Rare case of Angiostrongylus vasorum intraocular infestation in an asymptomatic dog

Angiostrongylus vasorum (Nematoda, Metastrongyloidea), commonly known as French heartworm, is a life-threatening nematode for dogs. General findings suggest that A. vasorum is occurred in isolated endemic areas. Since the first finding in Southern France in 1853 (Serres, 1854; Guilhon, 1963), the parasite was observed in Ireland (Roche & Kelliher, 1968), Switzerland (Wolff, 1969), Uganda (Bwangamoi, 1972), England (Simpson & Neal, 1982), Italy (Poli et al., 1984) and Denmark (Bolt et al, 1992). However, in recent years, autochthonous cases of infection are increasingly diagnosed in other European countries where the parasite previously did not occur, including Slovakia (Elsheikha et al., 2014).

The indirect life cycle of A. vasorum involves slugs and snails as intermediate hosts and frogs as paratenic hosts that harbour infective third stage larvae (L3). The definitive host becomes infected after ingestion of infected intermediate or paratenic host (Guilhon, 1963; Bolt et al., 1993).

The disease is most frequently presented as cardiorespiratory distress with a history of gagging, coughing, exercise intolerance and dyspnoea. Bleeding abnormalities, coagulopathy, neurological symptoms, general malaise, uveitis, depression, and anorexia are also described. Occasionally, cases of aberrant migration of A. vasorum to liver, pancreas, kidney even to CNS have been observed (Koch & Willesen 2009). The present study describes an atypical case of A. vasorum localisation in the anterior chamber of the right eye of an 18-month-old beagle from Slovakia.

An 18-month-old beagle male from Bardejov, north-eastern Slovakia was referred to a private veterinary clinic in Prešov (Slovakia) for sudden appearance of a filiform foreign body in the right eye. The dog was kept indoors in the city, was usually walked in the vicinity of a river and never moved outside the region. Initial clinical ophthalmological examination revealed the presence of a motile intraocular nematode in the anterior chamber of the right eye (Fig. 1). Apart from the infection, the eye appeared ophthalmologically normal. Clinical examination revealed no evidence of a systemic disease. The faeces were investigated by the Baermann technique and fl otation method with zinc sulphate solution (s.g. 1.2) (Bowman, 2014) with negative results. Other examinations were declined by the owner.

Fig. 1

Surgical removal of the parasite was performed under injection anaesthesia (Dexmedetomidine, Diazepam, and Ketamine). Removal of the parasite was performed by anterior chamber paracentesis and aspiration of the worm using 0.9 mm port. A 2 % methyl cellulose solution was injected into the anterior chamber and the inputs were sutured with 7/0 absorbable filament, then the eye was pro tem surgically covered with third eyelid.

Postoperative medication consisted of topical treatment with steroid solution of fl uoremetolon twice per day (Effl umidex Liquifilm Int Opu, Allergan Pharmaceuticals, Ireland), antibiotic instillation of tobramycinum four times per day (Tobrex Int Opo, S.A. Alcon-Couvreur, Belgium), and 1 % solution of atropine sulphate twice per day. The patient wore an Elizabethan collar until the stitches were removed day 4 post surgery. A follow up at day 4 revealed complete resolution without observable ophthalmologic after-effects seen in the right eye (Fig. 2). Specific anthelmintic treatment of angiostrongylosis consisted of single topical application of imidacloprid 250 mg/ moxidectin 62.5 mg (Advocate®,Bayer, Germany). A telephonic follow-up was performed six months post-surgery and the owner reported no evidence of systemic or ocular clinical signs.

Fig. 2

The extracted nematode was identified based on morphometric and characteristic morphological features according to species description by Costa et al. (2003) under the Leica DM4000B light microscope, Leica DFC 290 HD camera and Leica Application Suite V 3.8.0 software (Leica Microsystems GmbH, Germany).

The worm was identified as an adult female of A. vasorum. The body measured 24.3 mm in length and maximum body width was 0.534 mm. The buccal capsule directly joined the rhabditoid oesophagus with length 257.81 μm. The nerve ring was situated approximately in the middle of oesophagus. The excretory pore was located near oesophago-intestinal junction, 478.89 μm from the anterior extremity. The caudal end was ventrally curved and rounded. The vulva was situated 306.57 μm from the anus. The female cuticle was transparent. The ovarians filled with oocytes was twisted along the reddish intestine and created a “barber pole” appearance (Fig. 2).

The nematode was homogenized with 5 mm stainless beads (Qiagen®, Hilden, Germany) and ATL buffer in Qiagen TissueLyser (Qiagen®, Germany) for 30 Hz/6 min. DNA extraction was provided by a commercial isolation kit DNeasy Blood & Tissue (Qiagen®, Hilden, Germany), following the steps in protocol. A fragment of ITS2 rDNA was amplified by conventional PCR assay using the A. vasorum-specific primer set AV4/AV5 designed by Al-Sabi et al. (2010). A DNA fragment of 250 bp was separated on a 1.5 % agarose gel. The positive template was purified using NucleoSpin® Gel and a PCR Clean-up kit (Macherey-Nagel GmbH & Co., KG, Germany) and sequenced by Sanger sequencing in both directions. Sequences were compared by BLAST (Basic Local Alignment Search Tool) with sequences available in GenBank.

A 156 bp long overlapping fragment of A. vasorum revealed 99 % similarity with the isolate obtained from a dog from Italy (KF270683). The nucleotide sequence of A. vasorum ITS2 rDNA gene fragment obtained during the study was deposited in Gen-Bank under accession number MH018578.

The herein presented description of A. vasorum specimen found intraocularly in a dog from north-eastern Slovakia is an atypical but not sole case of ectopic location of A. vasorum in the eye. The ocular localisation of the parasite has to date been reported several times as summarized by Colella et al. (2016), however this patient is to the best of our knowledge the first reported case where any ocular pathology and any other clinical signs associated with A. vasorum infection were absent. Dogs of all ages can be infected with A. vasorum, however, several studies showed that dogs younger that one year are more susceptible to clinical infection, presumably due to riskier behaviour when scavenging or playing with snails (Chapman et al. 2004; Koch & Willesen, 2009). This is true also for the herein reported case where the dog was in the age of 18 months and the owner confirmed its curiosity regarding snails and frogs.

The previously reported 8 cases of ocular A. vasorum migration originated from endemic countries such as France, Great Britain, Denmark, Canada and Italy (Colella et al., 2016). In Slovakia, the first canine angiostrongylosis cases were reported in 2012 and 2013 from eastern Slovakia (Hurníková et al. 2013; Miterpáková et al. 2014). The following copro-epidemiological research in the territory of Slovakia revealed a relatively high prevalence of A. vasorum in dogs and red foxes (4.13 % and 5.43 %, respectively) (Miterpáková et al. 2015; Čabanová at al. 2018a, 2018b). Despite the fact that angiostrongylosis is usually presented with cardio-respiratory clinical signs, the majority of infected dogs identified within the above mentioned study were asymptomatic. Also here presented ocular localisation of A. vasorum reveals that angiostrongylosis should be included into differential diagnosis of unexplained canine eye disorders.