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Mycoplasma hyopneumoniae: new strategies for an old ‘bug’

Part 1: Underrated disease

Part 2: Understanding Mycoplasma hyorhinis

Part 3: New strategies needed

Managing Mycoplasma hyopneumoniae (M. hyo) is nothing new for US pig veterinarians and producers, but there are a number of new tools available to deal with the bacterium. In addition, veterinarians now have a better understanding of the prevalence of M. hyo within a population.

M. hyo is a difficult bug, so many producers have not used available diagnostic tools to effectively investigate their current status, Bill Hollis, DVM, swine veterinarian at Carthage (Ill.) Veterinary Service, told Pig Health Today. Understanding the prevalence of M. hyo in a herd, along with the organism’s behavior and the risks associated with it, can help veterinarians recommend better control and elimination strategies to their clients.

Underrated disease

Producers may not have fully appreciated the economic impact of M. hyo in the past, Hollis said.

“Once we began working on elimination programs, breeding stock populations [suppliers] gave clients the opportunity to have naive gilts enter the herd,” he said. “That is a very good tool, because now you can make a decision on what you’re going to do with females as they enter the sow farm. Having that naive population allows us to create naive commercial populations. Those pigs grow at a more efficient rate and require fewer antibiotics.”

Veterinarians have learned more about how to eliminate M. hyo from certain populations, but Hollis also recognises the risks associated with disease elimination.

“We have to understand the risk, the organism and the prevalence so we can choose the correct path,” Hollis said.

Areas of improvement

Researchers and veterinarians are working to understand where M. hyo is evading control measures. For example, if a gilt population is exposed either at entry into the herd or later, it may become a chronic shedding population in the gestation barn. If the goal is to have a naive population, Hollis said it’s important to understand the barriers to disease elimination.

“We can target specific populations with diagnostic tools, like tracheal swabbing and PCR [polymerase chain reaction] tests, for example,” Hollis said. “Vaccines and medications have been very effective over time, but there’s a cost…, so understanding when the disease is going to strike, at what level it will strike and preparing for that occurrence makes a big difference in a growing population.”

Right tools at the right time

Hollis provided an example to illustrate his point. Carthage Veterinary Clinic had a client with a naive population that became infected with M. hyo. He knew from experience that an aggressive therapeutic medication program and mass vaccination of the sow population would pay strong dividends in the future by reducing shedding of the organism downstream.

“That’s an extreme example of a population that became active,” he said.

The chronic, on-going status of M. hyo leads to an acceptance of the organism in the growing-pig population. When this happens, Hollis said veterinarians need to decide if the bacterium should be reduced or eliminated, then explain the benefits of taking action with their clients.

“This process helps us understand where to target vaccines, which medications should be used and what time periods will be most effective with the population,” Hollis said.

Veterinarians have learned where bacterial pathogens like M. hyo like to grow, particularly as a co-infection with other diseases.

“We’ve learned the length of time that very low-prevalence populations will grow the organism,” Hollis said. “We’ve also identified other strains of Mycoplasma: We have some populations that are free of M. hyo, and as we’ve done further investigation, we find Mycoplasma hyorhinis (M. hyorhinis) for example.

This strain is less pathogenic than M. hyo and is more prevalent in the upper airway of pigs, Hollis said, noting that control of M. hyorhinis is very different from control for M. hyo.

Hollis has seen herds where M. hyorhinis is doing no damage. He has also seen populations with limited exposure to M. hyorhinis, but when population dynamics change, or there’s a change in pig density in a growing environment, there is an increase in the level of M. hyorhinis, leading to an upper-airway infection.

He was quick to explain that the elimination of M. hyo doesn’t necessarily make pigs more susceptible to M. hyorhinis. They’re very different organisms and have different pathological presentations within the pig, “But they can confuse us in our diagnostics and also in the clinical presentation within the pig,” Hollis said.

“We can control M. hyorhinis with early medication,” he continued. “We can also harvest the organism…and put it into a vaccination programme that creates early recognition of the organism.”

New strategies

New strategies are available to help producers and veterinarians determine whether M. hyo can be controlled or eliminated in their systems, Hollis said, pointing to these tools:

• Early diagnostics, both in the breeding stock gilts and in the sow farm, help veterinarians understand the prevalence of that organism. Diagnostics through PCR testing or serum are critical in determining the status of the population.
• Audit and evaluation of vaccines and medications help veterinarians know how to use them and if they’re being targeted appropriately. This helps producers know if they are on-track with their disease-management strategies.
• Decision to eliminate or not: “There have been some very successful elimination programs that have stayed free of hyo for several years,” Hollis said. “Elimination is a scary topic for commercial producers because they don’t want to risk an outbreak. We do a great deal of work before the decision is made to help producers understand those risks and then, in many cases, take the plunge and get rid of the organism.”

Gauging a farm’s gilt-development strategy and knowing the prevalence of M. hyo in that population helps veterinarians identify the right approach for control, Hollis said.

As the industry has minimized the use of in-feed antibiotics, there has been a bigger push toward individual pig care, walking the pens, identifying the sick pigs early in development and giving whatever antibiotics or other interventions are needed at the time.

“The controlled, targeted use of antimicrobials is beneficial for everyone,” Hollis said. “In the case of some of these population diseases like M. hyo, pigs don’t present with an active cough at the beginning. You can’t walk into a population of 100-pound pigs and identify the ones that are M. hyo-positive.

“It’s a slow-growing organism that requires an understanding of the population,” Hollis added. “That makes it more challenging, but that’s all the more reason a judicious-use program is important.”