Dog bite can cause rabies. Which among the following other animals can also cause rabies?

1. Basics of Pathogens and Communicable Diseases (basic)

Welcome to our journey into human health! To understand infectious diseases, we must first distinguish between two broad categories of illness: Communicable and Non-communicable diseases. Non-communicable diseases (NCDs), such as diabetes, asthma, or cancer, are generally linked to genetics, lifestyle, or environmental factors and cannot be passed from one person to another. In contrast, communicable diseases are caused by biological agents called pathogens—microscopic organisms like bacteria, viruses, fungi, and protozoa—that can spread through air, water, physical contact, or vectors Science, Class VIII NCERT, Health: The Ultimate Treasure, p.32.

Pathogens are essentially "biological invaders." While bacteria are single-celled organisms that can live in various environments, viruses are unique because they are acellular and microscopic; they can only multiply once they enter a living cell of a plant, animal, or even a bacterium Science, Class VIII NCERT, The Invisible Living World: Beyond Our Naked Eye, p.17. Because pathogens function differently, our medical treatments must be specific. For example, antibiotics are effective only against bacterial infections because they target specific structures in bacterial cells that are absent in human cells. They are ineffective against viral diseases like the common cold or flu Science, Class VIII NCERT, Health: The Ultimate Treasure, p.39.

Feature	Communicable Diseases	Non-Communicable Diseases
Cause	Pathogens (Bacteria, Viruses, etc.)	Lifestyle, Diet, Environment, Genetics
Transmission	Spreads from person to person/animal	Does not spread between individuals
Examples	Typhoid, COVID-19, Chickenpox	Diabetes, Heart Disease, Cancer

Sources: Science, Class VIII NCERT, Health: The Ultimate Treasure, p.32; Science, Class VIII NCERT, The Invisible Living World: Beyond Our Naked Eye, p.17; Science, Class VIII NCERT, Health: The Ultimate Treasure, p.39

2. Zoonotic Diseases and Viral Spillover (intermediate)

At its core, a zoonotic disease (or zoonosis) is an infectious disease that has jumped from a non-human animal to humans. These pathogens—which can be viruses, bacteria, or parasites—do not respect species boundaries. According to the One Health approach, the health of people is closely connected to the health of animals and our shared environment. While some diseases stay within a single species, others are communicable, meaning they are caused by pathogens and can spread between individuals Science, Class VIII, Health: The Ultimate Treasure, p.32. Zoonoses represent a specific type of communicable disease where the initial source is animal-based.

The process of a pathogen moving from a wildlife population into humans is known as a viral spillover. This isn't a simple leap; it’s a complex journey where the virus must overcome several barriers: ecological (the human and animal must meet), behavioral (direct contact or shared resources), and molecular (the virus must be able to enter and replicate in human cells). For instance, the Rabies virus is a classic zoonotic pathogen that affects the central nervous system. While we often associate it with domestic dogs, it is naturally carried by various wild mammals like bats, mongooses, and foxes Environment, Shankar IAS Academy, Chapter 12, p.193. Interestingly, spillover is often restricted by biology; Rabies only affects warm-blooded mammals, meaning cold-blooded animals like crocodiles are naturally immune and cannot transmit it.

To understand the dynamics of these diseases, we must distinguish between where the virus lives and how it travels:

Term	Definition	Example in Zoonosis
Reservoir Host	A species in which the pathogen lives and multiplies without necessarily causing serious illness.	Fruit bats are a common reservoir for many viruses.
Vector	An intermediate organism (often an insect) that carries the pathogen from one host to another.	Mosquitoes transmitting Dengue or Chikungunya Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.79.

Environmental changes, such as habitat loss and the wildlife trade, increase the frequency of contact between humans and these reservoirs, significantly raising the risk of new spillover events. Understanding these animal-human links is the first step in preventing the next global pandemic.

Sources: Science, Class VIII (NCERT), Health: The Ultimate Treasure, p.32; Environment, Shankar IAS Academy (10th Ed), Animal Diversity of India, p.193; Environment and Ecology, Majid Hussain (3rd Ed), Natural Hazards and Disaster Management, p.79

3. One Health Approach and Public Health Policy (exam-level)

The One Health Approach is an integrated, unifying model that recognizes that the health of people is closely connected to the health of animals and our shared environment. In the context of public health policy, this means that a disease outbreak cannot be managed by doctors alone; it requires collaboration between veterinarians, ecologists, and policymakers. Since approximately 60% of known infectious diseases and 75% of emerging infectious diseases are zoonotic (spreading from animals to humans), this approach is critical for early warning and prevention. For example, managing a disease like Rabies—which is fatal but 100% preventable—requires not just treating human bites, but also mass dog vaccinations and managing waste to control stray animal populations.

India is particularly vulnerable and central to the One Health mission because of its massive biological interface. The country ranks first in the world in buffalo population and second in cattle and goats, with animal husbandry playing a vital role in rural livelihoods Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.158. This high density of livestock, combined with the intensification of farming through exotic breeds, creates a significant landscape for potential pathogen spillover. From a Medical Geography perspective, understanding the interface between human settlements and natural habitats is essential for epidemiology NCERT Class XII, Human Geography Nature and Scope, p.5.

Modern Indian health policy has gradually shifted toward this holistic view. The National Health Policy and the National Rural Health Mission have evolved to focus on preventive and promotive healthcare rather than just curative measures Spectrum, After Nehru, p.761/781. For instance, the Swachh Bharat Mission is not just a sanitation drive; it is a public health intervention based on the belief that a clean environment is the foundation of human health Spectrum, After Nehru, p.781. By integrating digital tracking through the National Digital Health Mission and insurance coverage under Ayushman Bharat, the policy framework aims to create a resilient system that can detect and respond to health threats at their source—whether that source is a farm, a forest, or a city drain.

Sources: Environment, Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.158; FUNDAMENTALS OF HUMAN GEOGRAPHY, CLASS XII (NCERT), Human Geography Nature and Scope, p.5; Rajiv Ahir. A Brief History of Modern India. SPECTRUM, After Nehru..., p.761, 781

4. Vector-Borne Diseases: Mosquitoes vs. Mammalian Vectors (intermediate)

To understand infectious diseases, we must distinguish between different types of vectors—the organisms that transmit pathogens from one host to another. While we often associate the term with insects like mosquitoes, certain mammals also act as critical vectors and reservoirs for some of the world's most dangerous diseases. Understanding the biological boundary of these diseases is essential for public health and UPSC preparation alike.

Mosquito-borne diseases, such as Malaria, Dengue, and Chikungunya, rely on the mosquito as a biological vehicle. In these cases, the pathogen often undergoes a part of its life cycle within the insect. Because these diseases are a significant burden in India, the government utilizes the National Vector Borne Disease Control Programme, which emphasizes integrated vector control and early case detection Environment and Ecology, Majid Hussain, Natural Hazards and Disaster Management, p.80. Interestingly, viruses themselves are often at the center of a biological debate; they do not show molecular movement until they infect a host cell, making them uniquely dependent on their vectors for survival and spread Science, class X (NCERT 2025 ed.), Life Processes, p.79.

In contrast, mammalian vectors involve a direct transmission—often through bites or saliva—of zoonotic diseases like Rabies. Rabies is a fatal viral infection of the central nervous system. A crucial biological distinction here is that Rabies is strictly a disease of warm-blooded animals (mammals). While domestic dogs are responsible for the vast majority of human cases, wild mammals like bats, foxes, and mongooses are significant reservoirs Environment, Shankar IAS Academy, Animal Diversity of India, p.193. Cold-blooded animals, such as crocodiles or snakes, cannot contract or transmit Rabies because their physiology does not support the virus's replication.

Feature	Mosquito Vectors (e.g., Malaria, Dengue)	Mammalian Vectors (e.g., Rabies)
Transmission Mechanism	Blood-feeding (proboscis)	Direct contact (bites, scratches, saliva)
Biological Host Range	Broad (can infect various vertebrates)	Restricted to warm-blooded mammals
Primary Control Strategy	Habitat destruction and insecticides	Vaccination (post-exposure and animal)

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Natural Hazards and Disaster Management, p.80; Science, class X (NCERT 2025 ed.), Life Processes, p.79; Environment, Shankar IAS Academy (10th ed.), Animal Diversity of India, p.193

5. Biological Susceptibility: Mammals vs. Reptiles (exam-level)

To understand why certain diseases affect some animals but not others, we must first look at the fundamental physiological divide in the animal kingdom: thermal homeostasis. Animals are broadly categorized as either warm-blooded (endotherms) or cold-blooded (ectotherms). Warm-blooded animals, which include all mammals and birds, maintain a relatively high and constant internal body temperature regardless of their surroundings through internal metabolic processes Environment, Shankar IAS Academy, Environment Issues and Health Effects, p.419. In contrast, cold-blooded animals like reptiles and amphibians cannot use metabolism to regulate heat; instead, their body temperature fluctuates based on the environment, often requiring them to move between sun and shade to stay functional Environment, Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.158.

This difference in internal temperature is a critical barrier for many pathogens. Many viruses and bacteria are thermally sensitive—they have evolved to thrive specifically within the stable, high-temperature environment of a mammal's body. For instance, the rabies virus targets the central nervous system of mammals because the mammalian physiology provides the exact metabolic conditions necessary for the virus to replicate. Because reptiles like crocodiles or lizards are ectothermic and have a much slower metabolism, they do not provide the 'biological machinery' or the consistent warmth required for such a virus to take hold.

Beyond temperature, mammals share specific biological traits that make them a unified group of potential hosts. These include having hair or fur, breathing with lungs, and females nursing their young with milk Environment, Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.154. Whether it is a land-dwelling dog, a flying bat, or an aquatic mammal, their shared 'warm-blooded' status makes them susceptible to a similar range of zoonotic diseases that simply cannot cross over into the cold-blooded reptilian world.

Feature	Mammals	Reptiles
Metabolism	High; generates internal heat (Endothermic)	Low; relies on environment (Ectothermic)
Body Covering	Hair or Fur	Scales or Scutes
Disease Susceptibility	High for warm-blooded specific viruses (e.g., Rabies)	Immune to mammalian-specific viruses
Thermoregulation	Automatic via physiological processes	Behavioral (moving to sun/shade) Environment, Shankar IAS Academy, Terrestrial Ecosystems, p.28

Sources: Environment, Shankar IAS Academy, Environment Issues and Health Effects, p.419; Environment, Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.154; Environment, Shankar IAS Academy, Indian Biodiversity Diverse Landscape, p.158; Environment, Shankar IAS Academy, Terrestrial Ecosystems, p.28

6. The Rabies Virus: Transmission and Reservoir Hosts (exam-level)

Rabies is one of the most lethal zoonotic diseases known to humanity, caused by the Rabies virus (a Lyssavirus). It is a neurological infection that targets the Central Nervous System (CNS), leading to encephalomyelitis. One of the most critical aspects to understand for the UPSC is that rabies is strictly a disease of warm-blooded mammals. Because viruses are microscopic and acellular organisms that require a living host cell to multiply Science, Class VIII NCERT, The Invisible Living World: Beyond Our Naked Eye, p.17, the Rabies virus has evolved specifically to exploit the biology of mammals, including humans, domestic animals, and wildlife.

Transmission primarily occurs through the saliva of an infected animal, usually via a bite, scratch, or even a lick on broken skin. While domestic dogs are the primary vector for human rabies—contributing to nearly 99% of cases globally—the disease has a wide variety of wildlife reservoirs. In the Indian context, susceptible wild animals include the tiger, lion, bear, mongoose, and squirrel Environment, Shankar IAS Academy, Animal Diversity of India, p.193. Interestingly, the movement of feral dogs into wilderness areas or carcass dumps can bridge the gap between human settlements and wildlife, facilitating the spread of the virus Environment, Shankar IAS Academy, Conservation Efforts, p.236.

It is vital to differentiate which animals can and cannot carry the virus. Since the virus requires the specific metabolic environment of a mammal, cold-blooded animals like reptiles (crocodiles, snakes, lizards) and amphibians are completely immune and cannot transmit the disease. Among mammals, bats serve as a significant and frequent reservoir host in many parts of the world, often transmitting the virus without the person even realizing they have been bitten due to the tiny size of bat teeth.

Susceptibility	Animal Groups	Examples
High Risk (Mammals)	Canines, Felines, Chiroptera, Rodents	Dogs, Foxes, Bats, Mongooses, Squirrels, Tigers
Zero Risk (Non-Mammals)	Reptiles, Fish, Amphibians	Crocodiles, Cobras, Frogs, Salmon

Sources: Science, Class VIII NCERT, The Invisible Living World: Beyond Our Naked Eye, p.17; Environment, Shankar IAS Academy, Animal Diversity of India, p.193; Environment, Shankar IAS Academy, Conservation Efforts, p.236

7. Solving the Original PYQ (exam-level)

This question bridges your knowledge of zoonotic diseases with the biological classification of animals. To solve this, you must apply the fundamental principle that the Rabies virus is strictly a disease of warm-blooded animals (mammals). By recalling that the virus targets the central nervous system, you can immediately narrow your focus to mammalian hosts. As we discussed in the modules regarding Environment, Shankar IAS Academy, understanding the reservoir of a virus is key to identifying potential vectors beyond domestic pets.

To arrive at the correct answer, use a process of prioritization and elimination. While any mammal can technically transmit the virus, (B) Bat is a globally recognized wildlife reservoir and a primary source of transmission to humans, especially in regions where canine rabies is managed. In the context of UPSC, the examiner is testing your awareness of epidemiological significance; while a Horse or Donkey can be infected, they are considered incidental hosts rather than major natural reservoirs that propagate the disease in the wild.

The primary trap in this question is the inclusion of the Crocodile. UPSC often includes a cold-blooded reptile to test whether you know the host limitations of the virus; because crocodiles are not mammals, they are biologically incapable of carrying the rabies virus. When faced with multiple mammals like the Donkey and Horse, you must select the animal most notorious in public health literature for its role as a carrier. Therefore, (B) Bat is the most robust and scientifically accurate choice for a secondary vector.