Infectious Diseases

Amino Acids Hold Clues to Infection Status in EPE

By Adam Marcus

Horses with either clinical or subclinical proliferative enteropathy experience changes in certain amino acid concentrations that could help equine veterinarians better identify active infections.

The findings come from a retrospective analysis of blood samples collected from farms in Japan that had been affected by outbreaks of equine proliferative enteropathy (EPE), which is caused by infection with Lawsonia intracellularis.

“This research helps illuminate the possibility that blood amino acid patterns—specifically involving alanine, citrulline and tryptophan—could serve as additional indicators [of EPE], especially when clinical signs are subtle or absent,” said Hidetomo Iwano, DVM, PhD, a professor at the Rakuno Gakuen University School of Veterinary Medicine, in Japan, who helped conduct the research. “We believe that amino acid profiling could help identify which horses are infected and assess the extent of spread within a group—particularly at an early stage of the disease—when Lawsonia infection is suspected in a population.”

Dr. Iwano and his colleagues published their findings in a recent issue of the Equine Veterinary Journal.

For the study, the researchers analyzed blood samples from 135 horses from 59 farms; 46 horses had been diagnosed with clinically evident EPE. Healthy horses (n=26) from farms where EPE had not been diagnosed served as the control group.

Blood samples were analyzed using the Phenomenex EZ:faast test, which uses gas chromatography to measure concentrations of amino acids.

Several amino acids were present in substantially greater concentrations among exposed horses versus healthy controls. These included aspartic acid, glutamic acid and glycine. Other molecules were scarcer in exposed animals than in their healthy counterparts—among them glutamine, isoleucine and asparagine. Upregulation of alanine and downregulation of citrulline and tryptophan were observed in horses with clinically apparent EPE.

Taken together, the researchers said, the test revealed a pattern that could indicate which animals have been exposed to L. intracellularis and which have not, even in the absence of symptoms of the infection.

Dr. Iwano stressed that infection with L. intracellularis leads to gastrointestinal illness, not metabolic disease. “Therefore, the primary focus must remain on appropriate antimicrobial treatment and identification and isolation of affected animals,” he said.

However, infections can damage the gastrointestinal mucosa, which in turn can lead to hypoproteinemia, hypoalbuminemia and systemic nutritional deficits. “The early changes in amino acid levels observed in this study may reflect a compensatory response to such deficits, and the fact that these changes occur early is particularly noteworthy,” he said.

Although more research is needed to validate the findings, the results could point to a new way to manage EPE in horses, said Yuya Mizuguchi, DVM, of the Mitsuishi Animal Medical Centre and the Hokkaido Agricultural Mutual Aid Association, who led the study.

“From a standpoint of amino acid theory, excessive amino acids are not stored in the body unless insufficient ones are not supplied,” Dr. Mizuguchi told Modern Equine Vet. “Although it is our conjecture, supportive care with specific amino acids combined with appropriate antibiotic treatment will hasten recovery from the clinical disease and negate or prevent development to a severely devastating state.”

Both Drs. Mizuguchi and Iwano said amino acid analysis is too expensive for widespread use. “I believe costs will likely decrease in the future as amino-acid–based diagnostics become applicable to a wider range of diseases, allowing for economies of scale,” Dr. Iwano said. “In the context of high-value animals, such as racehorses, the cost-benefit balance may already be justifiable, especially when early diagnosis and intervention could impact long-term health and performance.” MeV

For more information:
Mizuguchi Y, Niwa H, Inoue H, et al. Blood amino acid changes associated with Lawsonia intracellularis infection in horses. Equine Vet J. Published online May 22, 2025.
https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.14533