First report of Eucoleus boehmi (syn. Capillaria boehmi) in dogs in north-western Italy, with scanning electron microscopy of the eggs

Abstract

Dogs can be infected by several nematodes of the Trichuridae family. Trichuridae eggs are all similar, barrel shaped with polar plugs, and misdiagnosis among different species can occur. The most common species is Trichuris vulpis, while the respiratory parasites Eucoleus boehmi (syn. Capillaria boehmi) and Eucoleus aerophilus (syn. Capillaria aerophila) are rarely observed in pets. E. boehmi is reported for the first time in this study in north-western Italy with other Trichuridae. Dog faecal samples (270) were examined by flotation. E. boehmi (2.2%), E. aerophilus (4.4%) and T. vulpis (12.2%) were found; identification was done with measurements and through observation of morphological characters already known. The specific identification of E. boehmi was confirmed using scanning electron microscopy: its egg shell shows a dense network with a fine mesh, surrounding small pits, on the contrary E. aerophilus eggs present a thick mesh with wide depressions, while T. vulpis eggs surface is smooth.

Dogs can be infected by several nematodes belonging to the Trichuridae family. The most common species is the intestinal whipworm Trichuris vulpis (Frolich, 1789), while the respiratory parasites Eucoleus boehmi (syn. Capillaria boehmi) (Supperer, 1953) and Eucoleus aerophilus (syn. Capillaria aerophila) (Creplin, 1839) are rarely reported in pets.

All Trichuridae eggs are characterized by a similar barrel shape with polar plugs and misdiagnosis among different species can occur. E. boehmi eggs are 54- 60 × 30-35 µm in size, contain a multicellular embryo that does not fill the egg, are clear to golden in colour and show a delicately pitted surface (Campbell, 1991; Schoning et al., 1993; Zarnowsky & Patyk, 1960). E. aerophilus eggs measure 60-72 × 26-34 µm, are entirely filled by one- or two-cell embryo, have a net-like ornamented outer layer and are slightly asymmetrical. T. vulpis eggs measure 70-80 × 30-42 µm, have a brown-yellowish colour, a symmetrical shape with prominent plugs showing a ring-like thickening at the base and a smooth surface (Campbell, 1991; Conboy, 2009). Respiratory capillariosis in pets has recently received increasing attention in Europe and North America, although specific coprological diagnosis can be challenging (Conboy, 2009; Di Cesare et al., 2011).

The aim of this work is to report for the first time the observation of E. boehmi in dogs in north-western Italy, together with other Trichuridae, and to describe the egg surface with scanning electron microscopy, comparing with E. aerophilus and T. vulpis eggs.

Materials and Methods

From January 2010 to March 2011, as part of a wider study on canine endoparasites, 270 faecal samples of dogs living in a rural environment were randomly sampled in Liguria, north-western Italy. The examined population consisted of 161 male dogs and 109 females (age range: 6 months-14 years; average: 5.4 years). Samples were examined by centrifugal flotation with zinc sulphate (s.g. 1.350).

Trichuridae eggs were identified on the basis of morphologic and morphometric characteristics described in the literature (Campbell, 1991; Conboy, 2009; Schoning et al., 1993). E. boehmi eggs were also examined using scanning electron microscopy (JEOL JSM 5410 SEM). For SEM, eggs were isolated by flotation in a zinc sulphate solution and sieved, following the technique described in Al-Sabi et al. (2010), then mounted on aluminum stubs, air dried, gold coated with the sputtering technique, observed and photographed.

Sterile cotton tip swabs were inserted into each nasal passage for nasal examination, following the technique described by Schoning et al. (1993).

Results

Of the 270 examined faecal samples, 46 were positive for Trichuridae eggs: six dogs (2.2 %) were positive for E. boehmi (Fig. 1a), 12 (4.4 %) for E. aerophilus (Fig. 1b), and 33 (12.2 %) for T. vulpis (Fig. 1c). Five dogs presented a double infection (three cases of T. vulpis and E. aerophilus, Fig. 2a, two cases of T. vulpis and E. boehmi, Fig. 2b). Nasal swabs performed on all six dogs positive for E. boehmi were negative.An accurate morphological and morphometric analysis was carried out using the optical microscope to identify eggs of different species, following the already mentioned characteristics (Campbell, 1991; Conboy, 2009; Schoning et al., 1993).

Fig. 1.

Light microscopy: a. Eucoleus boehmi egg; b. Eucoleus aerophilus egg; c. Trichuris vulpis egg.

Fig. 2.

Light microscopy: a. Eucoleus aerophilus egg (bottom) and Trichuris vulpis egg (top); b. Eucoleus boehmi egg (right) and Trichuris vulpis egg (left).

Scanning electron microscopy highlighted the characteristics of the E. boehmi egg shell: the surface presented a dense network with a fine mesh, surrounding irregularly distributed small pits, which give the eggs a porous appearance (Fig. 3). These features clearly distinguish E. boehmi eggs from E. aerophilus and T. vulpis. With SEM, E. aerophilus eggs present a thick mesh with wide depressions, while T. vulpis eggs surface is completely smooth (Traversa et al., 2011).

Fig. 3.

Scanning electron microscopy of Eucoleus boehmi egg: a. whole egg; b. polar plug; c. egg surface.

In pet animals, respiratory capillariosis are likely to be underestimated because of difficulties in coprologic specific diagnosis. The confusion arises especially from the similarity of the barrel-shape of the Trichuridae eggs. The most reliable distinctive characteristic is the external structure of the shell (Zarnowsky & Patyk, 1960; Conboy, 2009). This feature can already be observed with an accurate morphological analysis of the egg surface using light microscopy (100 ×); scanning electron microscopy highlighted in details the characteristics of the egg shell structure which differentiate the three species.

Concerning the clinical aspects, only one dog infected in our study showed mild respiratory symptoms, such as nasal discharge and cough during exercise.

Although respiratory capillariasis is considered uncommon, clinicians should include these infections in the differential diagnosis of cardiopulmonary affections. Clinicians should thus consider performing accurate coprological examinations in the case of respiratory symptoms, using more sensitive solutions for flotation (zinc sulphate) (Conboy, 2009). Furthermore, the awareness of the possible presence of different species of capillarid nematodes in dogs is essential for a correct diagnosis. Epidemiological studies are required to ascertain the actual distribution of these neglected and emerging parasites.