How are diseases transmitted? - Coggle Diagram
How are diseases transmitted?
The same micro-organism mus be present in every disease host.
The micro-organism must be isolated and cultured in the laboratory and accurately described and recorded
When a sample of the pure culture is inculated into healthy host, this host must develop the same symptoms as the original host
The micro-organism must be able to be isolated from the second host and cultured and identified as the same as the original species.
Developed vaccines for chicken cholera, anthrax, rabies, and identified specific parasites responsible for silkworm disease.
Discovered attenuated (weakened) pathogens could cause immunity, showed relationship between anthrax spores and anthrax infection.
Disproved spontaneous-generation theory (that disease occur spontaneously), proved decay and disease were caused by air-borne microbes—germ theory.
Filled a swan-necked and a straight-necked flask with broth. Swan-necked remained clear, open flask became cloudy and smelly.
Pasteur’s 1862 classic XPT:
Proved that microbes caused fermentation (beer/wine), spoilage (food) and rotting.
Physical contact between an infected organism and a susceptible organism allows the transfer of infected bodily fluids.
Person-to-person contact; shaking hands, sexual intercourse etc.
Droplet spread includes when a person coughs, sneezes, talks etc.
Example: EBOLA - a viral disease directly spread through saliva, mucus, blood, sweat etc.
Can spread on a larger scale
Passed through intermediates including: air, food contamination, object contamination, vectors and water.
Example: MALARIA - Caused by a protist called plasmodium, this is transmitted through a vector. Symptoms inlclude; fever, muscle pain, headaches etc.
What is Infectious disease?
Disease is any process or condition that adversely affects the normal functioning of a living thing or parts of a living thing. An infectious disease is caused by (caught from) another organism or invective agent.
Bacteria: Unicellular prokaryotes. Can cause disease by competing with good bacteria or through exotoxins (secreted) or endotoxins (released upon death). Genetic material = 1 circular chromosome.
Fungus: Eukaryotic. Can be unicellular (yeast, e.g. thrush) or multicellular (mould, e.g. tinea). Usually attack body surfaces. Consist of branching filaments called hyphae which form a structure called mycelium. Opportunistic—waits for immune system weakness before becoming pathogenic.
Protozoan: Unicellular eukaryotes, parasites. Usually reproduce through binary fission, motile (moves with flagellum/cilia). Obligate—only continues life cycle in host.
Viruses: Cannot reproduce independently. Have nucleic acid contained in a protein coat/capsid. Can be DNA-based (adenoviruses, e.g. common cold) or RNA-based (retroviruses, e.g. HIV). Invades a host cell, where its nucleic acid is translated into proteins, forming new copies (virions). The cell is filled with these virions and bursts, releasing them. Obligate and intracellular—only reproduces in host.
Ecto-parasites: Usually arthropods (insects, spiders). Can directly inject toxins into the body or indirectly cause disease by acting as a vector (organism that transmits pathogen).
Endo-parasites: Usually helminths—worm-like organisms. Live on host’s nutrients, often in digestive system.
Prions: An abnormally folded protein. Can convert normal proteins into abnormal form. More stable and resistant to denaturation than normal proteins. There are no known cures. Aggregate together to form amyloid fibrils that cause disease.
Transmission may be assisted by:
Secretion of chemicals (TNF in prions)
Surface receptors (viruses)
Pilli and fimbria (bacteria)
adhesion molecules (fungus)
To enter an individual host and cause disease, pathogens must:
Enter the host.
Multiply in host tissues
Resist or not stimulate host defence mechanisms
Damage the host.
Causes and effects on disease in agriculture
: Farmers artificially select individual plants and animals with desirable characteristics and allow them to reproduce so that these characteristics can be passed on to the next generation. Artificial selection increases economically beneficial traits in crops. However, artificial selection decreases genetic variation so that the population is more susceptible to disease. An example is the devastating Irish Potato Famine, caused by genetically identical potato crops all susceptible to the same fungal pathogen. As a consequence, selection must be carefully controlled and farmers must use responsible breeding practices which promote biodiversity.
Intensive farming involves the use of various techniques to produce greater outputs, typically using the same amount of space or resources. Intensive farming typically involves housing crops in high densities. An example is the neurological condition known as mad cow disease, which spread as a result of farmers using leftovers from dead animals to feed their living animals. Farmers can reduce the likelihood of disease by housing animals in sufficiently sized enclosures, and growing plants with minimal pesticide and medicine use.
Movement of People and Goods
: Agricultural diseases can be spread through the movement of goods and people. This is particularly problematic if the resident organisms are naïve to the disease. A key example is foot-and-mouth disease, especially as it impacted the British agricultural industry following the importation of infected meat. To combat this, restrictions apply for the movement of goods, such as border control measures and quarantines.
microbial testing: Can be done by inoculating nutrient agar plates with food or water samples and incubating at 30 degrees for a few days.
Interpreting agar plates.
to avoid cross contamination you must:
Wipe all surfaces with alcohol solution to minimise the risk of contamination.
Remove all objects other than those required from the work area.
If food is being tested in test tubes, sterilise the test tubes by moving them through the blue flame of a Bunsen burner.
When opening the Petri dish, have the dish on the table and lift the lid at an angle no greater than 45°C, with the opening pointing away from any members of the group.
Do not breathe or cough over the open dish and work as quickly as possible.
Use an inoculating loop to spread your sample onto the nutrient agar. Sterilise this loop first by moving it slowly through the blue flame of the Bunsen burner.