bleeding from nose and venipuncture sites.

May also have maculopapular rash.
In what patients does Dengue Hemorrhagic Fever appear?
Patients who have already had a Dengue infection. Appears to have immunopathologic basis.
morbilliform : defn
looks like measles. The rash consists of macular lesions that are red and are usually 2-10 mm in diameter but may be confluent in places.
Tx of Dengue fever
Supportive: antipyretics, analgesics, fluids

AVOID aspirin
Tx of Dengue hemorrhagic fever
Intensive care support, IV fluids, maybe Oxygen, Transfusion of blood to control bleeding
Mortality for Dengue hemorrhagic fever
30-40% due to hemorrhagic shock syndrome
Where does Dengue hemorrhagic fever appear most frequently?
Occurs most frequently in areas where multiple types of dengue virus are simultaneously or sequentially transmitted
A mosquito-borne viral hemorrhagic fever characterized by hepatic, renal and myocardial injury
Yellow Fever
Where does Yellow Fever occur?
Disease occurs in tropical regions of South America and sub-Saharan Africa
What family is Yellow Fever in?
flavivirus
Transmission of Yellow fever is by
mosquitos
3 stages of Yellow Fever infection
period of infection, period of remission and period of intoxication
What occurs during First yellow fever stage: Period of Infection?
Viremia present
Sudden onset fever, headache, myalgias, anorexia, lumbosacral pain and pain in LE
Flushing of face and neck, conjunctival injection
What occurs during second yellow fever stage: Period of Remission?
Fever and symptoms abate/resolve.

May last 48 hours.

patients with abortive infection recover, 15% ENTER 3RD STAGE.
What occurs during third yellow fever stage: Period of Intoxication?
Viremia resolves and antibodies appear
Return of fever, nausea, vomiting, epigastric pain with jaundice, oliguria and hemorrhage
Hepatic dysfunction
Renal dysfunction
Hemorrhage – prominent feature
Myocardial injury
CNS dysfunction present in some cases
Mortality rate of those who enter third phase
20-30%
Yellow fever dx
Detection of virus by culture, PCR or by serology
Yellow fever tx
Symptomatic and supportive
Maintain nutrition to prevent hypoglycemia
FFP for bleeding problems
Dialysis if needed
Treatment of secondary infections
Yellow fever prevention
Live, attenuated vaccine. Recommended for travelers to endemic areas.

Control or avoidance of arthropod vector is mainstay of prevention.