Morphological and Molecular Characterization of Toxocara tanuki (Nematoda: Ascaridae) from Korean Raccoon Dog, Nyctereutes procyonoides koreensis

Abstract

Present study was performed to describe the morphological and molecular characterization of Toxocara tanuki (Nematoda: Ascaridae) from Korean raccoon dog, Nyctereutes procyonoides koreensis, naturally infected in the Republic of Korea (Korea). Juvenile and adult worms of T. tanuki were recovered in 5 out of 10 raccoon dogs examined and the larval worms were detected in 15 out of 20 muscle samples (75%). Small lateral alae were observed on the cranial end of the body in male and female adults and 2 long spicules (3.0-3.5 mm) were characteristically observed in the posterior end of males. In SEM observation, 18 pairs of proximal precloacal, a precloacal median, a postcloacal median and 5 pairs of postcloacal papillae were uniquely revealed in the posterior portion of males, but the proximal papillae were not shown in the lateral ends of females. Molecular analysis on the 18S rRNA partial DNA sequences was revealed the same finding in both samples, adult worms and muscle larvae, which are closely related to T. tanuki. In conclusion, it was confirmed for the first time that T. tanuki is indigenously distributed, the Korean raccoon dog is acted as the natural definitive host of this nematode in Korea and the morphological characteristics of T. tanuki were shown in specific structure for single postcloacal median papilla in male.

Keywords: Korea; Korean raccoon dog; Nyctereutes procyonoides koreensis; Toxocara tanuki; larva migrans; morphological and molecular characterization.

Fig. 1

Light micrographs of Toxocara tanuki. (A) Caudal end of adult male. Note the 2 separated spicules (arrows). (B) There is a ventriculus between the esophagus and the intestine. (C) Caudal end of adult female. (D) Egg from feces. Note the egg shall coated with albumin. (E) Larva from muscle. E, esophagus; I, intestine; V, ventriculus.

Fig. 2

Scanning electron micrographs of female Toxocara tanuki. (A) Ventral view showing anterior end. Cervical alae (arrows). (B) Frontal view showing dorsal labium, 2 ventral labium and oral aperture. (C) Dorsal labium showing a pair of big dorsolateral papillae, pit-like internal labial papillae (circles), dentigerous ridge (arrows) and oral aperture. (D) Amphid (arrow) and externo-lateral papilla on the ventral labium. (E) Ventral labium. Note the dentigerous ridge (arrows), pit-like internal labial papillae (circles), and pore (triangle) on the ventrolateral papilla. (F) Higher magnification of dorsolateral papillae on dorsal labium. Note the pore (triangle). (G) Dentigerous ridge showing unicuspid denticles. (H) Female caudal end showing anus (circle) and phasmid (square). (I) Higher magnification of phasmid. (J) Higher magnification of triradiate oral aperture. Note the median glove (arrows). D, dorsal labium; EP, externolateral papilla; OA, oral aperture; DP, dorsolateral papilla; V, ventral labium; VP, ventrolateral papilla.

Fig. 3

Scanning electron micrographs of male Toxocara tanuki. (A) Ventral view showing anterior end. Cervical alae (arrows). Lateral crest (arrow) run longitudinally behind cervical alae (square). (B) Frontal view showing dorsal labium, ventral labium and oral aperture. (C) Dorsal labium showing a pair of big dorsolateral papillae, pit-like internal labial papillae (circles), dentigerous ridge, oral aperture. (D) Amphid (arrow) and externolateral papilla on the ventral labium. Note the pore (triangle). (E) Denticles. Note the unicuspid, bicuspid (arrow) and pits (circle). (F) Latero-ventral view. Precloacal papilla (arrows and circle). Square is a magnified precloacal papilla. (G) A small precloacal median papilla (arrow), with clear visible hole in the middle. (H) Ventral view of postcloaca. A single postcloacal median papilla (circle). The first postcloacal ventral papillae (white squares). The second pair of postcloacal ventral papillae (arrows). (I) Latero-ventral view of distal end of the tail. The first postcloacal ventral papillae (white squares). A pair of second postcloacal ventral papillae (white arrows). A pair of third postcloacal ventral papillae (black arrows). Postcloacal ventro-lateral papillae (triangles). Phasmid (black circle). Mucron (white circle). D, dorsal labium; EP, externolateral papilla; OA, oral aperture; DP, dorsolateral papilla; S, spicule; V, ventral labium; VP, ventrolateral papilla.

Fig. 4

Phylogenetic tree (Neighbor Joining) based on sequence analysis.