Livestock Associated MRSA: Tiger or Pussycat? - Dr. Peter Davies, Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, from the 2013 Allen D. Leman Swine Conference, September 14-17, 2013, St. Paul, Minnesota, USA. More presentations at http://www.swinecast.com/2013-leman-swine-conference-material

1. Livestock Associated MRSA
Menace or Pussycat?
Tiger
Mirage
Peter Davies BVSc, PhD
University of Minnesota

2. “The larger the island of knowledge,
longer the shoreline of doubt”
the
Ralph Sockman
2

3. Outline




What are LA-MRSA?
What has been their impact on public health?
The plot thickens!
Where did they come from?


Recent research in pigs and swine veterinarians
What are LA-MRSA?
3

4. Staphylococcus
aureus

Common inhabitant of warm-blooded animals


‘Normal flora’ (20-30% of people)
Common opportunistic pathogen in humans





Insignificant to fatal
Broad clinical manifestations
Skin and soft tissue infections
Invasive: pneumonia, septicemia and death
Bacteremia: 80% fatality rate prior to antibiotic era

5. Methicillin resistant S. aureus
(MRSA)

From 1961 emerged rapidly to be a major
problem of chronically ill in health care institutions



Resistance linked to antimicrobial use in hospitals
Hospital Associated MRSA (HA-MRSA)
‘The truth’ prior to 1995

Not a concern for broader community

No epidemiologic role of animal reservoirs
5

6. In biology, the truth is a moving target!
6

7. MRSA: ‘Changing paradigms’

1990s : global emergence of community
associated infections (CA-MRSA)





Predominantly SSTI
CA-MRSA ‘clones’ distinct from ‘hospital’ strains
‘Quantum change in the epidemiology of MRSA’
2004…: detection/emergence of LA-MRSA
Novel lineage not reported previously among HA-MRSA
or CA-MRSA
7

8. Proportion of clinical S. aureus isolates
that are MRSA
8

9. Holland – an issue emerges!

Very low MRSA prevalence



2004: 6mo girl screened before surgery for a congenital
heart defect


Intensive screening and typing with sma1 PFGE
‘Search and destroy’ policy – isolation/decolonization
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
9

10. S. aureus subtyping methods
‘Livestock associated’

PFGE
Sma1 Untypable

MLST
ST398 (CC398)

SCCmec typing (I – XI)

Spa typing
III, IV, V

Ridom
t034, t011, t108……...

egenomics
539, ………………..…..
10

11. Matthew 7:7 - “Seek and ye shall find”
MRSA in market hogs (de Neeling et al,
2006)

National survey of slaughter pigs in Holland


All isolates a ‘single clonal group’




39% of 540 pigs positive (nasal swabs)
Nontypable (NT) by sma1 PFGE
MLST: ST 398
3 closely related spa types predominant (t011, t108,
t1254,…)
Uniformly resistant to tetracycline

Use of tetracyclines may be selecting for MRSA?
11

12. Matthew 7:7 - “Seek and ye shall find”
Colonization of farm workers

ST398 found in 23% of pig farmers


760x general population prevalence
Dutch health authorities changed MRSA screening
procedures



(Voss et al 2005)
People exposed to pigs and calves considered high risk
Isolated and screened before hospital admission
ST398 MRSA isolated from pork
2007)
(van Loo et al.,
12

13. MRSA in livestock:
An epidemic waiting to happen?
(Wulf and Voss, 2008)

Not just a “Dutch” problem

May become an important source of CA-MRSA

Epidemiology different to ‘classic MRSA strains’

Inter-human spread is possible

Probably ‘just a matter of time until an outbreak’
13

14. Blood in the water!
M
IS
IN
F
T
Y
M
O
RM
S
H
AT
IO
N

15. MRSA in animals – publication rate
12
10
Cattle
Pig, Sheep
Cat, Dog
8
Horse
N 6
4
2
0
70s 80s 9095
96
97
98
99
00
01
02
03
04
05
06
07
2010
>50
Years
15

16. ST398 (livestock associated) MRSA
Generally accepted facts

Occurs in livestock in many countries


High MRSA prevalence in livestock farmers,
veterinarians, slaughter plant workers



Pigs, cattle, avian, horse, ..?
20-50% in farmers (vs. ~ 0.5 - 2% in population)
Mainly LA-MRSA
Lingering questions


Are they truly colonized?
What is the consequent risk to health?
16

17. ST398 colonization and transmission

ST398 appears a ‘poor persistent colonizer’ in most people

van Cleef et al (2011)


Research workers (short term exposure)
Veal farmers in Holland
Graveland et al (2011)
ST398 less transmissible than non-ST398 MRSA

4-6x less transmissible in Dutch hospitals’
(Bootsma, 2010)
Wassenberg (2011)

‘insufficient to lead to an epidemic’
17

18. Burden of disease from ST398 MRSA
(review funded by National Pork Board)


89 papers/reports of ST398 associated clinical cases
through 2012
Data recorded





Numbers of isolates from screening vs. clinical infections
Clinical presentations
 bacteremia; pneumonia; skin or soft tissue infection, etc.
Number of cases with invasive infections (not SSTI)
Fatalities
History of animal contact
18

19. Disease burden from ST398 S. aureus
Cumulative data from 89 publications (n = 2,553 cases)


2,056 screening isolates
497 (19.5%) clinical




203 unspecified
125 ‘invasive’
5 fatal
Invasive disease


Many cases MSSA not MRSA
Livestock exposure very inconsistent
 Yes:10%
No:26%
Unknown: 64%
19

20. Geographic distribution of S. aureus
causing invasive infections in
Europe
Grundmann et al 2010

357 laboratories serving 450 hospitals in 26
countries (2006-2007)


ST 398 spa types (t011, t034, t571, t1255, and t2383)
identified on 12 occasions


2,890 MSSA and MRSA isolates from invasive infections
None harbored the mecA gene.
No cases of ST398 MRSA invasive disease

21. Burden of disease from ST398 MRSA
in North America

Retrospective study of human isolates in Canada



5 ST398 out of 3,687 MRSA isolates
4 skin/soft tissue infections
(Golding et al 2010)
CDC has examined >12,000 MRSA isolates in USA


ST398 not identified in a human clinical case (June 2011)
MN DOH – no ST398 among 7,000 isolates tested (2012)
21

22. ST398 genomic studies and virulence

> 30 known ‘virulence factors’ in S. aureus


Schijffelen (2010): full genome of ST398/t011 strain



Likely underpins the diversity in clinical expression
Just 2 virulence factors found
‘ lack of virulence factors may explain the infrequency of
serious clinical infections with ST398’
Argudin (2011): 100 ‘non-human’ ST398

Many resistance determinants but few virulence factors
22

23. Fatal ST398 infections


5 fatal cases reported
4 MSSA not MRSA



Spa type t571 (not common in swine)
No significant livestock contact
One MRSA with livestock contact


Spa type t011 (common in swine)
85yo man with lung carcinoma and COPD
23

24. Public health risk of ST398 MRSA


Elevated occupational risk of infection not well
documented
Current evidence suggests low transmissibliity






No reports of outbreaks
Current evidence suggests low virulence?
Significantly less invasive disease in Europe
Serious infections uncommon
General lack of virulence determinants
Few fatalities
24

25. ST398 MRSA in pigs in
Denmark (DANMAP 2012)
25

26. Human MRSA
infections in Denmark
(DANMAP 2012)
ST398
26

27. ST398 bacteremia cases
in Denmark (DANMAP 2012
<1% of bacteremic
S. aureus cases

Impact low





<1% of cases
Only 2 MRSA
cases
Trend concerning
No animal contact
in bacteremia
cases
Are they livestock
associated?

and how?
27

28. The plot thickens – Part One
Not all ST398 S. aureus are ‘livestock associated’
28

29. 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
Panton-Valentine Leukocidin (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”
29

30. More of the story
Davies P.R. et al, EID June 2011

t571 ST398 MSSA


Detected in 9 families from the Dominican Republic living in
Manhattan, NY
(Bhat et al., 2007)
Predominant MSSA type at Beijing hospital
(Chen et al 2010, Zhao et al 2012)




Case report from Colombia
(Jimenez et al 2011)
All with no apparent livestock contact
30% of ST398 bacteremia cases in 89 publications reviewed
were t571 MSSA
Some ST398 variants could be independent of livestock?

31. ‘Animal independent’ ST398 clinical
infections in NY city (Uhlemann et al, 2012)

Studied outpatient MRSA isolates, non-invasive MSSA
cases, and bloodstream MSSA isolates


ST398 t571: 5% of non-invasive MSSA; 2.5% of MSSA
bacteremias



No ST398 among outpatient MRSA cases
“Clinically important clone that differs significantly at the genome
level from its livestock associated counterpart”
Only reported ST398 infections in USA are t571 MSSA
without known livestock contact
Distinct ‘pig clade’ and ‘human clade’ of ST398 t571
31

32. The plot thickens - Part Two
ST398
ST5
t011, t108
t034, t567…
>30 spa types
t002
ST9
t899
t337
Not all ‘livestock associated’ MRSA are ST398
32

33. LA-MRSA: not just ST398 in pigs







ST9 (t899, t337) - Asia, Italy, Spain, USA
ST5 (t002) - North America (US, Canada)
ST1 - Denmark, USA, Switzerland, Italy
ST72 - USA, Korea
ST97 – Italy, Spain
ST49 – Switzerland
……
33

34. MRSA myopia

S. aureus considered ‘normal flora’ of pigs


No systematic study of S. aureus in pigs
Most studies focused on MRSA



MRSA
‘Tunnel vision’
‘Gotcha’ epidemiology (and journalism)
Need to understand S. aureus epidemiology to
understand LA-MRSA
34

35. Studies of S. aureus


Pilot study of ecology of S. aureus on swine
farms (NPB)
Longitudinal study of S. aureus and MRSA
colonization and infection in swine veterinarians


NIOSH (UMASH center)
68 swine veterinarians
35

36. Pilot study of of S. aureus in swine

Detailed longitudinal study of two multiple-site
systems in Minnesota



Anatomical site
Age/stage of production
Prevalence and diversity of S. aureus in pigs,
people, environmental, air samples


Spa typing
MSLT of selected isolates

37. Pilot study of S. aureus ecology in
pigs

2 farms: conventional (convenience)




Nose – tonsil – skin (axilla) – feces – (vagina)
S. aureus prevalent in all anatomical sites



2 cohorts per farm
Sows – suckling – nursery – finishing
Nose, tonsil and skin highest (59 – 66%)
No MRSA detected
Multiple spa types on both farms

Multiple spa types within pigs
37

38. Spa types by sample source
38

39. Diversity of S. aureus on pig farms




All MSSA
15 spa types detected
>95% of isolates ST398, ST9
or ST5
Complex and dynamic

40. S. aureus colonization and
infection in swine veterinarians


18 month longitudinal study 2012-2014
Nasal swabs collected monthly from 68 swine
vets





Self collected and mailed
S. aureus and MRSA
Characterized by MLST and spa typing
Survey of pig contact and clinical infections
>95% compliance for swabs and surveys over 13
months
40

41. Influence of time since pig contact


Prevalence higher if sampled
< 2days after last pig contact
Prevalence not affected by
delay in sample processing
41

42. Prevalence of MRSA/MSSA by month

Prevalence similar over
time



Verkade et al (2013)



MSSA: 54% - 84%
MRSA: 4% - 11%
MSSA: 72%
MRSA: 44%
Suggests less MRSA in
USA
42

43. S. aureus spa types in veterinarians



Striking similarity to pig data
3 spa types > 50%
Vast majority are
 ST398
 ST9
 ST5
43

44. S. aureus colonization patterns (x =MRSA)



Most positive for S. aureus at some time
Diversity among isolates within veterinarians over time
Spa types correspond with predominant pig isolates
44

45. S. aureus colonization patterns

Some consistently positive with same spa type
 ST398 (7): MRSA and MSSA
 ST5 (3): MSSA only
 ST9 (2): MSSA only
45

46. Summary – preliminary results

Patterns of colonization indicate





21% (14/67) of veterinarians are truly colonized
Transient contamination is more common
Positivity associated with recent pig contact
The veterinary nose: surveillance tool or
selective culture medium?
MSSA variants of common LA-MRSA types globally are
common in US pigs and swine veterinarians


Suggests prolonged association with swine
Host adaptation and virulence
46

47. Concepts of interspecies transmission
Complete host adaptation
No host adaptation
Human
flora
Human
flora
Swine
flora
No interspecies transmission
Some host adaptation
Common interspecies transmisssion
Swine
flora
Equal propensity to
colonize both species
Marked host adaptation
Rare interspecies transmisssion

48. LA-MRSA: models of host adaptation
ST398
48

49. LA-MRSA: models of host
adaptation
49

50. LA-MRSA: models of host adaptation

Diverse S. aureus flora
adapted to swine




ST398, ST5, ST9,…….
Likely similar in other
animals
Likely varied propensity for
interspecies transmission
Likely varied virulence in
other species
50

51. THANK YOU!




Jisun Sun
My Yang
Leticia Linhares
Srinand Sreevatsan



Swine faculty and
graduate students
NPB
UMASH
“The larger the island of knowledge,
the longer the shoreline of doubt”
51

52. HUGE
THANK
YOU
TO TEAM
NOSTRIL!island of knowledge,
“The larger the
the longer the shoreline of doubt”
52