L1 - pathogens and transmission of disease

• Disease: a particular abnormal condition that affects part or all an organism
• Communicable disease:

  -caused by pathogens that can infect other organisms

  -this includes bacteria, viruses, fungi, and protoctista

  -communicable diseases are infectious and can be passed from organism to organism
• Bacteria: tuberculosis (TB), bacterial meningitis, ring rot (potatoes, tomatoes)
• Virus: HIV/AIDS (human), influenza (animals), Tobacco Mosaic Virus (plants)
• Protoctista: malaria, potato/tomato late blight
• Fungi: black sigatoka (bananas), ring worm (cattle), athlete’s foot (humans)
• Infectious disease: a disease resulting from infection of a host organism by a pathogen

  -is a major cause of death worldwide

  -estimated 13.7 million deaths in 2019
• Bacteria:

  -most common organism for infection

  -not all bacteria are pathogens, most bacteria do not cause disease

  -bacteria are prokaryotes, they do not have membrane-bound organelles

  -often classified in two ways, by basic shape and by cell wall
• Rod shaped bacteria: bacillus
• Chain of rod shaped bacteria: streptobacilli
• Spherical shaped bacteria: coccus
• Pair of spherical bacteria: cocci
• Chain of sphere shaped bacteria: streptococci
• Cluster of sphere shaped bacteria: staphylococci
• Comma shaped bacteria: vibrio
• Spiral shaped bacteria: spirillum
• Corkscrew shaped bacteria: spirochaete
• Classifying bacteria by cell wall:

  -gram positive

  -gram negative
• Gram positive bacteria:

  -appear blue purple under a microscope after gram staining

  -e.g MRSA (methicillin-resistant staphylococcus)
• Gram negative bacteria:

  -appear red under a microscope after gram staining

  -e.g E.coli (escherichia coli
• Viruses:

  -non living infectious agents

  -contain a short section of nucleus acid surrounded by protein

  -invade cells by inserting its own RNA into the nucleus of a cell

  -the infected cell will then begin to produce more viruses

  -all natural viruses are pathogens

  -affect all types of organisms, even bacteria, these are bacteriophages
• Bacteriophages:

  -destroys the bacterial cell as the new viruses burst out. viruses have the same effect in multicellular organisms such as animals and plants

  
• Protoctista:

  -eukaryotic cells

  -they exist as single celled organisms and multi cellular organisms

  -a small percentage of protoctista act as pathogens, they can affect animals and plants. E.g plasmodium causes malaria

  -often protoctista require a vest or to transfer the disease
• Fungi:

  -not major problems in animals, but affect plants hugely

  -eukaryotes, unicellular or multicellular

  -many fungi are saprophytes (feed of dead decaying matter)

  -in plants fungi often infects leaves, preventing photosynthesis

  -fungi reproduction involves production of millions of spores that rapidly infect other organisms
• Mechanisms of disease:

  -pathogens can cause disease in two main ways (damaging cells and producing toxins)

  -for example, the symptoms of cholera are caused by an exotoxin secreted by the bacteria Vibrio cholerae. it increases the secretion of chloride ions into the lumen of the intestines, which can lead to severe diarrhoea
• Damaging cells:

  -malarial parasites cause disease symptoms by bursting red blood cells
• Producing toxins:

  -exotoxins are secreted by a living, normal pathogens, whereas endotoxins are released when the pathogen is damaged
• DAMAGE TO TISSUES: viruses:

  -takes over cellular metabolism. viral genetic material is inserted into the genetic material of the host cell. the host cell then makes more viruses which then burst out of the cell, destroying it
• DAMAGE TO TISSUES: protoctista:

  -they take over a cell, edgiest the insides and use this as a medium to reproduce, before bursting out
• DAMAGE TO TISSUES: fungi:

  -digest and destroy living cells
• Producing toxins:

  -most pathogenic bacteria will produce a toxin, which is a poison

  -this toxin damages the cells of the host organism, often breaking down the plasma membrane or inactivating enzymes

  -some fungi also produce toxins