4.1 Communicable Diseases Flashcards
what is a pathogen
A microorganism which causes disease to a host
what is a communicable disease
Diseases caused by infective organisms known as pathogens
what is bacteria
Prokaryotes which are capable of rapid reproduction. Bacteria can cause direct damage to cells or release toxic substances.
3 types of bacterial diseases & relevant information
Tuberculosis: Is cause by mycobacterium tuberculosis which often infects the lungs, killing cells & tissues
Bacterial Meningitis: Is caused by Neisseria Meningitidis which infects the meninges (membranes that surround the brain and spinal cord) leading to the brain & nerves
Ring Rot: This is a plant disease which causes decay of the vascular tissues in potatoes and tomatoes.
which 2 ways can bacteria be classified
Shape: Bacteria can have the following shapes: Rod shaped (bacilli), spherical (cocci), common shaped (vibrio), spiralled (spirilla), Corkscrew (Spirochaetes)
Cell Wall: Gram positive bacteria appear blue purple after gram staining e.g. MRSA. Gram Negative Bacteria appear red under a microscope after gram staining e.g. E-coli. This is useful as the type of cell wall affects how bacteria responds to antibiotics.
what are protist
eukaryotic cells that are single celled organism and multi-cellular organisms
what do protist mainly require
vectors
example of protist
malaria
Fungi
eukaryotes but can be unicellular or multicellular
how do Fungi work/function
They are saprophytes (sprays enzymes on dead matter to digest and absorb the nutrients). When fungi affect plants, they often infect the leaves preventing photosynthesis. Fungi produce many millions of spores that rapidly infect other organisms.
Virus definition
Not considered living by many scientists as they are non-cellular and only active when inside a host cell. Viruses consist of nucleic acids (DNA or RNA) surrounded by a protein coat. Despite their simplicity they are responsible for a wide range of common and life-threatening diseases.
3 viral diseases and relevant information
HIV/AIDS: caused by human immunodeficiency virus. It is a retrovirus (RNA is used to make DNA) and can splice its genes into the host’s chromosomes. The virus attacks & destroys T-helper cells thus compromising the host’s immune system possibly to AIDS
Influenza: occurs in several animal groups including birds & other mammals. An avian influenzas outbreak occurred in China in 2013.
Tobacco Mosaic Virus (TMV): A plant virus which cause ‘mosaic’ mottling. It does not kill the plant but can result in stunted growth and so reduced yield
what is direct transmission
Involves transmission when there is contact between infected person and suspectable person
4 examples of direct transmission
- Faecal-Oral: Contaminated food or water e.g. Cholera
- Droplet: Coughing or sneezing e.g. TB or influenzas
- Spores: Some bacteria and fungi produce reproductive spores which can travel through air e.g. Tetanus
- Invasion: Bacteria which use their flagellum and pili to swim towards the host and enter wounds in the plant
indirect transmission
This involves transmission of a vector which is another organism used by the pathogen to infect the host
6 factors effecting transmission in animals
Overcrowded living and working conditions
Poor nutrition
A compromised immune system, including having HIV / AIDS or needing immunosuppressive drugs off the transport surgery.
Climate change -This can introduce new vectors and new diseases, for example, increase temperature, promote the spread of malaria as the vector mosquito species is able to survive over a wider area.
Culture. An infrastructure- In many countries, traditional medical practises can increase transmission.
Socioeconomic factors- A lack of trained health workers, an insufficient public warning when there is an outbreak of disease can also affect transmission rate.
how does direct transmission occur in plants
Involves physical contact between plant and any part of diseased plant
example of indirect transmission
Soil contamination through infected plants, living pathogens or reproductive spores from protocosista or fungi in the soil. This can infect the next crop. Examples are black sigatoka spores, ring rot bacteria, spores.
4 examples of vectors transmitting diseases to plants
Wind- Bacteria, viruses, and fungal spores may be carried in the wind.
Water- Spores swim in the surface film of water on leaves; Raindrop splashes carry pathogens and spores. Examples are spores of P. infestans (potato blight) which swim over films of water on the leaves.
Animals- Insects and birds carry pathogens and spores from one plant to another as they feed. Insects such as aphids inoculate pathogens directly into plant tissue.
Human- Pathogens and sports are transmitted by hands, closing formats, farming practises and by transporting plants and crops around the world. For example, TMV survives for years in tobacco products, Ring Rot survives on farm machinery.
factors affecting plant disease transmission
Planting varieties of crops that are susceptible to disease.
Overcrowding increases the likelihood of contact.
Poor mineral nutrition reduces resistance of plants.
Damp, warm conditions increase the survival and spread of pathogens and spores.
Climate change- increased rainfall and went promote the spread of diseases; Changing conditions allow animal vectors to spread to new areas while drier conditions may reduce the spread of the disease.
5 physical defences in plants
Cellulose cell wall: Acts as a physical barrier as well as containing a variety of chemical defences that can be activated when a pathogen is detected.
Lignin thickening of cell walls: Lignin is waterproof and almost completely indigestible.
Waxy cuticles: These prevent water collecting on the cell surface is since pathogens collect in water, they need water to survive. The absence of water is a passive defence.
Bark: Most bark contains a variety of chemical defences that work against pathogenic organisms.
Callose: callose is a large polysaccharide that is deposited in the sieve tubes at the end of a growing season. It is deposited around the seed plates and blocks the flow. In the sieve tube, this can prevent a pathogen spreading around the plant. In addition, after an initial attack, callose is synthesised and deposited between the cell walls and the cell membrane in cell next to the infected cell. These act as barriers and prevent the passage and from entering the plant cells around the site of infection.
3 chemical defences in plants
Phenols: Have antibiotic and antifungal properties.
Alkaloids Better to prevent grazing and interferes with enzyme action
Hydrolytic enzymes: Breakdown fungal and bacterial cell walls. These chemicals can act on the pathogen and the vector (if present) or both. They are found in spaces between cells.
what is necrosis
The deliberate cell suicides.
how does necrosis happen
A few souls are sacrificed to save the rest of the plant. By killing cells surrounding the infection, the plant could limit the pathogens, access to water and nutrients and therefore stop it spreading further around the plant. Necrosis is brought about by intracellular enzymes that are activated by injury. These enzymes destroy damaged cells and produce brown spots on leaves or die back.
how is skin a physical defence
Skin cells are produced at the base of the epidermis. As they migrate towards the skin surface, they become keratinized, which serves as a barrier to pathogens. The skin also produces sebum, which is an oily substance to inhibit the growth of pathogens.
