Bacterial Disease - Clinical and Pathological Changes

Question 1

Commensal

Answer 1

• Stable polymicrobial communities present throughout life as part of ‘normal microflora’
• Found on skin and hollow organs whose surfaces are exposed to environment
• Acquired soon after birth

Question 2

Pathogen

Answer 2

• Microorganism which causes disease
• Competes with normal microflora to gain foothold within niche
• Evades or overcomes host defences
• Expresses genes which encode factors which cause disease

Question 3

Pathogenicity

Answer 3

Ability of a microbe to damage a host

Question 4

Virulence

Answer 4

Relative capacity of pathogen to damage a host

Question 5

Virulence factors

Answer 5

Bacterial traits that confer pathogenicity
* Adhesins
* Toxins
* Capsules

Question 6

When do clinical consequences of infection occur?

Answer 6

When pathogenicity exceeds host defences

Question 7

How do bacteria cause tissue damage?

Answer 7

Bacterial toxins
* Locally
* Systemically
Inflammatory reponse
Immune response

Question 8

Outcomes of infection

Answer 8

1. infection is eliminated and cleared
2. Clinical disease occurs
   * Acute
   * Subacute
   * Chronic
3. Subclinical infections
   * carrier for disease

Question 9

What determines shedding of agent?

Answer 9

Severity of disease
Type of pathogen
Tissues affected

Question 10

Carrier state

Answer 10

Intermittent shedding of agent

Question 11

Latent infection

Answer 11

Shedding of agent if disease is reactivated

Question 12

Clinical changes in bacterial infections

Answer 12

Pathognomonic clinical presentation
Inflammatory response (non-specific to bacteria)
Cardiovascular consequences (in advanced stages)

Question 13

Pathognomonic clinical presentation Example

Answer 13

Erysipelas in pigs
* Specific skin lesions

Question 14

Inflammatory response

Answer 14

Non-specific to bacteria
○ Systemic
E.g. Pyrexia (^HR, ^RR)
○ Local
E.g. pain, heat, swelling, erythema
○ Pus – neutrophils – acute
○ Granulomas – macrophages – chronic

Question 15

Cardiovascular consequences

Answer 15

Septicaemia
○ Congested mucous membranes
“Brick” or dark red
○ Toxic line
Purple line in gums near teeth – horses

Question 16

Clinical changes in blood during inflammation

Answer 16

Neutrophils
Acute phase proteins
Cardiovascular changes
Coagulopathy

Question 17

Neutrophil changes in inflammation

Answer 17

Number - up or down
Left-shift
□ Younger - strong response
Toxic change
□ Dysmaturation

Question 18

Toxic Change

Answer 18

Morphologic abnormalities acquired during maturation under conditions that intensely stimulate neutrophil production and shorten the maturation time in marrow
Refers to neutrophil in BLOOD
How well bone marrow is working

Question 19

Acute phase proteins

Answer 19

Fibrinogen
C Reactive Protein - dogs
Serum Amyloid A - horses/cats
Haptoglobin - cattle

Question 20

Cardiovascular changes in inflammation

Answer 20

Metabolic acidosis
Increased lactate

Question 21

Bacteraemia

Answer 21

Presence of bacteria in blood

Question 22

Septicaemia

Answer 22

Presence and replication on bacteria in blood

Question 23

Toxaemia

Answer 23

Toxins from bacterial infection present in blood

Question 24

Sepsis

Answer 24

Body’s extreme response to infection

Question 25

Can you identify bacterial infections by examining blood under microscope?

Answer 25

No (unless anthrax post-mortem)

Question 26

Clinical changes in tissue during inflammation

Answer 26

Number of neutrophils Type of neutrophils Macrophages - chronic or acute?

Question 27

What is the regenerative capacity of neutrophils in dogs?

Answer 27

Rapid

Question 28

What is the regenerative capacity of neutrophils in horses?

Answer 28

Intermediate

Question 29

What is the regenerative capacity of neutrophils in cows?

Answer 29

Slow

Question 30

What does neutropaenia indicate in dogs?

Answer 30

Very severe infection Can't keep up with demand

Question 31

What does neutropaenia indicate in cows?

Answer 31

Common in inflammation regardless of severity Common in early infections Better to rely on haptoglobin concentration

Question 32

What factors cause a shift from marginal to circulating pool?

Answer 32

* Epinephrine * Glucocorticoids * Infections * Stress

Question 33

Left shift

Answer 33

More immature neutrophils due to infection * Bone marrow producing more new neutrophils * Common in acute infections

Question 34

Regenerative

Answer 34

More segmented than immature Neutrophilia

Question 35

Degenerative

Answer 35

More immature than segmented Neutrophilia or neutropaenia

Question 36

Neutrophil toxic change

Answer 36

Sign of severe infection Rapid neutropoesis Not enough time to mature fully ○ Diffuse cytoplasmic basophilia Persistent of cytoplasmic RNA Incl segmented neutrophils ○ Döhle bodies Focal blue-grey cytoplasmic structures (RER/RNA) Foamy cytoplasm Dispersed organelles (not discrete –EDTA) Isolated finding in some healthy cats ○ Asynchronous nuclear maturation Finely granular nuclear chromatin but in “segments”

Question 37

Coagulopathy of sepsis

Answer 37

Factors stimulated by sepsis which make animals pro-coagulant Microthrombi in vasculature Lower platelet counts Lower coagulation factors

Question 38

Degernerate neutrophils

Answer 38

* Being broken down by body Cell is large with distended vacuolated cytoplasm * Swollen enlarged nucleus