Infectious Agents

Question 1

What are the five main types of infectious agents?

Answer 1

Viruses
Fungi
Bacteria
Protozoa
Helminths
[Very F*cking Big Pathogens Hurt ;) ]

Question 2

How do viruses evolve so quickly?

Answer 2

Viruses have very error-prone replication processes and they don’t correct their errors with very high efficacy.

Question 3

How do bacteria evolve quickly?

Answer 3

While having about the same mutation rate as humans, bacteria are haploid meaning they only need one faulty copy to express the phenotype (unlike some diploid genes).
They also have much shorter replication times, meaning genes can be selected for and spread in a population much more rapidly than can happen in humans.

Question 4

Do vaccines cause autism?

Answer 4

No.

Question 5

Does Bill Gates and “Big Pharma” have my family hostage, forcing me to make false statements about the efficacy of vaccines?

Answer 5

TheY definitEly don’t have my family hoStage!

Question 6

Why aren’t viruses cells in their own right?

Answer 6

They aren’t alive. They are obligate parasites meaning they have to infect other cells to replicate.

Question 7

What genetic material do viruses have?

Answer 7

DNA/RNA

Question 8

How do RNA viruses replicate within cells that use DNA?

Answer 8

They use reverse transcriptase enzymes to convert their genome into DNA for the human host cell to then transcript and translate into viral proteins and genetic material.

Question 9

What can viruses do to make themself harder to detect?

Answer 9

Envelop themself in a human host cell membrane.

Question 10

What is the name for when viruses envelop leave the cell while simultaneously coating themself in the cell membrane?

Answer 10

Budding.

Question 11

What is an example of a virus that can cause cancer?

Answer 11

The Human Papillomavirus or HPV can cause cancer, specifically cervical cancer. Thankfully, we have a vaccine for it now.

Question 12

Under what broad spectrum do bacteria fall under?

Answer 12

Prokaryotes

Question 13

What is a prokaryote (4 features)?

Answer 13

An organism with no internal membranes/membrane bound organelles.
They are also haploid, allowing them to mutate relatively quickly.
They have a poorly defined cytoskeleton in comparison to eukaryotic cells.
The cell wall contains peptidoglycan.

Question 14

What bacteria do have membrane-bound organelles?

Answer 14

Photosynthetic bacteria, but these are non-pathogenic.

Question 15

What is peptidoglycan?

Answer 15

A polymer consisting of sugars and amino acids.

Question 16

How do bacteria replicate? What is the significance of this?

Answer 16

Prokaryotes divide by binary fission, meaning they can rapidly proliferate.

Question 17

What are three features that bacteria can develop to help them survive?

Answer 17

Pilli on the cell envelope determine how they adhere to surfaces.
The bacteria capsule can prevent phagocytosis and dehydration.
Flagellum on a bacteria allow bacteria to swim better.

Not all bacteria have these features.

Question 18

What is Shigella, what does it do and how does it move?

Answer 18

Shigella is an invasive pathogenic bacteria. It infects the GI tract and in severe cases can cause huge amounts of tissue damage, leading to death.
The cell has no flagella but it uses the host cell’s actin to push it forward in the cytoplasm and infect neighbouring cells without having to go outside.

Question 19

What is neisseria meningitidis?

Answer 19

Neisseria meningitidis is a commensal pathogen that lives without causing harm in the naso-pharynx of about 20% of the population.

Question 20

What is a characteristic symptom of an infection caused by N.meningitidis?

Answer 20

A non-blanching rash.

Question 21

What deadly issues can N.meningitidis cause?

Answer 21

It can reach the bloodstream and cause rapid septicaemia with a severe inflammatory response - this has a 10% fatality rate.
It can also penetrate the blood-brain barrier and be found in the cerebral spinal fluid, causing meningococcal meningitis.

Question 22

How have we dealt with N.meningitidis?

Answer 22

Development of vaccines.

Question 23

What disease kills the most worldwide and why?

Answer 23

TB. For reasons we aren’t too sure of, the BCG vaccine doesn’t work as well in developing nations (though there doesn’t seem to be a genetic reason).
Current drug therapy also takes too long, about 6 months.

Question 24

How can we visualise the damage done to lung tissues?

Answer 24

PET-CT imaging.

Question 25

What can Heliobacter pylori cause?

Answer 25

Peptic ulcers and gastric cancer.

Question 26

What is a peptic ulcer?

Answer 26

A lesion in the lining (mucosa) of the digestive tract in the duodenum, caused by the digestive action of pepsin and stomach acid.

Question 27

What is one of the most studied pathogenic bacteria? Where does it live?

Answer 27

E.coli. It lives in the gut of humans and other animals.

Question 28

What are mycoses?

Answer 28

A disease caused by infection with a fungus.

Question 29

What sort of mycoses can fungi cause?

Answer 29

Fungi can cause cutaneous, mucosal and/or systemic mycoses.

Question 30

What are protozoa? What are some examples?

Answer 30

Protozoa are unicellular organisms. They include intestinal, blood and tissue parasites.

Question 31

How do protozoa replicate?

Answer 31

They replicate in the host by binary fission or by formation of trophozoites inside a cell.

Question 32

What are trophozoites?

Answer 32

A trophozoite is the activated, feeding stage in the life cycle of certain protozoa.

Question 33

Why do we often say protozoa have complex life cycles?

Answer 33

Their life cycle may involve multiple hosts, such as malaria which starts in a mosquito but then enters a human.

Question 34

What are two common protozoa?

Answer 34

Malaria and leishmaniasis.

Question 35

How do protozoa infect people?

Answer 35

Infection is acquired by ingestion or through a vector (e.g. insect/invertebrate)

Question 36

What are helminths?

Answer 36

Helminths are usually small worms, which are visible to the human eye.

Question 37

What type of organism are helminths?

Answer 37

Metazoan.

Question 38

What does metazoan mean?

Answer 38

They have cells that can differentiate to form tissues and so are multicellular.

Question 39

What are some examples of helminths?

Answer 39

Roundworms, flatworms and tapeworms.

Question 40

What sounds like a helminth, but isn’t? What is it actually?

Answer 40

Ringworm. Ringworm is the name given to a type of rash caused by a fungus. The rash looks like a worm forming a ring shape.

Question 41

Schistosoma Mansoni is a type of fluke (flatworm). Where does its lifecycle originate?

Answer 41

It starts inside a snail where it releases cercaria into water sources.

Question 42

What are cercaria?

Answer 42

A cercaria is the larval form of the parasite.

Question 43

Where do the cercaria of S.Mansoni go once they burrow into human skin?

Answer 43

They migrate to the liver where they pair with other adult worms. They release eggs into the hepatic portal vein.

Question 44

What happens to the eggs of S.Mansoni after being released into the hepatic portal vein?

Answer 44

Eggs make their way to the gut and are released in faeces.

Question 45

What does the movement of the egg through the tissues cause?

Answer 45

The eggs’ movement through the tissues causes huge amounts of inflammation that we see in the enlarged, distended abdomens of sufferers.

Question 46

How do we deal with protozoa like S.Mansoni?

Answer 46

Antimicrobial treatments are available, but programmes to remove freshwater snails have been very successful in limiting the amount of disease.