Which one of the following diseases is caused by bacteria?

1. Microbial Pathogens: Classification and Types (basic)

To understand infectious diseases, we must first look at the tiny organisms that cause them, known as microorganisms. While many microorganisms are beneficial—such as Lactobacillus used in curd making or nitrogen-fixing bacteria in soil—those that cause diseases are specifically called pathogens. These microscopic agents vary significantly in their structure, size, and biological behavior Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.25. Pathogens are generally classified into four main groups: bacteria, viruses, fungi, and protozoa. For example, bacteria often appear in distinct shapes like spherical, rod-shaped, or irregular forms, and unlike human cells, they possess a protective cell wall but lack a well-defined nucleus Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.18, 24.

Among these, viruses are unique because they occupy the border between living and non-living things. They are much smaller than bacteria and cannot reproduce on their own; instead, they must hijack the machinery of a host organism (like a human, plant, or animal) to multiply Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.24. This fundamental difference in biology is why medical treatments vary: antibiotics are designed to target specific parts of bacterial cells, making them effective against diseases like Tuberculosis (TB). However, because viruses function differently, antibiotics are completely ineffective against viral infections such as the common flu, polio, or chickenpox Science, Class VIII . NCERT(Revised ed 2025), Health: The Ultimate Treasure, p.39.

Pathogen Type	Key Characteristics	Examples of Diseases
Bacteria	Single-celled, cell wall, no defined nucleus.	Tuberculosis (TB), Cholera, Typhoid
Viruses	Extremely small, reproduce only inside host cells.	Influenza (Flu), Polio, Chickenpox
Protozoa	Single-celled organisms, often mobile.	Malaria, Amoebic dysentery
Fungi	Can be single or multi-cellular, have cell walls.	Skin infections (Ringworm), Athlete's foot

Sources: Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.18; Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.24; Science, Class VIII . NCERT(Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.25; Science, Class VIII . NCERT(Revised ed 2025), Health: The Ultimate Treasure, p.39

2. Modes of Disease Transmission (basic)

To master the study of infectious diseases, we must first understand modes of transmission—the specific pathways pathogens take to travel from a reservoir (like an infected person) to a healthy individual. Broadly, these are classified into direct and indirect transmission. Direct transmission occurs through physical contact, such as touching or sexual contact, or through droplet spread (large respiratory beads from a cough or sneeze that travel short distances). Indirect transmission is more complex, as the pathogen hitches a ride on a 'vehicle' like contaminated water, food, or air, or utilizes a living 'vector.' Waterborne and Foodborne Transmission occurs when pathogens enter the body via contaminated resources. This is common in areas with poor sanitation or during natural disasters like floods, which can lead to the spread of diseases such as Cholera, Hepatitis, and Gastro-enteritis Geography Class XI (NCERT), Natural Hazards and Disasters, p.62. When drinking water is contaminated by the excreta of an infected person, it serves as a primary route for diseases like Hepatitis A, Poliomyelitis, and Typhoid Science, Class VIII NCERT, Health: The Ultimate Treasure, p.44. Similarly, chemical or mineral contamination in water can lead to non-infectious but severe health issues like Minamata disease (from mercury) or Asbestosis Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.37. Vector-borne Transmission involves a living carrier, usually an arthropod, that transports the pathogen without getting sick itself. These 'vectors' are crucial in the lifecycle of many tropical diseases. For example, mosquitoes act as vectors for Malaria, Dengue, and Chikungunya Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.80. Understanding whether a disease is waterborne, airborne, or vector-borne is vital for public health officials to design the right prevention strategies—be it improving sanitation, using bed nets, or promoting hand hygiene.

Mode	Mechanism	Common Examples
Waterborne	Ingesting water contaminated by pathogens or excreta.	Cholera, Typhoid, Hepatitis A
Vector-borne	Bites from living organisms (mosquitoes, ticks).	Malaria, Dengue, Chikungunya
Airborne	Inhaling tiny particles or droplets suspended in air.	Tuberculosis, Influenza

Sources: Science, Class VIII NCERT, Health: The Ultimate Treasure, p.44; Geography Class XI (NCERT), Natural Hazards and Disasters, p.62; Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.37; Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.80

3. Antibiotics vs. Antivirals: Mechanisms of Action (intermediate)

To understand why we use different tools for different germs, we must first look at the biology of the target. Antibiotics (literally "against life") are substances designed to kill or inhibit the growth of bacteria. These drugs are effective because they exploit the biological differences between bacterial cells and human cells. For instance, many bacteria have a cell wall made of a unique substance (peptidoglycan) that human cells simply don't have. When Alexander Fleming discovered Penicillin in 1928, he observed a mold producing a substance that prevented bacteria from building these walls, causing them to burst without harming the host Science, Class VIII NCERT, Health: The Ultimate Treasure, p.40.

Antivirals, on the other hand, operate on an entirely different logic. Unlike bacteria, which are independent living cells, viruses are essentially genetic material wrapped in protein that must hijack a host's cellular machinery to replicate. Because viruses use our own cells to do their work, finding a drug that kills the virus without killing the healthy human cell is a significant challenge. Antibiotics are useless against viruses—like Influenza or Polio—because viruses lack the cell walls or specific metabolic pathways that antibiotics are designed to attack Science, Class VIII NCERT, Health: The Ultimate Treasure, p.39.

Feature	Antibiotics	Antivirals
Target Organism	Bacteria (Living, single-celled)	Viruses (Non-living genetic material)
Mechanism	Destroy cell walls or block bacterial protein synthesis.	Inhibit viral entry, replication, or release from host cells.
Example	Penicillin, Streptomycin	Oseltamivir (for Flu), Acyclovir

In the modern world, a major concern is Antibiotic Resistance. This happens when bacteria evolve to survive the drugs meant to kill them, often due to indiscriminate use or incomplete courses of treatment Science, Class VIII NCERT, Health: The Ultimate Treasure, p.41. Interestingly, while India is known as the "pharmacy of the world" for its massive production volume of these medicines, it remains heavily dependent on imports for the Active Pharmaceutical Ingredients (APIs)—the raw chemical building blocks—needed to make them Indian Economy, Vivek Singh, Indian Economy after 2014, p.238.

Sources: Science, Class VIII NCERT, Health: The Ultimate Treasure, p.39; Science, Class VIII NCERT, Health: The Ultimate Treasure, p.40; Science, Class VIII NCERT, Health: The Ultimate Treasure, p.41; Indian Economy, Vivek Singh, Indian Economy after 2014, p.238

4. Antimicrobial Resistance (AMR) and Global Health (exam-level)

To understand Antimicrobial Resistance (AMR), we must first look back at one of the greatest triumphs in medical history. In 1928, Alexander Fleming discovered penicillin, the first antibiotic, after noticing that a specific mould could kill harmful bacteria Science ,Class VIII . NCERT(Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p. 40. While antibiotics have since saved millions of lives, their indiscriminate use has triggered a biological arms race. AMR occurs when microorganisms—like bacteria, viruses, fungi, and parasites—evolve so that the medicines used to treat them become ineffective. When bacteria specifically become resistant, we often refer to them as 'Superbugs'.

How does this happen? It is essentially natural selection at high speed. When a patient takes an antibiotic unnecessarily or fails to complete the full prescribed course, the weaker bacteria die, but the stronger, more resilient ones survive and multiply Science ,Class VIII . NCERT(Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p. 41. These resistant strains can then spread through the community or through the food chain, especially since antibiotics are also widely used in the livestock industry Geography of India ,Majid Husain, (McGrawHill 9th ed.), Industries, p. 61. This makes standard treatments like those for Tuberculosis (TB) or pneumonia much harder to manage, leading to longer hospital stays and higher mortality rates.

Action	Impact on Resistance
Incomplete Course	Allows partially resistant bacteria to survive and mutate.
Over-prescription	Exposes bacteria to drugs unnecessarily, 'training' them to resist.
Poor Sanitation	Facilitates the spread of resistant microbes in the environment.

To tackle this global threat, we must practice Antibiotic Stewardship. This involves using antibiotics only when prescribed by a doctor, ensuring the correct dose, and never sharing medication. On a larger scale, international cooperation is vital, similar to the logic behind the Cartagena Protocol, which emphasizes biosafety and the sustainable management of biological risks Environment, Shankar IAS Academy .(ed 10th), International Organisation and Conventions, p. 396. Without urgent action, we risk entering a 'post-antibiotic era' where minor injuries and common infections could once again become fatal.

Sources: Science ,Class VIII . NCERT(Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p.40-41; Geography of India ,Majid Husain, (McGrawHill 9th ed.), Industries, p.61; Environment, Shankar IAS Academy .(ed 10th), International Organisation and Conventions, p.396

5. India's National Immunization Programs (exam-level)

In India, public health efforts to combat infectious diseases are anchored by the Universal Immunization Programme (UIP). Launched in 1985, the UIP is one of the largest health programs in the world, providing life-saving vaccines free of cost to children and pregnant women. While early efforts like the Expanded Programme on Immunization (1978) laid the groundwork, the UIP expanded the reach to target several Vaccine-Preventable Diseases (VPDs), including Tuberculosis (via the BCG vaccine), Diphtheria, Pertussis, Tetanus, Polio, and Measles Science, Class VIII NCERT, Health: The Ultimate Treasure, p. 34.

To ensure that the benefits of immunization reach the most vulnerable and remote populations, the government launched Mission Indradhanush in 2014. This is not a new program but a strategic intensification of the UIP. It specifically targets districts with low immunization coverage to ensure that all children under two years of age and pregnant women are fully vaccinated. Over time, this has evolved into 'Intensified Mission Indradhanush' (IMI) to further bridge gaps in urban areas and among migratory populations.

It is important for a UPSC aspirant to distinguish between various "Indradhanush" schemes. While the health mission focuses on vaccines, a separate Indradhanush Plan was introduced for the revival and governance of Public Sector Banks (PSBs), involving the creation of the Banks Board Bureau (BBB) Indian Economy, Nitin Singhania, Money and Banking, p.191. Furthermore, not all infectious diseases are managed through vaccines; for example, vector-borne diseases like Malaria and Dengue are primarily tackled through the National Vector Borne Disease Control Programme, which emphasizes vector control and early case detection Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.80.

Program	Focus Area	Key Strategy
UIP	Nationwide Routine Immunization	Free vaccination for 12+ diseases through primary health centers.
Mission Indradhanush	Gap-filling & Reach Extension	Targeting unvaccinated or partially vaccinated children in low-coverage districts.
NVBDCP	Vector-borne Diseases	Integrated vector management (spraying, nets) and surveillance Environment, Shankar IAS Academy, India and Climate Change, p.301.

Sources: Science, Class VIII NCERT, Health: The Ultimate Treasure, p.34; Indian Economy, Nitin Singhania, Money and Banking, p.191; Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.80; Environment, Shankar IAS Academy, India and Climate Change, p.301

6. Major Viral Diseases and Their Vectors (intermediate)

To understand viral diseases, we must first look at the nature of the pathogen. Unlike bacteria, which are complex, single-celled organisms capable of surviving on their own, viruses are microscopic and acellular. They essentially consist of genetic material (DNA or RNA) encased in a protein coat. A virus cannot reproduce by itself; it is an obligate parasite that must hijack the machinery of a living host cell to multiply Science, Class VIII. NCERT (Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p. 17. Because of this unique biology, viral infections do not respond to antibiotics, making vaccination and preventive hygiene our most effective tools for management.

Viral diseases are often categorized by how they travel from one host to another. Many common human viral infections, such as the Common Cold, Influenza (Flu), and Measles, are primarily respiratory. They spread through droplets in the air when an infected person coughs or sneezes, targeting the respiratory tract or the skin Science, Class VIII. NCERT (Revised ed 2025), Health: The Ultimate Treasure, p. 33. Other viruses, like Smallpox, are notably stable and can survive for long periods outside the human body, spreading through direct or indirect contact Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Natural Hazards and Disaster Management, p. 80.

Beyond human-to-human contact, many significant viral diseases involve animal reservoirs or vectors. Zoonotic diseases are those that jump from animals to humans. For instance, Rabies is a viral disease typically transmitted through the saliva of infected animals like dogs or monkeys Environment, Shankar IAS Academy (ed 10th), Animal Diversity of India, p. 193. Similarly, Avian Influenza (Bird Flu) poses a significant challenge to the poultry industry and public health, as it can spread from birds to humans, requiring active surveillance and strategic vaccine reserves to manage outbreaks Geography of India, Majid Husain (McGrawHill 9th ed.), Resources, p. 39.

Disease	Causal Agent	Primary Mode of Spread
Influenza / Measles	Virus	Airborne droplets / Respiratory tract
Rabies	Virus	Animal bites/contact (Zoonotic)
Chickenpox	Virus	Airborne / Direct contact with blisters
Foot & Mouth Disease	Virus	Contact (primarily affects livestock)

Sources: Science, Class VIII. NCERT (Revised ed 2025), The Invisible Living World: Beyond Our Naked Eye, p.17; Science, Class VIII. NCERT (Revised ed 2025), Health: The Ultimate Treasure, p.33; Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Natural Hazards and Disaster Management, p.80; Environment, Shankar IAS Academy (ed 10th), Animal Diversity of India, p.193; Geography of India, Majid Husain (McGrawHill 9th ed.), Resources, p.39

7. Bacterial Diseases: Tuberculosis and Beyond (intermediate)

When we discuss infectious diseases, understanding the biological nature of the pathogen is the first step toward effective treatment. Tuberculosis (TB) is a premier example of a bacterial disease, caused by the rod-shaped bacterium Mycobacterium tuberculosis. While it most famously colonizes the lungs (pulmonary TB), it is a systemic traveler that can affect the kidneys, spine, and even the brain Science, Class VIII. NCERT (Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p. 34. The hallmark symptoms of pulmonary TB include a persistent cough, chest pain, fever, and the characteristic "night sweats."

It is vital to distinguish bacterial infections from viral ones. Bacteria are complex, single-celled organisms that can survive on their own, whereas viruses require a host cell to replicate. This biological difference dictates our medical response: antibiotics are highly effective against bacteria like Mycobacterium, but they have no effect on viruses such as those causing Chickenpox or Influenza Science, Class VIII. NCERT (Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p. 39. However, vaccination remains a powerful preventative tool for both categories; for instance, the BCG vaccine is used globally to prevent severe forms of TB in children.

Beyond TB, other significant bacterial diseases include Cholera and Typhoid. While TB is primarily airborne (spread through tiny droplets when an infected person coughs), Cholera and Typhoid are usually transmitted through contaminated food and water Science, Class VIII. NCERT (Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p. 34. This highlights why public health focuses on different interventions—ventilation and masks for TB, but sanitation and clean water for intestinal bacterial infections.

Interestingly, the threat of bacterial pathogens isn't limited to humans. In the context of One Health (the intersection of human, animal, and environmental health), we see that Mycobacterium spp. can also infect wildlife such as deer and elephants, while other bacteria like Bacillus anthracis (Anthrax) pose a major threat to herbivores like the Gaur or Wild Pig Environment, Shankar IAS Academy (ed 10th), Animal Diversity of India, p. 193.

Disease	Causative Agent	Primary Organ Affected	Mode of Transmission
Tuberculosis	Bacteria (Mycobacterium)	Lungs	Airborne (Droplets)
Cholera	Bacteria (Vibrio cholerae)	Intestine	Contaminated Water/Food
Typhoid	Bacteria (Salmonella typhi)	Intestine	Contaminated Water/Food

Sources: Science, Class VIII. NCERT (Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p.34; Science, Class VIII. NCERT (Revised ed 2025), Chapter 3: Health: The Ultimate Treasure, p.39; Environment, Shankar IAS Academy (ed 10th), Animal Diversity of India, p.193

8. Solving the Original PYQ (exam-level)

You have just mastered the fundamental distinctions between different pathogens—bacteria, viruses, fungi, and protozoa. This question tests your ability to apply that classification to specific human diseases. As explored in Science, Class VIII NCERT, understanding whether a disease is bacterial or viral is not just academic; it determines the clinical approach, especially since antibiotics are only effective against bacteria. This question brings together your knowledge of pathogen types and specific disease profiles into a single application-based challenge.

To arrive at the correct answer, you must systematically identify the causative agent for each option. Tuberculosis is the correct answer because it is caused by the bacterium Mycobacterium tuberculosis. In contrast, Chicken Pox (Varicella-Zoster virus), Poliomyelitis (Poliovirus), and Influenza (Influenza virus) are all viral infections. Reasoning through elimination is a vital strategy here: if you recognize that the first three are viral, (D) Tuberculosis remains the only logical choice for a disease caused by bacteria.

UPSC often uses these specific distractors because they are common respiratory or highly contagious conditions, which students sometimes reflexively group together. Don't fall into the trap of assuming that a disease's severity or its mode of transmission (like air-borne droplets) automatically makes it bacterial. Always double-check the biological nature of the pathogen. While vaccines exist for all four, only the bacterial nature of Tuberculosis makes it susceptible to specific antibiotic regimens, a distinction frequently tested in the Civil Services Examination.