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Modelling the within-herd transmission of Mycoplasma hyopneumoniae in closed pig herds

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ABSTRACT

Background: A discrete time, stochastic, compartmental model simulating the spread of Mycoplasma hyopneumoniae within a batch of industrially raised pigs was developed to understand infection dynamics and to assess the impact of a range of husbandry practices. A ‘disease severity’ index was calculated based on the ratio between the cumulative numbers of acutely and chronically diseased and infectious pigs per day in each age category, divided by the length of time that pigs spent in this age category. This is equal to the number of pigs per day, either acutely or chronically infectious and diseased, divided by the number of all pigs per all days in the model. The impact of risk and protective factors at batch level was examined by adjusting ‘acclimatisation of gilts’, ‘length of suckling period’, ‘vaccination of suckling pigs against M. hyopneumoniae’, ‘contact between fattening pigs of different age during restocking of compartments’ and ‘co-infections in fattening pigs’.

Results: The highest ‘disease severity’ was predicted, when gilts do not have contact with live animals during their acclimatisation, suckling period is 28 days, no vaccine is applied, fatteners have contact with pigs of other ages and are suffering from co-infections. Pigs in this scenario become diseased/infectious for 26.1 % of their lifetime. Logistic regression showed that vaccination of suckling pigs was influential for ‘disease severity’ in growers and finishers, but not in suckling and nursery pigs. Lack of contact between gilts and other live pigs during the acclimatisation significantly influenced the ‘disease severity’ in suckling pigs but had less impact in growing and finishing pigs. The length of the suckling period equally affected the severity of the disease in all age groups with the strongest association in nursery pigs. The contact between fatteners of different groups influenced the course of infection among finishers, but not among other pigs. Finally, presence of co-infections was relevant in growers and finishers, but not in younger pigs.

Conclusion: The developed model allows comparison of different prevention programmes and strategies for controlling transmission of M. hyopneumoniae.

Electronic supplementary material: The online version of this article (doi:10.1186/s40813-016-0026-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus

Evaluation of the sensitivity of the outcome variable (disease severity = number of pigs per day either acutely or chronically infectious and diseased divided by the number of all pigs per all days in the model) to variation in the transition parameter ρ, when simultaneously changed for all age groups by multiplication with a factor between 0.2 and 2
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Fig5: Evaluation of the sensitivity of the outcome variable (disease severity = number of pigs per day either acutely or chronically infectious and diseased divided by the number of all pigs per all days in the model) to variation in the transition parameter ρ, when simultaneously changed for all age groups by multiplication with a factor between 0.2 and 2

Mentions: The sensitivity of the model to variation in the transition parameters β and ρ was assessed. The overall outcome “disease severity” was strongly influenced by the level of β, when simultaneously changed for all age groups by multiplying with values between 0.2 and 2 (Fig. 4), but not influenced by ρ, when simultaneously changed for all groups with factors ranging from 0.2 to 2 (Fig. 5).Fig. 4


Modelling the within-herd transmission of Mycoplasma hyopneumoniae in closed pig herds
Evaluation of the sensitivity of the outcome variable (disease severity = number of pigs per day either acutely or chronically infectious and diseased divided by the number of all pigs per all days in the model) to variation in the transition parameter ρ, when simultaneously changed for all age groups by multiplication with a factor between 0.2 and 2
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5382396&req=5

Fig5: Evaluation of the sensitivity of the outcome variable (disease severity = number of pigs per day either acutely or chronically infectious and diseased divided by the number of all pigs per all days in the model) to variation in the transition parameter ρ, when simultaneously changed for all age groups by multiplication with a factor between 0.2 and 2
Mentions: The sensitivity of the model to variation in the transition parameters β and ρ was assessed. The overall outcome “disease severity” was strongly influenced by the level of β, when simultaneously changed for all age groups by multiplying with values between 0.2 and 2 (Fig. 4), but not influenced by ρ, when simultaneously changed for all groups with factors ranging from 0.2 to 2 (Fig. 5).Fig. 4

View Article: PubMed Central - PubMed

ABSTRACT

Background: A discrete time, stochastic, compartmental model simulating the spread of Mycoplasma hyopneumoniae within a batch of industrially raised pigs was developed to understand infection dynamics and to assess the impact of a range of husbandry practices. A ‘disease severity’ index was calculated based on the ratio between the cumulative numbers of acutely and chronically diseased and infectious pigs per day in each age category, divided by the length of time that pigs spent in this age category. This is equal to the number of pigs per day, either acutely or chronically infectious and diseased, divided by the number of all pigs per all days in the model. The impact of risk and protective factors at batch level was examined by adjusting ‘acclimatisation of gilts’, ‘length of suckling period’, ‘vaccination of suckling pigs against M. hyopneumoniae’, ‘contact between fattening pigs of different age during restocking of compartments’ and ‘co-infections in fattening pigs’.

Results: The highest ‘disease severity’ was predicted, when gilts do not have contact with live animals during their acclimatisation, suckling period is 28 days, no vaccine is applied, fatteners have contact with pigs of other ages and are suffering from co-infections. Pigs in this scenario become diseased/infectious for 26.1 % of their lifetime. Logistic regression showed that vaccination of suckling pigs was influential for ‘disease severity’ in growers and finishers, but not in suckling and nursery pigs. Lack of contact between gilts and other live pigs during the acclimatisation significantly influenced the ‘disease severity’ in suckling pigs but had less impact in growing and finishing pigs. The length of the suckling period equally affected the severity of the disease in all age groups with the strongest association in nursery pigs. The contact between fatteners of different groups influenced the course of infection among finishers, but not among other pigs. Finally, presence of co-infections was relevant in growers and finishers, but not in younger pigs.

Conclusion: The developed model allows comparison of different prevention programmes and strategies for controlling transmission of M. hyopneumoniae.

Electronic supplementary material: The online version of this article (doi:10.1186/s40813-016-0026-1) contains supplementary material, which is available to authorized users.

No MeSH data available.


Related in: MedlinePlus