12 Communicable diseases Flashcards
What are communicable diseases?
Diseases that can be passed from one organism to another, of the same or different species.
What are pathogens?
- Microorganisms that cause disease.
- Types of pathogens include: bacteria, virsues, fungi and protoctista.
What are vectors?
A living or non living factor that transmits a pathogen from one organism to another e.g malaria mosquito
Which two ways can bacteria be classified into?
- By their basic shapes: rod shaped, spherical, corkscrew
- By their cell walls: the two main types of bacterial cell walls have different structures and react differently with a process called Gram staining.
What colour do Gram positive bacteria look under the light?microscope?
Purple-blue
What colour do gram negative bacteria look under the light microscope?
Red
What are viruses?
Viruses are non-living infectious agents.
What size is a virus?
At 0.02-0.3um in diameter, they are around 50 times smaller in length than the average bacterium.
What is the basic structure of a virus?
Genetic material (DNA or RNA) surrounded by protein.
How do viruses function?
- Viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cells to make more viruses.
- Viruses reproduce rapidly and evolve by developing adaptations to their host, which makes them very successful pathogens.
What are bacteriophages?
Viruses that attack bacteria by taking over the bacterial cells and using them to replicate and destroy the bacteria at the same time.
Are all naturally occuring viruses pathogenic?
Yes
What are protocista?
- A group of eukaryotic organisms with a wide variety of feeding methods.
- A small percentage of protoctista act as pathogens.
- The protists which cause disease are parasitic- they use people or animals as their host organism.
What are fungi?
- Fungi are eukaryotic organisms that are often multicellular.
- Fungi cannot photosynthesise and they digest their food extracellularly before absorbing the nutrients,
- Many fungi are saprophytes which means they feed on dead and decaying matter.
- However, some fungi are parasitic, feeding on living plants and animals.
Which different ways do pathogens attack?
1) Viruses take over the cell metabolism.
- The viral genetic material gets into the host cell and is inserted into the host DNA.
- The virus then uses the host cell to make new viruses which then burst out of the cell, destroying it and then spread to infect other cells.
2) Some protoctista also take over cells and break them open as the new generation emerge, but they do not take over the genetic material of the cell.
- They simply digest and use the cell contents as they reproduce. E.g malaria
3) Fungi digest living cells and destroy them.
- This combined with the response of the body to the damage caused by the fungus gives the symptoms of disease.
Which toxins damage host tissues?
- Most bacteria and some fungi produce toxins which affect the host cells and cause disease
- bacterial toxins damage the host cells by breaking down the cell membranes.
What is the tobacco mosaic virus?
- A virus that infects tobacco plants and around 150 other species including tomatoes, peppers.
- It damages leaves,flowers and fruit, stunting growth and reducing yields.
What is potato blight?
- It is caused by the protoctist oomycete.
- The hyphae penetrate host cells, destroying leaves, tubes and fruit.
What is black sigatoka?
- A banana disease caused by a fungus which attacks and destroys the leaves.
- The hyphae penetrate and digest the cells, turning the leaves black.
What is tuberculosis?
- A bacterial disease of humans, cows, pigs etc.
- Commonly caused by Mycobacterium tuberculosis.
- TB damages and destroys lung tissue and suppresses the immune system, so the body is less able to fight off other diseases.
What is bacterial meningtis?
- A bacterial infection of the meninges of the brain which can spread into the rest of the body causing septicaemia (blood poisoning) and rapid death.
What causes AIDS? (acquired immunodeficiency syndrome)?
HIV causes AIDS.
Human immunodeficiency virus
What does HIV do?
- HIV is a retrovirus with RNA as its genetic material, has reverse transcriptase enzyme that transcribes RNA into a single DNA strand in host cells, this DNA interacts with genetic material of host cell
- Targets T-helper cells in immune system, gradually destroying immune system so that people are more susceptible to other infections like TB and pneumonia
How is HIV passed from one person to another?
Via bodily fluids, most commonly through unprotected sex, shared needles, contaminated blood products and from mothers to their babies during pregnancy, birth or breast feeding.
What is influenza?
- A viral infection of the cilated epithelial cells in the gas exchange system.
- It kills them, leaving the airways open to secondary infection.
What is malaria?
- It is caused by the protoctista Plasmodium and spread by the bites of infected Anopheles mosquitoes.
- The plasmodium parasite invades the red blood cells, liver and even the brain.
What is ringworm?
- A fungal disease affecting mammals including cattle, dogs, cats and humans.
- It causes grey-white, crusty, infectious, circular areas of skin.
- In cattle, ringworm is usually caused by Trichophyton verrucosum.
What is athlete’s foot?
- A human fungal disease caused by Tinia pedia, a form of human ring work that grows on and digests the warm, moist skin between the toes.
- It causes cracking and scaling.
What the two main types of transmission?
1) Direct transmission
2) Indirect transmission
How are pathogens directly transmitted?
1) Direct contact
- Kissing or any contact with the body fluids of another person
- Direct skin-to-skin contact
- Microorganisms from faeces transmitted on hands
2) Inoculation
- Through a break in skin e.g during sex (HIV/AIDS)
- Through an animal bite
- Through a puncture wound or sharing needles
3) Ingestion: Taking in contaminated food or drink
How are pathogens indirectly transmitted?
1) Fomites : Inanimate objects such as bedding, socks can transfer pathogens.
2) Droplet infection: Inhaling droplets of saliva and mucus which contain pathogens.
3) Vectors: A vector transmits communicable pathogens from one host to another. E.g mosquitos, rats, bats
What factors increase the probability of catching a communicable disease?
- Overcrowded living and working conditions
- Poor nutrition
- Poor disposal of waste
- Climate change (can introduce new vectors and new diseases)
How are pathogens directly transmitted in plants?
Via direct contact of a healthy plant with any part of a diseased plant.
How are pathogens indirectly transmitted in plants?
1) Soil contamination: Infected plants often leaves pathogens or reproductive spores from protoctista or fungi in the soil. These can infect the next crop.
What polysaccharide do plants produce when attacked by pathogens?
Callose
What happens when a plant is attacked by pathogen?
1) Within minutes of inital attack, callose is synthesised and deposited between the cell walls and the cell membranes. This acts as barriers, preventing the pathogens entering the plant cells around the site of infection.
2) Large amounts of callose continue to be deposited in cell walls. Lignin is added, making the mechanical barrier to invasion even thicker and stronger.
3) Callose blocks sieve plates in the phloem, sealing off the infected part and preventing the spread of pathogens.
4) Callose is deposited in the plasmodesmata between infected cells and their neighbours, sealing them off from the healthy cells and helping to prevent the pathogen spreading.
What are the chemical defences against pathogens?(Plants)
- Insect repellents
- Insecticides
- Antibacterial compounds including antibiotics
- Antifungal compounds: e.g chitinases- enzymes that break down the chitin in fungal cell walls.
- Anti-oomycetes: E.g glucanases- enzymes made by some plants that break down glucans.
- General toxins- cyanide
What barriers does the body have to prevent the entry of pathogens?
1) The skin covers the body and prevents the entry of pathogens.
- It has a skin flora of healthy microorganisms that outcompete pathogens for space on the body surface.
- It also produces sebum, an oily substance that inhibits the growth of pathogens.
2) The airways of the gas exchange system are lined by mucous membranes that secrete sticky mucus.
- This traps microorganisms and contains lysozymes, which destroy bacterial and fungal cell walls.
- Mucus also contain phagocytes, which remove remaining pathogens.
3) Lysozymes in tears and urine, and the acid in our stomach, also help to prevent pathogens getting into our body.
What substances are secreted by platelets when you cut yourself?
- Thromboplastin, an enzyme that triggers a cascade of reactions resulting in the formation of a blood clot.
- Serotonin, which makes the smooth muscle in the walls of the blood vessels contract, so they narrow and reduce the supply of blood to the area.