Types of Pathogen
- A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals)
- Many microorganisms are pathogens including:
- Bacteria
- Fungi
- Protoctists
- Viruses
- Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protoctists are harmless and do not cause disease
- However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses)
Pathogenic bacteria
- Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces
- M. tuberculosis causes tuberculosis (TB) in humans
- The bacteria infect the lungs, causing a chronic cough and bloody mucus
- It is a disease often associated with poor hygiene and sanitation
- M. bovine in cows can also transmit to humans to cause TB
- N. meningitidis causes bacterial meningitis in humans
- Very few bacteria can cross the barrier created by the meninges (the tissue that surrounds the brain and spinal cord) however N. meningitidis crosses this barrier to cause acute inflammation
- Inflammation of the meninges causes symptoms such as fever, headache, neck stiffness and a characteristic rash
Pathogenic fungi
- Fungal diseases are much more common in plants than animals
- Cattle ringworm and athletes foot are fungal diseases that exist on the surface of the skin
- Fungal diseases in plants tend to be much more serious and can threaten entire crops
- Black Sigatoka is a fungal disease in bananas
- It spreads through the leaves of the plant, reducing its ability to photosynthesise
- The lack of photosynthesis causes parts of the leaf to die; producing black streaks
- Eventually, the whole leaf dies
Pathogenic protoctists
- Plasmodium falciparum is a protist that causes severe forms of malaria in humans
- The parasite is spread by mosquitoes
- Infected individuals experience fever, chills and fatigue
- P. infestans causes the infamous potato blight
- The pathogen is unusual as it has some fungal characteristics
- It is transmitted via spores
- The first signs of potato blight are small, dark brown marks on the leaves which quickly increase in size and number
- The protist destroys potato and tomato crops leaving them completely inedible