Dirofilaria repens infection in a dog imported to Norway

Abstract

Dirofilaria repens infection was diagnosed in a dog that had been imported to Norway from Hungary three years previously. The dog was a four-year-old castrated male mixed-breed dog and presented for examination of two masses on the right thoracic wall. Fine needle sampling from the subcutaneous nodules and subsequent cytological examination revealed a high number of microfilariae and a pyogranulomatous inflammation. At re-examination approximately 3 weeks later, both masses had apparently disappeared spontaneously, based on both inspection and palpation. However, examination of peripheral blood by a modified Knott's test revealed a high number of unsheathed microfilariae with mean length of 360 μm and mean width of 6-7 μm, often with the classic umbrella handle appearance of D. repens. Polymerase chain reaction and sequencing confirmed the D. repens diagnosis. Subcutaneous dirofilariosis caused by D. repens is probably the most common cause of human zoonotic dirofilariosis in Europe, but currently is rarely encountered in northern countries such as Norway. However, travelling, import and relocation of dogs have increased, and thus the geographical range of these parasites is likely to increase from traditionally endemic southern regions. Increasing numbers of autochthonous cases of D. repens infections in dogs have been reported in eastern and central Europe. Although infection with D. repens often induces only mild signs or subclinical infections in dogs, they nevertheless represent a reservoir for zoonotic transmission and thus a public health concern, and, in addition, due to the long prepatent period and the high frequency of subclinical infections or infections with unspecific clinical signs, could easily be missed. Lack of experience and expectation of these parasites may mean that infection is underdiagnosed in veterinary clinics in northern countries. Also, predicted climate changes suggest that conditions in some countries where this infection is currently not endemic are likely to become more suitable for development in the intermediate host, and thus the establishment of the infection in new areas.

Figure 1

Fine needle sample from a subcutaneous mass on the right thoracic wall. Blood contaminated basophilic background. Many macrophages and non-degenerate neutrophils. Macrophages exhibiting cytophagia. A low number of plasma cells, an eosinophil and a multinucleated macrophage. Modified Wright’s, original magnification 400×.

Figure 2

Fine needle sample from a subcutaneous mass on the right thoracic wall. Microfilaria with an obtuse cephalic end and a sharp and filariform tail dispersed in an inflammatory exudate. Modified Wright’s, original magnification 630×.

Figure 3

Microfilaria in Knott’s test. Typical example of microfilaria seen in Knott’s test as visualized under DIC. Note classic umbrella handle tail morphology.