Pathogens in the Twilight Zone: Update on emerging disease issues with implications for the pork industry - Dr. Peter Davies, University of Minnesota, from the 2011 The Allen D. Leman Swine Conference, September 17-20, 2011, St Paul, MN, USA.

1. PATHOGENS
iN
Peter Davies BVSc,
PhD
University of Minnesota

2. Emerging diseases in intensive livestock
production
 Media
 Shoot first – ask questions later (maybe)
 Blogosphere
 Just shoot and ask no questions
 Move on to next ‘crisis’
 Guilty until proven innocent
 Habitual overstatement of public health risks
2

3. Diseases in the twilight zone
 BSE
 Model prediction up to 50,000 human deaths from
variant CJD
 Lower limit of 5,000
 Global tally after 15 years is around 200.
 H5N1 avian influenza
 Guesstimates up to 150 million circulated
 564 Laboratory confirmed cases (August 9, 2011)
 330 fatalities.
3

4. Discovery vs. emergence
 Conventional microbiology reveals the tip of the
iceberg
 Today have very powerful diagnostic tools
 Closely related hosts (mammals, homeotherms) likely
to be colonized by ‘closely related’ organisms
 Discovery involves much uncertainty
 Interspecies transmission
 Virulence in various species
4

5. Diseases in the twilight zone
 Influenza viruses
 MRSA
 Clostridium difficile
 Noroviruses
 Sapoviruses
 Intestinal spirochetes
 ….
5

6. Recent Emerging Disease Issues in Swine
What Where When* Swine Health* Human Media
Health* hype*
Clostridium difficile (pigs) Global 1986 +/- ++(?) ++
PRRS Global 1987 +++++ - -
Salmonella typhimurium DT104 Global 1993 +/- ++ ++++
PCV2 Global 1996 +++++ - -
Hepatitis E infection USA/global 1995 - +/- +/-
Menangle virus Australia 1997 + +/- -
Nipah virus Malaysia 1998 ++ ++ ++
Bungowannah virus Australia 2003 + - -
MRSA ST398 EU/global 2004 - +/- +++++
virulent Streptococcus suis type 2 China 2005 ? ++ ++
H1N1 pandemic influenza Global 2009 + ++++(?) +++++

7. Recent Emerging Disease Issues in Swine
W Where When* Swine Health* Human Media
Health* hype*
Clostridium difficile (pigs) Global 1986 +/- ++(?) ++
PRRS Global 1987 +++++ - -
Salmonella typhimurium DT104 Global 1993 +/- ++ ++++
PCV2 Global 1996 +++++ - -
Hepatitis E infection USA/global 1995 - +/- +/-
Menangle virus Australia 1997 + +/- -
Nipah virus Malaysia 1998 ++ ++ ++
Bungowannah virus Australia 2003 + - -
MRSA ST398 EU/global 2004 - +/- +++++
virulent Streptococcus suis type 2 China 2005 ? ++ ++
H1N1 pandemic influenza Global 2009 + ++++(?) +++++

8. S. aureus and C. difficile
 Common commensals found in healthy people and animals
 Opportunistic pathogens increasing in incidence and clinical
severity
 Recognized human pathogens long before animal reservoirs
thought of epidemiological significance.
 Important nosocomial agents - hospital infections principal
concern
 Community acquired infections more important in recent
years.
 Animal colonization raises risk of livestock as sources of
community acquired infections.
 Both isolated from pork

9. MRSA in animals – publication rate
12
Cattle
10 Pig, Sheep
Cat, Dog
8
Horse
N 6
4
2
0
70s 80s 90- 96 97 98 99 00 01 02 03 04 05 06 07
95
2010: > 50 papers
Years
9

10. PFGE with the SmaI enzyme
Soge et al. J. Antimicrob. Chemother. 2009;64:1148-1155
MRSA isolated from
US West Coast public marine beaches

11. Holland – an issue emerges!
 Very low MRSA prevalence
 ‘Search and destroy’ policy
 Intensive screening and typing with sma1 PFGE
 2004: 6mo girl screened before for surgery for a
congenital heart defect
 MRSA isolate not typable with Sma1 PFGE
 2 other screening isolates not typable by Sma1 PFGE
 All 3 ‘cases’ epidemiologically linked to pigs
 Studies of MRSA prevalence in pigs, farmers and pork
11

12. S. aureus subtyping
‘Livestock associated’
 PFGE Sma1 Untypable
 MLST ST398 (CC398)
 SCCmec typing (I – VIII) III, IV, V
 Spa typing
 Ridom t034, t011, t108……...
 egenomics 539, ………………..…..
12

13. MRSA in market hogs (de Neeling et al,
2006)
 National survey of slaughter pigs in Holland
 39% of 540 pigs positive (nasal swabs)
 44 of 54 (81%) of farms positive
 All isolates a ‘single clonal group’
 Nontypable (NT) by sma1 PFGE
 MLST: ST 398
 3 closely related spa types predominant (t011, t108, t1254,…)
 Panton-Valentine Leucocidin (PVL) toxin negative
 Uniformly resistant to tetracycline
 Use of tetracyclines may be selecting for MRSA?
13

14. Colonization of farm workers
 ST398 also isolated from pig farmers (Voss et al 2005)
 23% of farmers positive on nasal swab
 760x general population prevalence
 Dutch health authorities changed MRSA screening
procedures
 People exposed to pigs and calves considered high risk
 Isolated and screened before hospital admission
 ST398 MRSA isolated from pork (van Loo et al.,
2007)
14

15. EFSA farm prevalence study (dust samples)

16. MRSA spa types in swine barn dust (EFSA, 2010)
Predominant in North America
*

17. ST398 MRSA
Not just a pig problem!
 Pigs – widespread (but not China, UK, Ireland, Japan)
 ST9
 Calves – Holland
 Horses – Austria, Belgium, France, Germany, Holland,
Canada
 Chickens – Belgium
 Dogs – Austria, Canada
 Lack of host specifity may indicate zoonotic risk!
17

18. MRSA in pigs in Ontario
(Khanna et al, 2007)
 Convenience sample of 20 Ontario herds
 25% (71/285) of pigs positive
 20% (5 of 25) farmers positive
 Predominant (75%) spa types similar to ST398
Dutch isolates
 Spa type t034 predominant
18

19. Livestock associated MRSA in USA
 Two farms in Iowa (Smith 2007)
 One positive – 70% of pigs (ST398)
 Slaughter pigs (Davies et al, 2009)
 539 pigs from 45 farms
 25% of pigs MRSA positive
 Diverse spa types - t034 predominant
19

20. Prevalence and characterization of MRSA in
pigs and farm workers on conventional and
antibiotic free swine farms in the USA
 Collaborative Study – National Pork Board
 54 farms across 3 centers (MN, IA-IL, OH_NC)
 18 farms per state
 9 conventional, 9 antibiotic free
 24 pigs per farm; any human volunteers
 Difficulties in finding farms
 45 farms enrolled (24 conv., 21 ABF)
 1084 pigs; 154 people
20

21. MRSA on conventional and ABF swine farms
 MRSA detected in pigs on 4 farms
 All 4 conventional farms in IA-IL
 All pigs negative in ABF farms
 45 (4.2%) of 1084 pigs positive
 29 (18.8%) of 154 people positive
 24 of 40 (60%) people positive on two farms with
highest pig prevalence
21

22. MRSA on conventional and ABF swine farms
32 spa type 539/t034
2 spa type 2/NT
2 other ‘LA’ (t011; t571

23. MRSA in farm workers on conventional and
ABF swine farms
17 spa type 539/t034
5 spa type 2/NT Not LA type 539/t034
1 other
23

24. MSSA isolates in MN
 98 isolates of MSSA characterized in MN
 92 from pigs, 6 from people
 Pig samples clustered on 4 farms (3 conv., 1 ABF)
 65 (71%) of pigs isolates were spa type 539/t034
 1 isolate from human
24

25. Summary
 MRSA detected in market hogs and
occupationally exposed people
 Spa type 539/t034 predominant
 Spa type 2/tunknown also detected in all studies
 Similar to Canada
 Lack of knowledge of S. aureus epidemiology in
pigs
 Spa type 539/t034 in MN
25

26. Exposure assessment – ST398
 High risk of exposure in groups with direct
livestock contact
 Major concerns about occupational risk
 Some exposure risk to direct family members
 Currently no indication of significant community
exposure
26

27. Risk assessment
 Consequences of occupational exposure
 Colonization vs. Infection
 What is the burden of disease?
 Virulence
 Transmission
 Diversity within ST398 lineage
 Animal vs. human isolates
27

28. Questions?
28

29. Current and future studies
 Epidemiology of S. aureus in multiple site pig
farms (NPB)
 MRSA colonization and infection in swine
veterinarians (NIOSH)
 70 ‘volunteers’
 Study duration of colonization over 18 months
 Prospective study of infection risk
29

30. Occupational exposure
 Consistent observations that people with
occupational exposure to animal species more likely
to be colonized with MRSA
 As yet minimal data indicating increased risk of infection
 Interspecies transmission of S. aureus
 Frequency, Quantity, Duration
 Burden of disease
 Primarily occupational?
30

31. 45
40 Clinical cases = 122
35 Invasive = 27
30
25
Burden of disease 20
15
from ST398 MRSA
10
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 Many reports don’t distinguish infection from
colonization
 Small number of serious infections
 Retrospective study of human isolates in Canada
 5 ST398 out of 3,687 (4 skin/soft tissue infections)
 CDC has examined >12,000 isolates
 ST398 had not identified in a human clinical case
 Current evidence suggests low pathogenicity?
31

32. Lethal pneumonia caused by an ST398
S. aureus strain Rasigade et al (2010)
 Observations
 Fatal necrotizing pneumonia in a previously healthy 14yo girl
 ST 398 - spa type t571
 PVL positive
 Tetracycline susceptible
 Methicillin susceptible (MSSA)
 No livestock contact
 Inference
 “spread of S. aureus ST398 among livestock is a matter of
increasing concern because strains of this sequence type were
able to acquire PVL genes”
32

33. No pigs
No MRSA
33

34. “One Health” means
more than one inference
 ‘.. concern because strains ST398 strains were
able to acquire PVL genes’
 But….
 Livestock strains almost uniformly tetracycline resistant
and PVL negative
 Spa type t571 uncommon in animal isolates
 Could adaptation of ST398 to livestock hosts
include loss of human virulence factors
34

35. The rest of the story
Davies et al, EID June 2011
 t571 ST398 MSSA detected in 9 families from the Dominican
Republic living in Manhattan
 with no apparent contact with livestock (Bhat et al., 2007)
 t571 the sole MSSA spa type in Dutch study of ST398 clinical
isolates, including 3 independent cases of nosocomial
bacteremia
 with no apparent livestock contact (van Belkum et al., 2008)
 t571 the predominant (11%) MSSA type at a Beijing hospital
 Livestock contact unlikely (Chen et al 2010)
35

36. Emergence of unusual bloodstream infections associated
with pig-borne-like Staphylococcus aureus ST398 in
France. (van de Marquet et al., 2011)
 Study of t571 MSSA strains from cases of bloodstream
infections in France
 The 30 isolates differed from pig-borne strains
 Isolates shared similarities with strains from humans in
China and virulent USA300 strains
36

37. The rest of the story……
 Understanding LA-MRSA is embryonic
 Naïve perceptions of complex epidemiology
 All MRSA found in livestock are ST398
 Livestock are the only reservoirs of ST398
 ST398 isolates of diverse genotype and geographic origin
may also be epidemiologically distinct
 Requires systematic investigation of S. aureus
epidemiology in animals and humans.
37

38. Community dissemination of MRSA ST398
Cuny et al (2009)
 Study of German farming community where
MRSA ST398 prevalent on pig farms
 Nasal swabs from
 Pig farmers and family members
 Swine vets and family members
 462 pupils (10 to 16 yo) in villages in the high density
pig farming area
38

39. Nasal colonization with ST 398
Cuny et al (2009)
Group N Pct Pos
Pig farmers 113 86% Prevalence
Ratio= 20
Farmer family members 116 4.3%
Swine Veterinarians 18 45% Prevalence
Ratio= 5
Vet family members 44 9%
Schoolchildren* 462 0.007% (3)
*All 3 positive children lived on pig farms 39

40. Communities in pig dense areas in Holland
(van Cleef 2010)
 Mailing in 3 selected municipalities in the Netherlands
where livestock MRSA prevalent
 Adults complete questionnaire and nose swab (n = 583)
 One of 534 persons without livestock-contact positive (0.2%)
 13 of 49 of farm residents/workers positive (26.5%)
 Conclusions:
 High prevalence of livestock-associated MRSA in people with
direct contact with farm animals.
 Not spread into the wider community
40

41. Exposure assessment – ST398
 High risk of exposure in groups with direct
livestock contact
 Major concerns about occupational risk
 Some exposure risk to direct family members
 Currently no indication of significant community
exposure
41

42. Risk assessment
 Consequences of occupational exposure
 Colonization vs. Infection
 What is the burden of disease?
 Virulence
 Transmission
42

43. Transmission of ST398 MRSA among people
 Studies of transmission in Dutch hospitals (Bootsma, 2010)
 ST398 is 5.9 times less transmissible than non-ST398 MRSA
in Dutch hospitals’
 ‘Spreading capacity per admission insufficient to lead to an
epidemic’
 ‘Nosocomial transmission of ST398 MRSA is 72% less
likely than non-ST398 MRSA strains’
Wassenberg (2011)
43

44. Distribution of LA MRSA and other MRSA clinical
isolates in Europe (van Cleef et al., 2011)
44

45. Diversity of genome of human and LA ST398
MRSA strains (Hallin et al., 2011)
 ‘LA-MRSA strains represent a homogenous
lineage distinct from co-local HA- and CA-MRSA
strains
 characterized by a lack of human-associated virulence
and adhesion determinants
 Absence of detectable enterotoxin gene among
ST398 LA-MRSA strains from a wide host range
is reassuring regarding their foodborne
pathogenic potential.’
45

46. Duration of colonization
 Research workers (short term exposure) van Cleef et al (2011)
 33 of 199 exposures led to positive culture on farm
 Only 3 of 33 retested positive after 24 hours
 Evidence suggests most short term exposure leads to short
term ‘colonization’
 Veal farmers in Holland Graveland et al (2011)
 Rapid decline in prevalence during absence of animal contact
 LA-MRSA poor persistent colonizers in most humans.
46