- A microorganism that causes disease.
- They belong to the kingdom prokaryotae.
- They are smaller than Eukaryote cells and reproduce rapidly.
- Their presence causes harm by damaging cells and releasing waste products/toxins.
- In plants, they often live in the vascular tissues
- E.g. Tuberculosis and ring rot
- Common fungal infections are where the fungi lives in the skin of an animal and its hyphae which forms a mycelium grows under the skin surface.
- The fungus can send out specialised reproductive hyphae which grow out of the skin surface to release spores.
- The hyphae may release extracellular enzymes called cellulases to digest the surrounding host tissue.
- E.g. Black sigatoka and athlete’s foot
- Viruses invade cells and take over the genetic machinery and other organelles of the cell.
- They reproduce by causing the host cell to replicate the virus and when the host cell eventually burst the many new viruses are released to infect healthy cells.
- E.g. Influenza and Tobacco mosaic virus
- Protoctista usually cause harm by entering the host cells and feeding on the contents as they grow.
- The malarial parasite plasmodium has immature forms that feed on haemoglobin inside red blood cells and inhibits the organisms ability to transport oxygen around in the blood properly.
- This slowly prevents the tissue cells from respiring aerobically.
Lifecycle of a pathogen
- Travelling from one host to another.
- Entering the hosts tissues.
- Leaving the hosts tissues.
Means of transmission
- Direct physical contact such as touching a person who is infected or touching contaminated surfaces including soil that harbour pathogens.
- E.g. HIV, bacterial meningitis, athletes foot and ring worm
- Faecal – oral transmission, usually by eating/drinking water contaminated by the pathogen.
- E.g. cholera
- Droplet infection – pathogen is carried by tiny airborne droplets.
- E.g. tuberculosis and influenza
- Transmission by spores which are a resistant stage of the pathogen – these can be carried in the air or reside of surfaces.
- E.g. anthrax and tetanus
Factors that affect transmission
Direct physical contact
- Hygiene – wash hands regularly.
- Keeping surfaces clean.
- Cleaning and disinfecting cuts.
- Sterilising surgical equipment.
- Using condoms during intercourse.
Faecal – oral transmission
- Treatment of waste water.
- Treatment of drinking water.
- Thorough washing of all fresh food.Careful food preparation and cooking.
- Catch it – bin it – kill it.
- Cover your mouth when coughing or sneezing.
- Use a tissue and dispose of it correctly.
Transmission by spores
- Use of a mask.
- Washing skin after contact with soil and/or contaminated surfaces.
- Overcrowding, poor ventilation, poor health, poor diets, homelessness and living and working with people who have migrated from areas where disease is more common, all may affect the likelihood of catching a disease.
- Some pathogens, like the protoctista plasmodium that causes malaria, use vectors for transmission.
- Indirect transmission of plant pathogen occurs as a result of insect attack.
- The fungus that causes Dutch elm disease is carried by the beetle Scolytus multistriatus.
That's the end of the topic!
Drafted by Bonnie (Biology)