Virus: Learn About Virus and their Types for UPSC Exam

A Virus is a microscopic infectious microbe. These are unique among other microbes because they can only remain alive and are able to multiply inside the living cells of other hosts which they have invaded. The core of a virus is made up of genetic material, which can be either DNA or RNA. Viruses are generally known for causing diseases. In the past, they have caused several global outbreaks of deadly diseases like Ebola, Swine Flu, COVID-19, etc.

The virus is an important topic of the UPSC IAS exam syllabus. This topic comes under the subject Science and Technology of the UPSC Mains GS Paper 3 syllabus and UPSC Prelims syllabus of the General Studies Paper -1.

UPSC Aspirants can improve their chances of selection through Testbook's UPSC CSE Coaching and boost their preparation for IAS Exam! Other important topics related to the UPSC IAS examination can also be accessed here on Testbook!

You can download Science and Technology Notes for IAS Exam here!

What is a Virus?

A virus is a microscopic agent that causes infection in living organisms. The term ‘Virus’ is derived from Latin, where it means ‘poison’ or ‘slimy liquid’. The genetic material in the core of a virus is either DNA or RNA. This core is surrounded by a protective layer made up of a protein called the capsid. Some viruses even have an additional coating of spikes called the envelope. Viruses are generally extremely small in size. On average, a virus is one hundred times smaller in size than most bacteria. 

Features of a Virus

The following are the general features of a virus:

• There is a huge difference between bacteria and virus. The unique feature of the virus is that it cannot replicate on its own, whereas the former can reproduce on its own through Binary fission.
• The virus utilises the machinery of the host cells that it has attached to replicate or make copies of itself. 
  • Viruses lack cell organelles called ribosomes, which help to synthesize protein.
  • Thus, viruses lack the ability to synthesize protein on their own.
  • They utilise the ribosomes of their host cells and translate their messenger RNA (m RNA) into proteins.
• After the replication, the virus often leads to the death of the host cell. This damages the organism which was infected. 
• Almost all living creatures are infected by viruses. These include plants, animals, and even microorganisms such as archaea and bacteria.
• Viruses can be found in almost all the ecosystems of the world. Among all the biological entities, these are the largest in terms of numerical strength.
• When an organism is infected with a virus, the body produces an immune response. Some of the viruses, like HIV, viral hepatitis, HPV (Human Papilloma Virus), etc., evade this immune response and become chronic infections (long-lasting and persistent).
• The immune response in the organism can also be produced artificially for a specific virus through vaccines. 
• There are several through which the virus spreads. These are explained below:
  • Through Vectors: In plants, generally, the viruses are spread through insects feeding on the sap or fruits. In animals, blood-sucking insects can also spread viruses such as Dengue, which is caused by the dengue virus spread through the Aedes mosquito.
  • Through Air: Some viruses like COVID-19, influenza, chickenpox, measles, smallpox, etc., spread through the droplets that spread in the air when someone sneezes or coughs.
  • Through Faecal-Oral Route: Some viruses transmit through fecal particles entering the body through food, water, or hand-to-mouth contact. These include Rotavirus, Norovirus, etc.
  • Sexual Contact: Viruses such as HIV, genital herpes, etc., are sexually transmitted viruses.

 Types of Viruses

The following are different types of viruses based on different criteria of classification:

Classification Based on Nucleic Acid

• DNA Virus: These viruses have DNA as their genetic material, e.g., Herpes Virus, Adenovirus, Papillomavirus, etc.
• RNA Virus: These viruses have RNA as their genetic material, e.g., Dengue Virus, COVID-19, SARS, MERS, Ebola Virus, etc.

Classification Based on Types of Host (by Homes, 1948)

• Phytophagineae (Plant Viruses): Causes plant diseases, e.g., Mosaic disease in tobacco and potato, Bunchy Top disease in banana, Leaf Curl virus in tomato, etc.
• Zoophagineae (Animal Viruses): Animals, including humans, are their hosts, e.g., Influenza, Small Pox, Hepatitis, COVID-19, etc.
• Phagineae (Lower Organisms): Lower organisms, such as bacteria, blue-green algae, fungi, algae, yeast, etc., are their hosts.

Classification Based on Structure

• Cubical Virus e.g Picorna Virus, Reo Virus etc.
• Spiral Virus, e.g., Orthomyxo Virus, Paramyxo Virus, etc.
• Radial Symmetry Virus, e.g., Bacteriophage.
• Complex virus, e.g., Pox Virus.

Read about the Zika Virus here!

Diseases Caused due to Viruses

Following are some of the diseases that are caused by viruses:

Read about the Earth Biogenome Project from here!

Coronavirus [COVID-19]

COVID-19, or Coronavirus disease, is a respiratory viral disease caused by SARS Cov-2 (Severe Acute Respiratory Syndrome Coronavirus-2) virus. Its first known case was found in Wuhan (China) in December 2019. In a few months, the disease spread around the globe, creating a pandemic. It is named Corona due to the spikes that exist on the surface of the virus, which resemble a crown. SARS (Severe Acute Respiratory Syndrome), Common Cold, MERS (Middle East respiratory syndrome), etc., are common examples of Corona Virus. COVID-19 was a new strain of this virus called SARS Cov-2. 

The general features of COVID-19 have been explained below:

Transmission

• COVID-19 transmits from one person to another through the inhalation of small airborne droplets. Any infected person releases these through coughing or sneezing.
• It is also spread when someone comes in contact with infected items like a door handle, towel, etc.
• The preventive methods include vaccination, face masks, appropriate social distancing, regular hand sanitization, washing, quarantining when virus symptoms occur, etc.

Testing

• The testing method includes taking samples of the nasal secretions from the back of the nose and throat.
• The nucleic acid of the virus in the sample is tested through RT-PCR (Reverse Transcription Polymerase Chain Reaction) test, RT-LAMP (Reverse Transcription Loop-Mediated Amplification) test, and TMA (Transcription Mediated Amplification) test.

Corona Virus Symptoms

• The Corona Virus Symptoms vary from person to person.
• Generally, the common symptoms include fever, cough, fatigue, difficulty breathing, headache, loss of taste and smell, etc. 
• These symptoms become noticeable between 1 to 14 days after the infection.
• In one-third of the cases, the symptoms are very mild and barely noticeable.
• It is studied that severe symptoms are developed in 14% of cases, and in 5% of cases, critical symptoms are developed.

Vaccination

• Several vaccines are developed and given to provide acquired immunity against COVID-19.
• Different types of vaccines that different countries have developed are given below:
  • mRNA Vaccines: These vaccines use RNA to induce an immune response in the organism. The mRNA COVID-Vaccines include Pfizer-BioNTech and Moderna.
  • Adenovirus Vector Vaccines: These vaccines are non-replicating viral vector vaccines that only produce the antigen that stimulates the immune response. These include Oxford-Astrazenca, Sputnik 5, Janssen, and Convidecia.
  • Inactivated Virus Vaccines: Uses virus particles grown artificially in culture and then killed (inactivated). These include CoronaVac, BIBP, WIBP, Covaxin, CoviVac, QazVac, and COVIran Barakat.
  • Subunit Vaccines: The protein subunits of antigens are used rather than the whole pathogen. These include Novavax, EpiVacCorona, Corbevax, Soberana 02, etc.

Read about the Difference Between Epidemic, Pandemic, and Endemic from here!

Conclusion

A virus is a unique microbe that is often called ‘the borderline between living and non-living organisms. This is because they usually become active inside a living host. Each year millions of people die due to diseases caused by viruses. The knowledge about the large range and types of viruses and their unique features require a lot of scientific research. 

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