The effect of vaccination on the transmission of Mycoplasma hyopneumoniae in pigs under field conditions

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Abstract

This study investigated the effect of vaccination against Mycoplasma hyopneumoniae on its transmission in nursery pigs under field conditions. Seventy-two pigs were randomly allocated at weaning into vaccinated (V) and non-vaccinated (NV) groups. Animals in the V group were vaccinated at 3 weeks of age with a commercial M. hyopneumoniae bacterin vaccine. Broncho-alveolar lavage fluid taken at weaning and at the end of the nursery period was assessed for the presence of M. hyopneumoniae by nested PCR, and the reproduction ratio of infection (Rn) was calculated. The percentage of positive pigs in the V and NV groups was 14% and 36% at weaning, and 31% and 64% at the end of the nursery period, respectively. The Rn-values for the V and NV groups were 0.71 and 0.56, respectively (P > 0.05). The study indicates that vaccination does not significantly reduce the transmission of this respiratory pathogen.

Introduction

Mycoplasma hyopneumoniae is the primary pathogen associated with enzootic pneumonia (EP) in pigs, a disease that causes significant economic loss to pig production worldwide (Thacker et al., 1999, Maes et al., 2003). M. hyopneumoniae is mainly transmitted through nose-to-nose contact, and indirectly via aerosol between susceptible pigs or through airborne transmission between farms (Goodwin, 1984, Goodwin, 1985, Thomson et al., 1992).

A sound understanding of the epidemiology and especially the transmission of the infection is a pre-requisite to optimal disease control. The transmission of this pathogen under experimental conditions has been quantified using a transmission ratio (Rn) (Meyns et al., 2006), and the values obtained indicated that vaccination did not significantly reduce pathogen transmission (Meyns et al., 2006). Similar studies quantifying transmission under ‘field’ conditions have not been carried out to the authors’ knowledge but are essential as transmission of infection under natural conditions may differ significantly from experimental settings. The nursery period in pig production is central to the transmission of M. hyopneumoniae (Clark et al., 1991, Sibila et al., 2009). At weaning, pigs infected during the suckling period are transferred to nursery units and mixed with susceptible non-infected animals, a process that facilitates the spread of pathogens such as M. hyopneumoniae.

Control of M. hyopneumoniae infection is largely achieved by improving management and production practices, by the use of antimicrobials and by vaccination (Maes et al., 2008). Commercially available bacterin vaccines are widely used and are efficacious in reducing clinical signs, secondary bacterial respiratory infections, the extent of lung lesions, and in improving production criteria (Thacker, 2004). However, experimental studies have shown that neither medication nor vaccination prevent colonisation of the respiratory tract by M. hyopneumoniae (Le Grand and Kobisch, 1996). As infection with this pathogen under natural conditions commonly occurs in weaned piglets (Sibila et al., 2009), it is important to assess whether the vaccination of suckling animals influences the extent of transmission of M. hyopneumoniae during the nursery period.

The aim of this study was to quantify the transmission of M. hyopneumoniae in nursery pigs under field conditions, and to assess the effect of vaccination. In addition, animal production criteria and the extent of lung lesions at slaughter were assessed.

Section snippets

Details of herd under study

The study was conducted in 2008 in a Belgian pig herd comprising 1200 commercial hybrid sows (PIC) that operated a 2-week batch production system. The sows were inseminated with Piétrain semen. The reproductive performance of the sows (the average number of live-born piglets was 11), and piglet health were good, although there had been some history of disease due to Streptococcus suis infection. The pre-weaning and nursery period mortality rates were approximately 9% and 2%, respectively.

Detection of M. hyopneumoniae by nPCR in broncho-alveolar lavage fluid

The number of nPCR-positive BAL fluid samples at 3, 9 and 27 weeks of age are presented in Table 1. The percentage of positive samples at 3 weeks was 14% (5/36) and 36% (13/36) in the V and NV groups, respectively (P > 0.05). At 9 weeks of age, the percentage of positive samples in the V and NV groups was 31% (11/36) and 64% (23/36), respectively (P < 0.05). All pigs that tested positive at weaning remained positive at 9 weeks.

Of the nPCR-negative BAL fluid samples at 3 weeks of age (n = 31, V group; n = 

Discussion

This study has quantified the transmission of M. hyopneumoniae in nursery-phase pigs under field conditions, and has assessed the effect of single-dose vaccination on pathogen transmission. The work additionally investigated the prevalence of M. hyopneumoniae infection, animal performance during fattening and the severity of lung lesions at slaughter. The calculated Rn-values indicate that, during the 6 week nursery period, infected pigs infect on average 0.56 susceptible pen-mates. This value

Conclusions

This field study has found that, similar to previous transmission studies of M. hyopneumoniae under experimental conditions (Meyns et al., 2006), vaccination with a bacterin-based vaccine does not significantly reduce the transmission of this pathogen between pigs. This finding implies that vaccination alone will not be effective in eliminating M. hyopneumoniae infection from herds.

Conflict of interest statement

None of the authors of this paper has a personal or financial relationship with other people or organisations that could inappropriately influence or bias the content of the paper.

Acknowledgements

This research was financially supported by Fort Dodge Animal Health. The authors are grateful to the herd-owner for their collaboration as well as to Hanne Vereecke for laboratory support.

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