Mycoplasma hyopneumoniae control: investigating the gilt acclimation alternativeMycoplasma Research LaboratoryLuiza R. Roos, Nitipong Homwong, Dr. Maria Pieters

2015 Allen D. Leman Swine ConferenceSeptember 21th 2015

OutlineBackground information

Objective

Materials and Methods

Results and Conclusion

Discussion

❑ Small bacterium (0,3µm – 0,8µm) – lack of cell wall (Thacker, 2004)

❑ Virulence factors: adherence proteins (Zielinski et al., 1990; Zhang et al, 1995)

❑ Cilia destruction: Enzootic pneumonia and Porcine

Respiratory Disease Complex (Mare and Switzer, 1965; Goodwin et al., 1965; Dee, 1996 )

❑ Economic losses: lung lesions, daily weight gain, feed

conversion and medication (Maes et al., 2008)

Mycoplasma hyopneumoniae

Background information

❑ Direct contact and aerosol

(Fano et al., 2005; Otake et al., 2010)

Direct contact ❑ Vertical: dam to piglets

❑ Horizontal: pig to pig – weaning/finishing

infected dam to negative dam

M. hyopneumoniae transmission

Gilt acclimation❑ Definitions

❑ Controlled exposure to pathogens

❑ Disease development and resolution

❑ Prevention of vertical transmission

❑ Decreased prevalence of colonization at weaning

• Chronic infection: ~250 days (Pieters et al, 2009)

• High replacement rate for genetic improvement

• Negative supply of gilts to positive farms

• Endemically infected farms receive negative gilts

• Failure to acclimate naïve gilts to farm’s pathogens

• Vertical transmission and prevalence at weaning

M. hyopneumoniae issue

Shedding sow/gilt to negative gilt/sow

Negativegilts

First farrow

2ndAI 3rd 4th 5th

Endemic scenario

300 days 250 days(Pieters et al., 2009)

Expected gilt shedding status in the acclimation process

Weaning21 days old

AcclimationBreeding

210 days oldFarrowing

325 days old

Acclimation to M. hyopneumoniae

To develop a protocol for controlled gilt exposure to M. hyopneumoniae prior to

entering the breeding herd

Evaluating the optimum seeder-to-naïve gilt ratio in a 4-week exposure period

Objective

• Two phases

Disease development: 21 Seeders

Transmission assessment: 21 Seeders + 39 Naïve6 groups w/ 10 gilts

Experimental design

Experimental design

Group S:N ratio

1 1 in 102 2 in 103 3 in 104 4 in 105 5 in 106 6 in 10

Meyns et al., 2004

Pieters et al., 2009

Rn = 1.16

Expected outcomes

Results

Disease development

Seeders

Disease development

Detection of M. hyopneumoniae specific circulating antibodies in experimentally inoculated gilts

❑ IDEXX ELISA – Cut-off S/P>0,4 (Suspect: 0,3 < S/P < 0,4)❑ Oral fluids: qPCR positive at 14 dpi

Status/dpi, (%) 28 42 56Positive 57 100 95

Suspect 24 0 0

Negative 19 0 5

Disease developmentSeeders

M. hyopneumoniae Ct values on laryngeal swabs (qPCR)

0 14 28 42 56 dpi

Ct v

alue

s

37

Disease developmentSeeders

Disease development

qPCR Laryngeal swabs Clinical signs

Seeders

Results

Transmission assessment

M. hyopneumoniae qPCR Ct values on laryngeal swabs

0 14 28 dpe

Ct v

alue

s

37

❑ Clinical signs: not observed on naïve gilts

❑ ELISA: 1 naïve gilt seroconverted

Transmission assessment

Transmission assessment

• Gross lung lesions scoring

• Histopathology

• Immunohistochemistry (monoclonal antibody)

• Results compatible with M. hyopneumoniae infection

Lung tissue evaluated post-mortem

M. hyopneumoniae qPCR Ct values on bronchial swabs

37

Ct v

alue

s (5

6 dp

i and

28

dpe)

Naïve Seeders

Transmission assessment

qPCR Laryngeal swab + - - - - -

qPCR Bronchial swab - + - - - -

ELISA - - + - - -

IHC - - - + - -

Histopathology - - - - + -

Gross Lung lesions - - - - - +

RESULT - + - + - -

Naïve gilts were classified positive to M. hyopneumoniae infection based on the following:

Diagnostic criteria

Naïve positive Naïve negative Seeders

Transmission assessment

Transmission rate (β) and probability of infection (ψ):

• S-I model based, infected remained infectious • Binomial regression with complementary log-log

link function (exponential distribution)

• β = 1.28 per pig/week; ψ = 0.6

• Interpretation: the addition of one infected shedding gilt in a group of 10 will result in the infection of 0.77 (1.28 x 0.6) susceptible pig after a week of exposure.

• 4 weeks = 3.08

Transmission assessment

Data analysis: logistic regression (p = 0.143)

Number of Seeders in the room

Pro

babi

lity

of a

Naï

ve g

ilt to

bec

ome

posi

tive

Transmission assessment

1 2 3 4 5 6

1.00

0.75

0.50

0.25

0.00

Optimal seeder-to-naïve ratio: 6 seeders and 4 naïve (60%)In the conditions of this study, 6 seeders

in a group of 10 was successful for exposure of all gilts in a 4-week period.

➢Variability is expected

Conclusion

❑ Transmission of M. hyopneumoniae occurred

in all ratios in this investigation, however a high variability

among ratios was observed

❑ Seeder gilts appeared to be at the peak of shedding when

naive gilts were introduced (28dpi)

❑ Naïve gilts did not show clinical signs during the study period

❑ Naïve gilts may have become seeders at 14 dpe and

hierarchy and young gilts behavior may have influence the

transmission

Discussion

❑ Single replicate

❑ Implications:

❑ Effective exposure of naïve gilts to knowingly shedders –

correct proportion of seeders in the exposure group

❑ Consistent acclimation of gilts before farrow – setting the

clock to zero

❑ Challenges:

❑ Size of exposure groups may influence acclimation

❑ Different strains may have distinct infection dynamic

❑ Identifying actively shedders in the field

Discussion

AcknowledgmentsBoehringer Ingelheim Vetmedica, Inc.Swine Disease Eradication Center UMN

Dr. Maria PietersDr. Eduardo Fano

Luiza R. Roosribei028@umn.edu

Thank you!