Disease Control in animals to benefit PH

Question 1

What is R nought (R0)

Answer 1

describes how many people each infected person will infect on average, assuming that there is no pre-existing immunity in the community.
Often estimated using 3 factors:
a) duration of contagiousness after a person becomes infected
b) likelihood of infection in each contact between a susceptible person and an infectious person or vector
c) frequency of contact

Question 2

Vet Med controlling infecction:

Answer 2

• Based on R0/Epidemic Theory infection can realistically be controlled by interventions that act in two ways

a) Prevent or Reduce Transmission
b) Reduce susceptible population

Question 3

Controlling infection - how to prevent/ reduce transmission?

Answer 3

Prevent contact between infected and susceptible individuals

e. g movement restriction, exclusion zones, biosecurity - Removal of infected individuals e.g. culling, treatment, isolation - Reduce ability to transmit e.g. vaccination (herd immunity), therapy

Question 4

Controlling infection - how to reduce the sysceptible population?

Answer 4

• Improve immunity e.g. vaccination, genetic resistance
• Make individual harder to infect e.g. probiotic/competitive exclusion
• Remove a susceptible population e.g. contiguous culling (non exposed but

Question 5

3 key food borne pathogens

Answer 5

1. salmonella enterica
2. Campylobacter
3. E coli

Question 6

2 types of salmonella enterica

Answer 6

1. Salmonella enterica serovar Typhimurium

2. Salmonella enterica serovar enteritidis

Question 7

Why did salmonella fall in the UK after endemic?

Answer 7

• Underpinning legislation for control
• Implementation of improved hygiene & biosecurity of hatcheries (used to be horrible places – send out chickens that are already infected)
• Improved farm biosecurity
• Introduction of vaccines
• Heat treatment of feed – reduced carriage of salmonella in feed stuff.
• Targeted approach to reduce serovars of greatest public health significance

Question 8

The lion mark and egg salmonella

Answer 8

a voluntary scheme of hygiene & biosecurity standards coupled to routine surveillance – first time routinely look at salmonella in flocks.

Question 9

Current salmonella surveillance in UK

Answer 9

1. Under NCP (National Control Plan) requirements
2. Broilers - Sampling of 2 boot swabs/socks per flock/house within 3 weeks of slaughter
3. Layers more intensive - Chicks-Chick boxes and any dead chicks sampled
   Pullets- 2boot swabs 2 weeks before placement
   Hens-2 boot swabs or pooled faeces at 22-26 weeks of age, then every 15 weeks in production
4. positive test means eggs can’t be sold as class A table eggs. Meaning they must be pasturised, become worthless, chickens get culled as cheaper to do this than sell these eggs

Question 10

How are salmonella vacciens given

Answer 10

1. live attenuated in drinking water = easier and mroe effective vaccines than previous

Question 11

NCP rule on salmonella vaccines

Answer 11

• All layers and breeding birds (layers & broilers) now vaccinated under NCP
• Production broilers not vaccinated – killed at such a young age, we can’t initiate sufficient immune response in that time.
• Regarded as single largest contributory factor to reduction of salmonellosis in UK

Question 12

Farm biosecurity

Answer 12

1. Largely indoor
2. major control barriers: entery, vermin proof, vechile wheel wash, concrete/ gravel around buildings, ventilation
3. All in all out system = disinfection between flocks and broiler crops
4. no sharing equipment between farms

Question 13

Biosecurity failure works well for salmonella byt what about campylobacter?

Answer 13

1. C is highly transmissible
2. small breakdown in biosecurity = positive flocks
3. fomite on boots, flies, clothing
4. Most likely breaksdown due to “thinning” where catchers remove chickens ready for slaughter, leaving those that aren’t to grow = spread by catchers

Question 14

Intensive production and the spread of campylobacter

Answer 14

1. infected during production, mainly caecal but liver and muscle infection inc common
2. Feed withdrawal and transport = stress and inc shedding from infected birds
3. at abbatoir macheines cross contam e.g. automated plucking
4. rapidly growing broiler breeds = relatively poor immune systems

Question 15

Contact, Exclusion zones and movement restrictions

Answer 15

• Less useful in enteric bacterial infections in livestock, more for viral e.g. avian influenza
• Include bans on movement, gatherings (markets, shows etc.) and exclusion zones around infected premises

Question 16

Culling

Answer 16

• Culling removes can remove an infected population reducing ability to transmit
• S. Enteritidis positive flocks are often culled as not economically viable as eggs cannot be sold as table eggs

Question 17

How can we reduce host suseptibility to salmonella/ campylobacter?

Answer 17

• Better welfare and housing reduce stress and susceptibility-stress hormones increase faecal shedding in cattle and chickens
• Poor house design can increase spread in herds-common in pigs where housing is variable (e.g. faecal material is chaneled through pens in some farms) and plays a role is Salmonella transmission

Question 18

Selective breeding good?

Answer 18

breeding for resistance
1. Chickens immune system is less polymorphic than mammals so stronger association between genome and disease resistance.

Question 19

Competitive exclusion, probiotics and prebiotics:

Answer 19

idea of manipulating the microbiome to increase resistance to pathogens is long-established in poultry
• Competitive exclusion (CE) involves giving a microflora to animals that excludes or competes (physically occupy space) with pathogens-occupying niches for colonization or producing metabolites that promote gut health and inhibit pathogens (e.g.butyrate - )
• Probiotics are (usually) single bacterial species (e.g. Lactobacillus) that promote gut health/inhibit pathogens
• Both CE and probiotics may promote immunological development in the
gut, but CE are only given at intervals, probiotics need regular
consumption
• Prebiotics are feed additives that promote a ‘good’ microbiome
-High firmicutes that produce butyrate, lower enterobacteriaciae
• No current product gives complete protection

Question 20

Slaughter and disease control

Answer 20

1. Care in and post slaughter
2. foodborne pathogens are gut/faecal associated processes in slaughter and processing should avoid gut/faecal contamination
3. Hides or ruminants should be free of gross faecal contamination
4. Care should be taken in removing the intestinal tract to avoid spillage & cross contamination
5. However this is challenging for poultry lines at around 200 birds per minute
6. Treatment of carcass - pathogen reduction treatment or gamma irradiation
   - widely used in US not so much here
   chlorination chicken in US to reduce salmonella and campylo

Question 21

Summary

Answer 21

• Salmonella in poultry is a good example of how to control a foodborne pathogen
• Key factors in Salmonella control including vaccination & biosecurity are not or cannot be incorporated into Campylobacter in broiler chickens or EHEC in cattle so are harder to control
• Effective control is based around combinations of measures-single measures alone are more likely to fail-e.g. vaccination not not be used to compensate for poor husbandry & biosecurity