Topic 6.2 Non-bacterial pathogens Flashcards
Anthroponoses
Diseases transmissible from human to human
Zoonoses
Diseases transmissible from living animal to humans (jumps species boundaries)
Sapronoses
Human diseases transmissible from abiotic environment (eg. soil, water, decaying plants, animal corpses etc)
Direct transmission
- Physical contact
- Exchange bodily fluids
- Contact with animals or animal waste
Indirect transmission
- Through intermediates/vectors
- Aerosols/droplets (airborne)
- Vehicle borne (surfaces/objects)
- Food and waterborne
Physical human contact (direct)
Where there is physical contact between an infected person and an uninfected person and the microbe is passed over.
(Chicken Pox, Hep A+B, measles, influenza etc)
Mother to child transmission (direct)
Transmission of a disease from an infected mother to her child during gestation and breast milk.
(HIV, hepatitis, syphilis, thrush)
Physical animal contact (direct)
When a susceptible animal comes in direct contact with an infected animal, its bodily fluids or tissues.
(Rabies, blastomycosis, cat scratch disease, CFJ disease etc)
Intermediates (vectors) (indirect)
Biological vectors may carry pathogens that can be delivered to hosts usually by biting.
(Dengue, yellow fever, Malaria, Japanese encephalitis etc)
Aerosol (airborne) (indirect)
Aerosols and droplets created from coughs and sneezes.
(Influenza, Tuberculosis, common cold, Ebola, Pneumonia)
Vehicle/fomite borne (indirect)
Contaminated surfaces (eg. benches, door handles etc. Could have been contaminated by contact, aerosol or food etc.
(Influenza, tetanus, ringworm, water infection)
Food and waterborne (indirect)
Contaminated food or water sources/ nutritional related.
(Cholera, Cruetzfeldt-Jakob disease, diphtheria, hookworm)
Virus structure
Virus entry
All viruses must get their genetic material, DNA or RNA, into a hot cell to replicate and start their life cycle.
- Some viruses, such as ones that infect bacterial cells (bacteriophages) inject only their DNA inside the host cell.
- Other viruses such as those that infect animal cells can be wholly engulfed (endocytosis) or have their lipid envelope fuse with the cell membrane.
Mode of transmission: Influenza
1) Droplets form coughs and sneezes
2) Direct contact with an infected person
3) Contact with contaminated surfaces (fomites)
4) Zoonotic infection: contact with animal
Mode of infection: Influenza
–> Ciliated epithelial cells of the respiratory tract.
1) Injects viral RNA into ciliated epithelial cells (bacteria enters a cell by endocytosis and forms a vesicle).
2) Viral RNA hijacks cell biochemistry to produce new virions; the virus insert sits DNA into the cell.
3) Cell lysis releases virions.
(Lytic cycle).
The Pathogenic effect: Influenza
- Lung inflammation caused by viral infection of the respiratory epithelium.
- Death of cili leave airways open to infection.
Headache, coughing & sneezing, sore throat, vomiting, fever, muscular/joint pain.
–> Symptoms last roughly 5-7 days.
Influenza
- Respiratory disease.
- Short incubation period.
- Mutate frequently so overcome immune response.
- 3 strains.
- Antigen markers e.g H1N1.
- Transmitted mainly airborne or contact with animal droppings or surfaces (fomites).
Treatment of flu
- No cure
- Vaccines
- Spreads as people carry on with flu and spread it
- Anti viral medicines
Fungi
- Fungi are single celled
- They have walls made of chitin and glycan
- They do not photosynthesise
- Spores are used for reproduction
Hyphae
Long thread-like filaments.
Many fungi grow as hyphae.
Some fungi can:
- Be poisonous
- Cause allergies
- Cause parasitic diseases (growing on areas of skin eg. athletes foot)
—> its rare for fungi to cause serious harm to humans.
Case study
Stem Rust Fungus (Puccinia graminis): Mode of transmission
- Wind dispersed urediniospores.
- Plants may become infected from parts of infected plant left in the soil.
—>The pattern of infection helps determine whether the source of infection is a local bush (a fan of infection) or a distant wheat field.
Case study
Stem Rust Fungus (Puccinia graminis): Mode of infection
- A hypha emerges form the spore and penetrates one of the stoma of the leaves or stem.
- The hypha secretes enzymes (eg. cellulases) which digest the plant cells and the nutrients which are absorbed into the fungus.
- The hyphae branch to form a mycelium that feeds and grows on the stem or leaves of a wheat plant.
- Grows best when it has hot days (25-30°C), mild nights (15-20°C) and wet leaves.
–> Spores need water to germinate.
Case study
Stem Rust Fungus (Puccinia graminis): Pathogenic effects
- Symptoms appear 7-15 days after infection.
- Rusty-red pastures break through the epidermis (release more spores when they burst).
- Breaking the epidermis, makes it more difficult to control transpiration, resulting in less efficient metabolism, making it more likely to dry out and give entry to other pathogens.
- It absorbs nutrients from the plants, reducing yield.
- Weakens stems, so plants fall over; can’t be harvested effectively.
- Less glucose to form starch.
Case study
Stem Rust Fungus (Puccinia graminis): Treatment and control
- Bigger spaces between plants to reduce moisture and increase distance for spore to travel.
- Reducing the application of fertilisers.
- Use of earlier-maturing crops which avoid the time of maximum spread.
- Fungicides will control the growth of stem rust- but the cost of this control measure is excessive (unprofitable).
Protists
Unicellular eukaryotic organisms.
- Slime moulds (fungal-like)
- Microscopic algae (plant-like)
- Protozoa (animal-like)
Malaria
Plasmodium falcoparum.
- Five species of a single cell protozoan parasite that can cause malaria in humans.
- Malaria vector feeds on living tissue.
- Female anopheles mosquito when pregnant (as they feed of blood).
- Transmitted through blood anticoagulant released and malaria.
- Affects liver and RBCs.
- Lytic cycle - asexual 48-72 hours.
- Some become gametocytes and are transmitted to a mosquito.
Protozoan life-cycles
- Some will reproduce asexually through binary fission.
- Others will carry out meiosis and reproduce sexually.
- Some will use vectors as part of their life cycle.
Malaria life-cycle: Part 1
The Human Host
1) Malaria parasite enters the mosquitoes saliva.
2) Carried in the blood stream to the liver.
(The parasite enters liver cells through Kupffer cells).
3) Reproduces asexually in the liver cells.
4) Leaves the liver cells destroying them.
5) The parasite infects RBCs.
6) Reproduces asexually in RBCs and destroys the cells.
Malaria life-cycle: Part 2
Mosquito host
1) Mosquito bites an infected individual.
2) Parasite is in the mosquitoes stomach.
3) Parasite reproduces sexually in the mosquito.
4) Fertilised form moves to the lining of the stomach and turns into a cyst.
5) Malaria parasite migrates to the salivary glands of the mosquito.
Endemic diseases
Endemic diseases which are constantly present in a country or area.
(eg. Malaria, chickenpox, common cold)
Why is Malaria still a global challenge?
- Increased resistance to antimalarial drugs and insecticides.
- Widespread poverty and availability of healthcare.
- Increased migration and global travel.
- New breeding sites for mosquitoes due to environment changes.
Antimalarial drugs
- Drugs act rapidly on the parasites in the blood and are able to destroy gametocytes reducing the transmission of the disease.
- Different combinations are prescribed depending on the severity of the disease and the presence of resistance to the drug in different areas.
Insecticide Treated Nets (ITN)
A meshed curtain draped over a bed treated with insecticide.
+Repels and kills mosquitoes.
+Low health risk to humans.
+Easy to make/maintain.
-The nets frequently need retreated/changed.
-The insecticide smells.
-The insecticide can cause headaches, dizziness and itchiness.
Indoor Residual Spraying (IRS)
The application of insecticide to internal walls and ceiling of housing structures.
+Mosquitoes are repelled and killed.
+Community-wide protective effect.
+Can last 3-12 months depending on insecticide.
+No serious effects on human health and the environment.
-Difficult to maintain.
-Requires removal of all belongings from the home.
Breeding site reduction
Antiviral operation causing the reduction or permanent elimination of mosquito breeding places or sites.
Biological Control of Mosquitoes
The use of living organisms/predators to suppress pest population.
+Environmentally friendly.
+Target selection.
+No resistance.
+Not harmful to non-target organisms.
-Susceptible to environmental changes.
-Slow effect.
-Requires well trained.
Sudden Death Mosquitoes
Sudden death mosquitoes are genetically modified mosquitoes created by injecting the male mosquitoes with a deadly gene that can kill young female mosquitoes.
+Lowers the population of disease-carrying biting insects over town.
+No significant impact on humans.
+Doesn’t require a lot of man power.
-The GMO mosquitoes can carry/develop unknown pathogens that hurt humans.
-Very expensive.
-Very time-consuming.
How is influenza treated
- Antiviral medication
- Antibiotics treat secondary bacterial infection
- Management of symptoms eg. painkillers.
