The mange Notoedrus cati var cuniculi is a borrowing mite commonly associated with skin problems in rabbits. The disease is very common in subtropical countries like India especially during rainy and winter season due to low temperature and high humidity (Kumar, 1998). Many drugs have been tried for chemotherapy of these mites. Ivermectin (since inception) has been drug of choice against parasitic nematodes and arthropods due to its high efficacy, easy applicability and wide range of safety margin. Recently introduced doramectin (Dectomax, Pfizer India Ltd.), a genetically engineered compound of ivermectin is reported to have wide spectrum of action (Goudie et al., 1993). The drug has been tried in dogs against sarcoptic mange (Jagannath and Yathiraj, 1999), cattle against sarcoptic mange (Gupta, 2002) and rabbits against N. cati (Singari et al., 2001). But there are few reports comparing efficacy doramectin with parent compound ivermectin. As such no work on comparative efficacy of both drugs involving mite counts/sq.cm. percentage reduction and morphological improvement have been reported. Hence, the present study was carried out.

Eighteen rabbits naturally infested with mange mites were selected from Punjab Veterinary Vaccine Institute, Ludhiana for the present study. The mites were identified as described by Greiner (1994). The affected animals were divided randomly into three groups of 6 animals each. All the rabbits were kept in separate cages so that no cross transmission may occur. Group 1 animals were treated with doramectin and Group 2 with ivermectin, both @ 400 jttgkg⁻¹ b.w. subcutaneously. While Group 3 animals were kept as infected control and injected with normal saline solution (Placebo). The skin scrapings were collected from 1 cm² area of the most affected part in 10% KOH and warmed. The mites were counted in the scrapings on day 0 (before treatment), 3, 6, 9, 12, 15, 21, 30 day and efficacy was judged don the basis of reduction in mite count, post treatment. The results presented are as mean ± S.E. Percentage efficacy of the individual drug was calculated using the formula:

where a = mite count on day 0 (before treatment)
b = mite count of the same treatment group on day 3, 6, 9, 12, 15, 21 and 30

Simultaneously, the clinical lesions were observed for the improvement in general body condition.

The mite infecting rabbits was identified as N. cati var. cuniculi. The decrease in mite count and percentage reduction are presented in Table 1. As depicted in Table 1, the mite count decreased in both, Group 1 and 2 but in Group 3, it increased throughout the period of study. It is pertinent to point out that in Group 1, the reduction in number of mites was faster when compared to Group 2. It was observed that by day 3 the reduction in Group 1 was better than Group 2 by more than 6% while on day 9, the difference of about 4% was observed. The faster reduction in mite count in doramectin treatment group showed a higher bio-availability of doramectin over ivermectin at the same dose rate (Toutain et al., 1999). The improvement in clinical symptoms was also better in the same group. Here it may also be appreciated that in Group 1, on day 9, the mites were absent from 3 rabbits while the remaining showed small crusts on ears indicating that the blood concentration was minimum in ears (Mckellar et al., 1992). Similarly, in Group 2, the same condition was observed on day 12 post-treatment. It was also observed that the mite count was zero in all the 6 animals in Group 1 on day 12 post-treatment, however, in Group 2, on day 12 none of the animals were devoid of mites.

As far as the improvement in lesion is concerned, d Group 1 showed complete shedding of crusts and new hair growth on day 12 while in Group 2 it was observed on day 15 post-treatment. In Group 1, hair growth was almost complete by day 21 and by day 30 it was almost normal whereas in Group 2, hair growth was almost complete by day 30 only. Throughout the period of study of 30 days, animals of both treatment groups remained free of mite with normal hair growth. In group 3, the mite count continued to increase and two animals died after showing the sign of the severe irritation and itching (day 9 and 15). From these results, it is apparent that doramectin is having better efficacy as compared to ivermectin at same dose rate and route. The possible cause is that plasma concentration of doramectin is higher as compared to ivermectin (Gayrard et al., 1992; Toutain etal, 1999).

The present findings are quite similar to that of Singari et al. (2001) who reported zero mite count on day 10 with doramectin given @ 400 jug kg^-1 b.w. Singla et al. (1996) and Singh and Gill (1989) also reported complete absence of mites on day 7 in rabbits on treatment with ivermectin @ 400 jug kg⁻¹ b.w. given subcutaneously. The possible reason of this difference is the intensity or duration of infection in those animals. It is also a possibility that the drug ivermectin showed reduced activity against these parasites due to its extensive use for treatment of ectoparasites.

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