Emergence of Parafilaria bovicola in Switzerland, including intraocular localization and report in an alpaca (Vicugna pacos)

Bovine parafilariosis caused by Parafilaria bovicola is a fly-borne disease, characterized by cutaneous haemorrhagic exudations ("bleeding spots") containing eggs and microfilariae. The disease seems to be emerging in Europe, where the face fly (Musca autumnalis) is the main vector. In Switzerland, parafilariosis was first reported in 2019 (Jura canton), and more recently an atypical intraocular localization in a heifer has been published. We report a case series of bovine parafilariosis, including intraocular localization, and the first description of P. bovicola infection in an alpaca (Vicugna pacos). In 2023, two cases were recorded: one involving several cattle with bleeding spots (Jura canton), and another represented by a 3-year-old cow with skin bleeding without apparent injury (Zurich canton). In 2024, four additional cases were registered: an adult cow with bleeding spots (St. Gallen canton), and three cases with intraocular localization of adult nematodes: a 2-year-old cow (Fribourg canton), an adult cow (Vaud canton), and a 3-year-old alpaca (Bern canton). All six samples (bloody exudate or worms) were examined microscopically and analysed by PCR-sequencing of the cytochrome oxidase subunit 1 gene fragment. The observed worms were morphologically consistent with P. bovicola. All samples resulted in a 649 bp sequence with a 99.8-100% identity amongst each other and with several P. bovicola GenBank sequences. The cattle with bleeding spots and the alpaca were treated with a single dose of ivermectin 0.2 mg/kg or doramectin 0.33 mg/kg s.c. The intraocular worms were surgically removed; the cows received moxidectin pour-on (0.5 mg/kg) 1-2 weeks prior to surgery and were treated with flunixin and tetracycline after surgery. The bleedings resolved following treatment. The distribution of cases across several cantons and the increasing number of detections over time suggest that parafilariosis is emerging in Switzerland. All three typical clinical cases occurred between April-June, whereas the three intraocular P. bovicola cases were detected between September and October. This is the first report of a P. bovicola infection in an alpaca worldwide.