5.1.1 History and Discovery of Virus

Introduction

The discovery of viruses is an important milestone in the history of biology. Viruses are infectious agents that are too small to be seen with a light microscope. Their discovery began with the observation that certain disease-causing agents could pass through filters that trapped all known bacteria. Over time, scientists were able to identify, characterize, and visualize these unique particles.

Definition

Virus: The word virus is derived from a Latin word "venom" meaning 'poison'. In the past, the term virus was associated with infectious diseases which have unknown cause.

In simple words: The term virus was originally used for any infectious disease with an unknown cause.

Core Concept

• The word virus comes from the Latin word venom, meaning poison.
• In the past, the term virus was associated with infectious diseases that had unknown causes.
• The first evidence of viruses came from filtration experiments.
• Charles Chamberlain (1884) found that the causative agent of rabies could pass through a porcelain filter (pore size 100–1000 nm).
• Such filters could remove all bacteria or other cells known at the time.
• Iwanowsky (1892) discovered that the tobacco mosaic disease agent could pass through a porcelain filter and still cause disease in healthy plants.
• By 1900, similar disease-producing substances were discovered in both plants and animals.
• These substances were named filterable viruses.
• W. M. Stanley (1935) crystallized the infectious particle, now known as tobacco mosaic virus (TMV).
• Later, many viruses were seen with the help of the electron microscope.
• The study of viruses is called virology.

Detailed Explanation

1. Charles Chamberlain (1884)

• Charles Chamberlain worked with Louis Pasteur.
• He was studying rabies.
• He found that the causative agents of rabies could pass through a porcelain filter.
• The porcelain filter had pore sizes of 100–1000 nm.
• Such filters could be used to completely remove all bacteria or other cells known at the time from a liquid suspension.
• This was the first evidence about the existence of viruses.

• Year: 1884
• Scientist: Charles Chamberlain
• Worked with: Louis Pasteur
• Disease: Rabies
• Finding: Causative agent passed through porcelain filter
• Importance: First evidence of viruses

2. Iwanowsky (1892)

• Tobacco mosaic disease was thought to be caused by bacteria.
• Iwanowsky extracted the juice from the leaves of tobacco having tobacco mosaic disease.
• In order to remove bacteria, the juice was passed through a porcelain filter.
• He then rubbed the filtered juice on the leaves of healthy plants.
• He expected no disease to develop.
• But the healthy leaves soon showed the symptoms of the disease.
• This showed that the disease-causing agent was smaller than bacteria and could pass through the filter.

• Year: 1892
• Scientist: Iwanowsky
• Disease: Tobacco mosaic disease
• Method: Filtration through porcelain filter
• Finding: Filtered juice still caused disease
• Importance: Discovered filterable viruses

3. Naming of Filterable Viruses (1900)

• By 1900, similar disease-producing substances had been discovered in both plants and animals.
• The name filterable viruses was given to these substances.
• "Filterable" referred to their ability to pass through filters that trapped bacteria.
• "Viruses" referred to their infectious nature.

• Year: 1900
• Name: Filterable viruses
• Finding: Similar agents in plants and animals
• Importance: Established the term "virus"

4. W. M. Stanley (1935)

• W. M. Stanley crystallized the infectious particle.
• The particle is now known as tobacco mosaic virus (TMV).
• Crystallization showed that the virus was a chemical substance, not a cell.
• This was an important step in understanding the nature of viruses.

• Year: 1935
• Scientist: W. M. Stanley
• Achievement: Crystallized TMV
• Importance: Showed viruses are chemical substances
• Award: Nobel Prize in Chemistry (1946)

5. Electron Microscopy (Later)

• Many other viruses have been seen with the help of the electron microscope.
• The electron microscope has a much higher resolution than the light microscope.
• It allowed scientists to see the structure of viruses.
• This led to the detailed study of viral morphology and classification.

• Technique: Electron microscopy
• Importance: Visualized virus structure
• Result: Detailed study of viral morphology

6. Virology

• The study of viruses is called virology.
• Virology is a branch of microbiology.
• It includes the study of:
• Virus structure
• Virus classification
• Virus replication
• Virus-host interactions
• Viral diseases
• Antiviral drugs and vaccines

• Virology = study of viruses
• Branch of microbiology
• Includes structure, classification, replication, diseases

Intermediate Level

Timeline of Virus Discovery

Key Experiments

• Disease: Rabies
• Method: Filtration through porcelain filter
• Finding: Filtered juice still caused disease
• Conclusion: Agent smaller than bacteria

• Disease: Tobacco mosaic disease
• Method: Filtration through porcelain filter
• Finding: Filtered juice still caused disease in healthy plants
• Conclusion: Agent smaller than bacteria

• Agent: Tobacco mosaic virus (TMV)
• Method: Crystallization
• Finding: Virus crystallized
• Conclusion: Viruses are chemical substances

Importance of Each Discovery

Important Points

• 1. The word virus is derived from a Latin word "venom" meaning 'poison'.
• 2. In the past, the term virus was associated with infectious diseases which have unknown cause.
• 3. The first evidence about the existence of virus came when (in 1884) Charles Chamberlain, who worked with Louis Pasteur, found that the causative agents of rabies could pass through the porcelain filter (pore sizes of 100–1000 nm).
• 4. However, such filters could be used to completely remove all bacteria or other cells known at the time from a liquid suspension.
• 5. Tobacco mosaic disease was thought to be caused by bacteria.
• 6. Iwanowsky (in 1892) extracted the juice from the leaves of tobacco having tobacco mosaic disease.
• 7. In order to remove bacteria, the juice was passed through porcelain filter.
• 8. He then rubbed the filtered juice on the leaves of healthy plants, expecting no disease to develop, but the healthy leaves soon showed the symptoms of the disease.
• 9. By 1900, similar disease-producing substances had been discovered in both plants and animals.
• 10. The name filterable viruses was given to these substances.
• 11. W. M. Stanley (in 1935) crystallized the infectious particle, now known as tobacco mosaic virus (TMV).
• 12. Subsequently, many other viruses have been seen with the help of the electron microscope.
• 13. The study of virus is called virology.

Remember

• - Virus = Latin for poison
• - Chamberlain (1884) = rabies agent passes through filter
• - Iwanowsky (1892) = tobacco mosaic disease agent passes through filter
• - 1900 = named "filterable viruses"
• - **Stanley (1935)** = crystallized TMV
• - Electron microscope = visualized viruses
• - Virology = study of viruses
• - TMV = tobacco mosaic virus
• - Filterable virus = virus that passes through bacteria-trapping filters

Common Mistakes

• 1. Thinking viruses were discovered before bacteria – Bacteria were discovered first; viruses were discovered later because they are smaller.
• 2. Confusing Chamberlain and Iwanowsky – Chamberlain studied rabies (1884); Iwanowsky studied tobacco mosaic disease (1892).
• 3. Thinking Iwanowsky named the virus – Iwanowsky discovered the filterable agent; the name "filterable viruses" was given in 1900.
• 4. Thinking Stanley discovered TMV – Stanley crystallized TMV; Iwanowsky discovered it.
• 5. Forgetting the pore size of the porcelain filter – 100–1000 nm.
• 6. Confusing the terms "virus" and "virion" – Virus = infectious agent; Virion = complete viral particle.
• 7. Thinking electron microscopy was available in the 1800s – Electron microscopy was developed in the 1930s.
• 8. Forgetting the Latin meaning of virus – Virus = poison.
• 9. Thinking all viruses cause disease – Some viruses are beneficial (e.g., in genetic engineering).
• 10. Confusing the scientists' contributions – Each scientist contributed to the discovery and understanding of viruses.
• 11. Thinking filterable viruses were immediately recognized as different from bacteria – It took time to understand that viruses are different from bacteria.
• 12. Forgetting the importance of crystallization – Crystallization showed that viruses are chemical substances, not cells.

Quick Revision

• The word virus is derived from a Latin word "venom" meaning 'poison'.
• In the past, the term virus was associated with infectious diseases which have unknown cause.
• The first evidence about the existence of virus came when (in 1884) Charles Chamberlain, who worked with Louis Pasteur, found that the causative agents of rabies could pass through the porcelain filter (pore sizes of 100–1000 nm).
• However, such filters could be used to completely remove all bacteria or other cells known at the time from a liquid suspension.
• Tobacco mosaic disease was thought to be caused by bacteria.
• Iwanowsky (in 1892) extracted the juice from the leaves of tobacco having tobacco mosaic disease.
• In order to remove bacteria, the juice was passed through porcelain filter.
• He then rubbed the filtered juice on the leaves of healthy plants, expecting no disease to develop, but the healthy leaves soon showed the symptoms of the disease.
• By 1900, similar disease producing substance had been discovered in both plants and animals.
• The name filterable viruses were given to these substances.
• W. M. Stanley (in 1935) crystallized the infectious particle, now known as tobacco mosaic virus (TMV).
• Subsequently many other viruses actually have been seen with the help of the electron microscope.
• The study of virus is called virology.

60-Second Revision

• Virus = Latin for poison
• Chamberlain (1884) = rabies agent passes through filter
• Iwanowsky (1892) = tobacco mosaic disease agent passes through filter
• 1900 = named "filterable viruses"
• **Stanley (1935)** = crystallized TMV
• Electron microscope = visualized viruses
• Virology = study of viruses
• TMV = tobacco mosaic virus
• Filterable virus = virus that passes through bacteria-trapping filters
• Warning: Viruses were discovered after bacteria. Chamberlain studied rabies (1884); Iwanowsky studied tobacco mosaic disease (1892). The name "filterable viruses" was given in 1900. Stanley crystallized TMV in 1935. Electron microscopy was developed in the 1930s. Viruses are chemical substances, not cells. The study of viruses is called virology.