⚡ Quick Revision : Causes & Control
1. What is a Disease?
A Disease is a departure from normal health through structural or functional disorder of the body. It is characterized by specific Symptoms (what the patient feels) and Signs (what the doctor observes).
2. Categories of Diseases
Diseases are broadly classified into two main types:
- A. Congenital Diseases: Present since birth (e.g., color blindness, hemophilia). They are usually caused by genetic defects.
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B. Acquired Diseases: Developed after birth. These are further divided into:
• Communicable (Infectious): Spread from person to person (e.g., Flu, COVID-19).
• Non-Communicable (Degenerative): Not spread through contact (e.g., Cancer, Diabetes).
3. Modes of Transmission
| Mode | Mechanism | Example Diseases |
|---|---|---|
| Direct Contact | Skin-to-skin contact or sores. | Chickenpox, Ringworm, AIDS. |
| Droplet Infection | Inhaling sneezed/coughed droplets. | Common Cold, Tuberculosis. |
| Contaminated Food/Water | Eating/Drinking pathogens. | Cholera, Typhoid, Hepatitis A. |
| Vector-borne | Spread by insects (mosquitoes, flies). | Malaria, Dengue, Plague. |
Question: Why is Tuberculosis called an "Air-borne" disease?
Answer: When a TB patient coughs or sneezes, tiny droplets (nuclei) containing the bacteria Mycobacterium tuberculosis stay suspended in the air for hours. A healthy person can contract the disease by simply breathing this contaminated air.
The Incubation Period is the time interval between the entry of the pathogen and the appearance of the first symptom. It varies for every disease!
⚡ Quick Revision : Causes & Control (Bacterial Diseases)
1. Cholera
A highly infectious disease characterized by severe diarrhea and vomiting, leading to rapid dehydration.
- 🦠 Pathogen: Vibrio cholerae (Comma-shaped bacteria).
- 💧 Transmission: Contaminated food or water; spread by houseflies.
- ⚠️ Symptoms: "Rice-water" stools, frequent vomiting, muscular cramps, and sunken eyes.
- 🛡️ Control: Proper sanitation, boiling water, and ORS (Oral Rehydration Solution).
2. Typhoid
Also known as "Enteric Fever," it mainly affects the intestines and can spread to the blood.
- 🦠 Pathogen: Salmonella typhi.
- 💧 Transmission: Fecal-oral route through contaminated food/water.
- ⚠️ Symptoms: Continuous high fever, slow pulse, abdominal pain, and rose-colored spots on the chest.
- 🧪 Diagnostic Test: Widal Test.
- 🛡️ Control: TAB vaccine provides immunity for about 3 years.
3. Tuberculosis (TB)
A chronic infectious disease that most commonly affects the lungs but can also affect bones and joints.
- 🦠 Pathogen: Mycobacterium tuberculosis.
- 🌬️ Transmission: Droplet infection (coughing/sneezing) or dust.
- ⚠️ Symptoms: Persistent cough, blood in sputum (hemoptysis), chest pain, and night sweats.
- 🛡️ Control: BCG Vaccine (Bacillus Calmette-Guérin) and DOTS (Directly Observed Treatment Short-course).
Question: Why is ORS given to a Cholera patient immediately?
Answer: Cholera causes massive loss of water and electrolytes ($Na^+, K^+, Cl^-$) from the body. This dehydration can lead to kidney failure or death. ORS replenishes both water and essential salts to maintain the body's osmotic balance.
Antibiotics (like Penicillin) are effective against bacterial diseases like TB and Cholera, but they have no effect on viral diseases like Polio or AIDS.
⚡ Quick Revision : Causes & Control (Viral Diseases)
1. AIDS (Acquired Immuno Deficiency Syndrome)
AIDS is not a single disease but a condition where the body’s immune system is so weakened that it cannot fight off even minor infections.
- 🦠 Pathogen: HIV (Human Immunodeficiency Virus). It is a Retrovirus (contains RNA).
- ⚠️ Target: It attacks Helper T-lymphocytes (WBCs), destroying the body's defense mechanism.
- 📍 Transmission:
• Sexual contact with an infected person.
• Transfusion of contaminated blood.
• Sharing infected needles/syringes.
• From infected mother to child through the placenta.
2. Chickenpox
A highly contagious viral infection causing an itchy, blister-like rash on the skin.
- 🦠 Pathogen: Varicella-zoster virus.
- 🌬️ Transmission: Direct contact or droplets from sneezing/coughing.
- ⚠️ Symptoms: Fever, headache, followed by red itchy spots that turn into fluid-filled blisters (vesicles).
- 🛡️ Control: Isolation of the patient and vaccination.
3. Hepatitis (Jaundice)
Inflammation of the Liver caused by various viruses, primarily Hepatitis A and B.
- 🦠 Pathogen: Hepatitis Virus (A, B, C, D, or E).
- ⚠️ Symptoms: Yellowing of eyes and skin (due to bilirubin), dark tea-colored urine, and loss of appetite.
- 🛡️ Prevention: Boiling water (for Hep-A) and using sterilized needles (for Hep-B).
Question: Why is it that an AIDS patient often dies of a simple common cold or pneumonia?
Answer: HIV specifically destroys T-cells, which are the commanders of the immune system. Without them, the body cannot produce antibodies. Consequently, even minor pathogens that a healthy body would easily defeat become life-threatening.
AIDS cannot be spread by shaking hands, hugging, sharing food, or through mosquito bites. HIV is only transmitted through specific body fluids like blood, semen, and breast milk.
⚡ Quick Revision : Causes & Control (Protozoan & Fungal)
1. Malaria
A major tropical disease that causes recurring high fever with chills. It is caused by a protozoan parasite.
- 🦠 Pathogen: Plasmodium (Species: P. vivax, P. falciparum, P. malariae).
- 🦟 Vector: Female Anopheles mosquito.
- ⚠️ Symptoms: High fever, shivering (chills), profuse sweating when the fever drops, and enlargement of the spleen.
- 🛡️ Control: Use of Quinine or Chloroquine. Eliminating stagnant water to prevent mosquito breeding.
2. Amoebic Dysentery (Amoebiasis)
An intestinal infection that causes diarrhea with blood and mucus. It is common in areas with poor sanitation.
- 🦠 Pathogen: Entamoeba histolytica (a protozoan).
- 💧 Transmission: Contaminated food/water or through the feet of houseflies.
- ⚠️ Symptoms: Abdominal pain, stools containing blood and mucus, and a feeling of incomplete bowel evacuation.
- 🛡️ Prevention: Drinking boiled water, washing vegetables thoroughly, and effective sewage disposal.
3. Fungal Diseases: Ringworm
Despite the name, it is NOT caused by a worm. It is a highly contagious fungal infection of the skin.
- 🦠 Pathogen: Fungi like Trichophyton or Microsporum.
- 📍 Transmission: Direct skin-to-skin contact or sharing combs, towels, and clothes.
- ⚠️ Symptoms: Red, itchy, circular (ring-like) scaly patches on the skin, nails, or scalp.
- 🛡️ Control: Antifungal creams and maintaining dry, clean skin.
Question: Why does a person with Malaria feel a chill followed by high fever?
Answer: When the Plasmodium parasites multiply inside the RBCs, the cells eventually burst, releasing a toxic substance called Haemozoin into the blood. This toxin is responsible for the characteristic shivering and sudden high fever.
Bacillary Dysentery is caused by bacteria (Shigella), while Amoebic Dysentery is caused by a protozoan. Though symptoms are similar, the medical treatment is completely different!
⚡ Quick Revision : Causes & Control (Helminthic & Non-Communicable)
1. Helminthic Diseases (Worm Infections)
These are caused by parasitic worms (helminths) that live in the human intestine or tissues.
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A. Ascariasis: Caused by the Roundworm (Ascaris lumbricoides).
• Transmission: Ingesting eggs through contaminated vegetables or water.
• Symptoms: Abdominal pain, indigestion, and in severe cases, intestinal blockage. -
B. Taeniasis: Caused by the Tapeworm (Taenia solium).
• Transmission: Eating undercooked "measly" pork containing larvae.
• Symptoms: Weight loss, abdominal pain, and nausea.
2. Non-Communicable Diseases (NCDs)
These are "lifestyle diseases" that cannot be passed from one person to another. They result from genetic, physiological, environmental, and behavioral factors.
| Disease | Cause/Mechanism | Key Symptom |
|---|---|---|
| Diabetes Mellitus | Deficiency of Insulin hormone from the pancreas. | High blood sugar, excessive thirst/urination. |
| Hypertension | Consistently high blood pressure against artery walls. | Headache, dizziness, risk of heart attack. |
| Cancer | Uncontrolled and abnormal cell division forming tumors. | Lumps, unexplained weight loss. |
3. Metabolic Disorders
- Goitre: Swelling of the thyroid gland due to Iodine deficiency.
- Obesity: Excessive accumulation of body fat, leading to heart and joint issues.
- Scurvy/Rickets: (Recall from Nutrition chapter) Diseases caused by specific vitamin deficiencies.
Question: Why is it dangerous to eat undercooked pork or beef?
Answer: Meat from infected animals may contain encysted larvae (bladderworms) of Tapeworms. If not cooked at high temperatures ($100°C+$), these larvae survive and develop into adult worms in the human intestine, absorbing the host's nutrients.
Benign Tumors stay localized and don't spread. Malignant Tumors are cancerous; they invade neighboring tissues and spread to distant organs (Metastasis).