Arbovirus Infections: Clinical Syndromes and Transmission Routes
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Questions and Answers

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?

<p>Specific receptors expressed on many different cell types (B)</p> Signup and view all the answers

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

<p>Fever, rash, headache, and joint pain (A)</p> Signup and view all the answers

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

<p>Sexually and vertically to the fetus (C)</p> Signup and view all the answers

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

<p>RT-PCR testing of viral mRNA (B)</p> Signup and view all the answers

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

<p>Eliminating the vector and breeding grounds (A)</p> Signup and view all the answers

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

<p>It is grown in monkeys, mosquitoes, and embryonic eggs (B)</p> Signup and view all the answers

Why are live vaccines available for some arboviruses but not for others mentioned in the text?

<p>The live vaccines are only for use in specific populations (A)</p> Signup and view all the answers

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

<p>Flaviviruses (C)</p> Signup and view all the answers

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

<p>At the 5′-end (D)</p> Signup and view all the answers

How do flaviviruses acquire their envelope?

<p>Budding into the endoplasmic reticulum (A)</p> Signup and view all the answers

What is the primary target cell type for flaviviruses?

<p>Monocyte-macrophage lineage (A)</p> Signup and view all the answers

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

<p>Sufficient viremia (C)</p> Signup and view all the answers

What effect does nonneutralizing antiviral antibody have on flavivirus infection?

<p>Enhances infection by promoting virus binding to Fc receptors (D)</p> Signup and view all the answers

Where do flaviviruses replicate to high titers within mosquitoes?

<p>Midgut (C)</p> Signup and view all the answers

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

<p>Exocytosis (C)</p> Signup and view all the answers

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

<p>Monocyte-macrophage lineage cells (C)</p> Signup and view all the answers

What causes death in a virus-infected cell due to increased permeability of the target cell membrane?

<p>Viral RNA produced during replication and transcription of the genome (A)</p> 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?

<p>Culex tarsalis (A)</p> Signup and view all the answers

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

<p>Alphaviruses (D)</p> Signup and view all the answers

Which type of arthropod primarily spreads arboviruses?

<p>Mosquitoes (B)</p> Signup and view all the answers

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

<p>Different mosquitoes have different preferences for vertebrate hosts (B)</p> Signup and view all the answers

What is the usual reservoir host for alphaviruses and flaviviruses?

<p>Birds (A)</p> Signup and view all the answers

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

<p>West Nile encephalitis virus (WNV) (C)</p> 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?

<p>Human presence that disrupts the natural cycle (A)</p> Signup and view all the answers

Why do health departments monitor birds and mosquitoes for arboviruses?

<p>To initiate insecticide spraying when necessary (B)</p> Signup and view all the answers

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

<p><em>Yellow fever and Zika</em> (D)</p> Signup and view all the answers

Which process allows alphavirus genomes to enter the cell cytoplasm?

<p>Fusion with the endosome membrane (C)</p> Signup and view all the answers

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

<p>Nonstructural early proteins (C)</p> Signup and view all the answers

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

<p>Components of the RNA-dependent RNA polymerase (A)</p> Signup and view all the answers

How are late mRNAs produced during alphavirus replication?

<p>From 26S positive-sense mRNA (C)</p> Signup and view all the answers

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

<p>Structural proteins (A)</p> Signup and view all the answers

How are alphavirus glycoproteins processed after translation?

<p>They are glycosylated and acylated in the Golgi apparatus (A)</p> Signup and view all the answers

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

<p>It associates with portions of the membrane expressing viral glycoproteins (B)</p> Signup and view all the answers

How are alphaviruses released from human cells after replication?

<p>By budding from the plasma membrane (A)</p> Signup and view all the answers

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

<p>Fever and joint pain (D)</p> Signup and view all the answers

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

<p>Individuals older than 50 years (A)</p> Signup and view all the answers

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

<p>High fever and headache (C)</p> Signup and view all the answers

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

<p>50% (D)</p> Signup and view all the answers

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

<p>Encephalitis (B)</p> Signup and view all the answers

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

<p>Higher risk of encephalitis (C)</p> Signup and view all the answers

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

<p>Petechiae (A)</p> Signup and view all the answers

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

<p>&quot;The Americas&quot; and Asia (C)</p> Signup and view all the answers

What determines the ultimate nature of alphavirus and flavivirus diseases?

<p>The specific tissue tropisms of the virus, concentration of infecting virus, and individual responses to the infection (D)</p> Signup and view all the answers

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

<p>Cytokine storm induced by immune responses (C)</p> Signup and view all the answers

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

<p>By infecting endothelial cells lining brain vessels (A)</p> Signup and view all the answers

Which response limits replication of alphaviruses and flaviviruses?

<p>Interferon (IFN)-α and IFN-β induction (D)</p> Signup and view all the answers

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

<p>By recognizing type-common antigens on all family viruses (C)</p> Signup and view all the answers

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

<p>Arthritides and systemic symptoms (D)</p> Signup and view all the answers

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

<p>Humans cannot spread the virus back to the vector (B)</p> Signup and view all the answers

How are secondary viremias related to targeting specific organs in alphavirus and flavivirus infections?

<p>Secondary viremias produce sufficient virus to infect target organs based on tissue tropism (D)</p> Signup and view all the answers

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

<p>Immunity protects against primary infection but can exacerbate immunopathogenesis (B)</p> Signup and view all the answers

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

<p>Antibodies neutralize viral attachment proteins (B)</p> Signup and view all the answers

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

<p>Infection of plasmacytoid dendritic cells causing cytokine production (C)</p> Signup and view all the answers

Why is inflammation a double-edged sword in response to alphavirus and flavivirus infections?

<p>Inflammation can destroy tissues but also contributes to pathogenesis like encephalitis (B)</p> Signup and view all the answers

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