Background
Parasite infestation with
Cheyletiellosis is a zoonosis, causing papular, pruritic dermatitis in humans
Rabbit with cheyletiellosis
Rabbit with cheyletiellosis. Rabbit with cheyletiellosis, with typical signs of seborrhoea and scaling over the withers and back.
Diagnosis of
A variety of antiparasitic treatment protocols have been successfully used for ectoparasitic mite infestation in small animal veterinary practice. In the literature there is evidence of efficacy using fipronil
Methods
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
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).
Treatment groups
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
Results
Group 1: Ivermectin injections
Nine rabbits out of 11 were classified as in remission at follow-up, whereas one was graded as treatment failure and one was recorded as relapse (table
Treatment results of rabbits treated with ivermectin injections. Treatment results of rabbits treated with ivermectin injections at 11 day (range 9–21 days) intervals. Relative outcome (%) in brackets.
No. of ivermectin injections
Treatment response (result)
Total
In remission
Failure
Relapse
Two
5 (45.5)
0
0
5 (45.5)
Three
4 (36.5)
1 (9.0)
1 (9.0)
6 (54.5)
Total
9 (82.0)
1 (9.0)
1 (9.0)
11(100)
Group 2: Ivermectin injection followed by oral ivermectin administration
Out of 27 rabbits, 14 were considered as in remission at follow-up. Among those, nine were examined at re-visit (two were skin scraped and confirmed microscopically negative) and five were assessed through telephone contact with the owner. Overweight status was recorded in three rabbits and one rabbit had concurrent conjunctivitis. The cage of one rabbit was cleaned mechanically, confirmed by telephone contact with the owner. Relapse, microscopically verified, was seen in seven rabbits within 7 months to 2 years after the last treatment. In this group one rabbit was overweight and one was in general poor condition at relapse. Six rabbits (four confirmed by visit and two by telephone contact) were graded as treatment failures and still showed clinical signs after treatment with 3–6 ivermectin doses (table
Treatment results of rabbits treated with ivermectin injections and oral administration. Treatment results of rabbits treated with ivermectin injections and oral administration according to different protocols. Treatment interval 10 days, second injection after 30 days (range 28–35, one after 48 days). Relative outcome (%) in brackets.
Treatment protocol
Treatment response (result)
Total
In remission
Failure
Relapse
Protocol 1
1 injection + 2 oral doses
3 (11.1)
1 (3.7)
2 (7.3)
6 (22.2)
Protocol 2
1 injection, 2 oral doses followed by 1 injection
4 (14.8)
1 (3.7)
2 (7.3)
7 (25.9)
Protocol 3
1 injection, 2 oral doses, 1 injection and 2 oral doses
7 (25.9)
3 (11.1)
4 (14.8)
14 (51.4)
Total
14 (51.9)
5 (18.5)
7 (25.9)
27 (100)
Group 3: Topical selamectin
Twelve rabbits out of 15 were assessed as in remission. Ten of the twelve were assessed through telephone contact and two through re-examination. In this group four rabbits were recorded as having other diseases (three had a stiff back and one had conjunctivitis) and three were overweight. Two rabbits had their cages cleaned mechanically. The only rabbit considered to be a treatment failure was overweight. Two rabbits relapsed within 3.5 and 8 months, respectively, after the last application and were re-treated with the same treatment protocol (table
Treatment results of rabbits treated with selamectin spot-on. Treatment results of rabbits treated with selamectin spot-on according to different protocols. Relative outcome (%) in brackets.
Treatment protocol
Treatment response (result)
Total
No. of treatments
Interval
In remission
Failure
Relapse
1
2 (13.3)
0
0
2 (13.3)
2
1 month
6 (40.0)
1(6.6)
1 (6.6)
8 (53.3)
3
1 month
2 (13.3)
0
0
2 (13.3)
3
3 weeks
1 (6.6)
0
0
1 (6.6)
2
2 weeks
1 (6.6)
0
1 (6.6)
2 (13.3)
Total
12 (8 0.0)
1 (6.6)
2 (13.3)
15 (100)
When comparing all treatment groups with each other no significant differences were found (p = 0.09, n = 53).
Discussion
This study indicates that all treatment protocols seemed to be sufficiently effective and safe and that cheyletiellosis in rabbits can be successfully treated using ivermectin or selamectin in clinical practice. Neither ivermectin or selamectin is currently approved for use in rabbits in Sweden. In the UK however a topical spot-on preparation containing ivermectin (Xeno 450, Genitrix) has just recently been initiated for use in rabbits, guinea pigs and ferrets.
Ivermectin and selamectin both belong to the macrocyclic lactones. All macrocyclic lactones have the same primary mode of action, namely to affect the chloride ion channel activity in the nervous system of nematodes and arthropods. Nerotoxicity however has been described in mammals, mainly in cases of ivermectin use in collies (and collie related breeds) and young animals or after overdosing
The doses of ivermectin recommended for cheyletiellosis in dogs and cats are oral or injectable formulas at 200–300 μgkg-1, at a 10–14 day interval during 6–8 weeks
Selamectin has been shown to have persistent efficacy against fleas after topical administration in dogs and cats for at least 28 days after application
The results from this field study may have been affected by uncontrolled events and factors. For example the chance that the treated rabbits in this study were asymptomatic carriers of
There may be several explanations as to why the combination of injection and oral administration of ivermectin (Group 2) has a tendency to be less effective, independent of treatment length. It is possible for example that oral bioavailability of ivermectin is not high enough in rabbits, explaining the higher number of rabbits experiencing relapse or treatment failure. Lower efficacy and shorter duration of action from orally administered ivermectin have been documented, for instance in cats where most of the drug is eliminated from plasma at 5 days
Why some rabbits still experienced clinical signs or relapsed even when living in single-rabbit households remains unanswered. Insufficient cleaning of the environment and in-contact dogs and cats not treated against
Possible side effects were only recorded in two cases, both in Group 1, the group receiving ivermectin injections. One rabbit experienced pain after the ivermectin injection and one developed ataxia at the second treatment. It could not be excluded that the symptoms were correlated to the ivermectin injection. The rabbit experiencing a short episode of ataxia at the second injection died a few months after the last treatment, without having had any relapses of neurological signs. No autopsy was performed. The almost total absence of neurotoxicity is remarkable, since the doses used in Group 2 (ivermectin injection and oral administration) were very high, up to 2732 μgkg-1, which is many times the dosage recommended by the manufacturer for treating ruminants and horses. In ruminants the toxicity dosage (4 mg kg-1) is 20 times the recommended dosage, given as injections, and in horses the toxicity dosage (2 mg kg -1, given twice in two days, orally) is 10 times the recommended dosage. Teratogenic studies in rabbits performed by the manufacturers concluded that ivermectin orally administrated daily to pregnant rabbits at the dose 6 mg kg-1 resulted in signs of toxicity after 7 days.
Conclusion
Results of this retrospective study suggest that both ivermectin and selamectin are effective and safe for clearance of clinical signs of cheyletiellosis in rabbits. In the group including oral administration of ivermectin (Group 2) a tendency towards a lower efficacy was registered, as compared to Groups 1 (ivermectin injections) and 3 (selamectin spot-on), although not statistically significant. Controlled prospective studies including larger groups are needed to further evaluate efficacy of the treatment protocols.
Competing interests
The author(s) declare that they have no competing interests.
Authors' contributions
MM collected and analyzed the data and drafted the manuscript. KB participated in planning the study and helped to draft the manuscript. All authors read and approved the final manuscript.