1. Pathogens

• Disease-causing organisms are called pathogens.
• They include bacteria, viruses, fungi, protozoans and helminths.
• Pathogens enter the body, multiply and interfere with normal body functions.

2. Typhoid

• Pathogen: Salmonella typhi (bacterium)
• Transmission: Contaminated food and water
• Symptoms: High fever (39–40°C), weakness, stomach pain, constipation, headache and loss of appetite.
• Test: Widal test
• Severe cases may cause intestinal perforation and death.

3. Pneumonia

• Pathogens: Streptococcus pneumoniae, Haemophilus influenzae
• Affected organ: Alveoli of lungs
• Transmission: Respiratory droplets/aerosols and contaminated utensils.
• Symptoms: Fever, chills, cough and headache.
• Fluid accumulates in alveoli, causing breathing difficulty.

4. Common Cold

• Pathogen: Rhinoviruses
• Affected: Nose and respiratory passage, not lungs.
• Symptoms: Nasal congestion, nasal discharge, sore throat, cough, headache and tiredness.
• Usually lasts 3–7 days.
• Spread through droplets and contaminated objects.

5. Malaria

• Pathogen: Plasmodium
• Species include P. vivax, P. malariae and P. falciparum.
• Most serious: P. falciparum → malignant malaria.
• Vector: Female Anopheles mosquito.
• Infective form entering humans: Sporozoites.
• Parasites multiply first in liver cells, then infect RBCs.
• RBC rupture releases haemozoin, causing recurring chills and fever.
• Plasmodium requires two hosts: humans and mosquitoes.

6. Amoebiasis

• Pathogen: Entamoeba histolytica
• Affected: Large intestine
• Symptoms: Constipation, abdominal pain/cramps and stools containing excess mucus and blood.
• Transmission: Contaminated food and water.
• Carrier: Housefly acts as a mechanical carrier.

7. Ascariasis

• Pathogen: Ascaris (roundworm)
• Symptoms: Internal bleeding, muscular pain, fever, anaemia and intestinal blockage.
• Transmission: Contaminated food, water, vegetables and fruits.

8. Filariasis / Elephantiasis

• Pathogen: Wuchereria bancrofti and W. malayi
• Vector: Female mosquito
• Causes chronic inflammation of lymphatic vessels, especially of lower limbs.
• May also affect genital organs and cause deformities.

9. Ringworm

• Fungi: Microsporum, Trichophyton, Epidermophyton
• Affected: Skin, nails and scalp.
• Symptoms: Dry, scaly lesions and intense itching.
• Favourable conditions: Heat and moisture.
• Spread through infected soil, towels, clothes and combs.

10. Prevention and Control

Personal hygiene:

• Keep body clean.
• Drink clean water.
• Eat clean and properly prepared food, vegetables and fruits.

Public hygiene:

• Proper disposal of waste and excreta.
• Regular cleaning and disinfection of water reservoirs and public places.

Vector control:

• Avoid stagnant water.
• Use mosquito nets.
• Clean coolers regularly.
• Use wire mesh on doors/windows.
• Use insecticides where appropriate.
• Gambusia fish feed on mosquito larvae.

11. Vaccination and Antibiotics

• Vaccination and immunisation have helped control many infectious diseases.
• Smallpox has been completely eradicated.
• Vaccines have greatly controlled diseases such as polio, diphtheria, pneumonia and tetanus.
• Antibiotics and other drugs help in treating many infectious diseases.