Microscopic Pathogens

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

1. attaches

2. enters by endocytosis

3. uncoats

4. replicates (in viral factory)

5. assembles new virions

6. 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

1. Plasmodium sporozoites migrate to the liver, replicating tens of thousands of daughter cells (merozoites).

2. Merazoites released in blood and invade red blood cells.

3. Stages of ring. trophozoite, and schizont replicating more metazoites.

4. a small proportion of parasites develop into gametocytes. Being taken up by the mosquito during feeding.

5. Sexual development occurs inside the insect, generating new sporozoites.

6. 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

1. ingest eggs from soil contaminated by human faeces or uncooked food from there.

2. eggs hatched in intestine

3. larvae get through intestinal wall, travel through the bloodstream to lungs

4. mature, move up the throat, coughed up and swallowed.

5. 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