Genotyping of Equine Lawsonia intracellularis Sampled in Japan by Using Multilocus Variable-Number Tandem Repeat Analysis.

The incidence of equine proliferative enteropathy, caused by Lawsonia intracellularis, is increasing around the world. To investigate the relationships of variable-number tandem repeat (VNTR) patterns with host species and clinical status in horses, multilocus VNTR analysis (MLVA) was applied to 98 L. intracellularis samples collected from horses, seven from pigs, seven from wildlife, one vaccine strain, and 17 public strains. The VNTR patterns were highly diverse: a total of 130 samples identified 99 distinct patterns, and the 98 horses were classified into 71 different patterns. A phylogenetic tree based on the MLVA showed three clusters: porcine, equine, and miscellaneous cluster. The equine cluster contained 46 horse samples, of which 42 (91.3%) were collected from two sampling areas. The MLVA could discriminate horse samples from pig, but the horse samples in the miscellaneous cluster could not be distinguished from wildlife samples. As for clinical data of the horses, the VNTR patterns were unrelated to horse age, clinical signs, and clinical outcomes. This study shows that VNTR patterns had no clear connection with equine clinical status, but the MLVA could be useful to investigate its epidemiological relationships, and interspecific transmission of L. intracellularis between horse and wildlife cannot be ruled out.