A New Rhabditoid Nematode Species in Asian Sciurids, Distinct From Strongyloides Robustus in North American Sciurids

Abstract

Strongyloides callosciureus n. sp. (Nematoda: Rhabditoidea), from Asian sciurids, is described based on morphology, morphometry, and the small and large subunit (SSU/LSU) ribosomal RNA gene (rDNA) sequences. This new species was collected from Pallas's squirrels (Callosciurus erythraeus) in the central part of mainland Japan (Honshu), which were originally introduced from Taiwan some decades ago, and plantain squirrels (Callosciurus notatus) imported from Malaysia as personal pets. For comparison, Strongyloides robustus Chandler, 1942 was collected from American red squirrels (Tamiasciurus hudsonicus) and southern flying squirrels (Glaucomys volans) imported from the United States as personal pets. The parasitic females found in North American and Asian sciurids shared some key morphological features such as the ovary running spirally around the gut, and the shapes of the stoma in the apical view and the tail. However, morphometric features of parasitic females in North American and Asian sciurids differed significantly from each other; the former was larger than the latter, and the relative position of the vulva to the whole body length from the mouth was different. The SSU/LSU rDNA sequences supported the division of sciurid Strongyloides isolates by geographical distribution of the host and morphological features, leading us to propose the erection of new species.

Gastrointestinal Parasitic Helminth Fauna of the Pallas's Squirrel (<i>Callosciurus erythraeus</i>) from the Uto Peninsula, Kumamoto, Kyushu, Japan and Analyses of the Abundance of an Alien Nematode, <i>Strongyloides callosciureus</i>

“…They occur in the indigenous and artificial distribution areas of this host species [17,[21][22][23][24]. These two species were likely introduced in the present area with the hosts.…”

“…We examined their gastrointestinal helminth fauna. Moreover, we conducted some ecological analyses regarding the abundance of Strongyloides callosciureus, which is a dominant nematode species of the gastrointestinal parasitic helminth fauna of this host species [14][15][16][17], to examine hostparasite ecological relationships between these sciurid host and nematode parasite species.…”

The stomal morphology of parasitic females of Strongyloides spp. by scanning electron microscopy

“…According to the traditional manner using light microscopy, the apical end of S. robustus Chandler 1942, the North American sciurid threadworm, was described as follows: cephalic extremity with complex X-shaped mouth, four papillae, and eight lobes on the circumoral elevation (one dorsal, two subdorsal, two lateral, two subventral, and one ventral; Bartlett 1995). Our recent SEM study (Sato et al 2007) disclosed the presence of four intra-stomal linguiform projections and that four of eight reported lobes on the circumoral elevation under oil immersion (Bartlett 1995) were these linguiform projections, and the remaining four were substantial lobes. It then became our concern to interpret ordinary light microscopical images based on SEM findings.…”

“…(Arizono et al 1976;Sakamoto et al 1981;Viney et al 1991;Sato et al 2007). According to the traditional manner using light microscopy, the apical end of S. robustus Chandler 1942, the North American sciurid threadworm, was described as follows: cephalic extremity with complex X-shaped mouth, four papillae, and eight lobes on the circumoral elevation (one dorsal, two subdorsal, two lateral, two subventral, and one ventral; Bartlett 1995).…”

“…Sediments were checked thoroughly under a dissection microscope, and the collected parasites were fixed in 10% neutral-buffered formalin. Strongyloides robustus and S. callosciureus were recovered from the small intestine of Mongolian jirds (Meriones unguiculatus) infected experimentally (Sato et al 2007). These species originated in imported American red squirrels (Tamiasciurus hudsonicus) or southern flying squirrels (Glaucomys volans), and feral alien Pallas's squirrel (Callosciurus erythraeus), respectively, and the filariform larvae for the experimental infection were obtained by the Petri dish fecal culture with an unglazed tile of rectal feces of these imported pet-squirrels.…”