Ear mite: Psoroptes cuniculi
Esther van Praag Ph.D.
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The rabbit ear mite parasite Psoroptes cuniculi is a cosmopolitan parasite. It has different life stages: egg, larva, protonymph, adult mite. The cycle lasts about 21 days, depending on environmental conditions, with eggs hatching after 4 days.
Psoroptes cuniculi is mainly found inside the ear pinnae. It is not uncommon that only one ear is affected. In older or sick animals, or if not treated properly, the parasite can spread to other regions on the body, and infest the head, neck, legs, ventral abdomen, and perianal region. The mucus and fecal material of the parasite induce an inflammatory reaction that leads the rabbit to scratch its ear. The blood that comes out of the scratched lesions serves as a source of nutrition for the parasite.
Symptoms and clinical signs
Itching ears, frequent shaking of the head, and scratching up to the stage of auto-mutilation. In the beginning, small, tightly adherent skin scales appear deep in the ear canal and the earlobes and are surrounded by alopecic (balding) regions. Those yellow-gray scales can become rather thick. They carry large numbers of the parasite, mite feces, skin cells, and blood.
If no treatment is started at this stage, the scales will grow into crust and may reach a thickness of 2 cm in extreme cases. The ear is no longer able to stand up, and droops. The scales/crust should not be removed; if removed, they leave bloody eroded skin. The crust will fall off within 10 days after the first administration of oral or injected ivermectin. Earlier removal is also very painful, and may lead to screaming.
Video by D. Hanson
Secondary bacterial or fungal infections are observed. If not treated, the bacteria will spread and cause hyperkeratotic (abnormal thickening of the skin), otitis externa (outer ear infection). If left untreated, the infection can spread deeper in the ear, causing the rupture of the tympanic membrane and subsequent inner ear infection. This can be accompanied by head-tilt.
Diagnosis can be difficult and visual examination is not always sufficient to confirm the presence of ear mites. Detection methods include the tape method, skin scraping (shallow if fur mites are suspected, deep if burrowing mites are suspected), or the vacuum aspiration method on a filter paper. Samples from scraping or aspiration should be spread on a microscope glass, dissolved in KOH, and examined under a microscope. Great is the chance to see at least one mite or a larva or eggs. Fur can also be sampled, dissolved in KOH, and examined under the microscope for the presence of eggs. If no mite is present in the first sample, other places on the body should be checked. If the presence of burrowing mites is suspected, but none found after a deep skin scraping, a biopsy on the area suspected of mite infestation is advisable.
The scales/crust should never be removed !!!
Removing them is horribly painful to the rabbit, leading to screaming (see video).
Ear mites are effectively eliminated by avermectins:
• Ivermectin: 0.4 mg/kg, PO (oral) or SC (subcutaneous injection), 3 times at intervals of 14 days (life cycle of Psoroptes cuniculi is 21 days); 0.2 mg/kg has been found ineffective.
• Selamectin: Revolution® (US) or Stronghold® (Europe) - Pfizer, 6-18 mg/kg. A single topical (local) dose should be sufficient; if not, repeat after 30 days. If the affected rabbit presents severe anemia, a transfusion of blood can be attempted from a healthy donor rabbit.
• Moxidectin (Quest® or Equest® - Fort Dodge). Secondary effects have not been observed when the medication was administered orally, on the contrary to subcutaneous administration.
These avermectin compounds are non-ovicidal (will not kill the eggs), but the drug remains in the tissue long enough to kill the larvae that emerge from the eggs. Ivermectin diluted in mineral oil, applied directly on the ear, is less effective than injected or oral ivermectin.
The use of over the counter products against mite or ear mites should be avoided. Most contain pyrethrin. While one of the least toxic insecticides for animals and rabbits, pyrethrins/pyrethroids are neurotoxins which lead to continuous "firing" of nerves. Observed problems in rabbits include limb paralysis, seizure, coma, tremor, sometimes death.
Many of those products contain additives that prolong the effect of the pyrethrins, and inhibit the breakdown of these products in the body. They can lead to toxic reactions in rabbits. Piperonyl butoxide is one of them. If no immediate death, there should be **slow** recovery with time, around 48 h. Ear mite infestation is accompanied by pain. An analgesic (pain relief medication, e.g., carprofen, ketoprofen, meloxicam) should be administered.
If the secondary bacterial infection is limited, it can be treated with antibiotic ear drops. It is important to check the eardrum before administration. Some ear drops have, indeed, ototoxic effects, and their administration when the eardrum is ruptured can have a fatal outcome.
If the ear infection is severe, eardrops and oral antibiotics are advisable. If the amount of pus and debris in the outer ear is high, the use of enzymatic solution such as Zymox Otic and flushing of the ear is recommended. This will help bring the medication deep in the ear canal. A bacterial culture is advisable, followed by a sensitivity test to determine the most efficacious antibiotics.
In case of inner ear infection, appropriate oral antibiotics should be administered.
Ear mites can fall off and contaminate the environment. While treating for mites, careful cleaning of the cage and environment is recommended. Treatment of the environment is important (boric acid such as Fleabusters®; Vet-Kem Acclaim Plus® - Sanofi; Staykil® - Novartis; Indorex® - Virbac; acaricide spray). When treating a carpet, vacuum first in order to further penetration of the spray or powder. Shampooing and steam cleaning are not ideal; their residual humidity can increase the mite problem. During treatment of the environment, rabbits should be kept in another part of the home to avoid the danger of contact with the products.
Thanks are due to Zahi Aizenberg, DVM (The Koret School of Veterinary Medicine, the Hebrew University of Jerusalem, Israel), to Dr. Orlando Diaz, (www.lakehowellanimalclinic.com), to Akira Yamanouchi, (Veterinary Exotic Information Network, http://vein.ne.jp/, Japan), to Crystal Gaydos and Caroline Charland (www.bunnybunch.org, USA), to Linda Baley (USA), and to Christine Macey (USA) for the permission to use their pictures. To Debbie Hanson for sharing the news related to Parker, to Hugh Hanson, for sharing the video showing life ear mites. To the rabbits Kaspi, Flora Adar, Parker and those whose name is unknown, but were severely affected by ear mite.
For detailed information on ear mite infestation in rabbits,
see: “Skin Diseases of Rabbits”, by E. van Praag, A. Maurer and T. Saarony,
408 pages, 2010.
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