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Case Reports |
Correspondence: 1Corresponding Author: Niina Airas, Department of Basic Veterinary Sciences, Faculty of Veterinary Medicine, P.O. Box 66, 00014 University of Helsinki, Finland. niina.airas{at}helsinki.fi
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Key Words: Cats • chronic dermatitis • Trichinella nativa • trichinellosis
An 8-year-old, male, neutered Domestic Shorthair cat with an ulcerative skin lesion was presented at a small animal referral practice. At the time of presentation, a 4-mm x 7-mm crusted ulcer was located on the skin below the left lower eyelid. The conjunctiva adjacent to the lesion was hyperemic and slightly swollen. The cat was otherwise healthy. The ulcer had appeared 2 months earlier and had not responded to oral antibiotic therapy with amoxicillin and clavulanic acid or to topical treatment with eye drops that contained fusidic acid. Finally, the skin lesion was excised, with clear surgical margins, with the cat under general anesthesia, and was submitted to a veterinary referral laboratory for histopathology.a Recovery of the cat from surgery was uneventful, and the operative site had healed by the time of suture removal.
The formalin-fixed skin biopsy specimen was routinely processed for histopathology. Sections were cut at 4 µm and stained with hematoxylin and eosin. Histologic examination showed that the biopsy specimen mainly consisted of interlacing bundles of spindle cells (Fig. 1A). The spindle cells were fibroblasts, with an elongated hypochromatic nucleus, dispersed chromatin, small nucleolus, and scant eosinophilic cytoplasm, with indistinct cell boundaries. Mitotic figures were rare. Numerous lymphocytes, histiocytes, plasma cells, and neutrophils were interspersed among the dense spindle-cell population, but none were as abundant as the spindle cells. Moderate perivascular lymphocytic infiltrates with fewer eosinophils were confined to the periphery of the lesion. The previously mentioned tissue reaction surrounded a well-preserved coiled nematode larva within a 400-µm x 250-µm elliptical cyst . The outer layer of the cyst-larval complex consisted of a thick (35 µm) hyaline capsule. The larva was 35-µm wide. The intestine, musculature, stichosome, and hypodermal bacillary bands were identified in transverse tissue sections. A mild lymphoplasmacytic inflammatory reaction was present at the polar ends of the longitudinally sectioned cyst. Because the inflammatory infiltrates and granulation tissue had replaced most structures of the dermis, the exact location of the cyst was not determined. However, at the periocular area, muscle fibers are usually located superficially when compared with other regions of the body. Therefore, the numerous myofibrils observed in the healthy skin adjacent to the inflamed area and located at the same depth as the encapsulated larva, might suggest that the cystic formation had originated within the myofibrils. Furthermore, the epidermis that covered the lesion was ulcerated, and there was moderate serocellular crusting.
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During the 1-year follow-up, the symptoms recurred; the cat scratched at the eye and squinted. Because of the reappearance and worsening of the clinical signs, the cat was referred to the Small Animal Hospital at the University of Helsinki (Helsinki, Finland). At the time of clinical examination, a V-shaped, alopecic area was observed at the lower eyelid at the site of the previous operation. Subjacent to the affected skin, a firm, subcutaneous mass was present in the periocular area (Fig. 1C). The mass was 1-cm wide and covered the entire lower eyelid and part of the upper eyelid. Ophthalmoscopic and fundic examinations were normal. Clinical laboratory results revealed an increased serum creatine kinase activity (1689 U/l; reference interval: 60–350 U/l), which could be related to the clinical condition of the cat. Other hematologic parameters were within reference intervals. The cat was also tested for Feline leukemia virus and Feline immunodeficiency virus, with negative results. Contrast computed tomography showed a muscular mass that did not infiltrate the bone. The cat was anesthetized, and several biopsy specimens were taken from the mass and the biceps femoris muscle.
Histopathologic examination of the specimen revealed that the lesion was highly cellular, composed mainly of haphazardly arranged fibroblasts with moderate anisocytosis, anisokaryosis, and rare mitotic figures. Scattered leukocytes were present throughout the lesion. The histopathologic findings were indicative of granulation tissue with inflammation and fibrodysplasia, but the marked proliferation of spindle cells and infiltrative growth warranted the consideration of low-grade fibrosarcoma as a differential diagnosis. Cats are prone to develop sarcomas secondary to chronic inflammation, with feline vaccine–induced sarcoma and feline ocular posttraumatic sarcoma being the classical examples of this kind of carcinogenesis.14 Interestingly, the role of chronic Trichinella sp. infection as an initiator and promoter of malignant transformation of host cells was discussed in a previous study15 that described a case of trichinellosis in a cat in association with oral squamous-cell carcinoma.
From the artificially digested muscle biopsy sample derived from the biceps femoris muscle (Table 1), one Trichinella-like larva was isolated and preserved in absolute ethanol at –20°C until analyzed. DNA was isolated from the individual larva, and a multiplex polymerase chain reaction (PCR) was performed according to procedures in a previous study19 (Table 1). The agarose gel electrophoresis of the PCR products demonstrated a distinct single band of 127 bp, which indicated T. nativa infection (Fig. 1D).
During the present study, the initial diagnosis was based on the finding of a nematode larva identifiable as Trichinella sp. within a skin biopsy specimen and then confirmed by the detection of Trichinella spp. antibodies in the serum of the cat. Later, PCR analysis revealed T. nativa as the causative species. Trichinella spp. have a wide range of host species, and cats have been found to be among the most permissive and susceptible hosts of this parasite. In fact, muscle larvae of Trichinella spp. were detected as early as 1845 in the cat.11 Cats are effective hunters and become infected upon the ingestion of meat that contains muscle-stage larvae. The cat in the present case had been observed preying on small mustelids. Trichinella nativa is the most common Trichinella sp. in Finnish wildlife, although Trichinella spiralis, Trichinella britovi, and Trichinella pseudospiralis are also present.16 Furthermore, Trichinella infections that occur in cats have been reported in several countries, including Finland.12,16 However, Trichinella infection rarely causes clinical signs in their natural hosts, unless they are infected with a very large number of larvae.7
The clinical effects of feline trichinellosis are primarily based on information obtained from experimental infections. Clinical signs, when present, include mild gastrointestinal disturbances, such as loose stools and vomiting, during the intestinal phase of the parasite's lifecycle.5,6 Clinical signs related to generalized disease (e.g., dull coat, weakness, muscle stiffness, discomfort, and death) have been reported in severe infections.5,6 However, clinically apparent natural infections seem to be extremely rare in cats. Before the present case, only 4 cases were described in the veterinary literature. The earliest cases, from Germany (1952), India (1954), and the United States, were summarized in detail.13 Briefly, the German case was of a heavy infection, characterized by gastrointestinal signs, wasting, weakness, and stiffness of the limbs, which resulted in death. The cat from India suffered from a lack of appetite, vomiting, diarrhea, and lockjaw 2 days before death. The postmortem examination revealed an intestinal phase of Trichinella sp. infection. The first case reported from the United States occurred in Massachusetts and was characterized by transient hemorrhagic enteritis with identifiable adult nematode worms within diarrheic stools. Migrating Trichinella larvae were found in the peripheral blood of the cat with a modified Knott's test.13 The muscle phase of the infection seemed to be clinically unapparent, although a moderate eosinophilia was present for 3 months. Since then, an additional case of trichinellosis was reported in association with oral squamous-cell carcinoma in a cat from New York.15
To date, published cases of clinical trichinellosis in cats demonstrated that, although the disease is rare, it can have several manifestations. The present case describes a nonhealing ulcerative skin lesion associated with T. nativa infection. There are several methods that can be used to confirm the clinical diagnosis of a suspected case of trichinellosis. Although, some assumptions concerning the Trichinella sp. involved can be made based on histopathology, techniques that use molecular biology are needed for reliable identification to the species level.
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TOPAbstractSources and manufacturersReferences |
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<?ENTCHAR ast?> ELISA = enzyme-linked immunosorbent assay; ES = excretory-secretory; IgG = immunoglobulin G; HRP = horseradish peroxidase; IHC = immunohistochemistry; DAB = 3,3'-diaminobenzidine; PCR = polymerase chain reaction.
<?ENTCHAR dagger?> See references 4, 10, 17.
<?ENTCHAR Dagger?> AbD Serotec, division of MorphoSys UK Ltd., Oxford, UK.
<?ENTCHAR sect?> See reference 8.
<?ENTCHAR par?> Tissue and Hair Extraction Kit for use with the DNA IQTM System, Promega Corp., Madison, WI.
<?ENTCHAR para?> See reference 19.
a. Patovet Ay, Helsinki, Finland.
b. AbD Serotec, division of MorphoSys UK Ltd., Oxford, UK.
c. Tissue and Hair Extraction Kit for use with the DNA IQTM System, Promega Corp., Madison, WI.
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