Viral Diseases

21. The HIV virus weakens the immunity of a person because it destroys

The HIV virus weakens the immunity of a person because it destroys

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mast cells
platelets
erythrocytes
lymphocytes
This question was previously asked in
UPSC CDS-2 – 2016
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The HIV virus weakens the immunity of a person because it destroys lymphocytes.
HIV primarily targets and infects CD4+ T lymphocytes (also known as T helper cells), which are critical components of the adaptive immune system. The virus replicates within these cells and eventually destroys them.
Progressive destruction of CD4+ T cells leads to a severe decline in immune function, making individuals susceptible to opportunistic infections and certain cancers that a healthy immune system would normally fight off. This advanced stage of HIV infection is known as Acquired Immunodeficiency Syndrome (AIDS).

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22. The causal organism of dengue fever is a mosquito-borne virus which be

The causal organism of dengue fever is a mosquito-borne virus which belongs to which one among the following categories?

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Flavi-ribo virus
Adenovirus
Vaccinia virus
Nipah virus
This question was previously asked in
UPSC CDS-1 – 2024
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The correct option is A) Flavi-ribo virus.
Dengue fever is caused by the dengue virus (DENV). DENV is a member of the genus *Flavivirus* within the family *Flaviviridae*. Flaviviruses are positive-sense single-stranded RNA viruses. The term “ribo-virus” is a general term for RNA viruses. Thus, “Flavi-ribo virus” is a descriptive categorization referring to the Flavivirus genus and its RNA nature, making option A the most appropriate choice among the given options. Adenoviruses and Vaccinia viruses are DNA viruses, and Nipah virus belongs to a different RNA virus family (Paramyxoviridae).
Flaviviruses are typically arthropod-borne viruses (arboviruses), transmitted by mosquitoes or ticks. Other well-known human pathogens in the Flavivirus genus include Yellow Fever virus, West Nile virus, Zika virus, and Japanese Encephalitis virus.

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23. Mutation in a virus is caused due to a change in its :

Mutation in a virus is caused due to a change in its :

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cell size.
genetic material.
shape.
colour.
This question was previously asked in
UPSC CDS-1 – 2022
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Mutation in a virus is caused due to a change in its genetic material.
Viruses store their genetic information in the form of either DNA or RNA. A mutation is a change in the sequence of nucleotides in this genetic material. These changes can occur spontaneously during replication or be induced by external factors (mutagens). Mutations are the primary source of genetic variation in viruses, which can lead to changes in their characteristics, such as infectivity, virulence, or ability to evade host immune responses.
Changes in cell size, shape, or colour are phenotypic changes, which may or may not result from an underlying genetic mutation, but the mutation itself is the alteration in the genetic code. Viruses do not have a cellular structure like bacteria or eukaryotic cells, so discussing “cell size” in the context of a virus is inaccurate.

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24. An antibiotic is not useful against a virus whereas a vaccine is. Whic

An antibiotic is not useful against a virus whereas a vaccine is. Which one of the following is the most appropriate reason for this ?

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An antibiotic can break RNA only, whereas virus has DNA.
An antibiotic is a carbohydrate in its chemical nature, whereas a vaccine is a protein which works well to kill a virus.
Only a vaccine can break the genetic material of a virus.
A virus does not use biochemical pathways which can be blocked by an antibiotic. But a vaccine can boost an immune system to fight the virus.
This question was previously asked in
UPSC CDS-1 – 2021
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Antibiotics are designed to kill bacteria by targeting biochemical pathways essential for bacterial life (like cell wall synthesis, protein synthesis, or DNA replication) which are not present or significantly different in host cells. Viruses, however, lack these metabolic pathways and hijack the host cell’s machinery for replication. Therefore, antibiotics are ineffective against viruses. A vaccine, on the other hand, contains weakened or inactivated viruses or viral components (antigens). When administered, it stimulates the host’s immune system to produce antibodies and other immune responses specific to the virus. This prepares the body to fight off the actual virus upon subsequent exposure.
Antibiotics target bacterial processes; viruses lack these processes. Vaccines stimulate the host immune system to recognize and fight specific pathogens like viruses.
The development of antiviral drugs is distinct from antibiotics and targets specific steps in the viral life cycle within host cells.

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25. Most viruses that infect plants possess

Most viruses that infect plants possess

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single-stranded DNA
single-stranded RNA
double-stranded DNA and RNA
double-stranded RNA only
This question was previously asked in
UPSC CDS-1 – 2017
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Plant viruses exhibit a diverse range of genome types, but the most common type is single-stranded RNA (ssRNA). Examples include Tobacco Mosaic Virus (TMV), Potato Virus Y (PVY), and many others. While other genome types like double-stranded RNA (dsRNA), single-stranded DNA (ssDNA), and double-stranded DNA (dsDNA) also exist in plant viruses, ssRNA viruses are predominant.
Knowing the typical types of genetic material found in plant viruses is a key aspect of virology.
Animal viruses and bacterial viruses (bacteriophages) also have varied genome types. The type of genome significantly influences the virus’s replication strategy.

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26. AIDS is caused by the Human Immuno-deficiency Virus (HIV). The transmi

AIDS is caused by the Human Immuno-deficiency Virus (HIV). The transmission of HIV infection generally occurs through

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eating contaminated food and water
transfusion of contaminated blood and blood products
inhaling polluted air
shaking hand with infected person
This question was previously asked in
UPSC CDS-1 – 2017
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HIV is primarily transmitted through specific routes involving the exchange of body fluids. The main modes of transmission are unprotected sexual contact, sharing of contaminated needles or syringes, transfusion of contaminated blood or blood products, and mother-to-child transmission during pregnancy, childbirth, or breastfeeding. Eating contaminated food/water, inhaling polluted air, or casual contact like shaking hands do not transmit HIV.
Understanding the modes of transmission of Human Immunodeficiency Virus (HIV) is crucial for preventing its spread.
HIV targets the immune system, specifically CD4+ T cells, leading to Acquired Immunodeficiency Syndrome (AIDS), a condition characterized by severe immune deficiency making the body vulnerable to opportunistic infections and cancers.

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27. Dengue virus is known to cause low platelet count in blood of patient

Dengue virus is known to cause low platelet count in blood of patient by :

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  • 1. interfering in the process of platelet production in bone marrow
  • 2. infecting endothelial cells
  • 3. binding with platelets
  • 4. accumulating platelets in intestine

Select the correct answer using the code given below :

1 and 2 only
1 and 3 only
3 and 4
1, 2 and 3
This question was previously asked in
UPSC CDS-1 – 2016
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Dengue virus can cause low platelet count through multiple mechanisms including interfering with platelet production, infecting endothelial cells, and binding with platelets.
Dengue-induced thrombocytopenia is multifactorial. Mechanisms include suppression of bone marrow (statement 1), direct or indirect damage to endothelial cells leading to increased platelet consumption (statement 2), immunological destruction of platelets through antibody cross-reaction or binding of viral/immune complexes to platelets leading to their removal (statement 3). Accumulation of platelets in the intestine (statement 4) is not a known primary mechanism of dengue-induced thrombocytopenia.
Thrombocytopenia is a common manifestation of dengue fever and a significant risk factor for hemorrhagic complications, especially in severe dengue.

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