Module 4: Communicable disease Flashcards
Name 4 groups of pathogen that can cause communicable disease.
The ones I need to know:
Bacteria - TB, ring rot in potatoes and tomatoes.
Fungi - Black sigatoka (bananas), athlete’s foot (human).
Protoctista - Malaria, potato blight.
Virus - HIV/AIDS (human), influenza (animal), Tobacco Mosaic Virus (plant).
What is a vector?
Carries pathogens from one organism to another.
What are protoctista?
Small eukaryotic organisms that are usually unicellular. Some are parasitic (feeds off a host cell), and some of those may need a vector to transfer them to hosts.
How do protoctista invade?
They take over cells and feed on cell contents and divide before breaking out of the cell.
What shapes can bacteria have?
Rod shaped, spherical (cocci), spiralled.
There are 2 types of bacteria cell …
Walls - gram positive bacteria look purple under light microscope after staining, gram negative look red. Distinguishing between these are important so we can see the effect of antibiotics.
How do bacteria cause disease?
Produce toxins that damage host cells. E.g. by breaking down their cell membranes, interfere with host cell’s genetic material so they can’t divide.
Describe the structure of a virus.
Genetic material (DNA/RNA) surrounded by a protein coat.
What is a bacteriophage?
Viruses that infect bacteria. The virus use the bacteria to replicate itself, destroying it at the same time.
What happens when a virus attacks a cell (like bacteria or human cell)?
- Virus attaches to host cell.
- Insertion of viral nucleic acid into host cell
- Replication of viral nucleic acid.
- Synthesis of viral protein.
- Assembly of virus particles.
- Lysis of host cell.
Why are viruses the ultimate parasite?
Only active inside host cell, have little structure and take over whole host cell.
What are fungi? How can some fungi cause death of plants?
Eukaryotic organisms that don’t photosynthesise. They digest food extracellularly and absorb nutrients after.
Fungal infections often effect leaves of plants so they can’t photosynthesise, quickly killing the plant.
Fungi digest living cells and destroy them.
Many fungi are …
Saprotrophs - feed on dead and decaying matter.
Give some ways pathogens can cause disease.
Viral genetic material inserted into host cell, completely digest living cells and destroy them (fungi),
Produce toxins which poison or damage host cells.
What is the difference between a virus and a bacterium?
Viruses are smaller and simpler than bacteria, they can only reproduce by invading host cells and using their cellular machinery. Bacteria are single-celled organisms that can reproduce on their own.
Give an adaptation of fungi.
When they reproduce, they produce millions of tiny spores that travel very far so they spread rapidly.
RINGROT in potatoes/tomatoes.
Bacterial disease caused by gram + bacteria. Damages leaves and fruit.
Spread by insects (vector), contaminated tools, planting infected seeds.
No cure. Once infects a field, it cannot be used to grow potatoes for at least 2 years.
TOBACCO MOSAIC VIRUS in plants.
Infects various plant species and damages leaves. Overcrowding, via infected sap in plants or contaminated tools.
It contains ssRNA, which is directly transcribed by host cell to assemble new virions. Virions enter other cells via plasmodesmata then enter xylem and phloem. This causes stunted growth too.
No cure, but there are resistant crops.
POTATO BLIGHT/TOMATO BLIGHT in plants.
Caused by a fungus-like protoctist. Mainly transmitted via spores through rain and wind. The hyphae penetrate host cells, destroying leaves and fruit. No cure but resistant strains and careful management can reduce the risk.
BLACK SIGATOKA in bananas.
Fungus destroys leaves - hyphae penetrate and digest cells, turning leaves black.
Spores transmitted via rain and wind. Resistant strains are being developed, good husbandry and fungicide kills fungi to control the spread of disease.
MYCOBACTERIUM TUBERCULOSIS.
Bacterial disease in humans, cows, badgers. TB damages and destroys lung tissue and suppresses immune system, so body is less able to fight off other diseases. TB bacteria target epithelial cells.
Droplet inhalation and touching surfaces.
In people TB is curable with antibiotics and vaccination.
TB bacteria have a waxy, thick cell wall. This helps protect against destruction by lysozymes.
They can lie dormant inside macrophages. Although they may be phagocytosed by macrophages, they are usually not completely destroyed due to their thick cell walls. This means that they can survive and lie dormant inside macrophages for a long period of time, and activate and reinfect the body at times when the host immune system is weak.
How does tuberculosis cause disease?
- Triggers inflammatory response by infecting phagocytes in lungs.
- Infected phagocytes are sealed in coated tubercles so bacteria remain dormant.
- If another factor weakens immune system, bacteria become active and destroy lung tissue.
HIV - Human immunodeficiency virus.
AIDS - Acquired immunodeficiency virus.
HIV targets T helper cells in the immune system, so the infected person develops acquired immunodeficiency syndrome (AIDS), where the immune system becomes progressively weaker due to depletion of immune cells. This exposes the person to other infections and cancers that may ultimately become fatal.
HIV targets and replicates inside helper T cells first at the beginning of its replication cycle, meaning the body’s normal immune response is disrupted and further spread of the virus cannot be stopped.
HIV can lie dormant in the body for many years.
HIV is a retrovirus (has RNA as its genetic material) and it contains reverse transcriptase that transcribes RNA to a single strand of DNA in the host cell, which interacts with the genetic material of the host cell.
HIV is transmitted through certain body fluids such as blood, semen. Unprotected sex, sharing needles, breastfeeding. Direct injection into the bloodstream.
No vaccine or cure, but anti-retro viral drugs slow the progression of the disease.
HIV has a high mutation rate. The antigens on HIV viruses can change rapidly, meaning that memory cells cannot recognise them and the body’s humoral immunity is ineffective.
How does HIV result in symptoms of AIDS?
- Attachment proteins bind to complementary CD4 receptor on T helper cells.
- HIV particles replicate inside T helper cells, killing them.
- AIDS develops when there are too few T helper cells for the immune system to function, so can’t destroy other pathogens.
MALARIA.
Caused by protoctista Plasmodium and spread through bites of infected female anopheles mosquito. They act as a vector by transferring Plasmodium parasite to another organism during feeding. The parasite reproduces asexually inside the female mosquito. The female needs to take two blood meals to provide protein to lay her eggs, this is when plasmodium parasite is passed to people. It invades red blood cells, liver, brain.
Malaria is usually only common in tropical regions which have the hot and humid climates necessary for mosquitoes to breed. Thus, malaria is considered to be endemic to this region.
Currently two vaccines and preventative measures can be effective. Anopheles mosquito can be destroyed by insecticides. Mosquito nets and door screens can prevent them biting people. 虫よけスプレー
Anti malarial drugs.
BACTERIAL MENINGITIS.
Bacterial infection of the meninges of the brain and spinal cord (protective membranes) that can spread to rest of body and cause septicaemia (blood poisoning) and rapid death. Spread through droplets by coughing and direct contact with saliva.
Cure - antibiotics if given early, vaccine can protect us from some forms of meningitis.
How do you know if you have septicaemia?
Red rash that doesn’t disappear when you press a glass against it.
Communicable pathogens transmitted directly and indirectly?
Directly - skin-to-skin contact like athletes foot or exchange of bodily fluids through STI, consuming contaminated food/drink, animal bite (rabies), sharing needles (septicaemia).
Indirectly - droplet infection (influenza/TB), vectors (rat fleas transmit bubonic plague).
What are exotoxins and endotoxins?
Exotoxins are soluble proteins produced by bacteria, as part of their metabolism or during reproduction. They can be highly toxic to the host, disrupting host cell structures or cell metabolism.
Salmonella produce endotoxins. They are part of the outer cell membrane in gram-negative bacteria. They can trigger inflammation and other immune responses, such as fever, in humans.
How do antibiotics work?
Antibiotics work by targeting specific processes in bacteria, such as their ability to produce cell walls or proteins. This leads to the death of the bacteria or stops their growth and spread. Different antibiotics target different parts of bacteria and work in different ways, making it important to choose the right antibiotic for a particular infection.
Bacteriostatic antibiotics disrupt the bacteria’s protein production, DNA replication, or metabolism, thus stopping the bacteria from growing or reproducing any further. Tetracycline is an example of bacteriostatic antibiotics.
Bactericidal antibiotics kill the bacteria. Usually by destroying bacterial cell wall, bactericidal antibiotics cause a lethal disruption of the bacteria’s cell structure. Penicillin is an example of this type of antibiotics.
Widespread use of antibiotics has led to …
Antibiotic resistance. Genetic mutations may occur in a bacteria. When the antibiotic is used, it leads to natural selection of the bacteria with the mutation (as all other bacteria without the mutation are affected), resulting in this resistant bacteria being able to reproduce greatly and pass on the mutation.
What are personalised medicines and synthetic biology?
Personalised medicines are individualised to the patients DNA. As genes play a role in how a person responds to a drug, different people may have different reactions to the same type of drug.
Synthetic biology can be used to create artificial biological compounds. It uses genetic engineering and other types of advanced technology. For example:
New types of T cell receptors has been created which can specifically bind to antigens found on cancer cells.
Bacteria can be reprogrammed to sense and target cancer cells at various stages of their life cycle.
What are the alternatives for treating bacterial infections?
Bacteriophages are viruses that specifically target and kill bacteria, prebiotics and probiotics support the growth of beneficial bacteria in the gut, helping to prevent infections.
What are vaccines?
Vaccines are dead or weakened viruses that can be injected into an individual, in order to stimulate the immune system to develop immunological memory against the pathogen. This way, when an individual comes into contact with the live virus, the body already has an efficient mechanism in place to rapidly detect and eliminate it.
Vaccines are currently only against viruses. It should be noted that currently vaccines are only designed against viruses.
Mass vaccination contributes to …
Herd immunity. When majority of population is vaccinated against a pathogen, it breaks the pathogen’s chain of infection. This means that the virus essentially disappears because it is unable to pass from person to person. This means that members of the population, such as infants, who have not received vaccinations, are protected against the pathogen.
