Abstract

Demodectic mites have been described in terrestrial mammals throughout the world including koala¹, panda⁵, cheetah⁶, black bear, bison, water shrew, raccoon, ferret, hamster, wild and domestic canines and felines⁷, tamarin and man⁴. The parasite lives in hair follicles and sebaceous glands completing a life cycle that includes, egg, larva, protonymph, nymph and adult stages. Each species appears to be uniquely adapted to its' specific host and is transmitted vertically from the host female to her offspring. Most infestations are clinically inapparent but young or stressed (immunologically compromised) animals may develop significant folliculitis and secondary bacterial infection.

A unique marine mammal species (D. zalophi) was documented in California sea lions (Zalophus californianus) in 1979³. Clinically significant dermatitis including hyperkeratosis, alopecia and puritis has been associated with demodex mites in northern fur seals ² and in other unidentified captive pinnipeds (Dunn, pers. com). Treatment with topical amitraz has appeared to be successful in these cases.

A 26 year old intact female Atlantic harbor seal (Phoca vitulina) housed since 1998 at the Alaska SeaLife Center was noted to have several small (3-4 mm diameter) foci of persistent hyperkeratosis and hyperpigmentation on the dorsal thorax and lumbar skin. These sites would occasionally become crusted with dead skin and bleed slightly when abraded but were otherwise static and seemed to cause no discomfort. A skin biopsy was performed at the largest site in March 2001 and revealed chronic, ulcerative and hyperplastic dermatitis with follicular acariasis and bacterial folliculitis.

Seven other subadult to adult harbor seals (mixed Atlantic and Pacific stock) and three juvenile Steller sea lions (Eumetopias jubatus) have been housed with this female over the past 4 years but no other animal has shown clinically detectable lesions. Occasional skin biopsies collected from these animals for other reasons have not contained any mites. All of these animals are part of an ongoing study of nutritional physiology and health at ASLC. The affected female has bilateral luxated cataracts and occasional mild uveitis but has shown no other health problems. The sites of infestation have remained small and have not appeared to spread or cause any debility. Additional follow up biopsies and skin scrapings over the past 12 months have consistently demonstrated presence of demodectic mites which appear to be a unique new species.

Acknowledgements

The authors wish to thank Michael Garner, D.V.M., Dipl. A.C.V.P., for the initial histopathology on this case and Dr. Cliff Desch, for assistance in classification of this parasite.

References

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