First report of Dracunculus insignis in two naturally infected cats from the northeastern USA

Abstract

Dracunculiasis is rarely reported in cats, yet over the last few years we have identified two cats with filarioid-like spirurid infections. Case 1 was a 9-year-old cat with pituitary-dependent hyperadrenocorticism from New York tate from which four adult dracunculoid nematodes were isolated from its torso. Based on morphometric characteristics and parasite geographic distribution, the specimens were identified as Dracunculus insignis females; at least one of the females was gravid, suggestive of patent infection. Species identification was confirmed through amplification and sequence analysis of nuclear and mitochondrial loci. Case 2 was a 14-year-old diabetic cat from Massachusetts. Formalin-fixed sections were obtained from a subcutaneous mass excised from the left foreleg. Histopathological examination revealed a large nematode with morphometrical characteristics of Dracunculus, surrounded by lymphocytes and sheets of eosinophils. These two cases appear to be the first published reports of dracunculiasis in domestic cats in the USA, and based on the findings from case 1, D insignis may be the species associated with both infections.

Case Report

Dracunculiasis is rarely reported in cats. ¹ In mid-February 2012, the owner of a 9-year-old neutered male domestic shorthair cat (Felis catus), with a 10-month history of pituitary-dependent hyperadrenocorticism, extracted a white nematode (12 cm × 0.3 cm) from the cat’s left flank and presented it to the veterinarian the same day. Pending identification of the nematode, the cat was scheduled for examination the following day, and the owner was sent home with instructions to treat the cat using Drontal (praziquantel/pyrantel pamoate; Bayer HealthCare) as per label (0.5–1.0 mg praziquantel and 20–40 mg pyrantel pamoate per kg bodyweight), with treatment to be repeated in 2 weeks’ time. Upon examination of the exit wound on the cat’s flank, a second ulceration was observed, and a second nematode was extracted intact by simple traction. The nematodes were submitted to the New York State Diagnostic Laboratory at Cornell University and identified as Dracunculus insignis, based on morphometric characteristics. Approximately 2 weeks after the emergence of the first nematodes, a third was visible under the skin in the same area. A fourth and final nematode was recovered approximately 1 month after the first. For the recovery of the third nematode, a wet compress was applied to the area and emergence occurred a week later. This specimen was a 14 cm × 0.15 cm, gravid Dracunculus female (Figure 1) from which numerous characteristic first-stage larvae were recovered (Figure 2); this nematode was presumed to be D insignis, based on its size, location and host. While these identification criteria are commonly used, when male specimens are not available for study, species determination may not be fully possible.^2–4 Furthermore, dracunculiasis in domestic cats in North America has not been previously reported. Dracunculus insignis is a generalist parasite, ⁴ and was previously reported from upstate New York in American mink (Mustela vison), otter (Lutra canadensis), raccoon (Procyon lotor) and striped skunk (Mephitis nigra), ⁵ as well as from domestic dogs (Canis familiaris). ⁶ Even though D insignis was the top differential etiology in this case, Dracunculus lutrae, and perhaps other unknown species of Dracunculus from wildlife, could overlap in this geographical setting. To confirm the species identity of the parasites from case 1, DNA from the gravid female was amplified at two loci: the small subunit ribosomal RNA gene and the cytochrome C oxidase subunit I from mitochondria. Polymerase chain reaction amplification was performed as previously described.^3,4 The resulting sequences were assembled and the final assemblies were compared with GenBank references using the Basic Local Alignment Search Tool (BLAST) algorithm through the SeqMan module of Lasergene v 9.0 (DNASTAR). The consensus sequence for the 18S rRNA showed 100% identity with the reported sequence of D insignis (GenBank accession number AY947719), with at least nine base-pair differences from a closely related member of the genus: Dracunculus medinensis (AY947720). Confirmatory sequencing data obtained from amplification of the mitochondrial gene had almost perfect identity (>99.2%) with at least 17 different isolates of D insignis, including accession numbers EU646545, EU646546, EU646536, EU646564 and EU646550. Similarly to the small subunit rRNA locus, there was >9% discrepancy with sequences of the closely related D medinensis (accession numbers JN555591 and HQ216219). No other sequences from other organisms had significant correspondence through BLAST searches. The DNA sequence analyses from the nuclear and mitochondrial loci confirmed the initial identification of this specimen as D insignis.

Figure 1

Gravid adult female Dracunculus insignis recovered from the subcutaneous tissue over the flank of a naturally infected domestic cat in case 1

Figure 2

First-stage larva of Dracunculus insignis from a gravid female worm recovered from naturally infected cat in case 1. Note the long tapering tail characteristic of first-stage larvae of this genus

Case 2, a 14-year-old diabetic neutered-male domestic longhair cat from Pembroke, MA, USA, had originally been brought to our attention the same month, 3 years previously (February 2009). The cat was brought to the clinic for examination of a mass on its left forelimb that had become evident over the last few days. Cat 2 was reported to have ample outdoor access and was known to be an avid hunter. The 1 cm × 2 cm mass ran along the craniolateral aspect of the leg proximal to the carpus, lateral to the cephalic vein and appeared to be confined to the subcutis. The cat had a subtle limp on that limb but otherwise appeared non-painful on examination. An aspirate of the mass revealed round cells, and the owners elected surgical removal and biopsy. Removal was accomplished primarily through blunt dissection, leaving the cephalic vein intact. The tissue was submitted for biopsy and microscopic examination, which revealed parasitic cellulitis: the deep dermis and subcutis contained sheets of eosinophils intermixed with moderate numbers of medium-sized lymphocytes, fewer, but numerous, plasma cells and scattered epithelioid macrophages. Pleocellular inflammatory infiltrate surrounded multiple cross-sections of a large nematode. Initial diagnosis based on the histological examination was that of a filarioid-like spirurid nematode infection. Further examination of the histological sections revealed the following features consistent with the genus Dracunculus: an approximate diameter of 250 µm, the lack of longitudinal ridges, numerous nuclei at the base of the lateral chords, gut with prominent inclusion of pigment, numerous tall, narrow muscle cells (of the polymyarian/coelomyarian type) and, finally, the location of the nematode in subcutaneous tissue (Figure 3). The lack of evidence of reproductive tubes in any of the sections and the measured size were features compatible with a male nematode, although we could not rule out an infertile, immature female. Comparison of this specimen with those from experimental infections in ferrets (Mustela putorius furo) with D insignis ⁷ demonstrated a high degree of similarity. Based on the morphometric characteristics, the site of infection and the geographic location where the infection was acquired, a presumptive diagnosis of D insignis was made. This diagnosis from case 2 is now strengthened by the molecular confirmation from case 1, supporting the notion that D insignis can naturally infect cats.

Figure 3

Cross-section through the nematode in the subcutaneous tissue of a naturally infected cat, case 2, with distinguishing features [approximate diameter of 250 μm, lack of longitudinal ridges, numerous nuclei at the base of the lateral chords, gut with prominent inclusion of pigment, numerous tall, narrow muscle cells (of the polymyarian/coelomyarian type)], allowing for its identification as a male Dracunculus insignis

Dracunculus species are parasites of the subcutaneous tissues of mammals and reptiles. Of these, four species are known to occur in mammals: ⁸ Dracunculus fuelleborni in opossums (Didelphis aurita); ⁹ D insignis mainly in raccoons, but also fisher (Martes pennanti), mink, marten (Martes americana), grey fox (Urocyon cinereoargenteus), skunk, dogs and otters;^{2,4–6,10,11} D lutrae only in otters; ⁴ and D medinensis in humans and, very rarely, in other animals in the Old World.^3,12 The life cycle of these parasites is well known^13,14 and involves the release into water of large numbers of first-stage larvae from ovoviviparous adult females present in the subcutaneous tissues of the vertebrate host. These larvae are ingested by copepods of the genus Cyclops, the intermediate host, in which they develop to their third and infective stage. Final hosts (raccoon, human, cat, etc) become infected when they ingest copepods containing viable third-stage larvae in drinking water, or within the tissues of paratenic (transport) hosts, such as tadpoles and frogs.^13–15 The pre-patent period is long (309–410 days), and culminates in the migration of the gravid female to an extremity where she induces the formation of a shallow ulcer. Upon contact with fresh water, the female protrudes her anterior end and prolapses a length of uterus which allows the release of first-stage larvae into the aquatic environment. Males are very small and are generally not recovered or seen. Although the infection does not appear to elicit a significant reaction from the host, the skin overlaying the ovoviviparous female may become inflamed and painful. ¹³ Wounds are known to heal rapidly when no secondary bacterial infection is present, usually within 2–4 weeks. Care must be taken not to rupture the nematodes, as this can lead to phlegmon. ¹⁶ Thus, the treatment of choice for such infections usually involves surgical resection of the nematodes; there is no anthelminthic treatment available.

Of the four species of Dracunculus reported in mammals, only D medinensis has been previously reported sporadically in cats;^17–19 the earliest may be a report from Sonsino in 1889. ²⁰ Muller^21,22 was also able to experimentally infect cats with D medinensis obtained from human patients; a single non-gravid adult female emerged from 1/9 cats, while juvenile stages were recovered from the tissues of 20/37 cats examined by dissection. Despite these observations it is a core premise of the Guinea Worm Eradication Program, that there are no animal reservoirs for this human pathogen. ²³ There are a few additional reports of Dracunculus species infection in cats that come from other areas of the world, including Israel ²⁴ and China.^25,26 These countries were never endemic for D medinensis and therefore these reports probably represent infections with a different species. It is likely that the cats involved in the present report became infected through the normal route: ingestion of a copepod intermediate host in water or through predation on tadpoles or frogs. Besides the dermatological ulcers in case 1 and the cellulitic mass in case 2, no additional clinical signs or complications were reported from either case. In both cases, the Dracunculus-associated wounds became apparent in February and eventually healed without complication. It is interesting that both of these cats had underlying chronic non-infectious conditions (hyperadrenocorticism and diabetes, respectively), although it is not clear whether these underlying conditions might have contributed to the infections and clinical presentation, or might have prompted the owners to seek veterinary care.

Conclusions

This appears to be the first published report of dracunculiasis in domestic cats in North America, and the first confirmed report of D insignis infections in a cat.