Almost all of the pig herds in the United Kingdom are infected with Mycoplasma hyopneumoniae and this is the reason that most herds now vaccinate against it. However this is not always sufficient to control all the respiratory infections because of the viruses that damage the immuno-defence systems, such as porcine reproductive and respiratory virus (PRRSV) and the increasingly recognised porcine circovirus type 2 (PCV-2) and enable secondary infections of a variety of bacteria to invade the respiratory tract and destroy the lung.

Many antibiotics are active against mycoplasma, such as valnemulin, tiamulin, tylosin and lincomycin, but lack the broader activity against the bacteria. This is why in the field combinations of anti-mycoplasma medicines are commonly combined with other compounds such as chlortetracycline (CTC) or sulphadimidine to enhance their spectrum of efficacy. In the case of the pleuromutilins such as valnemulin (Econor) and tiamulin (Tiamutin) another distinct advantage has been demonstrated that they act additively or even synergistically with chlortetracycline (Aurogran) further enhancing their activity and efficacy.

Recent work has looked at the efficacy of a number of antimicrobials and combinations to compare their efficacy against some of the common mixed infections that are encountered in the field. The test pigs were infected with M. hyopneumoniae at the start of the trial and then infected with Pasteurella multocida on day 8. On day 15 they were then infected with Actinobacillus pleuropneumoniae. Treatment was started on day 9 through to the end of the study day 22 when the pigs were autopsied and the pneumonic lung lesions examined, scored and recovery of the microbes was attempted.

Table 1. Comparative efficacy of various antimicrobials against a mixed respiratory infection challenge

The Econor and Tiamutin plus CTC groups showed an excellent response in comparison with the infected untreated control. They were equivalent or superior to the positive control tilmicosin and gave similar performance responses to the uninfected controls. The combination of lincomycin and chlortetracycline were not so effective in this trial.

When the lungs were tested for the presence of M. hyopneumoniae and A. pleuropneumoniae and compared with the pneumonic lung lesion scores it is clear how the products were exerting their disease control effect.

Graph 1. Comparison of pneumonic lesions (%) and reisolation of M. hyopneumoniae and A. pleuropneumoniae from the lesions for the various treatments

Econor and Tiamutin plus chlortetracycline inhibited completely the mycoplasma component due to their synergistic activity. Lincomycin plus chlortetracycline does not show this activity against mycoplasma, although it has been reported for some bacteria. All groups showed a good effect against A. pleuropneumoniae with only a minor variation between them.

Surprisingly even Econor at its lower preventive level of 25ppm seemed to show a good response with chlortetracycline at 400ppm. Field reports (Pig World, January 2003) confirm, that their combined use in young finisher pigs on the introduction to a unit will substantially control enteric spirochaetal problems and respiratory infections allowing them to grow rapidly and healthily, solving one major producer's problem.

 

Reference:
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.

 

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