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DIAGNOSIS Volume 33, No. 7 Lab Animal July/August 2004
Diagnosis:
Trixacarus caviae Infection
The guinea pigs had mange due to infection with the sarcoptid mite Trixacarus caviae. The clinical signs, as described in this colony of guinea pigs, are often dramaticintense pruritus, widespread alopecia, and hyperkeratosis. Confirmation of the presumptive clinical diagnosis can be obtained by taking several skin scrapings that reveal a massive T. caviae infestation (Fig. 5).
The Trixacarus mites burrow into the skin, creating epidermal tunnels1 and eliciting a cell-mediated immune response that causes the pruritus2,3 (Fig. 6).
Histologically, skin lesions consist of acanthosis, hyperkeratosis, and exfoliative dermatitis with accumulations of lymphocytes, monocytes, and eosinophils46 (Fig.
7). Pronounced reactive changes occur in the superficial lymph nodes, causing lymphadenopathy3. Dermatopathic lymphadenopathy is common in mammalian sarcoptid infections. Rothwell2 showed that guinea pigs with genetically determined resistance to the nematode parasite Trichostrongylus colubriformis developed more severe dermatitis, with greater mast cell hyperplasia and many more infiltrating eosinophils. His results emphasize the dramatic immune response hypersensitivity component to mange in guinea pigs.
Treatment of Trixacarus-induced mange involves ivermectin716. Various
authors recommend either 200 g/kg s.c.
repeated at 1014 day intervals or 300 g/kg s.c. repeated three times at 3-day intervals. In clinical practice settings or with valuable research animals, the guinea pig should also have a whole body washing with fipronil (Frontline Spray or Frontline Top-Spot, Merial, Duluth, GA)17. Fipronil in guinea pigs appears to be well tolerated and there are no reports of the problems observed with fipronil in rabbits (e.g., death, toxicity). Using fipronil spray regularly, especially to treat the guinea pigs environment, is becoming popular with pet guinea pig breeders for keeping T. caviae under control.
Other treatments reported in the literature that were effective at eliminating T. caviae include permethrin (e.g., Sectrol, Pyractone), a synthetic pyrethroid that is often used as spray (0.1%)8; 0.15% trichlorfon (e.g., Neguvon), an organo-phosphate applied topically on three separate occasions18; two immersions in 0.1% gamma benzene hexachloride, an organo-chlorine insecticide (e.g., Lindane, Kwell) a month apart6,11; and weekly washes of2.53% lime sulphur (calcium polysulfide) for 36 weeks19,20. Permethrin...