This set of notes explains how four major infectious diseases – cholera, malaria, tuberculosis (TB) and human immunodeficiency virus (HIV) – are transmitted. Understanding the routes of transmission is essential for disease control and prevention.
1. Cholera (Vibrio cholerae)
Cholera is an acute diarrhoeal disease caused by the bacterium Vibrio cholerae. The primary mode of transmission is the faecal‑oral route.
Contaminated drinking water or food (especially raw shellfish).
Inadequate sanitation leading to the spread of infected faeces into water supplies.
Person‑to‑person spread is rare; the disease spreads through the environment.
2. Malaria (Plasmodium spp.)
Malaria is caused by protozoan parasites of the genus Plasmodium. Transmission occurs via the bite of an infected female Anopheles mosquito.
When a mosquito feeds on an infected person, it ingests gametocytes.
Parasites develop in the mosquito’s gut and migrate to the salivary glands.
During a subsequent bite, sporozoites are injected into the human bloodstream.
Suggested diagram: Life cycle of Plasmodium showing mosquito and human stages.
3. Tuberculosis (Mycobacterium tuberculosis)
TB is a bacterial infection that primarily affects the lungs. Transmission is through the airborne route.
Infected individuals expel aerosolised droplets when coughing, sneezing, speaking or singing.
Droplets containing M. tuberculosis can remain suspended in the air for several hours.
Inhalation of these droplets by a susceptible person can lead to infection.
4. Human Immunodeficiency \cdot irus (HIV)
HI \cdot is a retrovirus that attacks the immune system. Transmission occurs through the exchange of certain body fluids.
Blood (e.g., needle sharing, transfusion with infected blood).
Semen and vaginal secretions (unprotected sexual intercourse).
Breast milk (from mother to infant).
Occasionally, from mother to child during pregnancy or delivery.
Summary Table of Transmission Routes
Disease
Pathogen
Primary Transmission Route
Key Risk Factors
Cholera
Vibrio cholerae (bacterium)
Faecal‑oral (contaminated water/food)
Poor sanitation, unsafe water, overcrowding
Malaria
Plasmodium spp. (protozoan)
Vector‑borne (bite of infected Anopheles mosquito)
Living in endemic areas, lack of mosquito control
Tuberculosis
Mycobacterium tuberculosis (bacterium)
Airborne droplets
Close contact, crowded indoor settings, immunocompromised hosts
HIV
Human Immunodeficiency \cdot irus (retrovirus)
Blood and sexual fluids (bloodborne & sexual transmission)
Identify the type of pathogen (bacterium, protozoan, virus) for each disease.
Match each disease with its principal transmission route.
Recall the main environmental or behavioural risk factors that facilitate transmission.
Understand how control measures target the specific transmission pathways (e.g., water treatment for cholera, insecticide‑treated nets for malaria, ventilation for TB, safe sex practices for HIV).