Pathogens
A pathogenMicroorganism that causes disease. is a microorganism that causes a disease. There are four main types of pathogen:
| Pathogen | Example in animals | Example in plants |
| Viruses | HIV potentially leading to AIDS | Tobacco mosaic virus |
| Bacteria | Salmonella | Agrobacterium |
| Fungi | Athlete's foot | Rose black spot |
| Protists | Malaria | Downy mildew |
| Pathogen | Viruses |
|---|---|
| Example in animals | HIV potentially leading to AIDS |
| Example in plants | Tobacco mosaic virus |
| Pathogen | Bacteria |
|---|---|
| Example in animals | Salmonella |
| Example in plants | Agrobacterium |
| Pathogen | Fungi |
|---|---|
| Example in animals | Athlete's foot |
| Example in plants | Rose black spot |
| Pathogen | Protists |
|---|---|
| Example in animals | Malaria |
| Example in plants | Downy mildew |
All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their hostThe organism lived on or in by a parasite. and infect other organismLiving entity, eg animals, plants or microorganisms.. They also all have structural adaptationA feature of an organism's body which helps it to survive. that make them successful at completing their life cycles, which enable them to cause further disease.
Diseases caused by pathogens are called communicable diseaseA disease that is caused by a pathogen and so is transmitted rather than inherited or caused by an environmental factor.. This means they can be transferred from one person to another.
There are other types of disease which cannot be caught:
- Inherited genetic disorders like cystic fibrosisA disorder that mainly affects the lungs, pancreas, liver, and intestine. The main symptom is difficulty breathing..
- 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 scurvyA deficiency disease that occurs when an individual has insufficient vitamin C. 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.
All organisms are affected by pathogens. Even bacteria are infected by certain types of virus. Some of these infections can be transferred to organisms of a different species.
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 | Examples |
| 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 | Direct contact |
|---|---|
| Examples | This can be sexual contact during intercourse or non-sexual contact, like shaking hands. |
| Type | Water |
|---|---|
| Examples | Dirty water can transmit many diseases, such as the cholera bacterium. |
| Type | Air |
|---|---|
| Examples | 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 | Unhygienic food preparation |
|---|---|
| Examples | Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning. |
| Type | Vector |
|---|---|
| Examples | Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers. |