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Questions and Answers
What type of viruses contain RNA and replicate without converting to DNA?
Which type of viral infection occurs without any viral production?
What is one of the morphological effects of viral infections on host cells?
What is meant by a latent viral infection?
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What process is described when viral proteins are inserted into the plasma membrane of host cells?
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Which type of virus begins with RNA but converts it to DNA in order to replicate?
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Which effect is NOT a physiological effect of viral infections on host cells?
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What potential long-term effect can result from genotoxic effects caused by viruses?
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Which type of virus is primarily known for causing respiratory illnesses such as pneumonia and bronchitis?
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Which virus is the smallest DNA virus that specifically causes disease in humans?
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Which of the following types of viruses includes the rabies virus?
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What disease is primarily associated with Togaviruses?
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Which viral family includes viruses that are transmitted by arthropods and are known for causing encephalitis?
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What is the main method by which retroviruses like HIV integrate into a host cell?
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Which viruses are known as the largest RNA viruses that can cause severe respiratory diseases?
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What common viral family includes Enteroviruses and Rhinoviruses, known for causing a variety of human illnesses?
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Parvoviruses are known for being the smallest DNA viruses, but which among them causes human disease?
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What type of viruses are associated with hepatitis diseases in humans, including hepatitis A, B, C, D, and E?
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Study Notes
Viruses
- Microscopic particles that infect cells and organisms
- Carry DNA or RNA but cannot reproduce independently
- Infect both eukaryotes and prokaryotes
- Bacteria-infecting viruses are called bacteriophages (phages)
Viral Genomes
- Can have double-stranded or single-stranded DNA (dsDNA, ssDNA) or RNA (dsRNA, ssRNA)
- Nucleic acids may be linear or circular, with species typically containing one form
DNA Viruses
- Contain DNA and replicate using enzymes that copy DNA
RNA Viruses
- Contain RNA and replicate directly without DNA
Reverse Transcribing Viruses
- Start with RNA but convert to DNA to replicate
Viral Infections
- Abortive Infection: Infection occurs without viral production
- Lytic or Cytocidal Infection: Results in the death of the host cell
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Persistent Infection:
- Chronic: Productive but not lytic
- Latent: Limited synthesis with no viral production; virus remains dormant (e.g., cold sores, shingles)
- Slow Infections: Prolonged incubation period; damage may take years before symptoms appear
- Transforming Infections: Viral nucleic acid remains in the host indefinitely without producing viruses, possibly leading to oncogenic changes
Host Cell Damage
- Morphological Effects (Cytopathic Effects): Changes in cell shape, detachment from surfaces, lysis, membrane fusion, altered permeability, inclusion bodies, and cell death
- Physiological Effects: Viral proteins inserted into plasma membrane alter cellular characteristics and activities
- Biochemical Effects: Viruses inhibit or modify host cell macromolecules (e.g., DNA, RNA, proteins)
- Genotoxic Effects: Genotoxic substances damage host cell DNA, leading to mutations and potential cancer initiation
Viral Proteins
- When incorporated into the host cell’s plasma membrane, viral proteins can change the cell's antigenic properties and its immune response
Major Groups of Viruses in Invertebrates
- Infection Process: Viruses cause disease by breaking through protective barriers and accessing underlying tissues
- Tissue Specificity: Most viruses target specific cell or tissue types, but multiple viruses can cause the same disease
- Viral Genomes: Viruses can have either DNA or RNA as their genetic material
Adenoviruses
- 57 serotypes identified in humans
- Highly resistant to chemical and physical agents
- Investigated as vectors for gene therapy
- Primarily respiratory illnesses; can also cause gastroenteritis, conjunctivitis, cystitis, and rashes
Hepadnaviruses
- Cause hepatitis in humans and animals (e.g., Hepatitis B)
- Can result in acute, chronic, symptomatic, or asymptomatic infections
Herpesviruses
- Includes Herpes simplex 1 and 2, and Varicella-zoster virus
Papillomaviruses
- Cause warts and are potentially linked to cervical carcinomas
Parvoviruses
- Smallest DNA viruses
- Only B19 causes disease in humans; others affect animals
- Causes a contagious facial rash
Poxviruses
- Largest viruses
- Known for causing smallpox
Bunyaviridae
- Arthropod-borne viruses (transmitted by insects)
Coronaviruses
- Largest RNA viruses
- Cause respiratory and enteric diseases, including Severe Acute Respiratory Syndrome (SARS) and SARS-CoV-2 (responsible for COVID-19)
- Rapidly acts as mRNA once inside host cell
Hepatitis Viruses
- Hepatitis A, B, C, D, and E
- Can lead to cirrhosis and hepatocellular carcinoma (liver cancer)
Orthomyxoviruses
- Influenza A, B, and C viruses
- Type A is the most virulent in humans
Paramyxoviruses
- Highly pleomorphic (ability to exhibit different shapes and sizes)
- Includes:
- Morbillivirus (e.g., measles)
- Paramyxovirus - highly pathogenic
- Pneumovirus (e.g., respiratory syncytial virus)
- Nipah and Hendra viruses (zoonotic diseases)
Picornaviruses
- Important pathogens
- Includes: Enterovirus, Rhinovirus, Hepatovirus, Aphthovirus, Parechovirus, Erbovirus, Kobuvirus, Teschovirus
- Enteroviruses and rhinoviruses are key causes of various human illnesses
Rhabdoviruses
- Infect a wide range of hosts: plants, insects, fish, birds, mammals, including humans
- Includes the Rabies virus, which was once fatal but is now preventable with a vaccine (available post-exposure)
Reoviruses
- Not linked to a specific disease
- Rotavirus causes gastroenteritis and is responsible for about 50% of childhood diarrhea cases that require hospitalization
Retroviruses
- Integrates a copy of its RNA genome into the DNA of a host cell
- Inside the cytoplasm, the retrovirus uses its own reverse transcriptase to convert its RNA genome into DNA (reverse of the normal flow: DNA → RNA → proteins)
- The newly formed DNA is integrated into the host genome by an enzyme called integrase, resulting in proviral DNA
- Divied into 3 subfamilies: Oncovirinae, Lentivirinae, and Spumavirinae
- Example: HIV, caused by a lentivirus
Togaviruses
- Alphavirus: Associated with infectious arthritis, encephalitis, and fever
- Rubivirus: Causes rubella (German measles)
Flaviviruses
- Includes viruses that cause yellow fever, encephalitis, dengue fever, hepatitis C, and the West Nile virus
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