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?

They act as antigens for the immune response Signup and view all the answers

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

It is a single-stranded RNA genome Signup and view all the answers

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

Antigenic drift Signup and view all the answers

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

Production of a new virus subtype with altered virulence and tropism Signup and view all the answers

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

To release H and N proteins from the virus Signup and view all the answers

Which type of cells are the target cells for papillomavirus?

Keratinocytes in the basal layer of the skin Signup and view all the answers

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

To inhibit the cell's tumour suppressor proteins Signup and view all the answers

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

Mimicking bases in DNA to inhibit virus replication Signup and view all the answers

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

Ability to produce vaccines with multiple antigens Signup and view all the answers

What is the target population for HPV vaccination?

Pre-pubescent girls and boys Signup and view all the answers

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

To form virus-like particles Signup and view all the answers

What is the limitation of antiviral treatment for viral infections?

All of the above Signup and view all the answers

What is the purpose of the quadravalent Gardasil vaccine?

To protect against HPV types 6, 11, 16, and 18 Signup and view all the answers

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

By binding to the HSV DNA polymerase and preventing DNA synthesis Signup and view all the answers

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

A purified protein from the HSV 2 capsid Signup and view all the answers

What is the primary target of HIV reverse transcriptase?

Converting ssRNA to dsDNA Signup and view all the answers

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

By blocking the processing of proteins for virus assembly Signup and view all the answers

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

To pass the virus onto T cells and macrophages Signup and view all the answers

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

They have a slow progression of the disease due to unknown factors Signup and view all the answers

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

By binding to picornaviruses and altering capsid conformation Signup and view all the answers

What is the effect of Interferons on virus protein production?

It inhibits the transcription of virus mRNA Signup and view all the answers

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

Nerve ganglia Signup and view all the answers

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

Chain termination of viral DNA replication Signup and view all the answers

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

Development of resistance to Aciclovir Signup and view all the answers

What is the primary route of transmission for HSV?

Through direct skin contact and body fluids Signup and view all the answers

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

It leads to a decrease in the severity of subsequent infections Signup and view all the answers

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

It converts Aciclovir to ACV-monophosphate Signup and view all the answers

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

To improve the oral bioavailability of the drugs Signup and view all the answers

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

It leads to encephalitis Signup and view all the answers

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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Description

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.