Study design and inclusion criteria
Totally 282 medical records of rabbits from two veterinary settings (Gästrike Animal Clinic, Sandviken, Sweden, and Animal Clinic Roslagstull, Stockholm, Sweden) were reviewed. Of these, 53 rabbits were included in the study. Prerequisites for selection were that clinical signs compatible with Cheyletiella infestation were verified by a demonstration of Cheyletiella mites through light microscopy examination of skin scrapings, material from flea combing or transparent tape preparations under 4 or 10 × 100 magnifications. Furthermore, the rabbits should have been treated with ivermectin or selamectin and a follow-up should be possible through telephone contact with the owner or through a revisit at the clinic. The following information was collected from the two veterinary settings: descriptions including age, sex, weight, clinical signs, diagnose verification, treatment protocol (substance, dose, route of administration and interval), number of rabbits in the household, other treatments and evidence of concurrent diseases. A record of overweight was made if the rabbit's weight was more than 20% above the recommended maximum weight of the breed according to the Nordic rabbit standard .
The rabbits were divided into three treatment groups, ivermectin (Ivomec®vet. injectable, 10 mg/ml, Merial SAS, Lyon) injections (Group 1), combination of injections and oral administration of ivermectin (Ivomec®vet. injectable, 10 mg/ml, Merial SAS, Lyon) (Group 2) and topical selamectin (Stronghold®/Revolution, 60 mg/ml, Pfizer Inc., New York) (Group 3).
Group 1 included 11 rabbits, all treated at the Gästrike Animal Clinic, with a mean age of 4.4 years (range 9 months to 7 years) with bodyweights ranging from 1.4 to 4.6 kg. Eight rabbits were male and three female. Most of the rabbits (n = 9) were from single-rabbit households. In the two multi-rabbit households, all in-contact rabbits were treated. The rabbits were treated with ivermectin injections subcutaneously at two (n = 5) or three (n = 6) occasions. The mean dose was 253 μg kg-1 (range 200–476) and the mean injection interval was 11 days (range 9–21).
Group 2 included 27 rabbits, all treated at the Animal Clinic Roslagstull, with bodyweights ranging from 1.6 to 6.5 kg and with a mean age of 4 years (range 6 months to 9.5 years). Twenty rabbits were intact males while the rest were four females and three castrated males. Most rabbits lived in single-rabbit households (n = 24) in this group as well, and the rest in households with two or more rabbits. All in-contact rabbits were treated in the multi-rabbit households. Treatment consisted of 3–6 ivermectin administrations at a 10 day interval. Initial subcutaneous injections at the first visit (mean dose of 1044 μgkg-1, range 618 to 2185) were followed by oral ivermectin, using the injectable formula (mean dose of 1324 μgkg-1, range 616–2732) twice and administered by the owner. Most rabbits (n = 23) were re-examined 30 days (range 28–35 days, one after 48 days) after the first visit. Depending on the clinical signs at the second visit they were either given no more treatment (n = 2) or continued treatment. Twenty-one rabbits had a second injection, 14 of which had two additional oral ivermectin treatments repeated, with the same doses and interval as initially. Most of the latter were considered to still have clinical signs (n = 8) or to be mite positive after microscopic control (n = 1).
Group 3 included 15 rabbits: one treated at the Gästrike Animal Clinic and 14 at the Animal Clinic Roslagstull. The mean age in this group was 2.2 years (range 3 months to 7 years) with bodyweights ranging from 1 to 7.4 kg. Eight rabbits were intact males while the rest were 5 females and 2 castrated males. Two rabbits belonged to multi-rabbit households. All in-contact rabbits were treated. Treatment consisted of administration of selamectin spot on topically at 1–3 occasions. The mean dose of selamectin used was 12.5 mgkg-1 (range 6.2 to 20.0).
Assessment of response to therapy
Clinical cure was assessed by re-examination or telephone contact with the owner. Treatment results were graded as in remission, relapse or treatment failure at the time of follow-up. Rabbits in remission were defined as having been free from clinical signs at re-examinations during the whole follow-up period. Relapses were defined as being free from clinical signs more than 3.5 months after treatment but showing signs again during the follow-up time. Treatment failures were cases that never cleared from clinical signs during the first 3.5 months or were recorded with relapse during this time. Adverse reactions of treatment were assessed by examination during revisit and by questioning the owner.
Statistical analysis was made by using χ2 test .