Influenza Virus: Structure, Transmission, and Pathology
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Questions and Answers

What is the primary site of influenza virus entry into the host?

  • Lymphoid organs
  • Lower respiratory tract
  • Upper respiratory tract
  • Epithelial mucosa (correct)

What is the function of the neuraminidase enzyme on the influenza virus?

  • It cleaves sialic acid sugars on the cell surface (correct)
  • It inhibits the immune response
  • It facilitates the release of the viral genome
  • It binds to sialic acid sugars on the cell surface

What is the primary factor contributing to the rapid evolution of the influenza virus?

  • The lack of proof-reading ability in RNA polymerase (correct)
  • The high error rate of DNA polymerase
  • The presence of multiple serotypes
  • The ability of the virus to infect multiple hosts

What is the primary role of the haemagglutinin and neuraminidase proteins on the influenza virus?

<p>They act as antigens for the immune response (D)</p> Signup and view all the answers

What is the characteristic of the influenza virus genome that contributes to its high mutation rate?

<p>It is a single-stranded RNA genome (B)</p> Signup and view all the answers

What is the term used to describe the continuous, rapid evolution of the influenza virus?

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

What is the outcome of genomic segment reassortment in co-infected cells?

<p>Production of a new virus subtype with altered virulence and tropism (A)</p> Signup and view all the answers

What is the purpose of detergent treatment in the production of influenza vaccines?

<p>To release H and N proteins from the virus (B)</p> Signup and view all the answers

Which type of cells are the target cells for papillomavirus?

<p>Keratinocytes in the basal layer of the skin (C)</p> Signup and view all the answers

What is the role of the E6 and E7 proteins in HPV infection?

<p>To inhibit the cell's tumour suppressor proteins (B)</p> Signup and view all the answers

What is the mechanism of action of nucleoside analogues as antiviral drugs?

<p>Mimicking bases in DNA to inhibit virus replication (A)</p> Signup and view all the answers

What is the advantage of recombinant DNA technology in vaccine production?

<p>Ability to produce vaccines with multiple antigens (B)</p> Signup and view all the answers

What is the target population for HPV vaccination?

<p>Pre-pubescent girls and boys (A)</p> Signup and view all the answers

What is the purpose of the L1 capsid protein in HPV vaccines?

<p>To form virus-like particles (C)</p> Signup and view all the answers

What is the limitation of antiviral treatment for viral infections?

<p>All of the above (D)</p> Signup and view all the answers

What is the purpose of the quadravalent Gardasil vaccine?

<p>To protect against HPV types 6, 11, 16, and 18 (B)</p> Signup and view all the answers

What is the primary mechanism by which Foscarnet prevents HSV replication?

<p>By binding to the HSV DNA polymerase and preventing DNA synthesis (A)</p> Signup and view all the answers

What is the primary component of the HSV 2 vaccine currently in Phase III clinical trials?

<p>A purified protein from the HSV 2 capsid (C)</p> Signup and view all the answers

What is the primary target of HIV reverse transcriptase?

<p>Converting ssRNA to dsDNA (D)</p> Signup and view all the answers

What is the primary mechanism by which Protease inhibitors block HIV replication?

<p>By blocking the processing of proteins for virus assembly (A)</p> Signup and view all the answers

What is the primary role of dendritic cells in the initial stages of HIV infection?

<p>To pass the virus onto T cells and macrophages (D)</p> Signup and view all the answers

What is the primary reason why some HIV-infected individuals appear to be immune to developing AIDS?

<p>They have a slow progression of the disease due to unknown factors (C)</p> Signup and view all the answers

What is the primary way that Pleconaril prevents polio virus replication?

<p>By binding to picornaviruses and altering capsid conformation (D)</p> Signup and view all the answers

What is the effect of Interferons on virus protein production?

<p>It inhibits the transcription of virus mRNA (C)</p> Signup and view all the answers

What is the primary site of latency for HSV in the body?

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

What is the primary mechanism of Nucleoside analogue drugs such as Aciclovir?

<p>Chain termination of viral DNA replication (A)</p> Signup and view all the answers

What is the result of excessive use of thymidine analogues in treating HSV infections?

<p>Development of resistance to Aciclovir (C)</p> Signup and view all the answers

What is the primary route of transmission for HSV?

<p>Through direct skin contact and body fluids (B)</p> Signup and view all the answers

What is the effect of reactivation of HSV on the immune system?

<p>It leads to a decrease in the severity of subsequent infections (D)</p> Signup and view all the answers

What is the role of HSV thymidine kinase enzyme in the activation of Aciclovir?

<p>It converts Aciclovir to ACV-monophosphate (A)</p> Signup and view all the answers

What is the primary reason for the development of newer prodrugs of Nucleoside analogue drugs?

<p>To improve the oral bioavailability of the drugs (C)</p> Signup and view all the answers

What is the primary effect of HSV infection on the CNS in rare cases?

<p>It leads to encephalitis (B)</p> Signup and view all the answers

Flashcards

Orthomyxoviridae

A family of viruses that includes influenza A, B, and C. Types A and B are responsible for seasonal flu outbreaks.

Enveloped

A type of virus that has an outer lipid envelope surrounding its genetic material. Its shape can vary.

ssRNA (-)

Influenza viruses have a single-stranded RNA genome, which is negative-sense, meaning it cannot be directly translated into proteins.

8 segments

The influenza virus genome is divided into 8 separate segments of RNA, each encoding different proteins.

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Types A, B, and C

Influenza viruses are classified into three types: A, B, and C. Types A and B cause the seasonal epidemics we experience.

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Host range

Influenza A viruses have a broad host range, but their primary host is birds, especially wild aquatic birds.

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Portal entry

Influenza viruses enter the body through the respiratory tract, mainly by inhaling infected droplets.

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Target cells

Influenza viruses primarily target the epithelial cells of the lower respiratory tract, specifically the lungs.

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Symptoms

Symptoms of influenza infection, which include coughing and fever, result from the virus damaging the respiratory tract.

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Pathology

Influenza viruses cause damage to epithelial cells lining the respiratory system, which can lead to pneumonia.

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Haemagglutinin (HA)

Haemagglutinin (HA) is a protein on the surface of influenza viruses that binds to sialic acids present on the surface of cells.

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Neuraminidase (NA)

Neuraminidase (NA) is another protein on the surface of influenza viruses that cleaves sialic acids, helping the virus release from infected cells.

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Antigens

Influenza viruses use their HA and NA proteins to recognize and infect cells, and these proteins are also the main targets for the immune system.

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Nomenclature

Influenza viruses are named based on their HA and NA subtypes, such as H5N1 (bird flu) and H1N1 (swine flu).

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Influenza virus evolution

The influenza virus replication process involves a complex interplay of enzymes, mutations, and reassortment, leading to viral evolution and antigenic changes.

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Polymerase enzymes

Influenza virus polymerase enzymes make copies of the viral genome during replication.

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RNA mutation rate

RNA genomes are prone to mutations because they lack the proofreading mechanisms that DNA genomes have.

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Antigenic drift

The constant and rapid accumulation of mutations in influenza viruses is known as antigenic drift, contributing to seasonal flu outbreaks.

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Antigenic shift

When two influenza viruses infect a cell, their RNA segments can mix and match, creating a new subtype with altered virulence and tropism.

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Vaccine development

The frequent emergence of new influenza virus subtypes makes it challenging to develop effective vaccines.

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Influenza vaccines

Most influenza vaccines are composed of inactive (killed) viruses, which are treated with detergents to release HA and NA proteins.

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Seasonal influenza

Influenza vaccines containing multiple strains are often used in the

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Papillomaviridae

Papillomaviruses are a diverse family of DNA viruses that infect epithelial cells.

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Host range

Papillomaviruses infect the skin and mucous membranes, with different types targeting specific sites and having varying effects on the host.

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Portal entry

Papillomaviruses enter the body through small wounds in the skin or mucous membranes, often during direct contact.

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Target cells

Papillomaviruses typically infect keratinocytes, which are the main cells of the skin.

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Pathology

Papillomavirus infections can cause benign skin growths (warts) or, in some cases, cervical cancer.

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Oncogenic HPV

Some papillomaviruses are oncogenic, meaning they can promote cancer development.

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Papillomavirus infection cycle

Papillomavirus infection can be acute, leading to latency, or it can reactivate later, leading to blisters and shedding.

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L1 protein

The L1 capsid protein of papillomaviruses is responsible for attaching the virus to the surface of host cells.

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HPV and cancer

HPV types 16 and 18 are responsible for approximately 70% of cervical and anal cancer cases.

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HPV vaccines

Vaccination against HPV, using virus-like particles, aims to prevent HPV infection and its associated diseases, particularly cervical cancer.

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Study Notes

Influenza Virus

  • Family: Orthomyxoviridae
  • Enveloped, pleomorphic, ssRNA (-) in 8 segments (1-2kbp)
  • Types: A, B, and C (A and B cause epidemics)
  • Host range: Specific mammals, but Type A's primary host is birds (natural reservoir in wild aquatic birds)
  • Portal entry: Epithelial mucosa via aerosol
  • Target cells: Lower respiratory tract
  • Symptoms: Cough, fever
  • Pathology: Epithelial cells, pneumonia
  • Envelope spikes: Haemagglutinin (binds to sialic acid sugars on cell surface) and neuraminidase (enzyme cleaves sialic acid)
  • Antigens: Haemagglutinin and neuraminidase for immune response
  • Nomenclature based on these glycoproteins (e.g., H5N1 "bird flu" and H1N1 "swine flu")
  • H1N1 pandemic in 1918 killed 50 million people

Influenza Virus Evolution

  • Polymerase enzymes involved in synthesizing new genomes during replication
  • RNA genomes mutate at a faster rate than DNA genomes due to lack of proofreading ability
  • Continuous, rapid evolution or "antigenic drift"
  • If cell is co-infected, genomic segment reassortment can produce new virus subtype ("antigenic shift") with altered virulence and tropism
  • Frequent emergence of new subtypes makes effective vaccine production difficult

Influenza Virus Vaccines

  • Mostly dead vaccines are employed, where several current isolates are detergent-treated to release H and N proteins ("Split Virion")
  • Used for seasonal influenza in "at-risk" individuals (adults, particularly 65+ and 50+ years old)

Papillomavirus

  • Family: Papillomaviridae
  • DNA genome
  • Host range: Specific types infect birds, mammals (humans, 60 types)
  • Portal entry/target cells: Small wounds in skin (keratinocytes) or mucosa via direct contact
  • Pathology: Benign tumors (warts), cervical cancer
  • Specific types infect specific sites and are oncogenic (cancer-causing)
  • Acute infection → latency
  • Later reactivation (e.g., when immunocompromised) produces local blisters (virus shedding)
  • Envelope spikes: L1 capsid protein binds to surface of cell
  • HPV and Cancer: E6 and E7 inactivate cell's tumor suppressor proteins, promoting cell growth → benign/premalignant tumors
  • HPV types 16 and 18 cause 70% of cervical (+ anal) cancer cases
  • HPV types 6 and 11 cause 90% of genital wart cases
  • HPV vaccines: Bivalent CERVARIX (GSK) and quadravalent GARDASIL (Merck)

Anticancer Vaccine

  • Consists of genetically engineered, purified L1 capsid protein that forms virus-like particles (VLPs)
  • Aim to vaccinate pre-pubescent girls before exposure to HPV

Recombinant Vaccine

  • Molecular biology techniques enable production of genetically engineered/recombinant DNA vaccines
  • Example: Hepatitis B surface antigen (1st recombinant vaccine)
  • Involves cloning the viral gene into a suitable DNA expression vector, transferring the clone into an appropriate cell line, and purifying the expressed protein

Antiviral Drugs

  • Three main problems for antiviral treatment:
    1. When clinical symptoms appear, virus replication has peaked – too late for therapy
    2. Difficult to discriminate between virus multiplication and cell processes
    3. Selection of resistant mutants
  • Most antivirals only target replicating (not latent) viruses
  • Nucleoside analogues mimic bases in DNA, activated by virus, stopping virus DNA synthesis and thus propagation
  • Inhibitors of attachment, release
  • Resistance/Other Treatment: Foscarnet (AstraZeneca) is a pyrophosphate analogue that binds to HSV DNA polymerase, preventing DNA synthesis

Varicella Zoster Virus

  • VZV – chicken pox and shingles
  • VZV is a herpes, not a pox virus
  • Shingles vaccine (prophylactic): Zostavax (Sanofi), contains live attenuated virus

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Test your knowledge of the influenza virus, including its structure, transmission, and effects on the human body. Learn about the different types of influenza, its host range, and the symptoms of infection.

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