Human dirofilariosis in Austria: the past, the present, the future

Abstract

Background: Dirofilariosis is a vector-borne parasitosis caused by filarial nematodes of the genus Dirofilaria. In humans, who represent accidental hosts, dirofilariosis is mostly caused by Dirofilaria repens and Dirofilaria immitis. In Austria, the first reported case occurred in 1978. Since then, several (case) reports have been published.

Methods: A systematic and retrospective review of collected published cases and new, unpublished confirmed cases of human dirofilariosis occurring in Austria was performed. A nematode was extracted from the eyelid of a previously unreported case and subsequently characterized histologically and using molecular biology techniques.

Results: Data on a total of 39 cases of human dirofilariosis in Austria occurring between 1978 and 2020 are summarized. Over the past four decades the incidence has markedly increased, in particular after 1998. Of the 39 patients, men and women were equally affected, and the mean age was 47.1 years. The area most frequently affected was the head (38.5% of cases). Confined ocular involvement was observed in 23.1% of cases, and nematodes were isolated from the neck/trunk, extremities and the genito-inguinal area in 25.6, 15.4 and 15.4% of patients, respectively. Microfilariae were detected in two cases. Of the 39 patients, only 73.9% tested positive for anti-filarial antibodies and 56.3% for eosinophilia, despite successful isolation of a nematode; consequently, these measures did not represent reliable markers for dirofilariosis. Most patients had a travel history to countries endemic for Dirofilaria species. One patient who had not traveled abroad represented the only autochthonous case recorded to date. Dirofilaria repens was the predominant species, identified in 89.7% of cases. In the newly reported case of subcutaneous dirofilariosis, a live non-gravid Dirofilaria repens adult female of 12 cm length was isolated from the eyelid of the patient, and a video of the extraction is provided.

Conclusions: The incidence of human dirofilariosis cases has increased strikingly over the last four decades in Austria. More cases can be expected in the foreseeable future due to changes in human behavior and (travel) activities as well as climate changes and the associated alterations in the availability of the natural reservoir, the vectors and the intrinsic characteristics of the parasite.

Keywords: Austria; Dirofilaria immitis; Dirofilaria repens; Dirofilariosis; Eyelid; Nematode.

Fig. 1

Cases of confirmed human dirofilariosis in Austria according to year of diagnosis

Fig. 2

a Cases of confirmed human dirofilariosis in Austria by age. b Localizations of Dirofilaria species-induced lesions and sites from which a nematode had been isolated. c Travel history of patients with human dirofilariosis. d Causative Dirofilaria species identified in the cases of human dirofilariosis

Fig. 3

a A long, winded, palpable, subcutaneous structure on the erythematous, left upper eyelid of a 64-year old woman who complained of recurrent creeping sensations. b Extraction of a 12-cm-long, live nematode. c Hematoxylin–eosin stained section of the adult, female nematode belonging to genus Dirofilaria. Scale bar is depicted

Fig. 4

Number of human dirofilariosis cases in Austria by year of diagnosis (red dashed line), average annual temperature (in °C; black dashed line), average summer temperature (in °C; blue dashed line) and average maximum temperature during the summer in Austria (in °C; green dashed line)