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. [email protected]
Thank you!