Human Health and Disease — Part 1: Infectious diseases: visual lesson, ISC Class 12 Biology

Lesson

Infectious diseases

Part 1 — diseases caused by viruses, bacteria, protozoa, worms and fungi, and how to prevent them.

In this lesson you will

Give the agent, transmission, symptoms and prevention of common viral and bacterial diseases
Explain the Widal test for typhoid
Describe amoebiasis, malaria with the life cycle of Plasmodium, ascariasis, filariasis and ringworm

Concept

Viruses multiply only inside host cells; antibiotics do not act on them.

Table of viral diseases with agents, spread and symptoms
Disease	Agent and spread	Main symptoms
Common cold	Rhinoviruses; droplets, contaminated objects	Infects nose and airways, not lungs: congestion, sore throat, cough, headache for 3–7 days
Chikungunya	Chikungunya virus; bite of Aedes mosquito	Fever with severe, lasting joint pain, rash
Dengue	Dengue virus; day-biting Aedes aegypti	High fever, severe headache, pain behind the eyes, joint and muscle pain, rash, fall in platelets

Concept

Many bacterial diseases can be treated with antibiotics and prevented by vaccines and hygiene.

Table of bacterial diseases with agents, spread and symptoms
Disease	Agent and spread	Main symptoms
Typhoid	Salmonella typhi; contaminated food and water	Sustained high fever (39–40 °C), weakness, stomach pain, constipation, headache; intestinal perforation in severe cases
Pneumonia	Streptococcus pneumoniae, Haemophilus influenzae; droplets, shared glasses	Alveoli fill with fluid; fever, chills, cough; lips and nails may turn bluish
Diphtheria	Corynebacterium diphtheriae; droplets	Sore throat, fever, a tough membrane in the throat; toxin may damage the heart
Plague	Yersinia pestis; bite of the rat flea	Fever, chills, swollen painful lymph nodes (buboes)