Nodular presentation of Dirofilaria repens infection in a cat mimicking a fibrosarcoma

Abstract

A cat with multiple subcutaneous nodules suggesting a soft tissue sarcoma by physical and computed tomographic examination was diagnosed as being affected by subcutaneous filariosis based on cytologic and ultrasonographic assessments. Nodules were surgically removed and extracted nematodes were identified by PCR as Dirofilaria repens. Furthermore, DNA of Dipetalonema dracunculoides (syn. Acantocheilonema dracunculoides) was detected by PCR, with no evidence of circulating microfilariae. To the best of the authors' knowledge, this represents the first report describing adults of D repens in multiple subcutaneous nodules in a cat. Cytopathologic examination allowed characterization of the parasitic nature of the nodules. Veterinary practitioners should be aware of the possible nodular presentation of D repens in cats and should include D repens in the differential diagnosis of subcutaneous neoformations in the cat.

Retrospective Analysis of Canine Vector-borne Diseases (CVBD) in Germany with Emphasis on the Endemicity and Risk Factors of Leishmaniosis

“…Cases of heartworm infections with a negative antigen result but with microfilaria circulating in the blood were also observed, but more rarely (Pantchev et al 2011). An adulticid treatment, only a few adults, delayed antigenemia or immune complexes are possible reasons for this constellation (Weil et al 1984, Pantchev et al 2011 (Pantchev et al 2011, Cabanova et al 2015, Ionica et al 2015, Manzocchi et al 2017. In the present study, D. immitis was detected only in dogs originating from endemic areas like Spain/ Portugal and Greece.…”

Positive PCR alone should not be considered sufficient to establish Dirofilaria repens as the cause of subcutaneous nodular lesions in the absence of a clear cytologic picture

“…This would appear to be a highly unusual finding considering the biology of this nematode. 3,4 While the larger hyaline structures identified as microfilariae in the report could be roughly around the same size of microfilariae of D repens, the smaller hyaline structures seem noticeably shorter than microfilariae of D repens (approximately 300 lm in cytology samples) 3 , considering the mast cells as comparison. Rather, in our opinion, these hyaline structures more closely resemble collagen fibers as they have been described in keloidal mast cell tumors.…”

“…The cytologic pattern of the nodules presented in the report is uncommon and does not agree with the cytology features described in previous cases of D repens. [3][4][5][6] The inflammatory population with prevalence of well differentiated mast cells is not typical of the cases of subcutaneous dirofilariosis previously described, rather a mixed inflammatory pattern with prevalence of lymphocytes, eosinophils, macrophages and neutrophils was reported in previous studies. [3][4][5][6] The structures interpreted as microfilariae, pointed out by yellow or red arrows in the figures of the report, are characterized by pink and hyaline color, indistinct outline, amorphous, or fibrillar texture ( Figure 1A,B).…”

“…[3][4][5][6] The inflammatory population with prevalence of well differentiated mast cells is not typical of the cases of subcutaneous dirofilariosis previously described, rather a mixed inflammatory pattern with prevalence of lymphocytes, eosinophils, macrophages and neutrophils was reported in previous studies. [3][4][5][6] The structures interpreted as microfilariae, pointed out by yellow or red arrows in the figures of the report, are characterized by pink and hyaline color, indistinct outline, amorphous, or fibrillar texture ( Figure 1A,B). In our opinion, no microscopic features characteristic of D repens microfilariae are visible in the figures of the report, such as the distinct outline, the blunt cephalic extremity, or the cuticolar transverse grooves ( Figure 1C,D).…”

“…In our opinion, no microscopic features characteristic of D repens microfilariae are visible in the figures of the report, such as the distinct outline, the blunt cephalic extremity, or the cuticolar transverse grooves ( Figure 1C,D). 3 In addition, there is remarkable diversity in length and wideness of those pink hyaline structures. This has never been reported before and the authors give no further explanation in the present case report.…”