When Lawsonia intracellularis was first discovered, University of Minnesota researcher Connie Gebhart says it was a wide-open field of opportunity. Not only was it challenging to research, but few people in the U.S. had addressed the issue of this pathogen.
No one could question the devastation Lawsonia caused in swine herds. For years, it was referred to as an adenomatosis or a cancer because of the way it proliferated cells. However, a group in Scotland discovered a lot of bacteria within the proliferating cells, Gebhart explains. Further research proved that it was the bacteria inside the cells causing the proliferation.
“I’ve been working with Lawsonia on and off for decades. My lab was instrumental in identifying the agent of the disease, developing diagnostics, including PCR and serology tests, and understanding the epidemiology. We were also involved in basic research to develop and evaluate methods of control,” she says.
To date, vaccines are the best way to control this disease that can be found in most pig herds in the U.S, Gebhart says. Although knowledge has evolved greatly since Lawsonia was first named and identified more than 25 years ago, many questions remain about how it causes disease and infects cells.
Why Is Lawsonia So Challenging?
Lawsonia is a cunning enemy because of how it attacks the pig, says Fernando Leite, DVM, technical manager for enteric diseases with Boehringer Ingelheim.
“Lawsonia only replicates inside of cells and preferentially those that line the intestine. When we think about what the intestine does, those cells are there to absorb nutrients,” he says. “It can have a large impact on production performance and overall health.”
Research has shown that Lawsonia can present in both chronic and acute forms. The challenge is that in its chronic form, it can be difficult to detect. It can cause slow or uneven weight gain. The acute form, which is not as common, is more devastating because it causes bloody diarrhea and/or sudden death of finishing pigs and gilts, Gebhart says.
How Does Lawsonia Impact the Gut?
The microbiome is a trending topic of interest in the swine industry. The more researchers learn about the microbial community in the gut, the more they connect dots between its role in production performance and overall health.
“The microbiome is a new variable that we have to consider,” Leite says. “We’re still learning a lot about how it impacts overall health and production.”
He says it raises an important question. How do we manipulate this variable to maximize swine performance and health, and how do we protect it?
Some research indicates that vaccination for Lawsonia may offer additional benefits to the pig beyond control of ileitis. Leite says a recent study shows that vaccinating a pig against Lawsonia can actually protect the pig from some of the negative impacts that Lawsonia has in the gut microbiome and in promoting other pathogens.
“As we better understand how the gut microbiome is associated with important variables like production performance and response to enteric and respiratory pathogens, the more we understand the importance of protecting that microbial community and the potential consequences that Lawsonia infection has when it damages that community,” Leite says.
In a University of Minnesota study, researchers learned that Lawsonia-vaccinated animals shed less Salmonella when compared to co-infected and non-vaccinated animals, an effect that was heavily associated with the microbiome response of vaccinated animals. Other studies have found that vaccinating for Lawsonia can lead to less Salmonella in lymph nodes, too.
He says it’s important to continue to go down this path to better understand how to manipulate the microbiome and to discover how it can influence outcomes of interest to the producer.
Lessons Learned
During the American Association of Swine Veterinarians (AASV) annual meeting, Leite summarized some of the lessons scientists have learned from 20 years of controlling Lawsonia.
First, it’s important to have a plan. Science reinforces this pathogen has an impact on performance, even if pigs aren’t experiencing visible signs of diarrhea.
“If you don’t have a plan in place, and you have naive animals that haven’t been exposed or haven’t been immunized with a vaccine, it can be a devastating disease,” Leite says. “Know your status and have a plan to combat it.”
In addition, Lawsonia can be a driver of antimicrobial use. As producers think more about stewardship and tools to help in their stewardship plans, he believes vaccination is a good tool that can help in the judicious use of, and at times decrease the need for, antimicrobials.
What’s Next?
Gebhart plans to continue studying Lawsonia. Currently she is investigating the mechanism by which Lawsonia causes proliferation in the pigs’ intestinal cells. She’s also working to develop a pen-side rapid test for Lawsonia shedding.
“As a scientist, the more we understand about a pathogen and how it causes disease, the more options we will have for treatment, prevention and control,” Gebhart says. “What’s of most interest to me is understanding the mechanism for the pathogenicity of Lawsonia.”
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