Abstract
Case series summary
This case series describes 21 client-owned cats with naturally acquired harvest mite infestation treated with a single oral dose of lotilaner. All cats were diagnosed at baseline by visual identification of characteristic orange larvae on the skin. A total of 12 cats underwent microscopic parasitological evaluation, including semi-quantitative mite scoring and assessment of mite viability, while nine cats were assessed clinically by visual inspection only. At baseline, inflammatory skin lesions and pruritus were present in 16/21 (76.2%) cats, whereas 5/21 (23.8%) were clinically healthy despite visible larvae. Lesions predominantly affected the head and neck region (n = 18/21, 85.7%). In the microscopically evaluated subgroup, live mites were detected in all cats on day 0, in 2/12 cats on day 7 and in none on day 14. Complete clinical resolution was observed in all cats by day 7 or, when applicable, day 14. No adverse events were reported.
Relevance and novel information
This case series provides clinical and parasitological observations in cats with naturally acquired harvest mite infestation treated with oral lotilaner. Although the absence of an untreated sentinel group precludes stronger efficacy claims, the consistent temporal association between treatment and clinical/parasitological improvement supports the practical use of lotilaner in affected cats and highlights harvest mite infestation as an important differential diagnosis in cats with seasonal head and neck dermatoses.
Plain language summary
Harvest mites are small parasites that can infest cats, especially during late summer and autumn. They are often found on the head and neck, where they can cause itching, skin lesions or, in some cases, no visible discomfort at all. Because the mites are very small, infestations can sometimes be overlooked or mistaken for other skin diseases. In this case series, we describe a group of cats naturally infested with harvest mites and treated with an oral antiparasitic drug (lotilaner). All cats were client-owned and examined under routine clinical conditions. The number of live mites and the clinical signs were monitored before and after treatment. After treatment, a marked reduction in live mites was observed in all cats, together with improvement or resolution of skin lesions when present. No safety concerns were identified during the observation period. These findings suggest that oral lotilaner may be a useful treatment option for cats with harvest mite infestation in everyday clinical practice. However, as this was a descriptive case series without a control group, further controlled studies would be needed to confirm these results.
Introduction
Feline trombiculosis is a seasonal parasitic dermatosis caused by the larval stage of harvest mites of Neotrombicula species, most commonly Neotrombicula autumnalis.1 –4 Cats acquire infestation through contact with soil, grass and low vegetation, typically during late summer and autumn in temperate climates. Clinical expression is variable, ranging from subclinical infestation to pruritus and inflammatory lesions. 5
Clinically, trombiculosis is characterised by the presence of macroscopic orange larvae attached to the skin surface. 5 Larvae preferentially attach to sparsely haired and exposed areas, particularly the pinnae, the peri-auricular region, chin, lips and distal limbs. 5 Pruritus ranges from absent to severe, suggesting involvement of host inflammatory and hypersensitivity mechanisms. 6
Diagnosis is usually based on history, clinical presentation and macroscopic identification of characteristic larvae. 1 Despite a recognisable presentation, treatment recommendations remain largely empirical, and controlled data on systemic options in cats are limited.
Isoxazolines are systemically acting ectoparasiticides. 7 Lotilaner is an orally administered isoxazoline licensed for monthly use in cats; in fed cats, it reaches peak plasma concentrations at approximately 4 h after treatment. 8 Lotilaner has demonstrated efficacy and safety against fleas, ticks and mites in laboratory and field studies.9 –15 However, data on its efficacy against harvest mites under natural field conditions are scarce.
This case series describes clinical and parasitological observations in cats with naturally acquired harvest mite infestation treated with oral lotilaner.
Case series description
This case series included 21 client-owned cats with naturally acquired harvest mite infestation treated with oral lotilaner. Cats were eligible for inclusion if they presented with visible harvest mite larvae. Exclusion criteria included cats aged younger than 2 months or weighing less than 1 kg, cats with systemic illness, and cats with current or previous clinical signs suggestive of allergic skin disease. Cats who had received acaricidal treatment within the previous 4–12 weeks, depending on the active substance administered, were also excluded.
The study population comprised 13 castrated males, seven spayed females and one intact male. The cats were aged 1–18 years (median 5, mean 6.9) and weighed 3.2–8.0 kg (mean 5.0). Most cats were domestic shorthairs (n = 17/21, 81.0%). All cats had outdoor access. Cats were enrolled between 7 August and 18 October, with the majority (n = 20/21; 95.2%) enrolled in August and September, corresponding to the early harvest mite season. Follow-up examinations were completed within 7–14 days after inclusion.
All cats received a single oral administration of lotilaner (Credelio; Elanco) at the licensed weight-based dose. No additional acaricidal or anti-parasitic treatments were administered during the study period. At baseline (day 0), cats underwent clinical examination. Pruritus severity was scored from 0 (no pruritus) to 10 (severe pruritus). 16 Lesion type and localisation were documented. Follow-up examinations were performed at day 7 and, when mites were still detected, at day 14. Clinical resolution was defined as absence of visible larvae, pruritus and inflammatory lesions attributable to trombiculosis.
At baseline, all cats were diagnosed with trombiculosis based on clinical examination and direct visual identification of characteristic orange larvae attached to the skin surface. Standardised parasitological evaluation using superficial skin scrapings was performed in a subset of cats. A total of 12 cats underwent microscopic mite assessment at day 0 and during follow-up. Parasite burden was assessed semi-quantitatively per affected anatomical site using a score of 0–3: 0 = no mites observed; 1 = low burden (<5 mites); 2 = moderate burden (5–10 mites); and 3 = high burden (>10 mites). When multiple sites were evaluated in the same cat, the highest score was retained for analysis. Mite viability was recorded at each assessment and classified as alive or dead based on observable movement.
In nine other cats, microscopic parasitological sampling was not performed because infestation was considered clinically unequivocal (abundant visible larvae) and/or skin scraping was not tolerated. In these cats, response to treatment was assessed by direct visual inspection for attached larvae combined with clinical evaluation of pruritus and inflammatory lesions.
Clinical and parasitological data were summarised descriptively. In the microscopically evaluated subgroup, within-cat comparisons of live-mite scores between baseline and follow-up assessments were performed using the Wilcoxon signed-rank test.
At day 0, inflammatory skin lesions attributable to trombiculosis were present in 16/21 (76.2%) cats. All 16 cats with inflammatory lesions were pruritic at day 0. Of the 21 cats, five (23.8%) were clinically healthy despite visible larvae.
Overall, involvement of at least one head/neck site (pinnae, face, chin or cervical region) was observed in 18/21 (85.7%) cats. The pinnae were the most frequently affected site in 12/21 (57.1%) cats. Isolated pinnal involvement occurred in 7/21 (33.3%) cats. Lesions involving the face and/or cervical region were recorded in 9/21 (42.9%) cats. The chin was involved in 2/21 (9.5%) cats. Ventral abdominal lesions were observed in 4/21 (19.0%) cats and interdigital lesions in 3/21 (14.3%). Only one (4.8%) cat had lesions restricted exclusively to non-head/neck regions. More than one anatomical site was involved in 11/21 (52.4%) cats.
Among pruritic cats (n = 16), head/neck involvement was present in 15/16 (93.8%). Only 1/16 (6.3%) pruritic cat (n = 1/21 overall) showed pruritus associated exclusively with non-head/neck lesions.
In the microscopically evaluated subgroup (n = 12), all cats had live mites detected at day 0. At day 7, live mites were still detected in 2/12 (16.7%) cats, while 10/12 (83.3%) were free of live mites. At day 14, no live mites were detected in any cat. The reduction in live-mite scores from baseline to follow-up was statistically significant (Wilcoxon signed-rank test, P <0.05) (Table 1).
Parasitological and clinical outcomes following oral lotilaner treatment in cats naturally infested with harvest mites
Data are n (%)
Complete clinical resolution was observed in all cats. By day 7 or, when applicable, day 14, no cats exhibited visible larvae, pruritus or inflammatory lesions attributable to trombiculosis. Cats without pruritus or lesions at baseline remained clinically normal throughout the study (Table 1). No adverse events or treatment-related complications were reported.
Discussion
This case series describes a consistent temporal association between oral lotilaner administration and clinical and parasitological improvement in cats with naturally acquired harvest mite infestation. In the microscopically evaluated subgroup, live mites were no longer detected by day 14, and complete clinical resolution was observed in all cats by day 7 or day 14. These observations support the practical use of oral lotilaner in affected cats.
In 2/12 cats, live mites were still detected at day 7. This pattern may reflect delayed clearance after treatment rather than immediate disappearance of infestation. Lotilaner is a systemically acting acaricide, and harvest mite larvae must attach and initiate feeding to be exposed to effective drug concentrations. Re-exposure between day 0 and day 7 also cannot be excluded in a field setting during the harvest mite season.
Previous studies have reported a more gradual reduction in parasite burden. In particular, Cadiergues et al 4 observed a progressive decrease in parasite scores over 28 days after topical application of a 10% w/v fipronil formulation, with some cats still harbouring low numbers of mites at the end of the study period. In the present case series, live mites were no longer detected by day 14 in all cats undergoing microscopic evaluation. This difference may reflect the systemic mode of action of lotilaner compared with topical acaricides that rely on cutaneous spread and direct contact and may be influenced by grooming behaviour, anatomical site and application technique.
Harvest mite infestation and associated lesions in this series showed a clear predilection for the head and neck region, particularly the pinnae, peri-auricular area and face. In a large retrospective study, Leone et al 5 reported ear involvement in more than 80% of cats with trombiculosis, with frequent localisation to Henry’s pocket and adjacent facial areas. The consistency between these findings and the present observations supports head and neck predilection as a characteristic feature of feline trombiculosis.
Marked inter-individual variability in clinical expression was observed. Although most cats exhibited pruritus and inflammatory skin lesions, 23.8% were clinically healthy at presentation despite visible infestation. This proportion is lower than that reported by Leone et al, 5 who described absence of pruritus in 57% of affected cats. This difference may reflect study design and case ascertainment, as retrospective data rely largely on owner-reported signs, whereas pruritus and lesion presence were actively assessed in the present series.
The overlap between lesion distribution and pruritus patterns observed here and those commonly associated with feline atopic skin syndrome has important diagnostic implications. In the absence of careful visual inspection, harvest mite infestation may be overlooked or misinterpreted as primary allergic disease, particularly in outdoor cats during late summer and autumn. These observations support the inclusion of trombiculosis as a relevant differential diagnosis in cats presenting with seasonal head and neck dermatoses.
The main limitation of this case series is the absence of an untreated sentinel group, which precludes stronger efficacy claims and limits separation of treatment effect from possible seasonal variation. Additional limitations include the open-label design, the relatively small sample size and the fact that microscopic parasitological evaluation was not feasible in all cats. Nevertheless, the consistency of the clinical course and parasitological findings across cases supports the practical use of oral lotilaner in affected cats. Future controlled studies would help clarify the respective roles of seasonal dynamics and treatment-associated clearance.
Conclusions
In this case series, oral lotilaner was well tolerated and was associated with rapid clinical and parasitological improvement in cats with naturally acquired harvest mite infestation. Harvest mite infestation should be considered in the differential diagnosis of cats presenting with seasonal head and neck dermatoses, particularly in outdoor cats.
Footnotes
Acknowledgements
The authors would like to thank Eloy Castilla for his valuable assistance in the clinical management and follow-up of cases. The authors also acknowledge Medivet SA, Lausanne, for their collaboration and support in case recruitment. Special thanks are extended to Marion Etter for her substantial contribution to the preparation of the study protocol and the overall coordination of the study.
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.
Informed consent
Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers, tissues and samples) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.
