Fipronil use for lice infection in horses

Successful resolution of natural Werneckiella equi infestation in two horses using pour-on Fipronil: A clinical observation

J Equine Vet Sci. 2026 Mar 20:105854. doi: 10.1016/j.jevs.2026.105854. Online ahead of print.
Authors
F R S C Duarte 1 , F R Lima 1 , G C Medeiros 2 , L L Furtado 3 , L P C T Aquino 3 , J H Fonteque 2 , A B Moura 1 , A L Chryssafidis 4
Affiliations

1 Laboratory of Parasitology and Parasitic Diseases – LAPAR-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090, Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000; Laboratory for the Development of Health Technologies – LADETES-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090 – Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000.
2 Veterinary Hospital – HCV-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090 – Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000.
3 Laboratory of Parasitology and Parasitic Diseases – LAPAR-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090, Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000.
4 Laboratory of Parasitology and Parasitic Diseases – LAPAR-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090, Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000; Laboratory for the Development of Health Technologies – LADETES-CAV-UDESC (Agroveterinary Sciences Center, Santa Catarina State University), Av. Luís de Camões, 2090 – Conta Dinheiro, Lages, Santa Catarina, Brazil, 88520-000. Electronic address: andreas.ch@udesc.br.

PMID: 41865911
DOI: 10.1016/j.jevs.2026.105854

Abstract

Werneckiella equi is an ectoparasite of equids, and control can be challenging because of the limited availability of licensed products. This case report describes the clinical observation of 1% fipronil pour-on against W. equi infestation in horses admitted to a veterinary hospital. Two horses were treated and observed between 2022 and 2023. Both exhibited pruritus, especially in the head, withers, and croup regions, and were diagnosed with severe W. equi infestation. The treatment consisted of a single topical application of 1% fipronil pour-on (1 mg/kg). Parasite reduction was assessed by complete physical examination, until complete parasite elimination. Demarcated areas were used for daily lice counts. Infestation was resolved within eight days (Horse 1) and twelve days (Horse 2), with no recurrence observed over six months. These preliminary observations suggest that 1% fipronil pour-on may offer a practical alternative for eliminating W. equi under clinical conditions, offering advantages such as minimized stress during application, precise dosing, and enhanced handler safety. However, due to the lack of a control group and small sample size, these results should be interpreted as preliminary clinical evidence.

Keywords: Antiparasitic; Ectoparasites; Equine lice; Welfare.

Copyright © 2026. Published by Elsevier Inc.
Conflict of interest statement

Declaration of competing interest None of the authors has any financial or personal relationships that could inappropriately influence or bias the content of the paper.