Virology Quiz: Virus Assembly and Cultivation

Virology - Lecture 1

• Nucleic acids (DNA and RNA) are hereditary material in nearly all organisms.
• DNA is located mostly in the cell nucleus.
• DNA has four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
• Human DNA has about 3 billion bases, with over 99% being the same in all people.
• The order of these bases determines the organism's information.
• DNA bases pair up: A with T, and C with G.
• A nucleotide is a base, sugar, and phosphate molecule.
• Nucleotides form two long strands that create a DNA double helix.
• RNA is an important molecule, also made of nucleotides.
• Each RNA nucleotide has a nitrogenous base, ribose sugar, and a phosphate, like DNA.
• RNA is typically single-stranded, in contrast to DNA's double helix.
• RNA contains ribose, while DNA has deoxyribose.
• RNA has the bases: Adenine (A), Uracil (U) (instead of thymine in DNA), Cytosine (C), and Guanine (G).

Virology - Viruses

• Viruses are the smallest unicellular infectious agents (20 nm to 300 nm in diameter).
• Viruses contain only one type of nucleic acid (RNA or DNA).
• The nucleic acid is encased in a protein shell (capsid).
• The capsid may be surrounded by a lipid membrane.
• Viruses are obligate intracellular molecular parasites.
• Viral genome is composed of DNA or RNA.
• Viruses synthesize virion components in a host cell.
• Progeny virus particles spread infection to new cells.

Virus Structure

• Viruses have various symmetries
• Icosahedral symmetry is a Platonic solid with twenty faces.
• Helical symmetry of the capsid forms a spiral-like structure.
• Complex symmetry structures have an undefined symmetry.

Virus Classification

• Virus classification considers nucleic acid type, capsid symmetry, presence of an envelope, and size.
• Seven groups exist: double-stranded DNA, single-stranded DNA, double-stranded RNA, single-stranded positive sense RNA, single-stranded negative sense RNA, single-stranded RNA with DNA intermediate, and double-stranded DNA with RNA intermediate.

Virus Replication

• Viral replication occurs in seven stages: attachment, entry, uncoating, transcription/mRNA production, synthesis of virus components, virion assembly, and release.
• Viruses attach to the host's cell membrane.
• Viral nucleic acid enters a host cell by endocytosis (animal cells) or pinocytosis (plant cells).
• Viral enzymes remove the capsid.
• Host cell machinery produces mRNA from viral nucleic acid.
• Viral components are assembled into new viruses.
• Newly formed viruses are released from the infected host cell, sometimes causing the cell to rupture.

Viral Infection of a Cell

• Viruses infect host cells (eukaryotic or prokaryotic), and are separated from host cells using centrifugation or filtration.

Cultivation of Viruses

• Viruses can be grown in vivo (in a living organism - e.g., embryonated eggs) or in vitro (in test tubes or cell cultures).
• Viruses need a host cell for replication.
• Filters are used to separate virions from larger particles

Anti-viral Chemotherapy

• Antiviral drugs target viral replication but do not harm host cells.
• Viral replication varies, and drugs must be selective.
• Difficult to develop effective antiviral drugs due to the dependence of viral replication on host machinery.

Viral Vaccines

• Viral vaccines stimulate an immune response.
• Killed-virus vaccines use inactivated viruses.
• Attenuated-live virus vaccines use weakened viruses.
• Extreme care is required to prevent the residual live virus in a killed-virus vaccine.
• Live viral vaccines may cause a less severe illness, but some must be boosted to maintain the immune response, whereas killed virus vaccines are generally easier to create and store but their effect often needs boosting to maintain response.

Pathogenesis of Viral Diseases

• Viruses enter, replicate, spread, and cause damage in susceptible cells.
• Viral spread can be via the bloodstream or lymphatic system.
• Viral infections may cause various effects in the body resulting in clinical illness including damage or destruction to host tissues.

Viral Shedding

• Viral shedding is the release of viruses from the host.
• The shedding occurs differently based on the agent and stage of disease (e.g., some shed in dead-end infections or different steps).

Cell Injury and Clinical Illness

• Virus-infected cells in the target tissue lead to the development of diseases.
• The degree of illness varies.

Genetic of Viruses

• DNA viruses infect animals with predominantly double-stranded DNA genomes.
• Exceptions exist in viral genomes including some RNA viruses.
• RNA viruses can have single-stranded RNA genomes, however some have double-stranded genomes.
• Retroviruses are a notable group of RNA viruses. The order mononegavirales (Rhabdoviruses, paramysxoviruses and Filoviridae) is unique in that their negative strand contains both (+) and (-) RNA

Orthomyxoviruses (Influenza Viruses)

• Influenza viruses are important respiratory pathogens, often causing worldwide epidemics.
• Influenza virus particles are usually spherical and about 100 nm in diameter. Single-stranded RNA genome.
• The subtypes differ based on HA and NA glycoproteins. This determine important antigens that determine the antigenic variability of the virus and host immunity.

Clinical Finding, Diagnosis, Serology

• Influenza attacks the upper respiratory tract, especially in high-risk populations, such as the elderly, the young and those with underlying conditions.
• Isolation of the virus from samples, serology (testing of antibodies), and other diagnostic methods aid in their diagnosis.

Paramyxoviruses & Rubella Virus

• Important respiratory pathogens in infants and young children (parainfluenza).
• Paramyxovirus particles are variable in shape and size, and can range up to 700nm.
• RNA is nonsegmented and linear, of negative-sense.
• The viral genome is about 15kb in size.
• Viruses contain six structural proteins, three involved in RNA and three that are part of the viral envelope.
• Direct viral antigen detection (e.g., immunofluorescent ) is frequently done, and nasal washes, Bronchoalveolar lavages, and lung biopsies are used for viral isolation.
• Lab Diagnosis include Antigen Detection, Isolation and Identification of virus, and Serology.

Rubella (German Measles)

• A mild viral illness, can be dangerous to unborn fetuses.
• The virus (Rubivirus) is a positive-sense single-strand RNA virus without segmentation or an envelope.
• Lab Diagnosis: Clinical diagnosis can be un-reliable. Isolation and Identification of the virus, (e.g., swabs taken six days before and after rash) is made. Serology (testing for antibodies) is often helpful but serum may need to be screened and specific antibodies tested

Enteric Viruses & Rhinoviruses

• Enteroviruses and rhinoviruses are common in the human gastrointestinal and respiratory systems.
• Enteroviruses inhabit the alimentary tract, and rhinoviruses are in the nose, and throat.
• Viral replication can lead to serious effects on the nervous system, but is dependent on the specific type of virus involved, and affects different areas of the body depending on the agent type(s).
• Diagnositic testing includes culturing the virus or PCR-based approaches to finding the virus, or by identifying antibodies indicative of a past or current infection

Herpes Viruses (HSV, VZV, CMV)

• Herpes viruses produce lifelong persistent infections.
• They have large genomes and diverse clinical effects that range from localized infections to those with much broader host ranges and systemic effects.
• Diagnosis can include identifying certain visible sores or lesions from the virus to directly identify the virus, as well as using PCR techniques or looking at antibodies indicative of past or current infections.

Oncoviruses

• Viruses can be an etiological factor in several types of human cancers, including cervical and liver cancer.
• Tumor viruses are important in carcinogenesis, acting as a factor in the process
• Viruses can be direct or indirect factors. Most DNA tumor viruses are direct, acting immediately on growth control and replication pathways within a target tissue. RNA tumor viruses must work via an intermediate step or stages, involving different parts of cellular response and genetic machinery of a susceptible cell.
• Human papilloma viruses (HPV), ,EBV (Nasopharyngeal carcinoma) and other tumor viruses can cause a number of cancers.

Hepatitis Viruses

• Hepatitis viruses cause inflammation of the liver.
• Types include Hepatitis A, B, C, D, E and other less common varieties.
• The virus causes inflammation and or acute illness in addition to damage.
• Hepatitis A is transmitted by the fecal-oral route, whereas B hepatitis is blood-borne, and C is similar. Other varieties may be more broadly transmitted or restricted.

Test your knowledge on viral assembly, replication, and cultivation methods in this comprehensive quiz. Explore the concepts of tissue tropism, viral classification, and the characteristics of different types of viruses. This quiz covers essential aspects of virology for students and enthusiasts alike.