Pathogens and Hosts

Question 1

What characterises a clinical infection?

Answer 1

• Inflammation
• Pain
• Pyrexia
• Tachycardia
• Rigors
• Increased white cell count
• Increased C reactive protein (CRP)

Question 2

What is a pathogen?

Answer 2

An organism which can cause disease

Question 3

What is a commensal?

Answer 3

An organism which is part of normal flora e.g E.coil in the gut, Staph aureus in the nose

Question 4

Define pathogenicity

Answer 4

The capacity of a micro-organism to cause an infection

Question 5

What are the requirements of pathogenicity?

Answer 5

Infectivity
Virulence

Question 6

Define infectivity

Answer 6

Ability to become established on or within a host

Question 7

Define virulence

Answer 7

Capacity to cause harmful effects (disease) once established.

Question 8

What is virulence conferred by?

Answer 8

Conferred by virulence factors.

• Genetically determined microbial components
• Invasiveness
• Toxin production
• Evasion of immune system

Question 9

What is virulence specific to?

Answer 9

Strains, not species

Question 10

What are exotoxins?

Answer 10

A toxin secreted by bacteria

Question 11

How are exotoxins released?

Answer 11

Exotoxins are released extracellularly by the micro-organisim

Question 12

What are endotoxins?

Answer 12

The main component of the outer membrane of the cell wall of Gram-negative bacteria.

Question 13

What do enterotoxins act on?

Answer 13

Enterotoxins are exotoxins which act on the GI tract

Question 14

Define colonisation

Answer 14

The presence of bacteria on a body surface(like on the skin, mouth, intestines or airway) without causing disease in the person.

Question 15

Define latent (aka asymptomatic) infection

Answer 15

An infection that usuallydoes not cause symptomsand can last a long period of time before becoming active and causing symptoms.

Question 16

When does an infection occur?

Answer 16

When a microorganism enters a person’s body and causes harm.

Question 17

What are the mechanisms of the innate immune system?

Answer 17

Physical
Physiological
Chemical
Biological

Question 18

What are examples of physical barriers of the innate immune system?

Answer 18

Skin - Tears, urine, saliva, bile, pancreatic secretions, mucus and sebaceous secretions

Mucous membranes of respiratory, gastrointestinal and urinary tracts

Question 19

What is the role of bronchial cilia?

Answer 19

Move microbes and debris up and out of the airways.

Question 20

What are examples of physiological barriers?

Answer 20

Diarrhoea
Vomiting
Coughing
Sneezing

Question 21

How does low pH act as a chemical barrier to pathogens?

Answer 21

The relativelylow pH in certain parts of the body prevents pathogen growth.

Question 22

What are examples of structures with low pH?

Answer 22

Skin–pH 5.5
Gastricacid–pH 1-3
Vagina–pH 4.4

Question 23

What is the main biological barrier to pathogens?

Answer 23

Normal flora found in the body

Question 24

Where can body flora be found?

Answer 24

Nasopharynx

Mouthand throat

Skin

GI tract

Vagina

Question 25

What are the mechanisms of the adaptive immune system?

Answer 25

Cell mediated immunity Humoral immuity

Question 26

What is cell mediated immunity mediated by?

Answer 26

T lymphocytes against intracellular pathogens

Question 27

What is humoral immunity mediated by?

Answer 27

Antibodies

Question 28

Discuss cell mediated immunity

Answer 28

An immune response that does not involve antibodies. Rather, phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

Question 29

What is humoral immunity based on?

Answer 29

Serum antibodies that are produced by plasma cells and bind to antigens in order to assist with their elimination.

Question 30

What is cell mediated immunity based on?

Answer 30

The action of cytotoxic cells that activate other immune cells and help eliminate pathogens and infected host cells.

Question 31

What is humoral immunity also known as?

Answer 31

Antibody-mediated immunity. With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen.

Question 32

What does the humoral immune system deal with?

Answer 32

Antigens from pathogens that are freely circulating, or outside the infected cells.

Question 33

What are common sites of viral entry?

Answer 33

Mucosal linings of the respiratory, alimentary, and urogenital tracts The outer surface of the eye The skin

Question 34

What is antigenic drift?

Answer 34

Minor changes (natural mutations) in the genes of flu viruses occurs gradually over time to generate antigenic variants

Question 35

What is antigenic shift?

Answer 35

Abrupt major changes in virus antigenic structure due to combination of different strains from different hosts

Question 36

What does influenza A virus infect?

Answer 36

Cells of respiratory system Destruction of respiratory epithelium - secondary bacterial infections

Question 37

What causes fever in influenza A virus?

Answer 37

Alterned cytokine expression leading to fever e.g interleukin-1 and interferon - Avian influenza virus (H5N1) causes cytokine storm

Question 38

What are enteroviruses?

Answer 38

Viruses that are: - Small - Icosahedral shaped - Non-envelope Virons are relatively simple, consisting of a: Protein capsid surrounding a single-stranded, positive sense RNA genome.

Question 39

What can enterovirus cause?

Answer 39

- Croup (breathing difficulty and harsh cough) - Mouth sores. - Skin rashes. - Sore throat. - Chest pain if the infection affects the heart muscle or sac-like covering around the heart (pericarditis)

Question 40

What are examples of enteroviruses?

Answer 40

- Poliovirus - Respiratory infections (many enteroviruses) - Myocarditis (coxsackie B viruses)

Question 41

What can viruses turn into?

Answer 41

When viruses cause an infection, they spread their DNA, affecting healthy cells' genetic makeup and potentially causing them to turn into cancer.

Question 42

What are the mechanisms in which a virus can turn into cancer?

Answer 42

- Directly damage DNA in host cells, resulting in cancer. - Altering the immune system - Chronic inflammation. - Disrupting the body's normal regulation of cell division.

Question 43

What can papillomaviruses and HPV infections casue?

Answer 43

Cervical carcinoma

Question 44

What can retroviruses cause?

Answer 44

Lymphomas and leukemias