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Questions and Answers
Which virus is an example of a retrovirus commonly involved in the replication process?
Which virus is an example of a retrovirus commonly involved in the replication process?
What is the viral replication step that occurs immediately after the virus enters the host cell?
What is the viral replication step that occurs immediately after the virus enters the host cell?
Which of these viruses is primarily known for causing liver disease with potential replication effects?
Which of these viruses is primarily known for causing liver disease with potential replication effects?
In the context of viral replication, which step follows the uncoating of the virus?
In the context of viral replication, which step follows the uncoating of the virus?
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Which of the following viruses is characterized by its ability to cause recurring infections due to latency?
Which of the following viruses is characterized by its ability to cause recurring infections due to latency?
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Which type of nucleic acid is found in all double stranded DNA viruses?
Which type of nucleic acid is found in all double stranded DNA viruses?
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What distinguishes enveloped viruses from nonenveloped viruses?
What distinguishes enveloped viruses from nonenveloped viruses?
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Which shape is associated with helical viruses?
Which shape is associated with helical viruses?
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What is the primary role of a viral capsid?
What is the primary role of a viral capsid?
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Which is true about prions?
Which is true about prions?
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What essential characteristic differentiates all RNA viruses from one another, except for Rotavirus?
What essential characteristic differentiates all RNA viruses from one another, except for Rotavirus?
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How do enveloped viruses typically exit host cells?
How do enveloped viruses typically exit host cells?
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What is the mode of release for enveloped viruses?
What is the mode of release for enveloped viruses?
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Which of the following describes a latent infection?
Which of the following describes a latent infection?
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Which of the following viruses is known to cause malignant transformation?
Which of the following viruses is known to cause malignant transformation?
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What is one of the challenges of antiviral drugs?
What is one of the challenges of antiviral drugs?
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What is the first step in the viral replication cycle?
What is the first step in the viral replication cycle?
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Arboviruses are primarily known for their transmission via which vector?
Arboviruses are primarily known for their transmission via which vector?
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Which of the following is a property of chronic viral infections?
Which of the following is a property of chronic viral infections?
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What part of the brain is commonly affected by the rabies virus?
What part of the brain is commonly affected by the rabies virus?
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Which virus is associated with feco-oral transmission?
Which virus is associated with feco-oral transmission?
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What role do antiviral drugs typically play in the treatment of viral infections?
What role do antiviral drugs typically play in the treatment of viral infections?
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Study Notes
Introduction to Virology (Lectures 13 & 14)
- Virology is the study of viruses
- Viruses are acellular infectious agents (non-living particles)
- Viruses are the smallest known infectious agents, ranging from 20 to 300 nm in diameter
- They can only be seen using an electron microscope
- They contain either RNA or DNA as their genome
- Viruses are metabolically inert, unable to generate or utilize energy
- Viruses are obligate intracellular parasites, replicating only inside living cells
Lecture Objectives
- Outline general properties of viruses
- Describe viral structure
- Classify medically important viruses
- Describe viral replication cycles
- Describe effects of viruses on host cells
- Mention clinical examples of viral infections
- Outline diagnostic methods of viral infections
Viral Structure
- A virus particle (virion) is made up of:
- Genome: DNA or RNA. All DNA viruses are double-stranded except for Parvovirus, and all RNA viruses are single-stranded except for Rotavirus.
- Capsid: A protein coat surrounding the genome. Capsid shapes include icosahedral (e.g., Adenoviruses, HBV), helical (e.g., Influenza viruses, Ebola virus), and complex (e.g., Monkeypox virus).
- Envelope: Acquired from the host cell membrane or nuclear membrane. Most icosahedral viruses are enveloped, while all helical viruses are enveloped.
- Spikes: Viral receptor proteins, enabling adhesion to the host cell.
General Properties of Viruses
- Viruses are acellular infectious agents
- They're among the smallest known infectious agents
- Their size ranges from 20 to 300 nanometers (nm)
- Viruses are only visible with an electron microscope
- Viruses contain either DNA or RNA, not both
- They are metabolically inert: they cannot produce energy on their own
- Viruses are obligate intracellular parasites which means they need a host to reproduce
Atypical Viruses
- Satellite viruses: These viruses depend on helper viruses to complete their infection cycle. An example is Hepatitis D virus (HDV), which relies on Hepatitis B virus (HBV) as a helper virus.
- Prions: Infectious proteins lacking nucleic acid. Misfolded proteins that can convert normal cellular prion proteins into misfolded forms, causing neural cell death and spongiform encephalopathy.
Classification of Viruses
- Viruses are classified based on:
- Nucleic acid type (RNA or DNA, single-stranded or double-stranded)
- Presence or absence of an envelope
- Symmetry of the capsid (icosahedral, helical, complex)
- Other factors aiding in classification include: host range, mode of transmission, pathogenicity, and tissue tropism
Viral Replication Cycle
- Absorption (attachment): Viruses attach to host cells via specific receptors on the host cell surface
- Penetration (entry): Viruses enter the host cell
- Uncoating: The viral capsid is removed, releasing the viral nucleic acid
- Transcription and translation: Viral genes are transcribed and translated into viral proteins
- Assembly: Viral components are assembled into new virions
- Release: New viruses leave the infected cell. Enveloped viruses bud from the host cell membrane; non-enveloped viruses cause lysis of the host cell.
Effect of Viruses on Host Cells
- Abortive: No viral replication or cell damage
- Acute: Viral replication and cell damage
-
Persistent:
- Latent Infection: The virus remains inactive in infected cells (e.g., HIV, Herpes viruses).
- Chronic Infection: Viral replication occurs, often with mild or few noticeable symptoms (e.g., HCV, HBV)
- Malignant Transformation (Oncogenic Viruses): Viruses cause cancerous changes in host cells. Example: HPV (cervical carcinoma) and HBV/HCV (hepatocellular carcinoma)
Clinical Examples of Viral Infections
- Skin Infections: Herpes simplex virus type 1 (HSV-1), Human papillomaviruses (HPV), and Monkeypox virus.
- Sexually Transmitted Diseases: Herpes simplex virus type 2 (HSV-2), HPV and Monkeypox virus.
- Central Nervous System Infections: HSV-1, HSV-2, Poliovirus, Rabies virus.
- Respiratory Tract Infections: Rhinoviruses, Influenza viruses, and Coronaviruses
- Gastroenteritis: Rotavirus, Enteroviruses, and Adenoviruses
- Hepatitis: HAV (fecal-oral), HBV (blood borne), and HCV (blood borne)
Diagnosis of Viral Infections
- Less used: Microscopy (electron and light), virus isolation
- More widely used: Serology (antigen and antibody detection), nucleic acid detection (e.g., PCR)
Antiviral Drugs
- Most viral infections resolve spontaneously
- Antiviral drugs inhibit viral replication
- They do not usually destroy the viruses, but inhibit replication to allow the immune system to eliminate the virus
- Antiviral drugs are only available for some viruses, such as HIV, herpes viruses, HBV, HCV, and some influenza viruses.
- It is challenging to develop antiviral drugs due to viruses being obligate intracellular parasites
- Rapid viral mutation can lead to resistance to antiviral drugs
Viral Replication Steps with Examples
- This section details specific examples of viruses to illustrate different replication steps.
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Description
Explore the fascinating world of viruses in Lectures 13 and 14 of our Introduction to Virology course. Learn about the structure, classification, and replication cycles of medically significant viruses, as well as their impact on host cells and methods for diagnosis. This quiz will enhance your understanding of viral properties and clinical examples.
