Pathogens
A pathogenMicroorganism that causes disease. is an organism that causes a diseaseIllness affecting plants and animals.. There are four main types of pathogen:
| Example in animals | Example in plants | |
| Viruses | HIV/AIDS | Tobacco mosaic virus |
| Bacteria | Salmonella | Agrobacterium |
| Fungi | Athlete's foot | Black rose spot |
| Protists | Malaria | Downy mildew |
| Viruses | |
|---|---|
| Example in animals | HIV/AIDS |
| Example in plants | Tobacco mosaic virus |
| Bacteria | |
|---|---|
| Example in animals | Salmonella |
| Example in plants | Agrobacterium |
| Fungi | |
|---|---|
| Example in animals | Athlete's foot |
| Example in plants | Black rose spot |
| Protists | |
|---|---|
| Example in animals | Malaria |
| Example in plants | Downy mildew |
All types of pathogen have a simple life cycle. They infect a hostThe organism lived on or in by a parasite., reproduce themselves or replicate if it is a virusAn ultramicroscopic infectious non-cellular organism that can replicate inside the cells of living hosts, with negative consequences., spread from their host and infect other organismLiving entity, eg animals, plants or microorganisms.. They also all have structural adaptations that make them successful at completing their life cycles, which enable them to cause more disease.
Diseases caused by pathogens are called communicable diseases. This means the disease can be transferred from an infected organism to another organism.
There are other types of disease which cannot be passed from organism to organism. These are called non-communicable diseases:
- Inherited genetic disorders like cystic fibrosisA disorder that mainly affects the lungs, pancreas, liver, and intestine. The main symptom is difficulty breathing. can be passed to offspring but not to anyone else.
- deficiency diseaseA disease that develops because an organism (plant or animal) does not have enough vitamins or mineral ions. which are caused by a lack of essential vitamins or mineralsNaturally occurring, inorganic chemical substances. Minerals are necessary for both plant and animal health., such as scurvy which occurs when an individual has insufficient vitamin C.
- Diseases like cancer that develop as a result of exposure to carcinogenA chemical or other agent that causes cancer. or develop naturally as cell division occurs incorrectly.
Transmission
transmission The spreading of pathogenic disease, for example by touch, food, water. can occur in a number of important ways, as shown in the table below.
| Type of transmission | Example |
| Direct contact | This can be sexual contact during intercourse or non-sexual contact, like shaking hands. |
| Water | Dirty water can transmit many diseases, such as the cholera bacterium. |
| Air | When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others. |
| Unhygienic food preparation | Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning. |
| Vector | Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers. |
| Type of transmission | Direct contact |
|---|---|
| Example | This can be sexual contact during intercourse or non-sexual contact, like shaking hands. |
| Type of transmission | Water |
|---|---|
| Example | Dirty water can transmit many diseases, such as the cholera bacterium. |
| Type of transmission | Air |
|---|---|
| Example | When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others. |
| Type of transmission | Unhygienic food preparation |
|---|---|
| Example | Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning. |
| Type of transmission | Vector |
|---|---|
| Example | Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers. |