Infectious diseases
Infectious diseases
- An infectious disease is caused by a pathogen — an organism that lives in or on a host and causes harm.
- These diseases are transmissible: the pathogen passes from one person to another.
- You need to know four key examples.
Practice
A pathogen is:
A pathogen causes an infectious (transmissible) disease — e.g. a bacterium, virus or protoctist.
Four diseases to know
| Disease | Pathogen | How it spreads |
|---|---|---|
| cholera | bacterium (Vibrio cholerae) | water/food contaminated with faeces |
| malaria | protoctist (Plasmodium) | bite of an infected mosquito (a vector) |
| tuberculosis (TB) | bacterium (Mycobacterium) | airborne droplets from coughs/sneezes |
| HIV/AIDS | virus (HIV) | unprotected sex, infected blood, mother to baby |
Practice
Cholera is caused by a bacterium and spreads through:
Cholera (Vibrio cholerae) spreads via water/food contaminated with human waste — hence clean water prevents it.
Practice
Malaria is caused by a protoctist (Plasmodium) carried by:
The mosquito is the vector that transmits the Plasmodium protoctist when it bites.
Practice
Match each disease to its type of pathogen.
Cholera & TB = bacteria; malaria = protoctist; HIV/AIDS = virus.
Why HIV is so serious
- HIV infects and destroys certain white blood cells.
- These are the cells that defend the body, so HIV slowly weakens the immune system.
- This leads to AIDS, when the body can no longer fight off infections.
Practice
HIV weakens the body because it:
HIV destroys certain white blood cells, so the immune system weakens and AIDS can develop.
You've got it
Key idea
- pathogen = organism that causes disease; infectious diseases are transmissible
- cholera (bacterium, dirty water), malaria (protoctist, mosquito vector)
- TB (bacterium, airborne droplets), HIV/AIDS (virus, sex/blood/mother-to-baby)
- HIV destroys white blood cells → weakens the immune system