Major Human Diseases
Diseases are among the most important topics in Biology for UPSC because they connect multiple dimensions such as public health, nutrition, immunity, environment, genetics, epidemiology, biotechnology, and current affairs.
In recent years, diseases like COVID-19, Dengue, Zika, Nipah, Mpox, Tuberculosis, and Influenza have repeatedly appeared in news, government reports, international health discussions, and UPSC examinations.
Therefore, instead of studying diseases in isolation, it becomes important to develop a broad conceptual understanding of their causes, transmission, symptoms, affected body systems, and public health significance.
The following tables provide a structured overview of major human diseases across different categories such as communicable, genetic, deficiency, lifestyle, autoimmune, and degenerative diseases.
You should note that not every disease mentioned here is equally important from the examination perspective. Greater emphasis should be given to diseases frequently appearing in current affairs, government health programmes, WHO reports, vaccination initiatives, and emerging outbreaks.
However, reading an overview of all these diseases is still extremely useful because it helps in developing comparative understanding, scientific vocabulary, analytical linkage, and elimination ability in objective questions.
For detailed study, you can directly click on the hyperlinked disease names to explore their complete description, symptoms, transmission, treatment, and associated concepts in depth.
Communicable Diseases Caused by Bacteria
| Disease | Causative Bacterium | Transmission | Key Symptoms | Affected Areas |
| Tuberculosis (TB) | Mycobacterium tuberculosis | Airborne (cough, sneeze) | Persistent cough, chest pain, fatigue, fever, night sweats, weight loss | Lungs, but can affect other organs |
| Cholera | Vibrio cholerae | Contaminated water/food | Severe diarrhoea, dehydration, electrolyte imbalance | Intestines |
| Typhoid Fever | Salmonella Typhi | Contaminated food/water | High fever, abdominal pain, rash, constipation/diarrhoea | Blood and intestines |
| Diphtheria | Corynebacterium diphtheriae | Respiratory droplets | Sore throat, fever, thick gray throat membrane, difficulty breathing | Throat and respiratory system |
| Pertussis (Whooping Cough) | Bordetella pertussis | Airborne droplets | Severe coughing fits with “whooping” sound, vomiting after coughing | Respiratory system |
| Leprosy (Hansen’s Disease) | Mycobacterium leprae | Prolonged close contact | Skin lesions, numbness, muscle weakness, deformities | Skin, peripheral nerves |
| Plague | Yersinia pestis | Flea bites, contact with infected animals | Swollen lymph nodes (buboes), fever, chills, septicemia, pneumonia | Lymphatic system, lungs |
| Tetanus (Lockjaw) | Clostridium tetani | Wound contamination (soil, rust) | Muscle stiffness, spasms, difficulty swallowing | Muscles and nervous system |
| Anthrax | Bacillus anthracis | Inhalation, ingestion, skin contact | Fever, chest pain, sores, difficulty breathing, gastrointestinal distress | Skin, lungs, gastrointestinal tract |
| Meningitis (Bacterial) | Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae | Close contact, droplets | Stiff neck, severe headache, fever, confusion, nausea | Brain and spinal cord membranes |
| Syphilis | Treponema pallidum | Sexual contact, mother-to-child | Sores (chancre), rashes, fever, neurological issues (in late stages) | Genitals, skin, nervous system |
| Gonorrhoea | Neisseria gonorrhoeae | Sexual contact | Painful urination, discharge, pelvic pain | Reproductive organs |
| Lyme Disease | Borrelia burgdorferi | Tick bite | Bull’s-eye rash, joint pain, neurological symptoms | Joints, skin, nervous system |
Communicable Diseases Caused by Viruses
| Disease | Causative Virus | Transmission | Key Symptoms | Affected Areas |
| COVID-19 | SARS-CoV-2 | Respiratory droplets, contact | Fever, cough, shortness of breath, fatigue, loss of taste/smell | Respiratory system |
| Influenza (Flu) | Influenza virus (A, B, C, D types) | Respiratory droplets, contact | Fever, chills, sore throat, body aches, fatigue | Respiratory system |
| Hepatitis A | Hepatitis A virus (HAV) | Contaminated food/water | Jaundice, fatigue, abdominal pain, nausea | Liver |
| Hepatitis B | Hepatitis B virus (HBV) | Blood, sexual contact, vertical transmission | Jaundice, abdominal pain, joint pain | Liver |
| Hepatitis C | Hepatitis C virus (HCV) | Blood, needles, sexual contact | Chronic liver disease, jaundice, fatigue | Liver |
| Hepatitis D | Hepatitis D virus (HDV) | Blood, sexual contact, vertical transmission | Jaundice, abdominal pain, joint pain | Liver |
| Hepatitis E | Hepatitis E virus (HEV) | Contaminated food/water | Jaundice, abdominal pain, nausea | Liver |
| HIV/AIDS | Human immunodeficiency virus (HIV) | Blood, sexual contact, vertical transmission | Weight loss, recurrent infections, fatigue | Immune system |
| Dengue | Dengue virus | Mosquito bite (Aedes aegypti) | High fever, rash, joint pain, severe cases: bleeding, shock | Blood, immune system |
| Chikungunya | Chikungunya virus | Mosquito bite (Aedes aegypti) | Fever, joint pain, rash | Joints, immune system |
| Zika Virus Disease | Zika virus | Mosquito bite (Aedes aegypti), vertical transmission | Fever, rash, joint pain, microcephaly (in foetuses) | Nervous system |
| Polio (Poliomyelitis) | Poliovirus | Faecal-oral, contaminated water | Paralysis, muscle weakness, fever | Nervous system |
| Rabies | Rabies virus | Animal bite (saliva) | Anxiety, hydrophobia, paralysis, fatal if untreated | Nervous system |
| Measles | Measles virus | Airborne droplets | Fever, rash, cough, conjunctivitis | Respiratory system, skin |
| Mumps | Mumps virus | Saliva, respiratory droplets | Swollen salivary glands, fever, headache | Salivary glands |
| Rubella (German Measles) | Rubella virus | Respiratory droplets, vertical transmission | Rash, fever, congenital abnormalities (in foetuses) | Skin, immune system |
| Chickenpox | Varicella-zoster virus | Airborne droplets, contact | Itchy rash, fever, fatigue | Skin, immune system |
| Herpes Simplex | Herpes Simplex Virus (HSV) | Contact, sexual contact, bodily fluids, vertical transmission | Painful blisters or ulcers, fever, headache, muscle aches | Different parts of the body (eyes, mouth area, genital area and fingers) |
| Ebola Virus Disease | Ebola virus | Body fluids, contact | Fever, bleeding, organ failure | Blood, multiple organs |
| Marburg Virus Disease | Marburg virus | Body fluids, contact | Severe bleeding, fever, organ failure | Blood, multiple organs |
| Yellow Fever | Yellow fever virus | Mosquito bite (Aedes aegypti) | Fever, jaundice, bleeding, kidney failure | Liver, kidneys |
| Japanese Encephalitis | Japanese encephalitis virus | Mosquito bite (Culex spp.) | Fever, headache, seizures, brain swelling | Nervous system |
| Common Cold | Rhinoviruses, Coronaviruses | Respiratory droplets, contact | Sneezing, nasal congestion, sore throat | Respiratory system |
| Smallpox (Eradicated) | Variola virus | Airborne droplets, contact | Fever, pustular rash | Skin, immune system |
| Human Papillomavirus (HPV) | HPV | Sexual contact | Warts, cervical cancer | Skin, reproductive organs |
| Norovirus Infection | Norovirus | Contaminated food/water | Severe vomiting, diarrhoea, stomach cramps | Gastrointestinal tract |
| Rotavirus Infection | Rotavirus | Contaminated food/water | Severe diarrhoea, vomiting, dehydration | Gastrointestinal tract |
| Hand, Foot, and Mouth Disease | Coxsackievirus and Enterovirus | Contact, droplets, faeces, contaminated objects | Fever, sore throat, painful blisters, loss of appetite | Hands, feet, mouth, and sometimes genitals and buttocks |
Communicable Diseases Caused by Protozoa
| Disease | Causative Protozoa | Transmission | Key Symptoms | Affected Area |
| Malaria | Plasmodium species (P. falciparum, P. vivax, etc.) | Bite of infected Anopheles mosquito | Fever, chills, anaemia, fatigue | Blood (RBCs), Liver |
| Amoebiasis | Entamoeba histolytica | Contaminated food/water | Diarrhoea, abdominal pain, blood in stool | Intestines, Liver (abscess in severe cases) |
| Giardiasis | Giardia lamblia | Contaminated food/water | Watery diarrhoea, nausea, bloating | Intestines |
| Kala-azar (Leishmaniasis) | Leishmania species | Bite of an infected sandfly | Skin ulcers, fever, weight loss, organ enlargement | Skin (cutaneous), Spleen, Liver (visceral) |
| Sleeping Sickness (Trypanosomiasis) | Trypanosoma brucei | Bite of infected tsetse fly | Fever, headache, neurological disorders | Blood, Central Nervous System (CNS) |
| Chagas Disease | Trypanosoma cruzi | Bite of infected Triatomine/kissing bug | Fever, swelling, heart/intestine damage | Heart, Digestive System, Nervous System |
| Toxoplasmosis | Toxoplasma gondii | Contaminated food, water, cat faeces | Flu-like symptoms, vision issues, pregnancy risks | Brain, Eyes, Muscles |
| Babesiosis | Babesia species | Bite of infected ticks | Fever, fatigue, hemolytic anaemia | Blood (RBCs) |
Non-Communicable Diseases Caused by Genetics
| Disease | Cause | Inheritance Pattern | Key Features |
| Cystic Fibrosis (CF) | Mutation in the CFTR gene | Autosomal Recessive | Affects lungs and digestive system; characterized by thick mucus production and recurrent infections. |
| Huntington’s Disease | Mutation in the HTT gene (trinucleotide repeat expansion) | Autosomal Dominant | Progressive brain disorder leading to movement, cognitive, and psychiatric issues. |
| Sickle Cell Anaemia | Mutation in the HBB gene | Autosomal Recessive | Red blood cells take on a sickle shape, leading to anaemia, pain, and organ damage. |
| Marfan Syndrome | Mutation in the FBN1 gene | Autosomal Dominant | Affects connective tissue; symptoms include tall stature, heart problems, and joint issues. |
| Haemophilia | Mutations in F8 or F9 genes | X-Linked Recessive | Blood clotting disorder leading to excessive bleeding. |
| Down Syndrome | Extra copy of chromosome 21 (Trisomy 21) | Not inherited (random chromosomal event) | Causes developmental delays, intellectual disabilities, and distinctive physical traits. |
| Turner Syndrome | Missing or partially missing X chromosome (Monosomy X) | Not inherited | Affects females; leads to short stature, infertility, and heart defects. |
| Type 1 Diabetes | Polygenic mutations (e.g., HLA genes) | Multifactorial | Autoimmune destruction of insulin-producing pancreatic cells. |
| BRCA-Linked Breast Cancer | Mutations in BRCA1 or BRCA2 genes | Autosomal Dominant (with variable expression) | Increases the risk of breast, ovarian, and other cancers. |
| Albinism | Mutations in genes affecting melanin production | Autosomal Recessive | Lack of pigmentation in skin, hair, and eyes; associated with vision problems. |
| Tay-Sachs Disease | Mutation in the HEXA gene | Autosomal Recessive | Causes nerve cell damage in the brain and spinal cord; typically fatal in early childhood. |
| Familial Hypercholesterolemia | Mutations in LDLR, APOB, or PCSK9 genes | Autosomal Dominant | Leads to high cholesterol levels, increasing risk of early heart disease. |
Non-Communicable Diseases Caused by Deficiencies
| Disease | Cause | Key Symptoms | Prevention/Treatment |
| Rickets | Vitamin D deficiency (or calcium, phosphorus) | Bone deformities, delayed growth, soft bones | Vitamin D, calcium, and phosphorus-rich diet; sunlight exposure |
| Scurvy | Vitamin C deficiency | Bleeding gums, joint pain, fatigue, poor wound healing | Vitamin C-rich foods (citrus fruits, peppers, etc.) or supplements |
| Pernicious Anaemia | Vitamin B12 deficiency | Fatigue, numbness, difficulty walking, memory issues | Vitamin B12 supplements or injections |
| Iron-Deficiency Anaemia | Insufficient iron intake or absorption | Fatigue, pale skin, shortness of breath, dizziness | Iron-rich diet (red meat, spinach) and supplements |
| Beriberi | Vitamin B1 (Thiamine) deficiency | Weakness, nerve damage, heart issues | Thiamine-rich foods (whole grains, pork) or supplements |
| Pellagra | Vitamin B3 (Niacin) deficiency | Dermatitis, diarrhoea, dementia, irritability | Niacin-rich foods (meat, fish, whole grains) or supplements |
| Goitre | Iodine deficiency | Enlarged thyroid gland, neck swelling | Iodised salt, iodine supplements |
| Hypocalcemia | Calcium deficiency | Muscle cramps, brittle nails, osteoporosis | Calcium-rich foods (dairy, leafy greens) or supplements |
| Night Blindness | Vitamin A deficiency | Poor vision in low light, dry eyes | Vitamin A-rich foods (carrots, liver) or supplements |
| Kwashiorkor | Protein deficiency | Swollen abdomen, irritability, poor growth | Protein-rich diet (eggs, fish, legumes) |
| Marasmus | General calorie and protein deficiency | Severe weight loss, muscle wasting, stunted growth | Balanced, high-calorie diet |
| Osteoporosis | Calcium and Vitamin D deficiency | Bone fractures, reduced bone density | Calcium and Vitamin D-rich diet, weight-bearing exercises |
| Hypomagnesemia | Magnesium deficiency | Weakness, muscle cramps, irregular heartbeat | Magnesium-rich foods (nuts, seeds, whole grains) |
| Hypokalemia | Potassium deficiency | Muscle weakness, fatigue, irregular heart rhythm | Potassium-rich foods (bananas, potatoes, citrus fruits) |
| Zinc Deficiency | Inadequate zinc intake | Delayed wound healing, growth retardation, hair loss | Zinc-rich foods (meat, shellfish, seeds) |
Non-Communicable Diseases Caused by Lifestyle
| Disease | Primary Cause | Key Symptoms | Prevention/Treatment |
| Obesity | High-calorie diet, physical inactivity | Excess body weight, joint pain, fatigue | Healthy diet, regular exercise, behavioural therapy |
| Type 2 Diabetes | Poor diet, obesity, sedentary lifestyle | Increased thirst, frequent urination, fatigue | Weight management, blood sugar control, medication |
| Hypertension (High Blood Pressure) | High-sodium diet, stress, obesity | Headaches, shortness of breath, heart strain | Low-sodium diet, regular exercise, stress management |
| Heart Disease (e.g., Coronary Artery Disease) | High-fat diet, smoking, lack of exercise | Chest pain, shortness of breath, fatigue | A balanced diet, exercise, medications, smoking cessation |
| Stroke | Smoking, poor diet, hypertension, obesity | Paralysis, speech difficulties, sudden weakness | Lifestyle changes, medications, rehabilitation |
| Liver Disease (e.g., Fatty Liver) | Excessive alcohol consumption, high-fat diet | Abdominal pain, fatigue, jaundice | Reduced alcohol intake, weight loss, medications |
| Chronic Respiratory Diseases (e.g., COPD) | Smoking, air pollution | Chronic cough, breathlessness, wheezing | Smoking cessation, medication, oxygen therapy |
| Cancer (e.g., Lung, Colorectal) | Smoking, poor diet, lack of exercise | Depends on cancer type (lumps, fatigue) | Early detection, treatment (surgery, chemo), lifestyle changes |
| Osteoarthritis | Obesity, repetitive stress on joints | Joint pain, stiffness, swelling | Weight management, physical therapy, medication |
| Gastroesophageal Reflux Disease (GERD) | Poor diet, overeating, smoking | Heartburn, regurgitation, throat discomfort | Weight loss, dietary changes, medication |
| Metabolic Syndrome | Poor diet, obesity, sedentary lifestyle | High blood pressure, high blood sugar, abdominal fat | Healthy diet, physical activity, medications |
| Depression and Anxiety Disorders | Chronic stress, lack of social support | Sadness, fatigue, difficulty concentrating | Therapy, stress management, medications |
| Alcohol-Related Disorders | Excessive alcohol consumption | Liver damage, addiction, memory problems | Counselling, rehabilitation, abstinence |
| Smoking-Related Disorders | Tobacco use | Lung damage, cardiovascular diseases | Smoking cessation, health monitoring |
| Sleep Disorders (e.g., Insomnia) | Irregular sleep patterns, screen time | Difficulty sleeping, fatigue, irritability | Sleep hygiene, reduced screen time, therapy |
Non-Communicable Autoimmune Diseases
| Disease | Causes | Key Features | Affected Area |
| Type 1 Diabetes | Genetic predisposition (HLA genes), environmental triggers (viral infections like Coxsackievirus). | Destruction of insulin-producing cells, leading to high blood sugar levels. | Pancreas (beta cells) |
| Rheumatoid Arthritis (RA) | Genetic factors (HLA-DR4), smoking, gut microbiome imbalance, and stress. | Chronic joint inflammation, pain, and stiffness. | Joints (and sometimes other organs) |
| Systemic Lupus Erythematosus (SLE) | Genetic predisposition, UV light exposure, infections (e.g., Epstein-Barr virus), hormonal changes. | Widespread inflammation and tissue damage in multiple organs. | Skin, joints, kidneys, heart, and more |
| Multiple Sclerosis (MS) | Genetic factors (HLA-DR2), infections (e.g., Epstein-Barr virus), low vitamin D levels, smoking. | Immune attack on myelin, leading to neurological symptoms like weakness, vision loss. | Central nervous system (brain and spinal cord) |
| Psoriasis | Genetic predisposition (PSORS1 gene), infections, stress, medications, and environmental factors. | Overproduction of skin cells causing scaly patches, often associated with arthritis. | Skin |
| Psoriatic Arthritis | Similar triggers as psoriasis, with additional joint-specific immune responses. | Joint inflammation along with symptoms of psoriasis. | Joints and skin |
| Graves’ Disease | Genetic predisposition, stress, smoking, iodine excess, and infections. | Overproduction of thyroid hormones (hyperthyroidism). | Thyroid gland |
| Hashimoto’s Thyroiditis | Genetic predisposition, selenium deficiency, excessive iodine intake, and infections. | Underproduction of thyroid hormones (hypothyroidism). | Thyroid gland |
| Celiac Disease | Genetic factors (HLA-DQ2 and HLA-DQ8), gluten consumption, and gut infections. | Gluten intolerance leading to intestinal damage and malabsorption. | Small intestine |
| Inflammatory Bowel Disease (IBD) | Genetic factors (NOD2 gene), altered gut microbiota, smoking (for Crohn’s), and immune dysregulation. | Includes Crohn’s disease and ulcerative colitis, causing chronic gut inflammation. | Gastrointestinal tract |
| Addison’s Disease | Autoimmune destruction of adrenal cortex, genetic predisposition, and infections like tuberculosis. | Insufficient hormone production from adrenal glands. | Adrenal glands |
| Pernicious Anaemia | Autoimmune destruction of stomach parietal cells, leading to vitamin B12 deficiency. | Autoimmune destruction of stomach cells leading to vitamin B12 deficiency. | Stomach lining and blood |
| Myasthenia Gravis | Antibodies against acetylcholine receptors, genetic predisposition, and thymus abnormalities. | Muscle weakness due to antibody interference with nerve signals. | Neuromuscular junction |
| Sjögren’s Syndrome | Genetic predisposition, hormonal factors (more common in women), and infections. | Dry eyes and mouth due to gland damage. | Salivary and tear glands |
| Scleroderma | Genetic factors, environmental triggers (silica dust, organic solvents), and vascular abnormalities. | Thickening and hardening of the skin and other tissues. | Skin and connective tissues |
| Vitiligo | Genetic predisposition, oxidative stress, and triggers like skin trauma or infections. | Loss of pigment in patches due to immune destruction of melanocytes. | Skin |
| Autoimmune Hepatitis | Genetic predisposition (HLA-DR3 and DR4), infections, and medications. | Chronic inflammation of the liver, leading to potential liver damage. | Liver |
| Ankylosing Spondylitis | Genetic factors (HLA-B27), infections, and environmental factors. | Chronic inflammation of the spine causing stiffness and fusion of vertebrae. | Spine and sacroiliac joints |
| Idiopathic Thrombocytopenic Purpura (ITP) | Autoantibodies against platelets, viral infections, and genetic predisposition. | Low platelet count due to immune destruction, leading to easy bruising/bleeding. | Blood (platelets) |
| Guillain-Barré Syndrome (GBS) | Triggered by infections (e.g., Campylobacter jejuni, Zika virus), vaccinations (rarely) | Acute nerve inflammation causing muscle weakness and paralysis | Peripheral nervous system |
Non-Communicable Degenerative Diseases
| Disease | Description | Key Risk Factors | Affected Area |
| Alzheimer’s Disease | Progressive loss of memory and cognition due to brain cell degeneration | Aging, genetics, lifestyle | Brain (neurons) |
| Parkinson’s Disease | A movement disorder caused by loss of dopamine-producing neurons | Aging, genetics, environmental toxins | Brain (motor control centres) |
| Multiple Sclerosis (MS) | Immune system attacks nerve coverings, causing neurological damage | Genetics, infections, environment | Nervous system (nerves) |
| Atherosclerosis | Hardening/narrowing of arteries due to plaque buildup. | Poor diet, smoking, lack of exercise. | Arteries, heart |
| Osteoarthritis | Joint pain and stiffness due to cartilage wear | Aging, obesity, joint injuries. | Joints (knees, hips, etc.) |
| Osteoporosis | Loss of bone density, making bones fragile | Aging, low calcium intake, inactivity | Bones |
| Cataracts | Clouding of the eye lens, leading to vision impairment | Aging, UV exposure, diabetes | Eyes (lens) |
| Cirrhosis | Scarring of liver tissue due to chronic damage | Alcohol use, hepatitis, toxins | Liver |