Pathogens and how infectious diseases are transmitted

Last time

Before we start: last time, in Disease control, antibiotics and resistance, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Small things, big diseases

Most of the organisms around you are harmless, but a few cause disease. Those are pathogens, and they come from four different groups: bacteria, viruses, protoctists and fungi. The group tells you how the disease spreads and what treatment can work, so the first job is to match each disease to its pathogen and its route.

Definitions

A pathogen is an organism or virus that causes disease. An infectious disease is one that can pass from one host to another. A disease is transmissible if the pathogen can be passed on. Transmission may be direct, by contact or droplets, or indirect, through water, food or a vector. A vector is an organism that carries a pathogen from one host to another, without usually being harmed. The Anopheles mosquito is one.

Bacterial diseases

Cholera is caused by the bacterium Vibrio cholerae. It is spread in contaminated food or water. The toxin causes severe diarrhoea and loss of water and ions. Tuberculosis, or T B, is caused by Mycobacterium tuberculosis, and Mycobacterium bovis in cattle. It attacks mainly the lungs. T B spreads in droplets when an infected person coughs. M bovis can pass from infected cows to people in unpasteurised milk.