Wild boars as potential reservoirs of Ascaris lumbricoides: Molecular evidence of a novel transmission route

Background The genus Ascaris includes A. lumbricoides , which primarily infects humans as its definitive host, and A. suum , which primarily infects pigs. Owing to their morphological similarities, the ability to distinguish between these two species in reported cases of ascariasis has been reliant on molecular techniques, particularly differences at the 133rd and 246th nucleotide positions of the internal transcribed spacer 1 (ITS-1) region. Although Ascaris nematodes have also been detected in wild boars, they are often classified as A. suum without molecular confirmation because of the close genetic relationship between wild boars and pigs. To address this gap, we conducted a molecular analysis targeting the ITS-1 region to identify the species of Ascaris worms collected from six wild boars captured in Ishikawa Prefecture, Japan. Results Sequence alignment analysis revealed a deletion at nucleotide position 129, a G at position 133, and a T at position 246. This configuration showed 100% identity with the A. lumbricoides reference sequence previously identified in humans. On the basis of these findings, the samples were classified as A. lumbricoides . Conclusions This study provides the first molecular evidence that A. lumbricoides , which was previously thought to be nearly eradicated in Japan, persists in wild boar populations. While infections with A. lumbricoides in Japan are currently believed to be limited to imported cases involving travelers and foreign residents, sporadic cases of unknown origin have been reported among Japanese individuals. Traditionally, potential infection sources have included organic vegetables, imported produce with contaminated soil, and imported kimchi. However, the detection of A. lumbricoides in wild boars highlights a possible zoonotic transmission route that has not been previously considered. This finding underscores the need for further research into wild boars as potential reservoirs of A. lumbricoides and the implementation of preventive strategies to mitigate the associated risks. Trial registration Not applicable.