Staving off antibiotic resistance

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by Sally Colby

Farmers are tasked with ensuring the health and well-being of their animals, and that sometimes involves the use of antibiotics. But farmers are also aware of growing concerns around antibiotic use.

Veterinarian Dr. Greg Habing, Ohio State University College of Veterinary Medicine, wants dairy producers to understand the importance of antibiotic stewardship in treating calves. He begins the stewardship discussion by defining bacteria and viruses along with the role of antibiotics, vaccines and anti-inflammatory drugs.

Bacteria are diverse, single-celled organisms and have a wide variety of shapes and sizes. “In contrast to viruses, bacteria can survive well and grow outside the host,” said Habing. “Some [bacteria] species are shared and spread between animals and humans, and that’s a key to understanding the impact of antibiotic resistance.” Habing added that some common calf diseases, including navel infections, pinkeye, some pneumonias and some types of diarrhea, are caused by bacteria.

Viruses are much smaller than bacteria and can’t reproduce outside the calf – they rely on the calf to survive. “Viruses infect host cells and make more viruses, causing infections to spread throughout the body,” said Habing. “Viruses are an important cause of disease in calves – some types of diarrhea and some types of pneumonia.”

Habing described antibiotics as medicines that inhibit or kill bacteria. “Antibiotics have been hugely important for saving human and animal lives,” he said. “But they do not fight viral infections and are not effective against protozoa, including cryptosporidia.”

Vaccines are used to prime the immune system against a particular pathogen, either virus or bacteria. Vaccines must be delivered far enough in advance of exposure to allow time for the immune response to develop, so if calf is already sick, it’s too late for a vaccine.

Vaccines work by stimulating the immune system. “We inject a component or modified version of that pathogen so the calf is exposed to it without getting sick,” said Habing. “Then when they’re exposed to the bacteria or virus, they’re better equipped to handle it.”

Anti-inflammatories are used to manage inflammation, which is the body’s response to irritation or injury. “Signs include redness, warmth, swelling and pain,” said Habing. “For calves, anti-inflammatories are useful to relieve pain associated with a joint infection. They can reduce stress through pain control and result in a better appetite – calves can recover quicker with anti-inflammatories.” He added that when used properly, anti-inflammatories don’t suppress the immune system.

There are misconceptions regarding antibiotic resistance among the non-ag public. “Calves don’t become resistant to antibiotics,” Habing said. “Antibiotic resistance is a property of the bacteria. Genetic change in the bacteria result in resistance to a previously effective drug.” In some cases, a particular antibiotic has never been effective against specific bacteria. Habing cites the example of penicillin, which works against the cell wall of the bacteria, but has never been effective against mycoplasma because that organism lacks a cell wall.

Although antibiotics can save an animal’s life, they are not without side effects. Broad spectrum antibiotics are not selective against pathogens – they don’t distinguish between good and bad bacteria and will cause disruption in a healthy microbiome, which can result in side effects.

Habing explained that antibiotic use should be a concern for producers because pathogens and the genes that mediate antibiotic resistance are shared between animals and humans. Using salmonella as an example, he explained the issue of resistance: “The strains that cause horrendous outbreaks of salmonellosis in calves are the same strains that cause disease in people. Likewise, the genes that mediate resistance to some of our important antibiotics are the same genes that are mediating resistance that results in treatment failures in people. Those pathogens and genes are transmitted between people and animals, through the food supply and direct contact. The antibiotics used to treat salmonellosis in calves are the same as are used to treat the same disease in a child, so we want to be careful about using those antibiotics.”

How does antibiotic use result in more resistant bacteria? If the gut contains a population of resistant and susceptible bacteria, the antibiotic clears out the susceptible population of bacteria and leaves behind resistant bacteria. “The resistant bacteria now have unlimited nutrients and space to multiply,” said Habing, explaining the process of selection pressure. “The competitive exclusion from the susceptible population is gone. When we treat a calf with antibiotics, there are more resistant bacteria.”

There are ways to stop antibiotic resistance, starting with targeted antibiotic use – antibiotics are used only when necessary from an animal welfare standpoint.

“We can identify alternatives to antibiotics,” said Habing. “Many cases of disease can be managed without medically important antibiotics – many cases of diarrhea can be managed with fluids and anti-inflammatories and have the same treatment outcome.” Disease prevention through management practices that reduce bacterial infections also reduce the need for antibiotics.

Antibiotics should be part of an all-encompassing strategy focused on reducing the need and better targeting the use of antibiotics in both human and veterinary medicine. Habing said this strategy should result in fewer new cases of disease, better treatment outcomes and less unnecessary antibiotic use. It will also demonstrate producers’ commitment toward more judicious antibiotic use.

Fewer cases of new disease can be achieved through adherence to prevention measures along with vaccination protocols. Better biosecurity decreases the spread of infections from farm to farm or calf to calf. Improving nutrition, training employees to conduct thorough calf assessments and providing better education regarding common calf medications to improve treatment outcomes all contribute to judicious antibiotic use that reduces resistance.

“Antibiotics are necessary to treat bacterial infections,” said Habing. “We aren’t saying ‘don’t use antibiotics.’ We want to better target antibiotic use to where they’re most necessary and most beneficial. Antibiotic resistance negatively impacts both calf and human health, and if we have comprehensive, well-developed antibiotic stewardship programs, we can minimize antibiotic use through disease prevention and targeted antibiotic use.”

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