1. The Past, Present and Future of Salmonella Control in Poultry:
The Example of Salmonella enteritidis
Prepared by
Richard K. Gast
United States Department of Agriculture Agricultural Research Service
Southeast Poultry Research Laboratory Athens, Georgia

2. Modified and presented by
Prof. Dr. Mohamed Refai
Department of Microbiology
Faculty of Veterinary Medicine
Cairo University, Giza, Egypt
At the International Poultry Conference
in Cairo

3. The genus Salmonella (Lignieres, 1900)
Salmonella choleraesuis ( Salmon, 1885)
Salmonella typhi (Schroeter, 1886)
Salmonella enteritidis (Gaertner, 1888)
Salmonella london, panama, cairo etc
Salmonella arizonae (Kauffmann, 1964)
Salmonella bongori (LeMinor, 1985)
Salmonella enterica (LeMinor, 1987)
Now we have more than 2300 Salmonellae

4. Classification of Salmonella into subgenera/ species
Kauffmann LeMinor 1970
Subgenus I = species enterica
Subgenus II = species salamae
Subgenus IIIa = species arizonae
Subgenus IIIb = species diarizonae
Subgenus IV = species houtenae
Subgenus VI = species indica

5. Salmonella species Three species
* S. cholerae-suis, S. typhosa, S. kauffmanni
* S. cholerae-suis, S. typhi, S. enteritidis
One species
* S. enteritidis
Two species
* S. enterica , S. bongori

6. Terminology of Salmonella
the complete nomenclature:
* S. enterica, subsp. enterica serovar Enteritidis
* or Salmonella enterica ser. Enteritidis
Salmonella ser. Enteritidis
Salmonella Enteritidis

7. Antigenic formulae of some serovars of Salmonella enterica
Group A 1,2,12:a:1, ser. Paratyphi-A
Group B 1,4,5,12:b:1, ser. Paratyphi-B
1,4,5,12:i:1, ser. Typhimurium
Group C 6,7:c:1, ser. Choleraesuis
Group D 1,9,12:-: ser. Pullorum
1,9,12:-: ser. Gallinarum
1,9,12:g,m:1, ser. Enteritidis
1,9,12:g,p: ser. Dublin

8. Salmonella Epidemiological Classification
Group 1. Anthropophilic serovars
Salmonella Typhi
Group 2. Zoophilic serovars
Salmonella Gallinarum poultry
Salmonella Choleraesuis swine
Group 3. Serovars with no particular host
All other serovars, including SE

9. Incidence of Salmonella Enteritidis infections in laying flocks
Environmental samples from 7.1% of commercial laying houses in the USA were positive for Salmonella Enteritidis
USDA, 2000

10. Salmonella Enteritidis infection in man in the USA
Salmonella Enteritidis constitued
5% in
25% in
of human Salmonella reported to CDC

11. Sources of SE outbreaks in the USA, 1995-1997
In 110 outbreaks reported by CDC
59% no confirmed vehicle
34% contaminated shell eggs
07% other than eggs

12. Salmonella Enteritidis contamination of shell eggs
The transmission of Salmonella Enteritidis by eggs has become a leading public health issue in the USA

13. Sites of human SE outbreaks in the USA, 1998-1999
Sites Outbreaks
Commercial food preparers 46
Private homes 19
Church/community events
Colleges/schools/camps
Nursing homes
Prisons

14. The problem in the past Before 1970
Cracked or dirty table eggs and processed egg products were often implicated in human salmonella outbreaks
attention was directed to:
external contamination of eggs

15. Control of External Contamination of eggs
Measures
*Stringent regulation for shell eggs inspection
*Pasteurization of liquid egg products
Results:
Eggs were nearly eliminated as significant source of human disease

16. Attention was directed to Internal contamination of eggs
The new problem
A dramatic increase in incidence of human Salmonella Enteritidis infection is principally caused by consumption of clean and intact but internally contaminated table eggs
Attention was directed to
Internal contamination of eggs

17. Epidemiology of Salmonella Enteritidis in poultry
Colonization of intestinal tract
Shedding in feces
Horizontal transmission
Invasion and dissemination
Deposition inside eggs
Vertical transmission

18. Internal contamination of eggs
Principally before oviposition
Fecal contamination and penetration of the shell
Contamination during breaking

19. Salmonella Enteritidis egg contamination
Incidence is relatively low, 0.005% in USA (USDA,2000)
Eggs contain small number of SE
95% of naturally contaminated eggs contain < Humphrey, UK
78% of contaminated eggs in experimental infection contain < Gast, USA

20. Salmonella Enteritidis infection in chickens and egg contamination
Consequences
Dangerous increase of SE in eggs not before the 3d week of storage at ambient temperature
Humphrey & Whitehead,1993

21. Site of bacterial contamination of eggs
* If it is within the nutrient-rich yolk
It would lead to rapid and explosive multiplication
* If it is in the albumin
Multiplication would be restricted by the several inhibitory factors

22. Site of bacterial contamination of eggs in experimentally infected hens
(Gast and beard, 1990)
*SE was isolated from albumin or entire yolk, including vitelline membrane
*SE could not be isolated by sampling only the interior contents of yolk

23. Site of bacterial contamination of eggs
Gast and Holt, 2000
SE can penetrate through the yolk membrane at warm temperature
Instances were reported in which yolk contamination occurred more often than albumin contamination

24. Detection of Salmonella Enteritidis in eggs is difficult
Low incidence of contamination
needs large number of eggs
to be examined, eggs
Low level of bacterial cells
needs long incubation
for one or more days

25. Human Salmonella Enteritidis outbreaks
Human infection requires:
* Ambient storage temperature that allow multiplication of SE
* Cross-contamination of kitchen surfaces and foods
* Improper food handling and preparation practices

26. Problems of Salmonella control in poultry
Infections can be inapparent
Newly hatched poultry are highly susceptible to Salmonella colonization
Salmonellae have a very wide host range
Salmonella can persist in the environment
Manure and dust are present in large quantities in poultry houses

27. Salmonella Enteritidis Control Strategies
Principal objectives
*To reduce incidence of infection in egg-laying flocks
*To improve the microbial safety of processing, storage and preparation practices for egg and egg-containing foods

28. Reducing egg contamination
Prevention of infection:
Elimination of sources and reservoirs of SE in poultry flocks and facilities
Control of transmission of SE within and between flocks

29. A. Elimination of sources and reservoirs of Salmonella enteritidis
Sources of contamination
Replacement chicks themselves
Environment of the poultry house,
Rodents, feeds, etc
Measures
. Using uninfected chicks
Hygiene (cleaning, disinfection, etc)
Rodent control

30. Cleaning and disinfection
eliminated SE from about 50% of environmentally positive houses
Henzler et al., 1998,
Schlosser et al.,1999

31. Rodent Control
Rodent control was the only practice that correlated well with successful control of SE in poultry houses
Henzler et al., 1998,
Schlosser et al.,1999

32. B. Control of Transmission within and between flocks
Sources of contamination
Direct contact between birds
Carriage by vectors (biological or physical)
Contamination of materials and surfaces within poultry houses
Air movement of contaminated dust

33. B. Control of Transmission within and between flocks
Measures
Reducing the concentration of the circulating particles by negative ionization has reduced experimental horizontal transmission of SE in chicks
Gast et al., 1999

34. Control of Transmission within and between flocks
2.Reducing the susceptibility of chicks to SE infection by vaccination of pullets or hens can significantly reduce fecal shedding, organ invasion and egg contamination
(Gast et al., 1992, Zhang-Barber et al., 1999)

35. Control of Transmission within and between flocks
Vaccination does not create impenetrable barrier against infection
Immunity is not solid and protection is insignificant
Davison et al., 1999

36. Control of Transmission within and between flocks
Prophylactic administration of probiotic bacterial cultures for competitive exclusion of pathogens from the intestinal tract prevents colonization
This approach is less useful in protecting mature hens against environmentally acquired SE

37. Controversial susceptibility issue
Forced molting of laying hens
by feed deprivation can increase frequency, transmission and severity of SE infection
(Holt, 1993,1995)

38. Back to the title of the lecture
The Past, Present and Future
of Salmonella Control in Poultry

39. Control of Salmonella Enteritidis in the USA: Past efforts, 90-95
Trace-back Testing Program
When eggs are implicated as source of human SE infection
*Laying flocks are identified
*Environmental samples,if + then
*Internal tissues are cultured

40. Trace-back Testing Program
In case of SE positive results:
Selling shell eggs is restricted
Producers have to choose between
*pasteurization of eggs or
*depopulating affected flocks

41. Trace-back Testing Program
Evaluation: During this program
304 SE outbreaks were reported
96 outbreaks were due to eggs
38 flocks were implicated
9 million layers were depopulated
I billion eggs were diverted for pasteurization

42. Trace-back Testing Program
Evaluation: During this program
SE in cecal samples from hens at slaughter increased from 27% in 1991 to 45% in 1995
SE in unpasteurized liquid eggs increased from 13% to 19%

43. Trace-back Testing Program
Conclusion: Evident failure
due to :
* Eliminating a presumably small number of infected flocks
*Potentially continuous reintroduction of SE into flocks from diverse environmental sources

44. Control of Salmonella Enteritidis in the USA: Present efforts
Risk Reduction Program
Microbiological Quality Assurance
Implemented by federal, state and poultry industry

45. Risk Reduction Program
* Use certified SE-free chicks
* Control pests, especially rodents
* Thorough cleaning & disinfection
* Heightened biosecurity
* Washing & refrigeration of eggs

46. Risk Reduction Program
Intensive testing approach
* qualifying serological tests
* series of environmental tests
Certification of negative flocks
Diversion of eggs from + flocks to pasteurization

47. Pennsylvania Egg Quality Assurance Program
Purchase chicks from uninfected breeder flocks
Maintain rodent control and biosecurity programs
Keep eggs under refrigeration
Culture environmental samples from chicks, pullets and layers for SE
If +, culture eggs, if +, divert eggs, clean and disinfect thoroughly between flocks

48. National Poultry Improvement Plan, monitoring breeding flocks
Chicks must originate from participating flocks
Feed must be free of SE
Hatching eggs must be promptly collected and sanitized or fumigated
Blood samples from 300 birds are tested for antibodies, if + culture for SE
Environmental samples are taken at 2-4 w and every 30 days. If + do blood testing

49. Risk Reduction Program
Results
38% of 47 flocks + in 1992
12% in 1995
**Egg diversion to pasteurization without compensation renders it unpopular by egg-producers

50. Risk Reduction Program
Alternative program
Single environmental test
Positive result requires:
* extra cleaning and disinfection
* overall review of control program implementation

51. United Egg Producers 5-Star Quality Assurance Program
Cleaning & disinfecftion of poultry houses
Rodent and pest elimination
Proper egg washing
Biosecurity
Egg refrigeration from packing to delivery
Environmental testing
Positive results trigger extra cleaning and disinfection plus review of program implementation

52. Control of Salmonella Enteritidis in the USA: The future
The most effective and sustainable approaches to control food–borne disease involve risk reduction practices that address a broad spectrum of current and prospective pathogens

53. Conclusions
The main aim of SE control is the consumer protection which can be achieved by:
Short-term measures
ensure that eggs are promptly refrigerated, processed, stored, handled, prepared safely and cooked adequately
Long-term measures
patient and persistent participation in risk reduction programs of verified efficacy

54. Final Concluion
Efforts to prevent or reduce Salmonella Enteritidis infections in poultry illustrate the evolution of strategies for salmonella control in general
which probably lead to control of other food-borne diseases

55. Thank you for your attention
Prof. Dr. Mohamed Refai
Department of Microbiology
Faculty of Veterinary Medicine
Cairo University