Virology: Structure and Function of Viruses

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Questions and Answers

What is the main function of viral proteins in a virus?

To destroy the host cell's immune system

To facilitate the transfer of the viral nucleic acid from one host cell to another (correct)

To facilitate the replication of the host cell

To protect the host cell from other pathogens

What is the primary function of hemagglutinin in viruses?

To protect the viral genome against inactivation by nucleases

To destroy the host cell's immune system

To cause red blood cells to agglutinate, or clump together (correct)

To facilitate the transfer of the viral nucleic acid from one host cell to another

What is the characteristic of viral nucleic acid that is used for classifying viruses into families?

Type of protein, its structure, and its function

Type of lipid, its structure, and its function

Type of symmetry, its shape, and its size

Type of nucleic acid, its polarity, and its size (correct)

What is the term for the 'core' or 'genome' of a virus?

Viral nucleic acid Signup and view all the answers

What is the characteristic of lipid-containing viruses?

They are sensitive to treatment with ether and other organic solvents Signup and view all the answers

What is the term for the symmetry of viruses with a polygon with 12 corners/vertices, 20 surfaces/sides?

Icosahedral Signup and view all the answers

What is the term for the symmetry of viruses with protein subunits (capsomeres) packed in a helical array around the viral nucleic acid?

Enveloped/Helical Signup and view all the answers

What is the main function of the viral lipid envelope?

To acquire lipid during maturation Signup and view all the answers

Which of the following viruses causes most epidemics and all global pandemics?

Influenza type A Signup and view all the answers

What is the natural reservoir of SARS-like coronaviruses?

Chinese horseshoe bats Signup and view all the answers

Which of the following viruses is characterized by causing common colds but can also cause serious respiratory illness?

Coronavirus Signup and view all the answers

What is a common symptom of parvovirus B19 infection?

Sore throat Signup and view all the answers

What is the type of RNA found in Orthomyxoviruses?

Single-stranded, negative-sense RNA Signup and view all the answers

Where do most RNA viruses replicate?

Cytoplasm Signup and view all the answers

Which of the following viruses is implicated in gastroenteritis in infants?

Coronavirus Signup and view all the answers

What is the main route of transmission for poliovirus?

Through the mouth, multiplying in the intestine Signup and view all the answers

What is the likely origin of the SARS virus?

Bats and was transmitted to humans Signup and view all the answers

What is the result of destruction of motor neurons in the spinal cord in poliovirus infection?

Flaccid paralysis Signup and view all the answers

What is the purpose of vaccination against poliovirus?

To prevent and control poliovirus infection Signup and view all the answers

What is the most common form of poliovirus infection?

Mild disease Signup and view all the answers

What is the duration of nonparalytic poliomyelitis (Aseptic Meningitis)?

2-10 days Signup and view all the answers

What is the outcome of a small percentage of cases of nonparalytic poliomyelitis?

Paralysis Signup and view all the answers

What is the result of HIV infecting T-Helper Cells?

A reduction of the adaptive immune response of the host Signup and view all the answers

What enables extremely virulent strains of viruses to evolve?

Mutation and natural selection within the virus population Signup and view all the answers

What is characteristic of Herpesviruses?

They are enveloped, large viruses with a double-stranded DNA genome Signup and view all the answers

What is the sequence of events following an initial Herpesvirus infection?

Acute infection followed by a period of latent infection Signup and view all the answers

What is a common source of Herpesviruses transmission?

Saliva, skin lesions, and respiratory secretions from infected, asymptomatic carriers Signup and view all the answers

What is a complication of HSV-1 infection?

Herpes encephalitis Signup and view all the answers

What is the route of transmission for HSV-2?

Sexual contact Signup and view all the answers

What is a possible consequence of oral to genital sex with HSV-1 positive individuals?

Infection of the genitals with HSV-1 Signup and view all the answers

What is the most common fungal bloodstream infection in hospitalized patients?

Candidemia Signup and view all the answers

Which of the following is a characteristic of Cryptococcosis?

Involving the meninges, lungs, and lymph nodes Signup and view all the answers

What is the mode of transmission of Cryptococcosis?

Through inhalation of spores Signup and view all the answers

What is the primary site of infection in Dermatophytosis?

Keratinized tissue Signup and view all the answers

What is the term for the presence of Candida species in the blood?

Candidemia Signup and view all the answers

Which type of mycosis is caused by dimorphic fungi?

Systemic mycosis Signup and view all the answers

What is the term for fungal infections that invade the deep organs?

Systemic mycosis Signup and view all the answers

Which of the following is a characteristic of Candidemia?

Mortality is very high Signup and view all the answers

Study Notes

Viral Structure and Composition

A virion is an intact infectious virus particle, consisting of viral protein, nucleic acid, and lipid envelopes.
Hemagglutinin is a naturally occurring glycoprotein that causes red blood cells to agglutinate or clump together.
Viral protein facilitates the transfer of viral nucleic acid from one host cell to another, protects the viral genome against inactivation by nucleases, and participates in the attachment of the virus particle to a susceptible cell.
There are two types of viral proteins: structural proteins present in the coat of the virus, and non-structural proteins, including hemagglutinin and enzymes.

Viral Nucleic Acid

Viruses contain a single kind of nucleic acid, either DNA or RNA, which encodes the genetic information necessary for replication.
The genome may be single or double-stranded, circular or linear, and segmented or non-segmented.
The type of nucleic acid, its polarity, and its size are major characteristics used for classifying viruses into families.

Viral Lipid Envelopes

Lipid is acquired when the viral nucleocapsid buds through a cellular membrane during maturation.
Lipid-containing viruses are sensitive to treatment with ether and other organic solvents, indicating that disruption or loss of lipid results in loss of infectivity.
Nonlipid-containing viruses are generally resistant to ether and detergents.

Symmetry of Viruses

Icosahedral viruses have a rigid, polygon-shaped structure with 12 corners/vertices and 20 surfaces/sides.
Examples of icosahedral viruses include herpesvirus, parvovirus, papovavirus, adenovirus, picornavirus, and reovirus.
Enveloped/helical viruses have protein subunits (capsomeres) packed in a helical array around the viral nucleic acid, forming a spiral tube or helix.
Complex viruses neither have icosahedral nor enveloped/helical structures.

Virulence Factors

Some viral particles can replicate during the defensive inflammation responses of the host, such as during virus-induced fever.
Extremely virulent strains can eventually evolve by mutation and natural selection within the virus population inside a host.

DNA Viruses: Herpesviruses

Herpesviruses are enveloped, large viruses with a double-stranded DNA genome, belonging to the family Herpesviridae.
Sources of herpesviruses include saliva, skin lesions, and respiratory secretions from infected, asymptomatic carriers.
Herpesviruses produce an initial acute infection followed by a period of latent infection, with reactivation resulting in recurrent infection.
Herpesviruses exhibit a wide spectrum of disease, including gingivostomatitis, pharyngitis or tonsillitis, lesion on the face, herpes encephalitis, and eczema.

RNA Viruses

RNA viruses replicate in the cytoplasm and have a simpler mechanism of replication, with early and late mRNA not clearly separated.
There is no host cell RNA polymerase that can use the viral parental RNA as a template for synthesis of complementary RNA strands.
Examples of RNA viruses include enteroviruses, polioviruses, coronaviruses, and orthomyxoviruses.

Enteroviruses

Enteroviruses are transient inhabitants of the human alimentary tract and may be isolated from the throat or lower intestine.

Polioviruses

Polioviruses are shed by infected individuals into the environment, spreading rapidly in areas of poor sanitation.
Poliovirus causes polio or poliomyelitis, entering through the mouth and multiplying in the intestine.
The virus mainly affects nerves in the spinal cord or brain stem, resulting in flaccid paralysis.
Prevention and control are achieved through a series of vaccinations.

Arboviruses in the Philippines

Examples of prevalent arboviruses in the Philippines include dengue (DEN), Japanese encephalitis (JE), chikungunya (CHIKV), and Zika virus (ZKV).

Coronaviruses

Coronaviruses are large, enveloped RNA viruses that cause common colds and may cause lower respiratory tract infections and gastroenteritis in infants.
Novel coronaviruses have been identified as the cause of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).

Fungal Infections

Yeast infections, such as candidemia, can spread through eyes, endocardium, meninges, kidney, liver, spleen, and bone, and may cause cross-infection (mother to baby).
Diagnosis is through blood culture test.
Cryptococcosis is a fungal infection caused by Cryptococcus neoformans, which is found worldwide and is an opportunistic invasive fungus.

Clinical Classification of Mycoses

Superficial mycoses affect the mucus membrane or keratinized tissue.
Subcutaneous mycoses are due to the implantation of environmental fungi.
Systemic mycoses cause widespread disease and are serious and fatal, often affecting healthy individuals and opportunistic infections in immunocompromised individuals.

Filamentous Fungi Infections

Examples of filamentous fungi infections include dermatophytosis (ringworm infection), which appears as red patches on the affected area of the skin and later spreads to other parts of the body.

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Description

This quiz covers the composition and properties of viruses, including their chemical makeup, proteins, and mechanisms of infection. Test your knowledge of viral structure and function!