Host-Microbe Relationships

Question 1

Describe the infectious disease process

Answer 1

Agent: Bacteria, viruses, fungi or parasites

Reservoir: Symptomatic - patients
-> Carriers
Incubatory -those who can transmit before symptoms
Inapparent - Never developing infection but can transmit
Convalescent - Recovered, transmittable
Chronic - recovers - carries the pathogen

Animals and insects - rabies from dogs, vectors

Environment - Soil

Portal of exit: Alimentary, genitourinary, respiratory, skin, transplacental

Modes of transmission: Direct and indirect transmission

Portal of entry: Inhalation, Absorption, Ingestion, inoculation, introduction

**Host susceptibility: Age, gender, lifestyle, nutritional; status, medical history, medications, host physical barriers, heredity

Question 2

How do humans and microorganisms interact constantly?

Answer 2

In/on the body
Soil
AIr
Water
Food

Question 3

What happens when microbes break human defences

Answer 3

Human defences- innate and adaptive immunioty

If broken down, transfer of virulence genes into avirulent bacterium

Question 4

What is commensalism?

Answer 4

Host provides shelter and food. Little interaction

Question 5

Mutualism…

Answer 5

Host and organism are mutually dependent - host would suffer if lost

Question 6

Parasitism….

Answer 6

Unilateral benefit to the organism. May cause damage to host. (e.g. pathogens)

Question 7

What are factors affecting outcomes of host-microbe interactions?

Answer 7

State of immune system (age, general nutrition, stress, underlying diseases, immunosuppressive therapy

Host physical barriers (Trauma and burns, stomach acidity, physical abnormalities)

Host genetics
(Tissue and host tropism, may affect ability of organism to bind)

Normal Flora (one of the first line of defences, stimulates adaptive immune system. absence or major alterations indicate underlying problem

Question 8

Anatomical barriers to infection - Skin

Answer 8

Very dry
Sweat and sebaceous glands produce lysozyme toxic fatty acids and lactic acid
Epithelial cells produce defensins
Resident microflora

Question 9

Anatomical barriers to infection - mucous membrane (mucosa)

Answer 9

Mucus - physical barrier
Moving - cannot attach
Organisms would bind to CHO in mucus
MALT

Question 10

Anatomical barriers to infection - Mouth and respiratory tract

Answer 10

Flow of saliva
Hair in nose
Sneeze response
Ciliated cells
Alveolar macrophages

Question 11

Anatomical barriers to infection - GIT

Answer 11

low pH in stomach
Bile salts
Resident flora in colon
Paneth cells