dr. peter davies - livestock associated mrsa: tiger or pussycat?

Livestock Associated MRSA

Peter Davies BVSc, PhDUniversity of Minnesota

Menace MirageTiger or Pussycat?

“The larger the island of knowledge, the longer the shoreline of doubt”

Ralph Sockman

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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?

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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

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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

In biology, the truth is a moving target!

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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

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Proportion of clinical S. aureus isolates that are MRSA

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Holland – an issue emerges!

Very low MRSA prevalence Intensive screening and typing with sma1 PFGE ‘Search and destroy’ policy – isolation/decolonization

2004: 6mo girl screened before 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

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S. aureus subtyping methods

PFGE

MLST

SCCmec typing (I – XI)

Spa typing Ridom

egenomics

‘Livestock associated’

Sma1 Untypable

ST398 (CC398)

III, IV, V

t034, t011, t108……...

539, ………………..…..

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National survey of slaughter pigs in Holland 39% of 540 pigs positive (nasal swabs)

All isolates a ‘single clonal group’ 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?

Matthew 7:7 - “Seek and ye shall find”MRSA in market hogs (de Neeling et

al, 2006)

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Colonization of farm workers

ST398 found in 23% of pig farmers (Voss et al 2005) 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)

Matthew 7:7 - “Seek and ye shall find”

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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’

MYTHS

MISINFORM

ATION

Blood in the water!

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MRSA in animals – publication rate

0

2

4

6

8

10

12

70s 80s 90-95

96 97 98 99 00 01 02 03 04 05 06 07

Years

Cattle

Cat, Dog

Horse

Pig, Sheep

2010>50

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ST398 (livestock associated) MRSA

Generally accepted facts

Occurs in livestock in many countries Pigs, cattle, avian, horse, ..?

High MRSA prevalence in livestock farmers, veterinarians, slaughter plant workers 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?

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ST398 colonization and transmission

ST398 appears a ‘poor persistent colonizer’ in most people

Research workers (short term exposure) van Cleef et al (2011)

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’

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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

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

Geographic distribution of S. aureus causing invasive infections in Europe Grundmann et al 2010

357 laboratories serving 450 hospitals in 26 countries (2006-2007) 2,890 MSSA and MRSA isolates from invasive

infections ST 398 spa types (t011, t034, t571, t1255, and

t2383) identified on 12 occasions None harbored the mecA gene.

No cases of ST398 MRSA invasive disease

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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)

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ST398 genomic studies and virulence

> 30 known ‘virulence factors’ in S. aureus Likely underpins the diversity in clinical expression

Schijffelen (2010): full genome of ST398/t011 strain 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

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

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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

ST398 MRSA in pigs in Denmark (DANMAP 2012)

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Human MRSA infections in Denmark (DANMAP 2012)

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ST398

ST398 bacteremia cases in Denmark (DANMAP 2012

Impact low <1% of cases Only 2 MRSA

cases Trend concerning No animal contact

in bacteremia cases

Are they livestock associated?

and how?27

<1% of bacteremic S. aureus cases

The plot thickens – Part One

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Not all ST398 S. aureus are ‘livestock associated’

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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”

More of the storyDavies 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?

‘Animal independent’ ST398 clinical infections in NY city (Uhlemann et al, 2012)

Studied outpatient MRSA isolates, non-invasive MSSA cases, and bloodstream MSSA isolates

No ST398 among outpatient MRSA cases

ST398 t571: 5% of non-invasive MSSA; 2.5% of MSSA bacteremias

“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

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The plot thickens - Part Two

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ST398t011, t108

t034, t567… >30 spa

typesST5t002

ST9t899t337

Not all ‘livestock associated’ MRSA are ST398

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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 ……

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MRSA myopia

S. aureus considered ‘normal flora’ of pigs No systematic study of S. aureus in pigs

Most studies focused on MRSA ‘Tunnel vision’ ‘Gotcha’ epidemiology (and journalism)

Need to understand S. aureus epidemiology to understand LA-MRSA

MRSA

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

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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

Pilot study of S. aureus ecology in pigs

2 farms: conventional (convenience) 2 cohorts per farm Sows – suckling – nursery – finishing

Nose – tonsil – skin (axilla) – feces – (vagina) S. aureus prevalent in all anatomical sites

Nose, tonsil and skin highest (59 – 66%) No MRSA detected

Multiple spa types on both farms Multiple spa types within pigs

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Spa types by sample source

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Diversity of S. aureus on pig farms

All MSSA 15 spa types detected >95% of isolates ST398,

ST9 or ST5 Complex and dynamic

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 months40

Influence of time since pig contact

Prevalence higher if sampled < 2days after last pig contact

Prevalence not affected by delay in sample processing

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Prevalence of MRSA/MSSA by month

Prevalence similar over time MSSA: 54% - 84% MRSA: 4% - 11%

Verkade et al (2013) MSSA: 72% MRSA: 44%

Suggests less MRSA in USA

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S. aureus spa types in veterinarians

Striking similarity to pig data

3 spa types > 50% Vast majority are

ST398 ST9 ST5

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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 isolates44

S. aureus colonization patterns

Some consistently positive with same spa type ST398 (7): MRSA and MSSA ST5 (3): MSSA only ST9 (2): MSSA only

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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

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Concepts of interspecies transmission

Humanflora

Swineflora

Complete host adaptation

No interspecies transmission

Humanflora

Swineflora

No host adaptation

Equal propensity to colonize both species

Marked host adaptation

Rare interspecies transmisssion

Some host adaptation

Common interspecies transmisssion

LA-MRSA: models of host adaptation

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ST398

LA-MRSA: models of host adaptation

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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

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“The larger the island of knowledge, the longer the

shoreline of doubt”

Jisun Sun My Yang Leticia Linhares Srinand Sreevatsan

Swine faculty and graduate students

NPB UMASH

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THANK YOU!

“The larger the island of knowledge, the longer the

shoreline of doubt”52

HUGE THANK YOUTO TEAM NOSTRIL!