An infectious disease is caused by a pathogen that can pass from one person to another. Cholera, malaria, TB and HIV/AIDS are caused by a bacterium, a protoctist, bacteria and a virus, and each one travels by its own route: water, a mosquito, the air and body fluids.
An infectious disease is caused by a pathogen, an organism or virus that causes disease, and it is transmissible: it can be passed from one host to another. Cholera is caused by the bacterium Vibrio cholerae and spreads by the faecal-oral route in contaminated water and food. Malaria is caused by the protoctists Plasmodium falciparum, P. malariae, P. ovale and P. vivax and is carried by a vector, the female Anopheles mosquito. Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis and M. bovis and spreads in airborne droplets, with M. bovis also caught from infected cattle in unpasteurised milk or undercooked meat. HIV/AIDS is caused by the human immunodeficiency virus and is passed in body fluids: unprotected sex, shared needles and infected blood, and from mother to baby.
The lab opens on cholera. Rotate each model and read the PATHOGEN and TYPE read-outs as you click through cholera, malaria, tuberculosis (TB) and HIV/AIDS.
| Disease | Pathogen | Type | Where it attacks |
|---|---|---|---|
| cholera | Vibrio cholerae | bacterium (prokaryote) | small intestine: a toxin makes cells secrete chloride ions, water follows by osmosis, causing severe watery diarrhoea and dehydration |
| malaria | Plasmodium falciparum, P. malariae, P. ovale, P. vivax | protoctist (single-celled eukaryote) | liver cells, then red blood cells, which burst as the parasites multiply |
| tuberculosis (TB) | Mycobacterium tuberculosis and M. bovis | bacteria (prokaryotes) | mainly the lungs; the bacteria survive inside phagocytes |
| HIV/AIDS | human immunodeficiency virus (HIV) | virus (a retrovirus) | T-helper lymphocytes; their loss weakens the immune system and leads to AIDS |
All four are infectious (caused by a pathogen) and transmissible (passed between people). Diseases such as sickle cell anaemia or lung cancer are not infectious: there is no pathogen to pass on.
Malaria is not caused by a bacterium or by the mosquito. The pathogen is the protoctist Plasmodium; the mosquito is only the vector that carries it. Name the pathogen with its genus (and species where asked), written in italics or underlined.
Pick each disease and follow the moving dots along its route. Read the labels in each scene: where does the pathogen leave one person and how does it enter the next?
HIV does not survive long outside the body and is not spread by touching, coughing, sharing cups or by mosquitoes. A mosquito transmits Plasmodium because the parasite completes part of its life cycle inside the insect; HIV does not.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the pathogens tab, what does the TYPE read-out show for malaria?
In the malaria model, what are the purple rings shown inside the red blood cell?
In the cholera scene of the transmission tab, where do the bacteria come from before they reach the drinking water?
In the TB scene, which setting does the lab label to show where TB spreads most easily?
Knowing exactly how a pathogen gets from one host to the next tells you where the chain of transmission can be broken.
| Disease | Route | Where the chain can be broken |
|---|---|---|
| cholera | water and food contaminated with faeces | sewage treatment, clean piped or chlorinated water, hygiene |
| malaria | female Anopheles mosquito | stop mosquitoes breeding or biting; treat infected people |
| TB | droplets in air; milk from infected cattle | less overcrowding, early diagnosis and treatment, BCG vaccine, pasteurisation |
| HIV | sex, blood, mother to baby | condoms, screened blood, clean needles, antiretroviral drugs |
The next lesson weighs these measures against the biological, social and economic factors that decide whether they work.
Unlocks once the four checks above are done. Worth more XP, written to AS Paper 1 and Paper 2 standard.
Which row correctly matches disease, pathogen and type of pathogen?
Which statement best explains why malaria is described as transmitted by a vector?
A cholera outbreak follows an earthquake that damages the water pipes and sewers of a city. Which explains the outbreak?
Why are people with HIV more likely to develop active TB?
This skill is now recorded on your profile. Keep the chain going.