Development of Infections

Question 1

What is the difference between signs and symptoms? What are examples?

Answer 1

Symptoms are subjective characteristics felt by patient
- pain, nausea, headache, fatigue, malaise

Signs are objective manifestations of disease observed by others
- swelling, rash, redness, pus formation, anaemia,

manifestations relate to the target organ
Some infections are asymptomatic or subclinical

Question 2

What are the stages of infectious disease?

Answer 2

incubation period
- no signs or symptoms

prodromal period
- vague, general symptoms

illness
- most severe signs and symptoms

decline
- declining signs and symptoms

convalescence
- no signs or symptoms

Question 3

What is the chain of infection?

Answer 3

infectious agent - microorganism that can cause infections

reservoir - habitat where micro-organism lives, grows and multiplies

portal of exit/way out - microorganism needs a way out in order to spread to from the infected person

mode of transmission - spreading from one person to another

portal of entry/way in - microorganism needs to find a way into the new person to infect them

susceptible host - person who is at risk of infection as they cannot defend themselves

Question 4

What is adhesion? What is the role of adhesion in infection?

Answer 4

Adhesion - process by which microorganisms attached themselves to cells

To accomplish adhesion, pathogens use adhesion factors
- specialized structures or attachment proteins

Some bacterial pathogens do not attach to host cells, but form biofilms

Question 5

What are virulence factors?

Answer 5

Pathogenicity
- ability of microorganism to cause disease
Virulence
- degree of pathogenicity

Neither addresses severity of the disease
- highly virulent almost always cause disease whereas less virulent (including opportunistic pathogens) cause disease only in weakened hosts or when present in overwhelming numbers

Extracellular enzymes
Toxins

Question 6

What extracellular enzymes act as virulence factors?

Answer 6

Hyaluronidase and collagenase degrade specific molecules to enable bacteria invade deeper tissues

Coagulase causes blood proteins to clot

Kinases digest blood clots, allowing subsequent invasion of damaged tissues

Question 7

What toxins acts as virulence factors?

Answer 7

Exotoxins
- cytotoxins, generally kill host cells or affect function
- neurotoxins, specifically interfere with nerve cell function
- enterotoxins, affect cells lining the GIT

Endotoxins
- Lipid A
- other parts of the bacterial cell

endotoxins are membrane compounds of gram-negative bacteria which elicit an inflammatory response in host, whereas exotoxins are secreted proteins which act locally and at distance of the bacterial colonization site
- endotoxins are released when the bacteria undergoes lysis (dead bacterium) whilst exotoxins are secreted by live bacterium

Question 8

What are antiphagocytic factors?

Answer 8

Capsules
- are effective as many capsules are composed of chemicals normally found in the body

e.g. hyaluronic acid capsules deceive phagocytic cells into treating them as normal part of body

Antiphagocytic chemicals
- produce chemicals preventing fusion of lysosomes with phagocytic vesicles

e.g. Leukocidins are chemicals capable of destroying phagocytic cells outright