Morphological diagnosis of Setaria labiatopapillosa in domestic bovids from Marajó Island, Brazil

May 24, 2021. *Corresponding author: lheaufra@gmail.com Abstract The genus Setaria is known worldwide for parasiting wild and domestic mammals, with 43 species registered, of which five occur in the American continent. The objective of this study was to characterize the occurrence, morphology and morphometry of S. labiatopapillosa in B. taurus and B. bubalis in Marajó Island, Brazil. Carcass inspections of 420 cattle were carried out in two slaughterhouses in Pará. The nematodes were found on the white and serous viscera of the small intestine, being cleaned and discussed for analysis by light microscopy and scanning electron microscopy. The morphological and morphometric characteristics are compatible with S. labiatopapillosa parasitizing both species, with a prevalence of 25% ( B. bubalis ) and 24% ( B. taurus ). Information obtained by scanning electron microscopy was added to the description of the species, in addition to expanding the distribution of The quantity and distribution of sexual papillae varies according to the species. Desset (1966) reports 3 pairs of precloacal papillae, 3 medium papillae and 4 pairs of postcloacal papillae in the species Setaria cornuta . Rhee et al. (1994) showed 3 pairs of precloacal papillae in the species Setaria digitata , 1 pair of adcloacal papillae and 3 pairs of postcloacal papillae, diverging from the results of the present study. The male specimens showed 17 cloacal papillae: 3 pairs of precloacal papillae, 1 medium papilla, 1 pair of adcloacal papillae, and 4 pairs of postcloacal papillae; characteristic of the species Setaria labiatopapillosa , observed by Becklund & Walker (1969). Watermeyer et al. (2013) report the presence of 4 pairs of precloacal papillae, one median papilla and 6 pairs of postcloacal papillae for the species Setaria graberi , diverging from what was observed in the present study.

Nematodes of this genus are not pathogenic (Gomez-Puerta & Mayor, 2017), but there have been reports of injuries to the central nervous system of its hosts related to infection by Setaria in ruminants caused by erratic microphilary migrations (Soulsby, 1982). Among the rare zoonotic cases, there is a reported occurrence of Setaria sp. parasitizing the ocular conjunctiva of human beings, in Cluj-Napoca, Romania, which represents a potential danger to human health (Ţălu et al., 2012).
Despite the zoonotic potential, the occurrence of Setaria sp. is neglected in domestic ruminant breeding in Brazil, especially in rural areas where the presence of vectors is more frequent. The objective of this study is to characterize the occurrence, morphology and morphometry of S. labiatopapillosa in B. taurus and B. bubalis in Marajó Island, Brazil.

Materials and Methods
During the period from August 2017 to May 2019, nematodes were collected from the serosa of the duodenum and the free abdominal cavity and from intestine of 244 Bubalus bubalis and 176 Bos taurus slaughtered at the official municipal slaughterhouse in Soure (00°43′00″S; 48°31′24″W) on Marajó Island, Pará State, in the eastern Brazilian Amazon. Nematodes were fixed in AFA solution (93 parts 70% ethyl alcohol, 5 parts formaldehyde, and 2 parts glacial acetic acid). For morphological and morphometric analysis, the nematodes were dehydrated in an ethanol series, clarified with Aman's Lactophenol (20%) and observed using a light microscope, and LEICA DM2500 camera with an imaging capture system according to method described by Pinheiro et al. (2019). Measurements are given in micrometers unless otherwise noted and are presented as the mean followed by the range (minimum and maximum values) in parentheses. Taxonomic classification of nematodes was in accordance with Vicente et al. (1997) and Anderson (2000).
For scanning electron microscopy, 6 nematodes were washed in phosphate-buffered saline (pH 7.0), post-fixed in 1% osmium tetroxide, dehydrated to the critical point of CO 2 , metalized with gold-palladium, and analyzed with a scanning electron microscope (VEGA 3/TESCAN) at the Laboratório de Microscopia Eletrônica de Varredura, Instituto da Saúde e Produção Animal, Universidade Federal Rural da Amazônia -UFRA, state of Pará, Brazil. The ecological indexes of parasitism were used according to Bush et al. (1997) and Bautista-Hernández et al. (2015).
Specimens were deposited in the Coleção de Invertebrados of the Museu Paraense Emílio Goeldi (acronym MPEG), Belém, Pará, Brazil: from 10 females and 5 males of Bubalus bubalis (Vouchers number MPEG 00264 to MPEG 00266 respectively) and 10 females and 5 males of Bos taurus (Vouchers number MPEG 00265 to MPEG 00267 respectively). This work obtained a release for the scientific collection provided by the Comitê de Ética em Uso de Animais of Universidade Federal Rural da Amazônia (CEUA/ UFRA) (license number 066/2017).

Results
A total of 136 nematodes were recovered from cattle and buffalo showing a prevalence of 24% and 25% and mean intensity of 1.37 and 1.1 respectively. All nematodes were measured and morphologically characterized (Figure 1a-h). The morphological and morphometric characteristics of the nematodes recovered from B. bubalis and B. taurus are presented below and in Table 1.
The specimens were long and thin with the cephalic and caudal ends tapering more than the rest of the body. In the anterior region, a small oral capsule and elliptical oral opening were observed 2 bifurcated cephalic elevations, 2 pairs of ciliated papillae, 2 pairs of simple papillae, 2 amphidial papillae (Figure 2a-c). Conical deirids ( Figure 2d) and nerve ring at the height of the muscular esophagus. In females, the vulva was located at the level of the deirids, and in the posterior region the lateral appendages and the tapered tail were visualized, ending in a rougher region that resembled spines (Figure 2e). In the posterior region of the males, 3 pairs of precloacal papillae, one median papilla, one pair of adcloacal papillae and another 4 pairs of postcloacal papillae, and pair of lateral appendages, uneven spicules, ventral bands (Figure 2f-g and 2h).

Morphological and morphometric characterization of nematodes recovered from Bubalus bubalis
Male (

Discussion
The specimens analyzed in the present work belong to the genus Setaria parasites of the abdominal cavity the serous layers of the small intestines of the host buffaloes and cattle, reported by Nakano et al. (2007) in Japan, Watermeyer et al. (2013), in South Africa, Gomez-Puerta & Mayor, 2017in Peru, Shin et al. (2017 in South Korea and Mrifag et al. (2021) in Morocco.
With the scanning electron microscopy, it was possible to view in the previous elliptical oral opening, 1 pair of bifurcated head elevations, 2 pairs of ciliated cephalic papillae, 2 pairs of cephalic papillae without eyelashes and a papilla over amphids and deirids of conic shape. These findings are compatible with those in Mrifag et al. (2021) since they are specific characteristics of the species Setaria labiatopapillosa. However, they differ from the findings of Watermeyer et al. (2013) who studied Setaria parasites of Redunca arundinum in South Africa and they did not observe ciliated papillae. Another relevant feature for differentiating species of Setaria is related to the shape of the deirids, as reported of Desset (1966). Watermeyer et al. (2013) report bifid deirids in the species Setaria graberi in Redunca arundinum, while in present study the deirids are conical in form. In this sense, the findings in the present study are similar to those of Desset (1966), who found conical deirids for the species Setaria bidentata and Setaria digitata. This was also corroborated by Rhee et al. (1994) for Setaria digitata, and for Becklund & Walker (1969) for the species Setaria labiotopapillosa since they also have conical deirids.
In the posterior region, the tails of males and females showed two lateral cuticular appendages, corroborating the results of Mrifag et al. (2021), when they reported the occurrence of Setaria labiatopapillosa in cattle in Morocco. The final portion had a conical shape and in females, spike-like structures typical of females of the genus Setaria were observed, which is similar to the findings of several other authors (Desset, 1966;Becklund & Walker, 1969;Rhee et al., 1994;Kim et al., 2010;Singh et al., 2015;Mrifag et al., 2021).
The quantity and distribution of sexual papillae varies according to the species. Desset (1966) reports 3 pairs of precloacal papillae, 3 medium papillae and 4 pairs of postcloacal papillae in the species Setaria cornuta. Rhee et al. (1994) showed 3 pairs of precloacal papillae in the species Setaria digitata, 1 pair of adcloacal papillae and 3 pairs of postcloacal papillae, diverging from the results of the present study.
The male specimens showed 17 cloacal papillae: 3 pairs of precloacal papillae, 1 medium papilla, 1 pair of adcloacal papillae, and 4 pairs of postcloacal papillae; characteristic of the species Setaria labiatopapillosa, observed by Becklund & Walker (1969). Watermeyer et al. (2013) report the presence of 4 pairs of precloacal papillae, one median papilla and 6 pairs of postcloacal papillae for the species Setaria graberi, diverging from what was observed in the present study.
That said, this is the first report of Setaria labiatopapillosa in the northern region in Brazil, thus constituting a new geographical record for the occurrence of the species of the present study, bovine abdominal cavity parasites in the Amazon.

Conclusions
After morphological and morphometric analyses Setaria labiatopapillosa was found to occur parasitizing Bos taurus and Bubalus bubalis on the island of Marajó, Pará, Brazil.