New reports of parasitism by Synhimantus (Dispharynx) nasuta (Rudolphi, 1819) (Nematoda: Acuariidae) in wild birds in Brazil

Abstract The aim of this study was to register the first occurrence of Synhimantus (Dispharynx) nasuta (Nematoda: Acuariidae) in some species of wild birds in Brazil. In addition, the aim was to deepen the knowledge about the morphology of this species through analysis using scanning electron microscopy. Nematodes were collected in wild birds of the species Turdus leucomelas, T. rufiventris, Mimus saturninus, Pitangus sulphuratus, Megascops choliba, Tyto furcata, and Falco sparverius. The morphological and morphometric data observed in the nematodes prove that these parasites are S. (D.) nasuta. This study also provides morphological data from light microscopy and scanning electron microscopy (SEM), as well as the morphometry of this nematode in each host species. Therefore, the current study confirms the first record of this nematode in F. sparverius and T. furcata in South America and, at the same time, these findings expand the host range of this parasite species worldwide, through the first records in M. choliba, M. saturninus, T. leucomelas and T. rufiventris.

The aim of this study was to register the first occurrence of S. (D.) nasuta in some species of wild birds in Brazil. In addition, the aim was to deepen the knowledge about the morphology of this species through analysis using scanning electron microscopy analyses.

Material and Methods
Were necropsied a total of 69 wild birds of the species The parasites collected in these birds were fixed in 4% Formalin at room temperature (nematodes were dead at the time of collection) and kept in this fixative for 7 days and stored in 70ºGL ethanol (Vieira et al., 2015). For morphological and morphometric studies in the light microscope Olympus BX41 with drawing tube, the nematodes, after washing in current water, were clarified in Amann's lactophenol and mounted in temporary slides (Amato & Amato, 2010). The number of nematodes analyzed in light microscopy was selected according to the morphological condition of the parasites and the size of the infrapopulations in each host specimens. Photographs in light microscopy were taken under differential interference contrast microscopy (DIC) using an Olympus BX51 microscope coupled with an Olympus UC 30 digital camera. For scanning electron microscopy (SEM) a sample of these helminths was dehydrated in increasing series of ethanol, dried in 97% 1,1,1,3,3,3-Hexamethyldisilazane, mounted in stubs with carbon tape, gold coated, and analysed in a scanning electron microscope JEOL JSM 6390LV SEM (Vieira et al., 2015), in the Plataforma de Microscopia Eletrônica -Rudolf Barth, Instituto Oswaldo Cruz, FIOCRUZ, Rio de Janeiro.
The identification to generic level of the nematodes collected in the proventriculus was made according to Chabaud (1975). For the specific identification, studies with morphological and morphometric data of Synhimantus (Dispharynx) were consulted (Zhang et al., 2004;Dewi et al., 2006;Bartmann & Amato, 2009;Oyarzún-Ruiz et al., 2016;Hernandez-Urraca et al., 2022). The morphometric data are provided in micrometers (µm), except when another unit is informed. The prevalence, mean intensity, and mean abundance of helminth were calculated according to Bush et al. (1997). Voucher specimens have been deposited in the Coleção Helmintológica Odile Bain (CHOB), Departamento de Zoologia, Universidade Federal de Juiz de Fora, in the state of Minas Gerais, Brazil.

Description
Synhimantus (Dispharynx) nasuta (Rudolphi, 1819) ( Figures 1 and 2, Table 1) General: White-colored nematodes. Robust, filiform body with transversally striated cuticle ( Figure 2A, 2D, 2F). Sexual dimorphism present, with females larger than males. Two pseudolips small and conical ( Figure 2C), with one small amphid in each ( Figure 2C). Short buccal capsule striated transversely. Esophagus divided into short muscular and long glandular portions. Four distinct, unanastomosed, convoluted branch, beginning on the dorsal and ventral surface of the oral opening, extending to the posterior region of the muscular esophagus ( Figure 2A, 2C). Nerve ring anterior to muscular esophagus. Excretory pore posterior to the nerve ring. Deirids bicuspid or tricuspid ( Figure 2B), at level of excretory pore, located between recurrent branches of the cords ( Figure 2A).

Discussion
The morphological and morphometric data observed in the nematodes of the present study, such as the shape of the curved body in the males, striated cuticle of considerable thickness, the mouth has two conical pseudolabia close to where the cephalic attachment structures (cephalic cords) appear, are coincident with those described by previous authors (Cram, 1927;Macko et al., 1974;Zhang et al., 2004), and make it evident that the nematodes found in the present work belong to the species S. (Dispharynx) nasuta.
It can be observed measurement variation related to the host species (Table1). However, this values are within the limits of variation that have been reported for S. (D) nasuta in several descriptive studies (Zhang et al., 2004;Dewi et al., 2006;Bartmann & Amato, 2009;Oyarzún-Ruiz et al., 2016;Hernandez-Urraca et al., 2022).
Differential interference contrast (DIC) microscopy evaluations showed cuticular projections with rounded edges in the cloacal opening of males ( Figure 1A): one just before the anterior edge of the cloacal opening and the other after the posterior edge ( Figure 1A). These projections were not mentioned in the previous descriptions of S. (D.) nasuta available in the literature (Cram, 1927;Macko et al., 1974;Zhang et al., 2004;Dewi et al., 2006;Bartmann & Amato, 2009;Gómez-Puerta et al., 2009;Oyarzún-Ruiz et al., 2016;Hernandez-Urraca et al., 2022). However, in one of the figures published by Zhang et al. (2004), there are indications of the presence of these projections, although they were not highlighted by those authors. Findings like these emphasize the need for new taxonomic studies on some nematode species, especially those that have been referred to as having low specificity. Such studies should address morphology, light and scanning electron microscopy (SEM) and molecular biology.
In the present study, some morphological particularities are showing for the first time at SEM images, for example the two conical pseudolabia with a pair of labial papillae on each side and amphids ( Figure 2C), and the two morphological types of deirids, i.e. bicuspid and tricuspid ( Figure 2B). The images also revealed in detail the morphology of the descending and ascending cephalic cords (Figures 2A, 2C). These details at SEM were not provided by previous authors (Rodrigues et al., 2003;Dewi et al., 2006).
The SEM images also showed the rough area of the males, a region that assists in attachment for copulation ( Figure 2E) and showed post-cloacal papillae ( Figure 2D) and two papillae near the cloaca (Figures 2D, 2E). These had not been reported in any previous study with species description. In the study by Dewi et al. (2006), it was possible through SEM to observe in detail the pre and post cloacal papillae in males, similar to those observed in the nematodes collected in the present study. Scanning electron microscopy has become an important technical instrument for determining the taxonomy of this group since the species of the subgenus and genus have similarities with minimal morphoanatomical divergences.
In general, the prevalences recorded in the present study varied according to the host species, as observed by Zhang et al. (2004), Oyarzún-Ruiz et al. (2016), and in the review provided by Hernandez-Urraca et al. (2022), from several hosts in different localities.
Among the host species in which S. (D.) nasuta was found in the present study, there have been previous records of these nematodes in F. sparverius in the United States (Taft et al., 1993) and T. furcata in Italy (Santoro et al., 2012). Therefore, it can be said that the findings of the present study constitute the first record of S. (D.) nasuta in F. sparverius and T. furcata in South America and, at the same time, these findings expand the host range of this parasite species worldwide, through the first records in M. choliba, M. saturninus, T. leucomelas and T. rufiventris.