Infectious Agents

Question 1

What is a biofilm?

Answer 1

A biofilm is a coordinated functional community of microbes

Question 2

What does a biofilm do?

Answer 2

Attached to a surface and protects bacteria from antibiotics, desiccation and destruction by the immune system and provided bacteria with nutrient and removal of wastes

Question 3

What is bacteria growth increased by?

Answer 3

• Water or moist environment
• Temperature close to 37
• pH close to 7
• Oxygen
• Nutrients
• Isotonic surrounding
• Environments where they are not easily removed

Question 4

What are the 4 main types of virus?

Answer 4

Acute lytic, sub-clinical, latent and chronic

Question 5

Describe an Acute-lytic virus

Answer 5

Acute lytic infection refers to the rapid replication of the viral genome. Eventually, the host immune system overcomes the virus. Memory cells in the immune system will protect against future infection by the same virus e.g influenza

Question 6

Describe a sub-clinical virus

Answer 6

There are no recognisable signs and symptoms of the virus. The patient recovers unaware of having the identified disease e.g HPV/measles

Question 7

Describe a latent virus

Answer 7

The virus starts as acute-lytic then the patients makes an apparent recovery but the virus is not completely eliminated. The virus can be reactivated e.g cold sore

Question 8

Describe a chronic virus

Answer 8

Virus remains in host and replication of virus continues at a low level. E.g Hepatitis B

Question 9

What are other pathogens?

Answer 9

Fungi, protozoa, prions, helminths, parasites

Question 10

Describe fungi

Answer 10

Able to grow in conditions where bacteria could not survive
• Minimal moisture
• High sugar or salt conditions • Acidic pH
• Cold

Question 11

Describe a Protozoa

Answer 11

Eukaryotic, widespread in moist environments
• Movement by flagella, cilia or pseudopodia
• Some are parasitic and absorb nutrients from the host
• Infection occurs via
Ingestion(e.g.cryptosporidiumorgiardia
intestinalis)
Vector transmission (e.g. malaria or leishmaniasis)

Question 12

Describe a Prions

Answer 12

Begin as normal proteins in the plasma membrane of brain cells
• They become incorrectly folded and cause adjacent proteins to miss-fold
• Prion proteins clump together forming small fibrils which eventually kill the brain cell
• Highlytransmissible
• Rare but fatal
• CreutzfeldtJakobdisease (CJD)

Question 13

Describe a helminths

Answer 13

Common type of parasitic infection widespread within communities
• Often linked to poor sanitation and hygiene practices
• Enter host by ingestion of food and water
• May produce eggs in human intestine which are then shed in faeces
• Pinworm (or threadworm)
• Live in large intestine
• Female emerges at night to lay eggs around anus
• Transmitted when picked up on fingers and ingested by same or other host
• Causes disturbed sleep and infects most children at some time

Question 14

What different types of parasites are there?

Answer 14

Fleas, lice, scabies, ticks

Question 15

What are the four stages of infection

Answer 15

Incubation period
Prodromal stage
Illness stage
Convalescence stage

Question 16

Describe the incubation period

Answer 16

Interval between entry of pathogen to appearance of first symptoms (can vary from days, weeks, even years)
• Pathogen growing in numbers
• The patient is infectious at this time

Question 17

Describe the prodromal stage

Answer 17

Interval from onset of non-specific signs (malaise, headache, lack of appetite) and symptoms to general signs and symptoms (fever, pain, inflammation)
• Pathogen grows in numbers and multiply
• The patient is infectious at this time

Question 18

Describe the illness stage

Answer 18

Phase of rapid multiplication
• Signs and symptoms are disease-specific and very pronounced • May be considered the acute phase
• The patient is infectious at this time

Question 19

Describe the Convalescence stage

Answer 19

Interval when acute symptoms disappear (could be days to months) • Pathogen load declining but may still be present
• The patient may still be infectious at this time

Question 20

Virulence means:

Answer 20

The potency of a pathogen to infect a host and cause death of the host

Question 21

Define a pathogen

Answer 21

A disease causing microorganism

Question 22

What is a vector of disease?

Answer 22

An insect, bird or rat which carries disease from one organism to another but doesn’t have the disease themselves

Question 23

Lysozyme is an example of

Answer 23

An enzyme which is bacteriocidal

Question 24

What are the differences between bacteria and fungi infections?

Answer 24

Bacterial infection can be treated by antibiotics, whereas fungal infection can’t