1.0 Understanding Diseases: An Overview
A Disease is any condition that interferes with the normal functioning of the body. To study them effectively for the ICSE board, we classify them into two broad categories based on how they are spread.
1.1 Categories of Diseases
| Category | Description | Examples |
|---|---|---|
| Communicable | Infectious diseases spread from an infected person to a healthy person. | Cholera, Malaria, Tuberculosis, AIDS. |
| Non-Communicable | Do not spread through contact; caused by organ failure, diet, or genes. | Diabetes, Cancer, Scurvy, Hypertension. |
1.2 Important Terminology
You must be clear on these three terms for "Define the following" questions:
- Pathogen: A specific disease-causing microorganism (Bacteria, Virus, etc.).
- Incubation Period: The time interval between the entry of the pathogen and the appearance of the first symptom.
- Susceptibility: The lack of resistance in a host to a particular pathogen.
Diseases present from birth are Congenital (e.g., color blindness), while those developed after birth are Acquired. Most ICSE questions focus on the acquired group, particularly infectious ones.
A disease that is constantly present in a specific area is called Endemic (like Goitre in sub-Himalayan regions), while a sudden outbreak over a wide area is an Epidemic.
2.0 Common Bacterial Diseases
Bacterial diseases are generally treated with Antibiotics. However, prevention through hygiene and vaccination remains the most effective control strategy.
2.1 Profile of Major Bacterial Infections
| Disease | Causative Agent | Symptoms & Control |
|---|---|---|
| Typhoid | Salmonella typhi | Continuous high fever, intestinal inflammation. Control: TAB Vaccine. |
| Cholera | Vibrio cholerae | Painless "rice-water" stools, severe dehydration. Control: ORS and Chlorination of water. |
| Tuberculosis (TB) | Mycobacterium tuberculosis | Persistent cough, blood in sputum, chest pain. Control: BCG Vaccine. |
2.2 Transmission: How Bacteria Spread
Most bacterial diseases in the ICSE syllabus are Water-borne or Air-borne. Understanding the route is key to prevention.
Typhoid and Cholera spread through the Faeco-oral route (contaminated food/water). Houseflies act as mechanical vectors.
TB spreads through Droplet nuclei released when an infected person coughs, sneezes, or talks.
When writing scientific names of bacteria (like Vibrio cholerae), always underline them separately if you are writing by hand. In your Edudias posts, use italics to ensure scientific accuracy.
Tuberculosis is treated using DOTS (Directly Observed Treatment, Short-course). This ensures the patient completes the full course of antibiotics to prevent the bacteria from becoming drug-resistant.
3.0 Viral Infections and Their Control
Viral diseases can range from the common cold to life-threatening conditions. Unlike bacteria, viruses "hijack" host cells, making them harder to target without damaging the host's own tissues.
3.1 AIDS (Acquired Immuno-Deficiency Syndrome)
AIDS is caused by the Human Immunodeficiency Virus (HIV). It specifically attacks the Helper T-cells of the immune system, leaving the body vulnerable to "opportunistic infections."
[attachment_0](attachment)- Unprotected sexual contact with an infected person.
- Transfusion of contaminated blood.
- Use of infected needles or syringes.
- From an infected mother to her child through the placenta.
3.2 Other Major Viral Diseases
| Disease | Target Organ | Key Symptom |
|---|---|---|
| Hepatitis (Jaundice) | Liver | Yellowing of eyes/skin, dark urine. |
| Chicken Pox | Skin / General | Dew-drop-like rashes, fever. |
| Poliomyelitis | Nervous System | Paralysis of limbs (leg muscles). |
In "State whether True or False" or "Give Reasons" questions, remember: AIDS cannot be spread by casual contact like shaking hands, hugging, sharing food, or through insect bites (like mosquitoes).
When our cells are attacked by a virus, they produce a special protein called Interferon. This protein doesn't save the already infected cell but "warns" and protects neighboring healthy cells from the virus.
4.0 Protozoan and Fungal Infections
Protozoa are microscopic single-celled animals, while fungi are non-green saprophytic plants. Both groups contain species that are specialized parasites in humans.
4.1 Malaria: The Global Challenge
Malaria is caused by the protozoan Plasmodium. It is transmitted through the bite of an infected female Anopheles mosquito.
[attachment_0](attachment)- Periodic recurrence of high fever with chills and shivering.
- Profuse sweating as the temperature drops.
- Enlargement of the spleen and anaemia (due to destruction of RBCs).
Control: Antimalarial drugs like Quinine and preventing mosquito breeding.
4.2 Amoebic Dysentery (Amoebiasis)
Caused by Entamoeba histolytica. It resides in the human large intestine and spreads via contaminated food and water.
- Symptoms: Frequent stools with mucus and blood, abdominal pain.
- Prevention: Proper sanitation and drinking boiled water.
4.3 Fungal Diseases (Dermatomycoses)
Fungal infections of the skin are usually spread through direct contact or sharing personal items like towels and combs.
| Disease | Symptoms |
|---|---|
| Ringworm | Red, itchy, circular scaly patches on the skin or scalp. |
| Athlete's Foot | Infection between the toes leading to softening and cracking of the skin. |
Be careful in "Distinguish between" questions. Bacillary Dysentery is caused by bacteria (Shigella), while Amoebic Dysentery is caused by a protozoan. Mentioning the type of pathogen is vital for full marks.
Quinine is a natural alkaloid extracted from the bark of the Cinchona tree. It has been used for centuries to treat Malaria and was one of the first effective chemical treatments for an infectious disease.
5.0 Helminths and Non-Communicable Diseases
While infectious diseases are caused by external pathogens, non-communicable diseases are often the result of our genetics, environment, or lifestyle choices.
5.1 Helminthic (Worm) Diseases
These are caused by parasitic flatworms or roundworms. They usually enter the body through contaminated food or skin contact with infected soil.
| Disease | Causative Agent | Key Impact |
|---|---|---|
| Ascariasis | Ascaris lumbricoides (Roundworm) | Intestinal blockage, abdominal pain, and stunted growth in children. |
| Taeniasis | Taenia solium (Tapeworm) | Weight loss and digestive disorders; spreads via undercooked pork. |
| Elephantiasis | Wuchereria bancrofti (Filarial worm) | Severe swelling of the limbs due to blockage of Lymphatic vessels. |
5.2 Non-Communicable Diseases (NCDs)
These diseases cannot be "caught" from another person. They are often chronic and require long-term management.
Caused by insufficient Insulin hormone. Results in high blood sugar levels. Symptoms include excessive thirst and frequent urination.
Commonly known as high blood pressure. Can lead to heart disease or stroke if left untreated.
Uncontrolled and abnormal cell division leading to the formation of a tumor.
In "Identify the odd one out," remember that Scurvy and Rickets are deficiency diseases (NCDs), while Malaria and Cholera are infectious. If you see them mixed, group them by communicability.
- Can you define the "Incubation Period"?
- Do you know the difference between HIV and AIDS?
- Can you name the vector for Elephantiasis?
- Do you know which organ is affected by Hepatitis?