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

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

Box plots describing the severity of M. hyopneumoniae infection (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) in a batch of 293 pigs, when three protective factors are all absent (Vac[−], Acc[−], Suc[−]) and two risk factors are both present (Con[+], Inf[+]). Values represent results of 1,000 iterations of the stochastic compartment model. The disease severity is a ratio between the number of pigs per day being infectious divided and the number all pigs per day in the model
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Fig3: Box plots describing the severity of M. hyopneumoniae infection (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) in a batch of 293 pigs, when three protective factors are all absent (Vac[−], Acc[−], Suc[−]) and two risk factors are both present (Con[+], Inf[+]). Values represent results of 1,000 iterations of the stochastic compartment model. The disease severity is a ratio between the number of pigs per day being infectious divided and the number all pigs per day in the model

Mentions: The outcomes of various scenarios were plotted as line charts and compared with recently published data on the prevalence of M. hyopneumoniae infection in pigs at different age. When all protective factors were present ([P] = Positive; Vac[P], Acc[P], Suc[P]) and risk factors were absent ([N] = Negative; Con[N], Inf[N]), the percentage of finishing pigs susceptible to M. hyopneumoniae at the end of the fattening period was >85 % on average and the percentage of pigs, which had been infected during their growth period was <10 % (mean; evidenced by details in Table 2 and ‘Additional file 1’). Mortality that can be observed in this scenario is attributed to ‘baseline mortality’, which is approx. 15 to 20 % from birth to slaughter [23]. The observation of less than 10 % potentially seropositive pigs (due to exposure to M. hyopneumoniae followed by latency until seroconversion = Ia + Ic + R) and the absence of biologically significant within-herd transmission in most simulations are consistent with findings of a recent study [26]. In the latter, no spread of the pathogen and no disease could be confirmed in well-managed pig herds. In such scenarios, all animals should be seronegative at the end of the fattening period, because of waning of maternally derived antibodies, waning of antibodies after vaccination and the absence of exposure to the pathogen. In contrast, nearly all susceptible pigs became exposed and subsequently infectious (Fig. 2), when all protective factors were absent (Vac[N], Acc[N], Suc[N]) and all risk factors were present (Con[P], Inf[P]). The ‘disease severity’ in this ‘high risk’ scenario (Fig. 3) was well in accordance with findings in the field, where herds with similar risk and protective factors show comparable results in terms of pathogen transmission [26]. In contrast, the ‘disease severity’ was negligible in the ‘low risk’ scenario. Details can be studied in a graph provided as ‘Additional file 2’.Table 2


Modelling the within-herd transmission of Mycoplasma hyopneumoniae in closed pig herds
Box plots describing the severity of M. hyopneumoniae infection (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) in a batch of 293 pigs, when three protective factors are all absent (Vac[−], Acc[−], Suc[−]) and two risk factors are both present (Con[+], Inf[+]). Values represent results of 1,000 iterations of the stochastic compartment model. The disease severity is a ratio between the number of pigs per day being infectious divided and the number all pigs per day in the model
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig3: Box plots describing the severity of M. hyopneumoniae infection (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) in a batch of 293 pigs, when three protective factors are all absent (Vac[−], Acc[−], Suc[−]) and two risk factors are both present (Con[+], Inf[+]). Values represent results of 1,000 iterations of the stochastic compartment model. The disease severity is a ratio between the number of pigs per day being infectious divided and the number all pigs per day in the model
Mentions: The outcomes of various scenarios were plotted as line charts and compared with recently published data on the prevalence of M. hyopneumoniae infection in pigs at different age. When all protective factors were present ([P] = Positive; Vac[P], Acc[P], Suc[P]) and risk factors were absent ([N] = Negative; Con[N], Inf[N]), the percentage of finishing pigs susceptible to M. hyopneumoniae at the end of the fattening period was >85 % on average and the percentage of pigs, which had been infected during their growth period was <10 % (mean; evidenced by details in Table 2 and ‘Additional file 1’). Mortality that can be observed in this scenario is attributed to ‘baseline mortality’, which is approx. 15 to 20 % from birth to slaughter [23]. The observation of less than 10 % potentially seropositive pigs (due to exposure to M. hyopneumoniae followed by latency until seroconversion = Ia + Ic + R) and the absence of biologically significant within-herd transmission in most simulations are consistent with findings of a recent study [26]. In the latter, no spread of the pathogen and no disease could be confirmed in well-managed pig herds. In such scenarios, all animals should be seronegative at the end of the fattening period, because of waning of maternally derived antibodies, waning of antibodies after vaccination and the absence of exposure to the pathogen. In contrast, nearly all susceptible pigs became exposed and subsequently infectious (Fig. 2), when all protective factors were absent (Vac[N], Acc[N], Suc[N]) and all risk factors were present (Con[P], Inf[P]). The ‘disease severity’ in this ‘high risk’ scenario (Fig. 3) was well in accordance with findings in the field, where herds with similar risk and protective factors show comparable results in terms of pathogen transmission [26]. In contrast, the ‘disease severity’ was negligible in the ‘low risk’ scenario. Details can be studied in a graph provided as ‘Additional file 2’.Table 2

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 &lsquo;disease severity&rsquo; 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 &lsquo;acclimatisation of gilts&rsquo;, &lsquo;length of suckling period&rsquo;, &lsquo;vaccination of suckling pigs against M. hyopneumoniae&rsquo;, &lsquo;contact between fattening pigs of different age during restocking of compartments&rsquo; and &lsquo;co-infections in fattening pigs&rsquo;.

Results: The highest &lsquo;disease severity&rsquo; was predicted, when gilts do not have contact with live animals during their acclimatisation, suckling period is 28&nbsp;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&nbsp;% of their lifetime. Logistic regression showed that vaccination of suckling pigs was influential for &lsquo;disease severity&rsquo; 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 &lsquo;disease severity&rsquo; 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