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Toxocara tanuki larval distribution in mice and the infectivity of tissue larvae

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Toxocara tanuki is a common large roundworm in raccoon dogs. Experimental infection studies of T. tanuki in mice were conducted to clarify the distribution and infectivity of larvae in tissue. Groups of BALB/c and C57BL/6 mice (n = 5 mice/group) were each inoculated with 1000 embryonated T. tanuki eggs and necropsied at 7, 31, 91, and 182 days post inoculation (dpi). The number of larvae in the central nervous system, heart, lungs, kidneys, spleen, gastrointestinal tract, liver, and carcass was examined. Larvae obtained from the aforementioned mice on different days of the necropsy were orally inoculated into four groups of ICR mice (n = 6 mice/group) that were then necropsied at 21 dpi. Larvae were recovered from all mice. In the BALB/c and C57BL/6 mice, most of the larvae (> 88.7%) were recovered from the liver and the remainder from other tissues. The total number of larvae recovered from C57BL/6 mice was significantly higher than that from BALB/c mice, but no difference in the relative larval distribution within the viscera between the two mouse strains was observed. The mean recovery percentage of larvae from ICR mice infected with 182-day-old tissue larvae was 3.3%. Our findings showed that T. tanuki larvae migrated predominantly to the liver of mice and that the larvae maintained their infectivity for at least half a year.

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We thanked Ms. Hiroka Kaneda for her technical assistance.


This study was partially supported by the Center for Human and Animal Symbiosis Science, Azabu University.

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NO and KT substantially contributed to the study conceptualization. NO and KT significantly contributed to data analysis and interpretation. NO, KT, and HKO contributed to the manuscript drafting. All authors critically reviewed and revised the manuscript draft and approved the final version for submission.

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Correspondence to Kensuke Taira.

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The study was carried out in accordance with the rules and regulations set by the Institutional Animal Care and Use Committee at Azabu University (Permit Number: 190220–4).

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The authors declare no competing interests.

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Okada, N., Ooi, HK. & Taira, K. Toxocara tanuki larval distribution in mice and the infectivity of tissue larvae. Parasitol Res 122, 1327–1332 (2023).

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