Acanthocheilonema delicata n. sp. (Nematoda: Filarioidea) from Japanese badgers (Meles anakuma): Description, molecular identification, and Wolbachia screening

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Abstract

Acanthocheilonema delicata n. sp. (Filarioidea: Onchocercidae: Onchocercinae) is described based on adult filarioids and microfilariae obtained from subcutaneous connective tissues and skin, respectively, of Japanese badgers (Meles anakuma) in Wakayama Prefecture, Japan. No endemic species of the genus had been found in Japan. Recently, some filarioids (e.g., Acanthocheilonema reconditum, Dirofilaria spp., and Onchocerca spp.) have come to light as causative agents of zoonosis worldwide. The new species was readily distinguished from its congeners by morphologic characteristics such as body length, body width, esophagus length, spicule length, and the length of microfilariae. Based on the molecular data of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene, A. delicata n. sp. was included in the clade of the genus Acanthocheilonema but differed from two other congeneric species available for study, A. viteae and A. reconditum. Acanthocheilonema delicata n. sp. did not harbor Wolbachia. It is likely that the fauna of filarioids from mammals on the Japanese islands is characterized by a high level of endemicity.

Highlights

► We found a filarial Acanthocheilonema delicata n. sp. from endemic badgers in Japan. ► We made morphologic description and analyzed the phylogeny based on the cox1 gene. ► The species together with A. reconditum has the smallest adult worms in the genus. ► The microfilariae of the species occurred in the skin of the host animals. ► Endosymbiont bacteria Wolbachia were absent in the species.

Introduction

Cobbold created the genus Acanthocheilonema with one species, Acanthocheilonema dracunculoides, from specimens collected from the aardwolf (Proteles cristatus: Hyaenidae) in South Africa [1]. The genus consists of 14 species which have a wide range of mammalian hosts (Carnivora, Macroscelidea, Rodentia, Pholidota, Edentata, and Marsupialia) from the major continents of the world.

Although a high degree of endemicity appears to characterize the species among several genera of filarioids obtained from mammalian hosts in Japan [2], [3], [4], [5], [6], [7], no endemic species have yet been found in the genus Acanthocheilonema. The widespread species recorded in Japan are: A. reconditum (Grassi, 1889) from dogs in Okinawa [8]; A. odendhali (Perry, 1967) and A. spirocauda (Leidy, 1858) from Pinnipedia in the coasts of Hokkaido [9], [10].

Acanthocheilonema reconditum may be a zoonotic agent as shown recently in Australia [11], similar to several filarial species from dogs, the most common being Dirofilaria immitis (Leidy, 1856) and Dirofilaria repens Railliet and Henry, 1911 [12], [13], and Onchocerca lupi Rodonaja, 1967 with a single case from Turkey [14]. Onchocerca dewittei japonica Uni, Bain and Takaoka, 2001 from wild boar was identified as a zoonotic agent in Japan [15], [16], [17]. Because of the potential of onchocercid worms to infest humans, research endeavors on the fauna of filarial parasites and on their vectors are needed for public health [18].

In this article, we describe a new species of Acanthocheilonema based on adult filarioids and the microfilariae collected from Japanese badgers and show its phylogenetic relationships by an analysis of the DNA sequences of its mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. We also indicate the absence of the endosymbiont bacteria Wolbachia in the new species, because Wolbachia have biological and evolutional relationships to the Onchocercidae, as well as pathologic significance to humans [19].

Section snippets

Materials and methods

The host animals examined for filarioids were Japanese badgers (Meles anakuma Temminck, 1844), an endemic animal of Japan. Twenty-five animals were found in road-kill between December 2005 and May 2010 in the vicinity of Tanabe City, Wakayama Prefecture, Japan. The carcasses were shipped refrigerated to a laboratory for filarial examination one or two days after being found.

For the detection of microfilariae, skin snips were taken from the face, ears, neck, back, limbs, and tail of each animal

Description of Acanthocheilonema delicata Uni & Bain, n. sp.

Small, thin, and delicate filarioids. Females long, twice as long as males (Table 1). Anterior extremity slightly bulbous, bearing two sets of four papillae and amphids (Fig. 1A-B). Buccal cavity distinct; buccal capsule with thick buccal ring (Fig. 1C–E). Esophagus divided into short anterior muscular portion and long, broad posterior glandular portion (Fig. 1A). Deirids at level of junction of muscular and glandular portions of esophagus (Fig. 1F–G). Caudal extremity of females and males

Discussion

Species of Cercopithifilaria and Onchocerca were also found to be monophyletic, and clustered together; the cluster of these two genera was grouped with that of Acanthocheilonema (Figs. 8 and 9). Mansonella (C.) perforata was basal to the cluster consisting of three genera (Cercopithifilaria, Onchocerca, and Acanthocheilonema). F. martis was found to be basal to all of these filarioids. These findings obtained by the molecular analysis established the genus Acanthocheilonema defined by

Acknowledgements

We are grateful to Academician Dr. Yong Hoi Sen, Senior fellow of Academy of Sciences Malaysia, and Professor Emeritus, University of Malaya, who has warmly encouraged us in our research efforts. We heartily thank Professors Dr. Mohd Sofian Bin Azirun, Dean, the Faculty of Science, University of Malaya; Dr. Rosli Bin Hashim, Head, the Institute of Biological Sciences, Faculty of Science, University of Malaya; and Dr. Rosli Bin Ramli of the same institute, who likewise have supported our study.

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