57 Questions
What is the main reason alphaviruses and flaviviruses are classified as arboviruses?
They are spread by arthropod vectors
Which type of RNA genome do alphaviruses possess?
Positive-sense, single-strand RNA
What anchors the carboxy terminus of the glycoproteins in alphaviruses' envelope?
Capsid
How do alphaviruses attach to host cells?
Specific receptors expressed on many different cell types
What are common symptoms of the disease caused by the virus discussed in the text?
Fever, rash, headache, and joint pain
How can the virus be transmitted even in the absence of symptoms?
Sexually and vertically to the fetus
What method is commonly used for detecting and characterizing alphaviruses and flaviviruses?
RT-PCR testing of viral mRNA
What is the primary means of preventing the spread of arboviruses like dengue and chikungunya?
Eliminating the vector and breeding grounds
What is a characteristic of the yellow fever vaccine mentioned in the text?
It is grown in monkeys, mosquitoes, and embryonic eggs
Why are live vaccines available for some arboviruses but not for others mentioned in the text?
The live vaccines are only for use in specific populations
Which virus family translates its entire genome into a single polyprotein, similar to picornaviruses?
Flaviviruses
Where are the structural genes typically located in the flavivirus genome?
At the 5′-end
How do flaviviruses acquire their envelope?
Budding into the endoplasmic reticulum
What is the primary target cell type for flaviviruses?
Monocyte-macrophage lineage
In arthropods, what must be maintained in the vertebrate host to allow acquisition of the virus?
Sufficient viremia
What effect does nonneutralizing antiviral antibody have on flavivirus infection?
Enhances infection by promoting virus binding to Fc receptors
Where do flaviviruses replicate to high titers within mosquitoes?
Midgut
What is the mode of release of flaviviruses from infected cells?
Exocytosis
Which type of cells express Fc receptors for antibody and release cytokines upon challenge?
Monocyte-macrophage lineage cells
What causes death in a virus-infected cell due to increased permeability of the target cell membrane?
Viral RNA produced during replication and transcription of the genome
Which mosquito species is mentioned as a normal vector for WEEV but unable to transmit certain strains to humans?
Culex tarsalis
Which virus family's genome organization displays temporal distinction in protein translation?
Alphaviruses
Which type of arthropod primarily spreads arboviruses?
Mosquitoes
Why is the spread of arboviruses usually restricted to a specific genus of mosquitoes?
Different mosquitoes have different preferences for vertebrate hosts
What is the usual reservoir host for alphaviruses and flaviviruses?
Birds
Which virus was first noted in 1999 after causing unusual deaths in captive birds at the Bronx Zoo?
West Nile encephalitis virus (WNV)
What factor increases the risk of human infection by arboviruses when traveling into the ecologic niche of the mosquito vector?
Human presence that disrupts the natural cycle
Why do health departments monitor birds and mosquitoes for arboviruses?
To initiate insecticide spraying when necessary
Which arboviruses are transmitted by Aedes mosquitoes in an urban cycle?
Yellow fever and Zika
Which process allows alphavirus genomes to enter the cell cytoplasm?
Fusion with the endosome membrane
What components are included in the initial polyprotein translated from the alphavirus RNA?
Nonstructural early proteins
What is the function of the nonstructural early proteins in alphavirus replication?
Components of the RNA-dependent RNA polymerase
How are late mRNAs produced during alphavirus replication?
From 26S positive-sense mRNA
What type of proteins are encoded by the 26S RNA in alphavirus replication?
Structural proteins
How are alphavirus glycoproteins processed after translation?
They are glycosylated and acylated in the Golgi apparatus
What happens once the icosahedral capsid formed by C proteins is completed in alphaviruses?
It associates with portions of the membrane expressing viral glycoproteins
How are alphaviruses released from human cells after replication?
By budding from the plasma membrane
What is the typical presentation of a symptomatic chikungunya virus infection?
Fever and joint pain
Which age group is at higher risk for serious disease associated with West Nile Virus (WNV)?
Individuals older than 50 years
What symptoms are indicative of dengue fever according to the text?
High fever and headache
What is the mortality rate associated with yellow fever during epidemics?
50%
Which type of diseases are EEEV, WEEV, and VEEV infections known to progress to in humans?
Encephalitis
What can be a consequence if an individual infected with West Nile Virus is immunocompromised?
Higher risk of encephalitis
What symptom can occur if an individual has dengue fever according to the text?
Petechiae
In which regions is dengue most commonly found according to the text?
"The Americas" and Asia
What determines the ultimate nature of alphavirus and flavivirus diseases?
The specific tissue tropisms of the virus, concentration of infecting virus, and individual responses to the infection
What causes systemic symptoms such as fever, chills, and headaches within 7 days of infection?
Cytokine storm induced by immune responses
How does the virus access the brain in the case of alphaviruses and flaviviruses?
By infecting endothelial cells lining brain vessels
Which response limits replication of alphaviruses and flaviviruses?
Interferon (IFN)-α and IFN-β induction
How does immunity to one flavivirus potentially provide protection against other flaviviruses?
By recognizing type-common antigens on all family viruses
What is a common consequence of excessive interferon and cytokine responses?
Arthritides and systemic symptoms
Why are humans considered 'dead-end' hosts for arboviruses like alphaviruses and flaviviruses?
Humans cannot spread the virus back to the vector
How are secondary viremias related to targeting specific organs in alphavirus and flavivirus infections?
Secondary viremias produce sufficient virus to infect target organs based on tissue tropism
How is immunity both beneficial and harmful in response to alphavirus and flavivirus infections?
Immunity protects against primary infection but can exacerbate immunopathogenesis
What is the role of antibodies in blocking viremic spread of viruses?
Antibodies neutralize viral attachment proteins
What initiates rapid onset flulike symptoms in mild systemic disease caused by alphaviruses and flaviviruses?
Infection of plasmacytoid dendritic cells causing cytokine production
Why is inflammation a double-edged sword in response to alphavirus and flavivirus infections?
Inflammation can destroy tissues but also contributes to pathogenesis like encephalitis
Learn about the clinical syndromes and transmission routes of arbovirus infections, with a focus on alphaviruses and flaviviruses. Understand the risk of transmission after potential exposure to endemic regions and the characteristic symptoms of these infections.
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