With PMWS and PRRS continuing to pose serious viral threats to the UK pig herd, there has been increasing interest in eliminating various associated infectious agents, which may help reduce the level of secondary infections and high mortality.

Mycoplasma hyopneumoniae, the cause of enzootic pneumonia (EP), has been shown to be a major complicating factor in the above disease complexes, even after vaccination, in some cases. When the immune system is damaged by the PMWS and/or PRRS viruses extensive pneumonias can result, with a severity well in excess of that associated with EP alone, with 70-80% of the lung affected in some instances.

 

PMWS - lesions of severe pneumonia in a pig lung

 
Eradication of M. hyopneumoniae and any other associated pathogen makes very good sense therefore, and a number of methods have been employed to achieve this aim.

As far back as the seventies, UK breeding companies were trying to establish mycoplasma-free herds using medicated early weaning programs. Sows were treated five days before farrowing and five days after and piglets were treated five days before and after their weaning and removal to a new clean site. The antimycoplasmal treatment of choice was tiamulin (Tiamutin - Novartis) administered at 10mg/kg bodyweight (Alexander and others, 1980).

This method was modified in the nineties by Baekbo and others (1994) in Denmark to help eradicate EP. They successfully used partial depopulation of all stock under 10 months of age, coupled with treatment with tiamulin alone or tiamulin and chlortetracycline for two weeks. This was part of the Danish SPF (specific pathogen free) herd program, designed to establish herds that were free of certain diseases.

Partial depopulation is important, to maintain good genetics and minimise production disruptions. Animals in excess of 10 months of age, have normally built up high levels of immunity to mycoplasma, lesions have healed and shedding of the infective agent is low. Pigs less than 10 months of age are often found to be highly infectious, shedding mycoplasma profusely and are often impossible to treat. There was also no farrowings for 14 days. All breeding animals were medicated for 14 days with tiamulin at 10mg/kg either in water or in feed during this time, or a combination of tiamulin 5mg/kg and chlortetracycline 15 mg/kg in feed. All units and pens were cleaned, disinfected and repaired.

The herds were monitored clinically for upto 30 months and also by serological testing and by monthly slaughterhouse checks. No EP lung lesions were observed.

Further modifications of the method, where partial depopulation and medication of sows and suckling pigs with tiamulin have also been described in Norway and Finland (Lium and others, 1992; Heinonen, 2003).

Why was tiamulin or a combination of tiamulin and chlortetracycline used? In a comparative treatment trial the combination appeared to eliminate the mycoplasma better than other products and combinations such as tilmicosin 300ppm and lincomycin 100ppm plus chlortetracycline 400ppm. Tiamulin and chlortetracycline have an enhancing even synergistic effect together against mycoplasma.

 

Graph 1. Comparison of tiamulin plus chlortetracycline in the reduction of pneumonic lesions and the elimination of M. hyopneumoniae and A. pleuropneumoniae

(From Stipkovits and others 2001)

From a cost perspective, the breeding stock treatment can be a major expense but the combination is very cost effective in comparison with tilmicosin and even tiamulin alone. (See table 1)

 

Table 1. Comparative inclusion costs of various medication programs for the eradication of Mycoplasma hyopneumoniae

 
Normally mycoplasma does not survive for a long time outside the pig's body hence a relatively short treatment period is required for eradication. In many cases 'add-on' infections can also be eliminated. If it is swine dysentery then a treatment program can be adapted and prolonged (upto 60 days) to ensure the organism has died out in the faeces, slurry and farm environment to prevent reinfection. Other 'add-ons' have been very successful, such as mange eradication and PRRS virus has been reportedly eliminated in the USA with the use of live vaccines given twice to breeding stock, to stop virus shedding (Dufresne, 2003). Eradication of Streptococcus suis, Actinobacillus pleuropneumoniae and Haemophilus parasuis are difficult and unreliably eliminated. Further work on Lawsonia intracellularis is ongoing in Denmark and that may also be possible with a combination of hygiene controls and tiamulin treatment (Johansen and others, 2001).

Overall mycoplasma eradication is feasible and highly successful (approximately 90%) but it is essential to plan the program meticulously and also consider what else you can reasonably eliminate to improve the future performance and disease status of the herd.

 

References:
Alexander, T.J.L., Thornton, K., Boon, G., Lysons, R.J. and Gush, A.F. (1980) Medicated early weaning to obtain pigs free from pathogens endemic in the herd of origin. Veterinary Record 106, 114-119

Baekbo, P., Madsen, K.S., Aagard, M. and Szancer, J. (1994) Eradication of Mycoplasma hyopneumoniae from infected herds without restocking. Proceedings 13th International Pig Veterinary Society Congress Bangkok, Thailand, p135

Lium, B., Skomsoy, A., Jorgensen, A., Loe, B. and Szancer, J. (1992) An attempt to eradicate Mycoplasma hyopneumoniae from selected Norwegian farrowing to finishing herds. Proceedings 12th International Pig Veterinary Society Congress The Hague, Holland, p300

Heinonen, M. (2001) Health classification of Finnish swine herds - development measures and results (Dissertation) Faculty of Clinical Veterinary Sciences, University of Helsinki, Finland

Stipkovits, L., Miller, D., Glavits, R., Fodor, L. and Burch, D. (2001) Treatment of pigs experimentally infected with Mycoplasma hyopneumoniae, Pasteurella multocida and Actinobacillus pleuropneumoniae with various antibiotics. Canadian Journal of Veterinary Research 65, 213-222.

Dufresne, L. (2003) Control and elimination of PRRS in multiple site production. Proceedings of the American Association of Swine Veterinarians Miami, Florida, USA, pp541-547

Johansen, M., Baekbo, P., Jensen, T., Moller, K and Nielsen, V.R. (2001) Attempt to eradicate Lawsonia intracellularis by medication in 8 newly established sow herds - preliminary results. Proceedings International Symposium on Swine Disease Eradication St Paul, Minnesota, USA, pp71-73

 

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