Arbovirus Infections: Clinical Syndromes and Transmission Routes

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What is the main reason alphaviruses and flaviviruses are classified as arboviruses?

They are spread by arthropod vectors (correct)

They infect only vertebrates

They replicate in invertebrates

They have a broad host range

Which type of RNA genome do alphaviruses possess?

Positive-sense, single-strand RNA (correct)

Double-strand RNA

Negative-sense, single-strand RNA

Positive-sense, double-strand RNA

What anchors the carboxy terminus of the glycoproteins in alphaviruses' envelope?

Capsid (correct)

RNA genome

Viral proteins

Icosahedral capsid

How do alphaviruses attach to host cells?

Specific receptors expressed on many different cell types Signup and view all the answers

What are common symptoms of the disease caused by the virus discussed in the text?

Fever, rash, headache, and joint pain Signup and view all the answers

How can the virus be transmitted even in the absence of symptoms?

Sexually and vertically to the fetus Signup and view all the answers

What method is commonly used for detecting and characterizing alphaviruses and flaviviruses?

RT-PCR testing of viral mRNA Signup and view all the answers

What is the primary means of preventing the spread of arboviruses like dengue and chikungunya?

Eliminating the vector and breeding grounds Signup and view all the answers

What is a characteristic of the yellow fever vaccine mentioned in the text?

It is grown in monkeys, mosquitoes, and embryonic eggs Signup and view all the answers

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 Signup and view all the answers

Which virus family translates its entire genome into a single polyprotein, similar to picornaviruses?

Flaviviruses Signup and view all the answers

Where are the structural genes typically located in the flavivirus genome?

At the 5′-end Signup and view all the answers

How do flaviviruses acquire their envelope?

Budding into the endoplasmic reticulum Signup and view all the answers

What is the primary target cell type for flaviviruses?

Monocyte-macrophage lineage Signup and view all the answers

In arthropods, what must be maintained in the vertebrate host to allow acquisition of the virus?

Sufficient viremia Signup and view all the answers

What effect does nonneutralizing antiviral antibody have on flavivirus infection?

Enhances infection by promoting virus binding to Fc receptors Signup and view all the answers

Where do flaviviruses replicate to high titers within mosquitoes?

Midgut Signup and view all the answers

What is the mode of release of flaviviruses from infected cells?

Exocytosis Signup and view all the answers

Which type of cells express Fc receptors for antibody and release cytokines upon challenge?

Monocyte-macrophage lineage cells Signup and view all the answers

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 Signup and view all the answers

Which mosquito species is mentioned as a normal vector for WEEV but unable to transmit certain strains to humans?

Culex tarsalis Signup and view all the answers

Which virus family's genome organization displays temporal distinction in protein translation?

Alphaviruses Signup and view all the answers

Which type of arthropod primarily spreads arboviruses?

Mosquitoes Signup and view all the answers

Why is the spread of arboviruses usually restricted to a specific genus of mosquitoes?

Different mosquitoes have different preferences for vertebrate hosts Signup and view all the answers

What is the usual reservoir host for alphaviruses and flaviviruses?

Birds Signup and view all the answers

Which virus was first noted in 1999 after causing unusual deaths in captive birds at the Bronx Zoo?

West Nile encephalitis virus (WNV) Signup and view all the answers

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 Signup and view all the answers

Why do health departments monitor birds and mosquitoes for arboviruses?

To initiate insecticide spraying when necessary Signup and view all the answers

Which arboviruses are transmitted by Aedes mosquitoes in an urban cycle?

Yellow fever and Zika Signup and view all the answers

Which process allows alphavirus genomes to enter the cell cytoplasm?

Fusion with the endosome membrane Signup and view all the answers

What components are included in the initial polyprotein translated from the alphavirus RNA?

Nonstructural early proteins Signup and view all the answers

What is the function of the nonstructural early proteins in alphavirus replication?

Components of the RNA-dependent RNA polymerase Signup and view all the answers

How are late mRNAs produced during alphavirus replication?

From 26S positive-sense mRNA Signup and view all the answers

What type of proteins are encoded by the 26S RNA in alphavirus replication?

Structural proteins Signup and view all the answers

How are alphavirus glycoproteins processed after translation?

They are glycosylated and acylated in the Golgi apparatus Signup and view all the answers

What happens once the icosahedral capsid formed by C proteins is completed in alphaviruses?

It associates with portions of the membrane expressing viral glycoproteins Signup and view all the answers

How are alphaviruses released from human cells after replication?

By budding from the plasma membrane Signup and view all the answers

What is the typical presentation of a symptomatic chikungunya virus infection?

Fever and joint pain Signup and view all the answers

Which age group is at higher risk for serious disease associated with West Nile Virus (WNV)?

Individuals older than 50 years Signup and view all the answers

What symptoms are indicative of dengue fever according to the text?

High fever and headache Signup and view all the answers

What is the mortality rate associated with yellow fever during epidemics?

50% Signup and view all the answers

Which type of diseases are EEEV, WEEV, and VEEV infections known to progress to in humans?

Encephalitis Signup and view all the answers

What can be a consequence if an individual infected with West Nile Virus is immunocompromised?

Higher risk of encephalitis Signup and view all the answers

What symptom can occur if an individual has dengue fever according to the text?

Petechiae Signup and view all the answers

In which regions is dengue most commonly found according to the text?

"The Americas" and Asia Signup and view all the answers

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 Signup and view all the answers

What causes systemic symptoms such as fever, chills, and headaches within 7 days of infection?

Cytokine storm induced by immune responses Signup and view all the answers

How does the virus access the brain in the case of alphaviruses and flaviviruses?

By infecting endothelial cells lining brain vessels Signup and view all the answers

Which response limits replication of alphaviruses and flaviviruses?

Interferon (IFN)-α and IFN-β induction Signup and view all the answers

How does immunity to one flavivirus potentially provide protection against other flaviviruses?

By recognizing type-common antigens on all family viruses Signup and view all the answers

What is a common consequence of excessive interferon and cytokine responses?

Arthritides and systemic symptoms Signup and view all the answers

Why are humans considered 'dead-end' hosts for arboviruses like alphaviruses and flaviviruses?

Humans cannot spread the virus back to the vector Signup and view all the answers

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 Signup and view all the answers

How is immunity both beneficial and harmful in response to alphavirus and flavivirus infections?

Immunity protects against primary infection but can exacerbate immunopathogenesis Signup and view all the answers

What is the role of antibodies in blocking viremic spread of viruses?

Antibodies neutralize viral attachment proteins Signup and view all the answers

What initiates rapid onset flulike symptoms in mild systemic disease caused by alphaviruses and flaviviruses?

Infection of plasmacytoid dendritic cells causing cytokine production Signup and view all the answers

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 Signup and view all the answers