Skin lesions in rabbits caused by parasites and fungi
Rabbits presence at owners home is increasing in the last years, specially as single. These pets may get ectoparasites or dermatophytes infections by the contact with other rabbits, at the purchase point or at the veterinary clinic.
In this case, the rabbit fur mite (Cheyletiella parasitivorax) is important. The direct transmission of this parasite is through body contact, but it may occur indirectly, by the use of combs in several animals. This mite is not host specific, it can affect the owner or other pets causing irritation.
This mite infection causes in rabbits itch and scales production. The neck is the preferred body location of this parasite. If the scales are retired with a comb, the mites can be seen if over a dark underlay. For the diagnose, it is recommended to take this scales with a tape and observe them with the microscope over a slide. Typical of these mites are the pedipalpes, which are curved to the inside and are used to hold the food (scales).
Figure 1: Cheyletiella parasitivorax
If we take a skin scrape and it is not in this moment fixed, we may only find the eggs, because the mites are gone. Additionally to the treatment of these mites by the rabbit, possible with the use of several antiparasitic products, it is very important to control the environment (cleaning and disinfecting), even if these mite do not survive a long time away from the host.
The second important mite is the rabbit ear mite Psoroptes cuniculi. We do not find this mite in rabbits that live alone, but in populations (breeders or farms), usuallyonly locally. The affected ears show stratified accumulations. The propagation occurs by direct body contact, but the indirect transfer by vectors is also possible (specially combs and clothes). These parasites can survive out of the host for 2-3 weeks.
If the affected rabbits are in a horse stable, the horses should be controlled. The children usually transmit the mites from rabbits to horses and back.
Figure 2: Psoroptes cuniculi
Additionally to the specific therapy against mites, it is to be considered to clean and disinfect the rooms where the rabbits are. All the animals that live together have to be treated, even those that do not show any symptoms. Another mite is Leporacarus gibbus, it is considered to be less pathogen. This parasite lives in the fur and put its eggs over the hairs. It produces some itching, but not quite limited.
Figure 3: Egg from Leporacarus gibbus
Other ectoparasites not very often found are the rabbit flea and the rabbit louse
Figure 4: Rabbit flea (Spilopsyllus cuniculi)
This flea behaviour is like other species, the realise the whole methamorphose (egg, larvae and pupal stadium) over the host until they reach the adult stadium. It is specially important by the rabbit because of it is a myxomatose (leporipoxvirus) vector (by sucking). Additionally to the treatment of the affected animals, it is necessary the control of the environment, by cleaning and disinfecting it. The louse of the rabbit (Haemodipsus ventricosus) is, like the other lice, host-specific. It produces itch and oft lack of appetite. Additionally to a specific therapy, where the louse are killed, nits have to be considered. For this reason it is necessary to treat again later. Retiring the nits is possible but difficult, by longhaired rabbits it is easier to cut the hair.
The extra-label use of the antiparasitic products is necessary, because these products are not approved for rabbits. Well tolerated products are selamectine, doramectine or ivermectine, and also pyrethroid contained shampoo or powder. Only the use of fipronil is dangerous.
With the therapy we only kill the adult stages, therefore, a new therapy 8-10 days later is recommended, in order to reach the following generation of parasites. If the rabbits have access to an outside area, other parasites, like ticks and chigger (also called red bugs), and other non specific parasites, like fly maggots, are to be considered. The maggots appear after diarrhoea or over abscesses, which are usually very pestilent. The owner usually identify the problem very late. The therapy consists in recollecting the maggots and the eggs, and treat the original cause. It is possible to prevent this problem by using Deltamethrin (e.g. Butox®) at the beginning of the year (extra-label use is necessary).
Rabbits, similar to other rodents like guinea pig and chinchilla, often suffer latent without clinical signs fungal infections. Round areas without hairs, and also wet and partially with scales or hairless areas around the eyes, ears and nose are to be considered as dermatophytes infection suspection. These lesions rarely appear in other areas.The sample should be taken from the border of the lesions, and the extraction of hairs or taking a swab is recommended.
Hygienic measures have to be taken because of the zoonotic risk of Dermatophytes.The scales or hairs are the best material for the microscopical examination, it has to be put on a slide with a cover and paraffin oil.
The sample taken from a swab can be observed with caustic potash solution (10-20%) instead of paraffin oil because it helps better to wipe out the scales and the spores that could be attached around the hairs. But with the use of this caustic potash solution the sample suffers desiccation and crystals are formed, what difficulties the microscopical evaluation. The finding of groups of spores indicates the cause of the skin lesions.
Figure 5: Spore structures around a hair
A bacteriological examination of the swab over several specific culture media is also important. For a better application of the swab, a NaCl solution can be added. We use in our lab in the routine a Sabouraud agar with gentamicine and chloramphenicol to inhibit the growth of bacteria, and also Sabouraud culture media with gentamicine and cycloheximide (Actidion) to inhibit the growth of molds.
The incubation takes until 4 weeks at 28°C. The cultures are observed for the first time after 4 days. The examination of the cultures is done visually from the upper and reverse side and microscopically.
Figure 6: Trichophyton mentagrophytes upper and reverse side of the culture
The suspected colonies are examined microscopically using a tape film and one drop of lactophenol cotton blue for the staining and with the x40 objective. The forms of microconidia, macroconidia and spiral hyphae are studied.
Figure 7: Macroconidia and microconidia
Trichophyton mentagrophytes is the most common fungus found in skin lesions in rabbits. This fungus is not species-specific, but it is very well adapted to rodents like guinea pig and rabbits.
In 2010 we studied 658 skin scrapes from rabbits for mycological examination. In about 21% (n=140) a relevant fungal growth was found. We divided the results in dermatophytes, yeast and molds. Within the positive cultures with dermatophytes, 30% were Trichophyton mentagrophytes and 5,0% Trichophyton terrestre. These fungi are geophile fungi, that use a previous lesion of the skin to colonise the skin and show the dermatomycosis symptoms.
Figure 8: Distribution of the positive cultures 2010
Mikrosporum gypseum was found in 2.1 % of the positive cultures. This fungal is a normal soil resident, but may colonise the skin and show the symptoms of dermatomycosis. If we consider all the yeast within the positive cultures, with Candida spp., Candida albicans and Malassezia pachydermatis and also the non pathogen yeast Rhodotorula rubra, this group reach around the 28%.
In a case of yeast infection, smeary seborrhoeic skin lesions are expected. In the group of the molds, usually considered as a secondary contamination, we found Scopulariopsis brevicaulis in 27.2 % of the cases. It is an ubiquitous fungus, usually non pathogen, that may be found in previously damaged skin.
The relevance of the presence of this fungus has to be evaluated together with the clinical signs. However, this fungus was often found in a big amount as a pure culture. The presence of latent infected spore carriers increase the susceptibility of suffering a fungal disease. Stress conditions, like internal fights, dirtiness or an inadequate diet are cofactors that help the beginning of the clinical signs of a fungal infection.
A local therapy can be effective when only local lesions are present. In this case, it is important to control the success of the therapy in the borders of the lesion. The treatment muss be applied consequent for 3-4 weeks.
For the local therapy Enilkonazol (e.g. Imaverol®) is recommended, it has to be used with a 0,2% dilution each 3-4 days. The skin will be dried. If at the same time, the lesions are itching, clotrimazol (e.g. Surolan®) can be used. This product has to be applied over the skin, and it will help because of ist antiinflammatory effect and the fattening effect. If the lesions are generalised, a systemic treatment is necessary.
Itrakonazol (Itrafungol®) can be used (extra-label use), with a dosage of 5-10 mg/kg BW, and like in the cat, it has to be given alternatively, one week given, one week break. And this protocol has to be done at less twice. The skin of the rabbits is thicker than by the cats, the higher dosage should be used. Another option is the extra-label use of griseofulvine, the dosage is 50 mg/kg BW SID. This drug cannot be used during pregnancy. Another option is terbinafin, from the human medicine (extra-label), used by 30 mg/kg BW. Also Lefonuron (Program®) can be taken into consideration, because this drug is used for the treatment of ectoparasites and also attack the fungi wall.
100 mg/kg BW have to be given each second week. Three applications are usually enough. In the cases where yeast are found, other problems, like vitamin deficiencies, metabolic diseases like diabetes mellitus, have to be also considered and treated simultaneously to the yeast infection.
Although the systemic medicaments reach good concentrations at the skin, sometimes the spores situated over the skin are so many that environment disinfection and protection of other animals and owners is necessary. Additionally to the oral application, the bath or washing with Imaverol® is recommended.
Disinfection and environment manage
In order to avoid the transmission to other animals or human, it is necessary to treat the environment. Additionally to normal cleaning, for example, by using a vacuum cleaner, it is recommended to disinfect the room with bleach (5% natrium hypoclorit), easy to buy in shops. With this concentration it is easy to apply, it kills the spores, but it has to be used carefully because it is irritant. Enilkonazol (Imaverol®), with a 2% dilution, is another option to treat the environment.