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Questions and Answers
What is the primary characteristic that distinguishes viruses from bacteria?
What is the primary characteristic that distinguishes viruses from bacteria?
Which of the following types of nucleic acid can be found in a virus?
Which of the following types of nucleic acid can be found in a virus?
What term did Jacob Henle propose in the 1840s regarding unobservable infectious agents?
What term did Jacob Henle propose in the 1840s regarding unobservable infectious agents?
Which structure is present in bacteria but absent in viruses?
Which structure is present in bacteria but absent in viruses?
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What is the replication method utilized by viruses?
What is the replication method utilized by viruses?
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Which of the following is NOT true about the sensitivity of viruses?
Which of the following is NOT true about the sensitivity of viruses?
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What is the significance of the size difference between bacteria and viruses?
What is the significance of the size difference between bacteria and viruses?
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In which aspect are bacteriophages similar to viruses?
In which aspect are bacteriophages similar to viruses?
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What was one of the early challenges in studying viruses during the 19th century?
What was one of the early challenges in studying viruses during the 19th century?
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Which of the following statements about metabolic activity in viruses and bacteria is accurate?
Which of the following statements about metabolic activity in viruses and bacteria is accurate?
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Study Notes
Virology Introduction and History
- Virology is the scientific study of viruses.
- Viruses are either:
- Human: Smallpox, HIV, Hepatitis A, B, C, D, E, G, Poliomyelitis, Rabies
- Animal: RVF, FMD, RP, BVD
- Bird: NDV, Gumboro, IBV, ILT
- Bacterial: Bacteriophages
- Insect: Baculovirus
- Mycoplasma: Mycoplasmalphages
Definition of Virus
- A virus is a very small, obligatory intracellular parasite that lacks metabolic enzymes.
- Size: 20-300 nm (nm = 10⁻⁷ cm)
- Dependent on host cells for replication.
- Lack the machinery for energy production and macromolecule biosynthesis.
Origin of the Term "Virus"
- Originates from the Latin word "virus" meaning poison.
- Initially referred to as poisonous fluid, saps of plants, and slimy liquids.
- Later meaning was related to a specific and potentially harmful substance.
Differences Between Viruses and Bacteria
| Feature | Bacteria | Virus |
|---|---|---|
| Cell Wall | Present | Absent |
| Organelles | Present | Absent |
| Nuclear Membrane | Present | Absent |
| Metabolism | Present | Absent |
| Nucleic Acid | DNA and RNA | DNA or RNA |
| Infectious NA | Not infectious | Infectious |
| Size | Over 300nm | Under 300nm |
| Interferon Sensitivity | +ve | -ve |
| Antibiotic Sensitivity | +ve | -ve |
| Replication | Binary fission | Host cell dependent |
Origins of Virology
- Ancient civilizations (e.g., Egypt, 3700 BC) had knowledge and record of viral infections (e.g., polio).
- Ancient people researched causes and prevention of viral diseases.
Historical Background
- Pharaoh Ramses V (1196 BC) possibly had smallpox.
- Variolation (inoculation of smallpox pus) developed in China (1000 BC).
- Early 19th century understanding of a diverse microbial world (bacteria, fungi, protozoa).
- Jacob Henle (1840) hypothesized the existence of very small, infectious agents.
- Adolf Mayer (1886-1903) studied tobacco mosaic disease.
- Dmitri Iwanowski (1892) discovered that the disease could be transmitted through filters that retained bacteria.
- Martinus Beijerinck (1898) coined the term "virus".
- Foot-and-mouth disease in animals was identified (1898).
- Poliomyelitis was confirmed as a viral infection (1909).
- Bacteriophages (viruses that infect bacteria) were discovered (1915, 1917).
History of Virology (20th Century)
- Walter Reed (1900) linked yellow fever to viruses transmitted by mosquitoes.
- Max Theiler (1930s) developed an attenuated yellow fever vaccine and propagated the virus in chick embryos.
- Cell culture methods were developed allowing viruses to be cultivated
- Enders & colleagues (1949) were able to grow polioviruses in primary human cell cultures.
- Serological/Immunological methods (complement fixation, radioimmunoassays, enzyme-linked immunosorbent assays (ELISAs), etc.) refined in the mid and late 20th century
- Electron microscopy (1931) allowed visualization of viruses (magnifications over 100,000x).
Virus Shapes
- Virions (virus particles) are inert carriers of genetic material.
- Assembled inside cells, from virus-specified components.
- Do not grow or divide.
- Exhibit various shapes (e.g., HIV, phage $29$, influenza, smallpox, etc.).
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Description
This quiz covers the fundamentals of virology, including the definition of viruses, their classification, and historical context. Explore the differences between viruses and bacteria, and learn about various types of viruses affecting humans, animals, and more.
