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Infectious Disease Unit 2 > Arboviruses > Flashcards

Arboviruses Flashcards

1
Q

What is an arbovirus?

A

Viruses maintained in nature in cycles involving hematophagous arthropod vectors and susceptible vertebrate hosts

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2
Q

What kinds of nucleic acid do most arboviruses have?

A

nearly all have RNA genomes

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3
Q

Arthropod vectors

A

Primarily mosquitoes, but also ticks, biting flies

Infected vectors transmit virus to vertebrate hosts during feeding

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4
Q

Two types of vertebrate hosts for arboviruses

A
  1. Those that serve as main sources of infections for vectors (reservoirs): may or may not develop disease
  2. Those that don’t serve as reservoirs, but in which disease may occur (humans for most of these)

Has to do with how high titer the serum viremia is (if high enough, can be a reservoir)

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5
Q

What are the exceptions to humans being a dead-end host of virus?

A

Dengue virus

Yellow Fever virus

Zika virus

Some alphaviruses:
Ross River virus
Chikungunya virus
Venezuelan equine encephalitis virus

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6
Q

Role of Mosquito in Arbovirus Transmission

A
  1. Female mosquito ingests blood from viremic vertebrate.
  2. Virus replication in the mosquito midgut.
  3. Systemic spread in mosquito.
  4. Virus replicates and accumulates in salivary glands.
  5. Mosquito injects saliva/virus into skin during next blood meal.
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7
Q

After biting an infected vertebrate host, is a mosquito immediately infectious for humans?

A

No, because virus has to replicate in mosquito first

Extrinsic incubation period

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8
Q

Arboviruses: Major outcomes of human infection

A

In order of how common:

  1. Asymptomatic
  2. Febrile illness
  3. Neurologic disease: encephalitis, meningitis
  4. Arthritis/MSK disease signs
  5. Hemorrhagic fever
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9
Q

What are the three taxonomic families that contain most of the arboviruses of public health importance?

A

Bunyaviridae
Flaviviridae
Togaviridae

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10
Q

Major global arboviruses

A 
Dengue viruses (DENV)
West Nile virus (WNV)
Zika virus (ZIKV)
Chikungunya virus (CHIKV)
Yellow Fever virus (YFV)
Japanese encephalitis virus (JEV)
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11
Q

Major arboviruses found in the United States

A 
West Nile virus (WNV)
St. Louis encephalitis virus (SLEV)
La Crosse virus
Eastern equine encephalitis virus
Colorado Tick Fever virus
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12
Q

Dengue virus sypmtoms

A

75% asymptomatic

Cause two syndromes:
1. Dengue Fever (DF) 24%
• An acute febrile illness characterized by headache, muscle and joint pain, and rash.

  1. Dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS) 1%
    • Characterized by thrombocytopenia, capillary leakage, damage to liver
    • Fluid loss in tissue spaces can lead to hypovolemic shock and death (DSS)
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13
Q

What percent of the world population is a risk of dengue viruses?

A

50%!

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14
Q

Factors contributing to re-emergence of dengue viruses and DHF

A 
Cocirculation of all 4 serotypes
Global pop growth
Increased air travel
Unplanned, uncontrolled urbanization
Lack of effective mosquito control
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15
Q

Dengue virus characteristics

A

4 serotypes (1-4)

Members of the Flavivirus genus of the Flaviviridae

Mosquito-borne
• Aedes aegypti
• Aedes albopictus

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16
Q

Transmission of dengue viruses

A

Maintained in human-mosquito-human transmission cycle

17
Q

Risk factors for development of DHF/DSS following dengue virus infection

A
  1. A second dengue infection by a different serotype
  2. Age (under age 15)
  3. Host genetic background
  4. Viral genotype
  5. Each of the 4 DENV serotypes is composed of several genotypes

Disease severity is determined by a combination of host and viral factors: Pre-existing immunity and virus genetics are critical determinants

18
Q

Antibody-dependent enhancement (ADE) of disease severity Hypothesis

A

Ab response to 1st infection protects against a 2nd infection from that serotype

But those Ab can cross-react with other serotypes at first but over time lose their cross-reactive Ab

2nd infection with a different serotype: cross-reactive Ab are subneutralizing. They mediate enhanced infection of specific cells via FcγRs.

Leads to increased viral replication and immune activation (increased cytokines etc.)

19
Q

Chikungunya virus

A

Reemergence of mosquito-transmitted alphavirus

Can cause chronic MSK disease

Acute stage: fever, severe pain in joints

For many, that pain can last for months to years

No specific treatments, just for symptoms

20
Q

Zika virus

A

Flavivirus transmitted by Aedes species of mosquitoes

Prior to 2007, only 14 documented cases of human Zika virus disease

Similar to CHIKV, ZIKV has spread dramatically in the last 5-8 years

Infection: asymptomatic (80%) to fever, muscle/joint pain, conjuctivitis (20%)

Microcephaly in newborns?

21
Q

Yellow fever and dengue fever in the US

A

Historically caused infection, but not really today because of socioeconomic factors (air conditioning, higher per capita income)

22
Q

West Nile Virus

A

Encephalitic flavivirus

Encephalitis

Maintained in an enzootic cycle involving mosquitoes and birds

Humans are a dead-end host

Seasonal (end of summer)

Treatment is supportive

23
Q

Arbovirus disease burden in US

A

Pretty low

West Nile is most common in US

24
Q

Symptoms of west nile virus disease

A

Majority (~80%) are asymptomatic

WNV Fever (~20%)
• Abrupt onset of fever, headache, fatigue

WNV neuroinvasive disease ( less than 1%)
• Fever, headache, altered mental status, neck stiffness
• Typically manifests as encephalitis (63%), meningitis (33%), or acute flaccid paralysis (3%)
• Most cases occur in elderly people and those with impaired immune systems
• Long term neurological sequelae are common

25
Q

West Nile Virus pathogenesis

A

Virus replicates locally at site of inoculation (Keratinocytes,
dendritic cells)

Infected cells migrate, spread virus to lymph nodes

Seeds primary viremia

Virus gains access to the CNS

Mechanism by which WNV invades CNS is unclear

WNV directly infects neurons

Neuronal injury in brain stem, hippocampus, cortex,
cerebellum, spinal cord

26
Q

Non-mosquito transmission of WNV

A

Solid organ transplantation and blood transfusion

27
Q

What do Dengue viruses and Yellow Fever virus cause

A

Hemorrhagic fever

28
Q

What do Japanese encephalitis virus and West Nile virus cause

A

Encephalitis

29
Q

What does Chikungunya virus cause

A

Acute and chronic arthritis

Infectious Disease Unit 2 (22 decks)

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