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What is a pathogen
Organism that produces a disease (also called germs or infectious agent)
They cause pathogenic effects which:
vary with organism
can affect different parts of the body
can vary in severity
are acute or chromic
What size/what is a virion
A typical virion is small (10-400nm range) that needs a host cell to replicate (obligate parasite).
What makes up the core of a virus
The core of the virus is a genome either DNA or RNA
What protects the genome in a virus
A coat called the capsid protects the genome. some viruses have a phospholipid envelope also.
What can be found on the surface of virion
On the surface, there are spike proteins, so the virus can attach to a target cell surface.
Give examples of viruses and the infections that they cause
Influenza virus causes flu
variola virus causes small pox
What are the steps of a virus life cycle
attaches
enters by endocytosis
uncoats
replicates (in viral factory)
assembles new virions
progeny leaves
What are challenges for the host in the virus life cycle
large quantity of virions produced
controlling infected cells
handling viral infection
Give an example of a viral disease
Measles
how many unprotected people are effected by measles if exposed
9 out of 10
What is measles and what and the primary and secondary viraemia
Highly contagious, respiratory virus
primary viraemia : lymph nodes
secondary viraemia : (day 4 to 7) general infection of liver, epithelium, monocytes, dendritic cells, lymphocytes etc.
Describe the symptoms and their timeline in measles
starts with cold- like symptoms (after 10 days incubation: cough, fever, conjunctivitis)
few days later (day 14-16), a generalised rash
day 19-23, cleared infection, immunity developed
describe the treatment and prevention of measles
treatment : N/A
Prevention : MMR vaccine > 90% effective
describe the casualties of measles
complications:
affect hearing, throat, pneumonia, diarrhoea, seizures, swelling of the brain.
virus-induced immunosuppression can allow other opportunistic infections to flourish, affect central nervous system, coma, and death.
Describe the structure of bacteria and name the 3 main shapes
Prokaryotes, unicellular, have no nucleus, large DNA molecule in cytoplasm, size range between 500nm to 2uM.
Rigid cell wall, maintain definite shape
3 main shapes: spherical, rod, or spiral
They have a capsule around the cell wall and outside structures i.e. flagellum and/ or pili (depending on species)
Variations of bacteria properties
all organs are susceptible, although specific organ targeted by specific species.
extracellular or intracellular
What is meant by extracellular bacteria
Multiply in the host but on surfaces and in cavities.
e.g. Staphylococcus aureus.
Use virulence mechanisms to evade the immune system
What is meant by intracellular bacteria
Invade host cells to multiply.
e.g. salmonella enterica
Name an example of a bacterial disease
Tuberculosis
How many people are effected with TB
A quarter of the world population are infected, not everyone gets sick
What causes tuberculosis
Caused by Mycobacterium tuberculosis, spread by cough and sneeze
where does tuberculosis attack
Attacks lung first, pulmonary TB
(~ 2 weeks post infection, night sweat, persistent fever, weight loss)
Intra-macrophage, therefore can spread to kidney, spine, and brain.
Treatment of tuberculosis
antibiotics (rifampicin/isoniazid)
~ 6 to 9 months treatment, but pb with resistance bacteria, long, expensive
Prevention of tuberculosis
BCG vaccine
vaccinating with a weaker strain results in…
~ 70-80% effective against most severe TB (Meningitis) not pulmonary TB.
Is fungi prokaryotic or eukaryotic
Eukaryotic
Name the 3 basic cel types that cycle in fungi
spore, hyphae, yeast
What is the size of fungi, how may infect humans
3-15um length and 2-8um diameter.
~ 300+ infecting humans.
structure of fungi
nucleus, organelles, chitin cell wall
What type of infection is a fungal infection (who does it effect)
Opportunistic (targets weakened immune systems) , very abundant in environment.
What type of cells do fungal infections target? Extracellular or intracellular?
Infect endothelial or epithelial cells intracellularly. (induced endocytosis or active)
Where does active endocytosis occur via in fungal infection
Active via tip of hyphae
Where does induced endocytosis occur via in fungal infection
Induced via proteins on fungal cell surface
What is the role of spores in fungal infection
Spores germinate to produce a mycelium (branched hyphae)
What do mycelium produce in some fungi
In some fungi, mycelium produce fruiting bodies that then produce spores. Spores are dispersed.
Name a type of fungal infection
Candidiasis
what causes candidiasis
Infection by Candida albicans
Where does candidiasis enter the body
Fungus enters any mucosal surfaces: gut, lungs
What type of people does candidiasis effect
Opportunistic disease: infection happens for immunosuppressed people.
e.g.
HIV, cancer, diabetes patients.
Where is candidiases very abundant on the body
Very abundant on the surface of skins
part of normal mucosal surfaces : mouth, rectum and vagina
What form of fungus does candidiasis exist in
Exist mainly as yeast as part of a biofilm, but can switch between yeast and filamentous forms.
Life cycle of Candida albicans
Budding yeast → pseudohypha → hypha
What is the mortality of untreated candidiasis
30-50% mortality
Symptoms of candidiasis
Macronodular skin lesions (approx 10%)
candidal endophthalmitis (inflammation in the eye) (approx 10-28%)
Occasionally, septic shock (hypotension, tachycardia, tachypnea)
Treatment for candidiasis
Antifungal (topical, intravenous, if needed immune system treatment)
Prevention for candidiasis
Immunity support/ lifestyle
What is a protozoa
Eukaryotic organisms between 1um (plasmodium spp) to 30um long (trypanosoma brucei).
Are protozoa intracellular or extraceullar
Both.
Can invade (plasmodium) or reside on surface (trypanosome)
Where is the protozoa infection site, how is it spread
Infection site varies
spread via insects (ticks, mosquitos), contaminated food or water, or sexually.
When is a protozoa infection caused
Infection caused when immune system cannot control parasite
Give an example of a protozoa infection
Malaria
What causes malaria
Infection is initiated by a feeding mosquito.
stages of malaria infection
Plasmodium sporozoites migrate to the liver, replicating tens of thousands of daughter cells (merozoites).
Merazoites released in blood and invade red blood cells.
Stages of ring. trophozoite, and schizont replicating more metazoites.
a small proportion of parasites develop into gametocytes. Being taken up by the mosquito during feeding.
Sexual development occurs inside the insect, generating new sporozoites.
these will migrate to the salivary glands, being injected in the vertebrae host skin during the next blood meal.
Treatment for malaria
antimalarial medications varies on type of plasmodium infecting.
What countries are mostly effected by malaria
Malaria is a major cause of death in tropical and subtropical regions, particularly in sub-saharan Africa.
What are the most vulnerable groups to malaria
children under 5 years
pregnant women
individuals with HIV/AIDS
travellers
why is there a mortality reduction for malaria
Due to better prevention and control measures, including insecticide-treated bed nets, spraying, and better diagnostics and treatment.
Where do extracellular parasites live
Live outside, in intestine but some in blood vessels or lymphatic tissues.
Can cells kill extracellular parasites
NO, they are too big (up to 15m for tapeworm) for cells to kill the whole organism.
Give examples of extracellular parasites
roundworms (nematodes) : e.g. ascaris
flatworms e.g. tapeworms
other worms e.g. pin worms
Where do extracellular parasites infect through
Infection through different routes:
injection of larvae (meat-tapeworm) or eggs (soil/food - ascaris)
skin contact (hookworm)
mosquito bite (filarial worm)
How many people are infected by ascaris
576-740 million people infected
What do ascaris cause
anaemia in 10% of cases
impair the physical and intellectual development of children
Stages of the infection cycle of ascaris
ingest eggs from soil contaminated by human faeces or uncooked food from there.
eggs hatched in intestine
larvae get through intestinal wall, travel through the bloodstream to lungs
mature, move up the throat, coughed up and swallowed.
return to intestine to grow as adult
symptoms of ascariasis
diarrhoea, blood in faeces, passing a worm, mild-severe stomach pain, nausea, vomiting, weight loss
treatment for ascariasis
Anti-parasitic medications like albendazole or mebendazole.
surgical extraction in severe cases
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