Microbial Infection

Question 1

What is a zoonotic infection

Answer 1

An infection that doesn’t normally circulate in humans as it has an animal reservoir . Eg. Hammerhead fruit bat doesn’t get infected because it has a receptor mutation which means it gets low grade symptoms if at all

Question 2

What does obligate parasite mean

Answer 2

It can only survive by invading eukaryotic cells ( eg. Viruses)

Question 3

How does a virus cause disease/ symptoms ?

Answer 3

Contains RNA or DNA as genetic material. Replicates using host cell machinery and shows host specificity but can infect almost all other life forms including bacteria.

Released by budding out of host cell( cytopathic) or by cytolysis

Question 4

Routes of infection for viruses

Answer 4

Faecal-oral, airborne, insect vector or blood borne

Question 5

Examples of viruses

Answer 5

Smallpox, polio, Ebola, measles

Question 6

Do bacterial cells have internal membranes ?

Answer 6

No although photosynthetic bacteria are the exception. Bacteria are prokaryotes but eukaryotes have internal cell walls

Question 7

What are the effects of bacterial cells being haploid

Answer 7

This means that if there is a mutation it will be instantly expressed (theres no rescessive/dominant gene alleles because there is one copy.

Eukaryotes can be haploid or diploid

Question 8

Difference between cytoskeleton in eukaryotes and prokaryotes

Answer 8

Bacteria are prokaryotes and so bacteria have a poorly defined cytoskeleton while eukaryotes have a well defined cytoskeleton

Question 9

Cell wall of bacterial cells

Answer 9

• cell wall contains peptidoglycan (can be used to target)
  ○ determines shape (rod, coccus, spirochaete)
  ○ basis of Gram stain - differentiates between Gram +ve and -ve
  Bacteria are identified by how they look under the microscope, and how they Gram stain.
  If it’s blue, it’s Gram +ve;
  pink = Gram –ve.

        This is because the outside cell membrane of the Gram –ve bacteria blocks the stain from penetrating the cell wall

Question 10

Adaptive features of bacterial cells

Answer 10

Flagella to scale from neutrophils , capsule can help prevent phagocytosis and pilus influence how they adhere to surfaces

Question 11

Shigella

Answer 11

Shigella - infectious dose is only 10-100 bacteria
Faecal-oral transition
Attacked Gets phagocytosed by epithilial cells in them - can move within the cells - no flagella, it uses host components - uses actin to push it between cells.
Severe if untreated, causes a lot of damage. It can swim between cells and destroy stuff.
Lots of bloody diarrhoea

Question 12

Neisseria meningitidis

Answer 12

Neisseria meningitidis - commensal to pathogen (so it exists in most of us -It chills in the epithelium in the nasopharynx - but can switch and becomes a hostile pathogen.)

- Causes non-blanching rash
- Septicaemia
- Blocks blood vessels
- Rapid 
- If it crosses blood/brain barrier then it causes meningitis.

Question 13

Example of hospital acquired ( nosocomial) infections

Answer 13

• Clostridium difficile - spore stage so v difficult to get rid of.
  
  • Methicillin Resistant Staphylococcus aureus

Question 14

Mycobacterium tuberculosis

Answer 14

• Dificult to diagnose
  
  • Treatment takes a long time - 6 months
  • Also difficult to supply therefore
  • New drugs to combat anti-microbial resistance and shorten treatment
  • Better vaccines for adult population in high burden countries
  • Better tools for early diagnosis

Question 15

What cancers and ulcers does H.pylori lead to

Answer 15

Gastric cancer and peptic ulcer

Question 16

Why do viruses have more point mutation rates

Answer 16

Viruses have error prone replication and they don’t corrrect the mistakes with high effectiveness. Bacteria and vertebrates also have polymerases which are able to fix any errors that occur

Question 17

Bacteria vs human mutation

Answer 17

Have similar mutation rates but more mutations when the generation time is short ( in bacteria). - They only have one copy of the genetic material so every mutation is expressed
- They have a very quick generation time so there are more mutations.

Question 18

Fungi

Answer 18

○ Eukaryotic
○ Cause cutaneous (scalp), mucosal and/or systemic mycoses occur as yeasts, filaments or both
○ yeasts bud or divide; filaments (hyphae) which have cross walls or septa

Question 19

Protozoa

Answer 19

Unicellular eukaryotic organisms
- Include intestinal, blood and tissue parasites
- Replicate in the host by binary fission or by formation of trophozoites inside a cell
- asexual reproduction
- many have a complicated life cycle involving two hosts
- infection is acquired by ingestion or through a vector
eg insect or invertebrate vector

Question 20

Examples of Protozoa

Answer 20

Leishmaniasis and Malaria plasmodium

Question 21

Malaria

Answer 21

• Infection is acquired via a mosquito vector
  
  • blood and tissue parasites
  • formation of trophozoites inside a cell
  • Sickle-cell and β-thalassaemia – can’t be affected by malaria

Infection depends on the vector. So the pattern of disease depends on the distribution of the vector e.g. The ‘malaria belt’ across the equator which reflects the altitudes at which mosquitoes exist.

Question 22

Leishmaniasis

Answer 22

Sandfly vector
Blood and tissue parasite infection
Has a trophozoitic stage

Cutaneous - skin lesions
Visceral forms - huge internal organ swelling
Zoonotic - often dogs are the resevoir

Question 23

Helminths

Answer 23

Metazoa with eukaryotic cells (a whole organism)
Multi-cellular; visible to the naked eye
Life cycles outside the human host - live in soil/water and are picked up.
Roundworms e.g. Ascaris
Flatworms (flukes)
Tapeworms
Treatable but no vaccine
Faecal-oral transmission. Worms in gut lay eggs which are excreted into the environment and are picked up by people e.g. If there is poor water sanitation.

Question 24

What are metazoa

Answer 24

Contains cells that have differentiated into tissues and organs

Question 25

Shistosomiasis/flukes

Answer 25

Intermediate vector is a snail.
Adult worm lives in the hepatic portal vein in humans. They produce spiney eggs which allows them to migrate to the gut. This causes inflammation and swelling.
These are excreted and they infect snail.
People wash in the water etc. And the cercaria can burrow through the skin and start the process all over again.
Can manage through snail management.
Basophils are involved in response to parasitic or helminth infections NOT bacterial