BANFF, Alta. – The practice of treating sick pigs with common antibiotics may have to be revisited because some of those treatments hurt the natural immune system.
Brazilian veterinarian Flavea Reis, who works with Elanco Animal Health, told the Banff Pork Seminar on Jan. 18 that while antibiotics are often used to treat secondary infections, the emergence of immunosuppressive viral diseases in pigs makes treatment difficult in diseases including porcine circovirus 2, swine influenza, pseudorabies and swine fever.
“Traditionally, important health problems have been reduced in impact or eradicated,” she said.
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“New severe syndromes have appeared and are mostly viral associated.”
Producers facing these diseases need to review their sanitary challenges and management methods. Some diseases can be prevented or controlled with better hygiene, using an all-in, all-out system in which different-aged pigs are housed at different sites.
Veterinarians sometimes prescribe sick pigs a combination of antibiotics such as a mix of tetracycline and sulfa drugs.
“Sometimes the dosages are much higher than any we see in the literature,” Reis said.
The path of diseases must also be considered. Viruses are intercellular while bacterial infections tend to be extracellular. Many medications do not penetrate cell walls.
It is already known in human medicine that antibiotics can suppress immune systems and make it harder to recover.
Tetracycline is a broad spectrum antibiotic often used in swine medicine, but its benefits can be hindered by immune suppression, toxicity and chelating effects. Doxycycline appears to have the most potent inhibiting effects.
“The depletion of the immunity system is intensified if the drug was used for a prolonged period of time and in higher doses,” Reis said.
Low concentrations of tetracycline delay division of leukocyte cells, which means the drug slows the number of natural antibodies to guarantee an immune response.
This increases susceptibility to other infections such as salmonella, E. coli and overgrowth of yeast in the colon.
“Considering these adverse effects in the immune system, tetracyclines may not be the best choice of immune-compromised animals,” Reis said.
Sulfamethazine use may increase risk of pulmonary infection.
Studies on chickens showed the drug significantly decreased the total number of leukocytes available and produced an immunosuppressant effect. The macrolides class of antimicrobials can enhance the performance of certain aspects of cellular immune system but do not cross the blood brain barrier.
An example is tilmicosin, a semi-synthetic macrolide antibiotic. Its effects on the immune system are extensively studied and it has proven effective because it helps increase the amount of antibacterial enzymes that destroy harmful bacteria.
