Pathogens Flashcards
Pathogens
Disease causing organisms
4 main types of pathogens
- Bacteria
- Viruses
- Fungi
- Animal parasites
Bacteria
Microscopic, unicellular prokaryotic organisms (lack organelles including nucleus, their DNA floats freely in the cytoplasm or is in the form of small circular plasmids)
Bacteria other information
- Reproduce by binary fission
- Can be treated by antibiotics
- Most are non-pathogenic
- DNA - Single chromosome
Bacteria structure
Cell wall and membrane, some with slime capsule and flagella.
Viruses
Microscopic particles with genetic material (DNA or RNA) surrounded by a coat of protein or lipid envelop. They can only be seen with electron microscopes.
Viruses are obligate intracellular parasites
They cannot be grown outside of the cell
How do viruses work
Infect living cells and cause them to manufacture more virus particles (intracellular replication)
Drugs against viruses
Some drugs can control infections (e.g. antivirals) but no drugs known can kill them. Antibiotics cannot be used to treat viral infections
Bacteriophage
Viruses that multiplies in bacterial cells causing death of bacteria
Fungi
Sometimes attack the tissues of humans and cause disease. Mould spores can cause mild to serious injuries.
Animal parasites
Organisms which live on or in other living things.
Ectoparasites
Parasites which live on the outside of the body (lice, scabies, ticks)
Endoparasites
Parasites which live on the inside of the body (protozoans, tapeworm, amoeba.)
Transmission of pathogens
- Contact (indirect or direct)
- Body fluids
- Droplets
- Ingestion
- Airborne transmission
- Vectors
Direct physical contact
Touching an infected person (skin infections and some STI’s)
Indirect physical contact
Touching an object that has been touched by an infected person (drinking from same cup) e.g conjunctivitis
Body fluids
Transfer of one person’s fluids to another. Fluid (e.g. blood, semen, saliva) contacts mucous membranes or bloodstream. E.g. HIV, Hep B, etc.
Droplets
Tiny droplets of moisture may contain pathogenic organisms. These are emitted when you breath, talk, sneeze or cough.
How are droplets infectious
Droplets may be breathed in by another person or settle on food and then ingested. Cold and flu are spread by droplets
Ingestion
Contaminated food or drink may result in disease. E.g. food poisoning, salmonella, dysentery, etc.
Airborne transmission
When airborne moisture evaporates, some bacteria and viruses are able to survive as spores. These can be inhales and cause infection. (Anthrax spores)
Vectors
Transfer of pathogens by other animals. Insects like ticks, mites, mosquitos and flies. Vector borne diseases can be specific, e.g. malaria, Lyme disease etc.
