First Report of Resistance to Ivermectin in Parascaris univalens in Iceland.

The research article primarily focuses on the discovery of resistance in the Parascaris univalens species found in Icelandic horses against the commonly used antiparasitic drug, ivermectin. The study suggests that the resistance may have developed independently due to over a millennium of isolation of these equine parasites from the global horse population, which could have important implications for treating such infections.

Research Aim and Methodology

• The main aim of the study was to investigate the effectiveness of ivermectin in treating helminth infections caused by a particular species of Parascaris (P. univalens) in foals, referring to horses that are less than a year old. This was studied through fecal egg count reduction (FECR) tests. The research also strove to identify the specific Parascaris species present in the west and north of Iceland.
• The study ran from September to November 2019 and involved 50 foals from 8 farms, including a control group of 6 untreated foals. The subjects ranged from 3 to 5 months old and had not been previously treated with anthelmintic drugs.
• The treatment involved subcutaneous injections of either Ivomec® or Noromectin® at a specific dose. The efficacy of the medication was calculated using the eggCounts package in R and the Presidente formula (FECRT).

Research Findings

• The results showed ivermectin efficacy levels between 0% and 80.78% across all the farms, thus indicating the existence of ivermectin resistance. Such a discovery poses a serious challenge to the current modes of treatment for Parascaris infection in foals.
• Additionally, the research was able to establish that the species of equine ascarid affecting horses in the north and west of Iceland is P. univalens. This was confirmed through karyotyping.

Implications and Further Inquiries

• The fact that ivermectin resistance has been discovered in an equine parasite population that has been isolated for over 1,000 years suggests that the resistance alleles may have developed independently. This critical evidence implies there is a possibility of similar developments in other isolated Parascaris populations.
• Although the exact clinical impact of this resistance to ivermectin is unclear, the researchers recommend considering alternative treatment options for P. univalens infection in Icelandic foals.