PRELIMS

Human Diseases: Protozoa, Bacteria, and Viruses

Diseases are categorized based on their causative agents. Understanding the vector (carrier) and the affected organ is crucial for public health.

I. Diseases caused by Protozoa

• Malaria: Affected Organ: RBC & Liver. Parasite: Plasmodium. Carrier: Female Anopheles. Symptoms: Fever with shivering.
• Pyorrhoea: Affected Organ: Gums. Parasite: Entamoeba gingivalis. Carrier: —. Symptoms: Bleeding from gums.
• Sleeping Sickness: Affected Organ: Brain. Parasite: Trypanosoma. Carrier: Tse-Tse flies. Symptoms: Fever with severe sleep.
• Diarrhoea: Affected Organ: Intestine. Parasite: Entamoeba histolytica. Carrier: House flies. Symptoms: Mucous & blood in stool.
• Kala-azar: Affected Organ: Bone marrow. Parasite: Leishmania donovani. Carrier: Sand flies. Symptoms: High fever.

• Discovery: Charles Leveran (1880) discovered Plasmodium; Ronald Ross (1897) confirmed the mosquito carrier.
• Filariasis (Elephantiasis): Affected Organ: Lymphatic system. Parasite: Wuchereria bancrofti (a nematode, not protozoan, but grouped here for vector recall). Carrier: Culex mosquito. Symptoms: Swelling of limbs/tissues.

II. Diseases caused by Bacteria

• Tetanus: Affected Organ: Nervous system. Name of Bacteria: Clostridium Tetani
• Cholera: Affected Organ: Intestine. Name of Bacteria: Vibrio cholerae
• Typhoid: Affected Organ: Intestine. Name of Bacteria: Salmonella typhosa
• Tuberculosis (TB): Affected Organ: Lungs. Name of Bacteria: Mycobacterium tuberculosis
• Diphtheria: Affected Organ: Respiratory tube. Name of Bacteria: Corynebacterium diphtheriae
• Plague: Affected Organ: Lungs/Groin. Name of Bacteria: Pasteurella pestis
• Pneumonia: Affected Organ: Lungs. Name of Bacteria: Diplococcus pneumoniae
• Leprosy: Affected Organ: Nervous system/Skin. Name of Bacteria: Mycobacterium leprae
• Gonorrhea: Affected Organ: Urinary Path. Name of Bacteria: Neisseria gonorrhoeae
• Syphilis: Affected Organ: Urinary Path. Name of Bacteria: Treponema pallidum

• Note: Robert Koch (1882) discovered Cholera and TB bacteria.

III. Diseases caused by Viruses

• AIDS: Affected Organ: Immune system (WBC). Name of Virus: HIV. Symptoms: Loss of immunity.
• Dengue: Affected Organ: Whole body/Joints. Name of Virus: Dengue virus (Flavivirus). Carrier: Aedes aegypti mosquito. Symptoms: High fever, platelet count drop, joint pain ("breakbone fever").
• Chikungunya: Affected Organ: Joints. Name of Virus: Chikungunya virus. Carrier: Aedes mosquito. Symptoms: Severe joint pain, fever.
• Polio: Affected Organ: Throat/Backbone/Nerves. Name of Virus: Poliovirus. Symptoms: Muscle paralysis.
• Influenza: Affected Organ: Whole body. Name of Virus: Myxovirus (Orthomyxovirus). Symptoms: Sneezing, headache.
• Small Pox: Affected Organ: Whole body. Name of Virus: Variola virus. Symptoms: High fever, eruptions. (Declared eradicated globally by WHO in 1980.)
• Chicken Pox: Affected Organ: Whole body. Name of Virus: Varicella virus. Symptoms: Light fever, eruptions.
• Measles: Affected Organ: Whole body. Name of Virus: Measles virus (genus Morbillivirus). Symptoms: Reddish eruptions.
• Rabies: Affected Organ: Nervous system. Name of Virus: Rabies virus. Symptoms: Madness, hydrophobia.
• Hepatitis/Jaundice: Affected Organ: Liver. Name of Virus: Hepatitis A/B/C/D/E viruses — A and E spread via contaminated food/water; B, C, and D spread via blood/body fluids. Symptoms: Yellow urine/skin.
• Trachoma: Affected Organ: Eyes. Name of Virus: —. Symptoms: Redness and pain.
• Meningitis: Affected Organ: Brain. Name of Virus: —. Symptoms: High fever.

• AIDS: Acquired Immuno Deficiency Syndrome. ELISA Test is used for HIV detection.

UPSC Relevance

Infectious diseases are a priority in GS-III Health and S&T.

• Vectors: Recalling that Sand flies carry Kala-azar and Tse-tse flies carry Sleeping Sickness.
• Pathogens: Differentiating between viral (AIDS, Hepatitis) and bacterial (TB, Cholera) diseases for vaccination policy questions.
• Diagnostics: The significance of the ELISA test for HIV and BCG vaccine for TB.
• Confused Pair — Vector-borne disease agents: Malaria (Plasmodium, protozoan) and Filariasis (Wuchereria, nematode worm) are NOT bacterial/viral despite being mosquito-borne like Dengue/Chikungunya (viral). Do not conflate "mosquito-borne" with a single pathogen category.
• Confused Pair — Sleeping Sickness vs Kala-azar: Both spread by flies (not mosquitoes) — Sleeping Sickness by Tse-Tse fly (Trypanosoma, affects brain); Kala-azar by Sand fly (Leishmania, affects bone marrow/spleen).
• Vaccine-preventable diseases (India's Universal Immunization Programme): BCG (TB), OPV/IPV (Polio), DPT (Diphtheria-Pertussis-Tetanus), Measles-Rubella (MR), Hepatitis B, Pentavalent vaccine — relevant for Mission Indradhanush.