Outcome 2.1 - Aetiology

Question 1

Name the 2 categories of pathogen + example

Answer 1

Opportunistic pathogen(Staphylococcus epidermis) or true pathogen(HIV)

Question 2

What are true pathogens?

Answer 2

Microbes with well-developed character of virulence that are capable of causing disease in healthy individuals

Question 3

What are opportunistic pathogens?

Answer 3

Microbes which normally do not cause disease in healthy individuals but can in immuno-compromised indivduals

Question 4

What is virulence?

Answer 4

The severity of pathogenicity(disease causing properties)

Question 5

Define aetiology

Answer 5

The study of the causation of disease, the study and identification of microbes responsible for disease

Question 6

Define epidemiology

Answer 6

Study of the occurence, spread and control of disease in defined populations

Question 7

What is Koch’s postulates used to prove

Answer 7

That a particular microbe is the cause of a particular disease

Question 8

Name the 4 Kochs postulates

Answer 8

1. The microbe must be present in every case of the disease
2. The microbe must be isolated from the patient and grown in pure cultures
3. The disease must be reproduced when the culture is introduced to a non-diseased susceptible host
4. The microbe must be shown to be isolated from the experimentally infected host

Question 9

What is a portal of entry?

Answer 9

The portal through which a microbe invades, gaining acces to the hosts tissue and sometimes cells

Question 10

Name the 4 portals of entry

Answer 10

Skin
Respiratory Tract
Gastrointestinal Tract
Urogential Tract

Question 11

Describe skin as a portal of entry

Answer 11

Skin be a portal of entry for a microbe that invades via infecting wounds(Staphlococcus epidermis), bites from infected insect carriers(malaria), abbrasions in skin like cold sores and genital herpes can admit viruses (Human Papillomavirus)

Question 12

Describe the respiratory tract as a portal of entry

Answer 12

Microbes can enter the oral or nasal apertures and infect the upper respiratory tract (influenza virus or strep throat caused by bacteria) or the lower respiratory tract (pneumonia - caused by streptococcus pneumoniae bacteria or the fungi pneumocyctis)

Question 13

Describe the gastronintestinal tract as a portal of entry

Answer 13

GI pathogens can be ingested in food or drink. Salmonella is caused by bacteria and cryptosporadium is a protazoa which causes diarehea.

Question 14

Describe the urogenital tract as a portal of entry

Answer 14

Microbes infecting the urogenital tract can be transmitted during sexual intercourse.
Viruses - HIV and Hepatitis B
Bacteria - Syphillis, chlymadia, gonorhea
Fungus - yeast

Question 15

Infection can occur directly or indirectly - explain

Answer 15

Hosts can be infected by direct means - contact with an infected person. Or indirect means - contact with contaminated articles or surfaces

Question 16

Define infective dose

Answer 16

The number of organisms required to establish a productive infection. The smaller the infective does required, the more virulent the organsim

Question 17

Name the 5 portals of exit

Answer 17

Skin
Respiratory
Urogenital
Faecal route
Blood-borne infections

Question 18

Describe skin as a portal of exit

Answer 18

As dead skin cells are constantly shed from skin, this allows transmission of HPV, Herpes simplex virus Staphylococcal bacteria etc from boils

Question 19

Describe the respiratory portal of exit

Answer 19

Coughing spreads droplets containing aerosols of pathogen. E.g tuberculosis, influenza and measles

Question 20

Describe the faecal route as a portal of exit

Answer 20

Enteric (meaning intestinal) pathogens cause watery diarrhoea which provides a mechanism through which copius amounts of pathogen are released

Question 21

Describe the urogenital tract as a portal of exit

Answer 21

Semen and vaginal secretions can contain pathogens such as HIV chlymadia.
Urine can release pathogens that infect the bladder or kidneys

Question 22

Descibe blood borne infections in the context of portals of exit

Answer 22

Some viruses and protazoans can be transmitted by blood if it enters wounds of another person. E.g needle sharing - HIV and mosquito bites - plasmodium (malaria)

Question 23

Define localised and systemic infection

Answer 23

Localised infection - The infection is limited to a specific tissue
Systemic infection - The infection can be spread throughout the body, typically via the bloodstream

Question 24

Give an example of a localised infection and an example of a systemic infection

Answer 24

Localised infection - a wart or boil

Systemic infection - HIV

Question 25

What is toxaemia

Answer 25

The result of a localised infection producint toxins which cause systemic damage after transportation in the blood e.g tetanus enters through a skin wound but toxins are carried in the blood which damage nerve cells

Question 26

What are mixed infections

Answer 26

When two or more pathogens infect an
individual. The first or primary infection can overload or damage the host defences enough to facilitate a secondary infection.

Question 27

Name the four stages of patient response to pathogenic infection

Answer 27

1. Incubation period
2. Prodromal stage
3. Period of invasion
4. Convalescent period

Question 28

Describe the incubation period of patient response to pathogenic infection

Answer 28

The pathogen has not replicated sufficiently to generate symptoms, but replication continues. This period can last up to 30 days

Question 29

Describe the prodromal stage of patient response to pathogenic infection

Answer 29

The earliest symptoms occur such as general malaise, headache, muscle pains-appear. This lasts a few days

Question 30

Describe the period of invasion of patient response to pathogenic infection

Answer 30

The organism is in its invasive phase and toxins may be
produced to give rise to many symptoms and discomfort. The organism replicates at high levels. The host immune system will give rise to symptoms also e.g. fever, mucus production etc.

Question 31

Describe the convalescent period of patient response to pathogenic infection

Answer 31

the immune system gradually brings the infection
under control and usually eliminates the microbe. Although the microbe can become latent, that is still capable of causing disease, but temporarily inactive- early HIV infection is an example of this phenomenon