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Diagnosing and treating feline demodicosis

10 April 2019, at 9:30am

What to look for in demodicosis cases to ensure you are effectively eliminating the right mite

Feline demodicosis is a disease associated with three Demodex mites. These are Demodex cati, Demodex gatoi and a third unnamed Demodex species.

Demodex cati

This is a long-bodied mite (Figure 1) found in the hair follicles and ears. Disease may be localised or generalised.

FIGURE (1) Long-bodied Demodex cati
FIGURE (1) Long-bodied Demodex cati

© David Scarff

Clinical Signs

Localised disease involves the eyelids, periocular area, head or neck, and lesions consist of localised alopecia, variable pruritus and erythema. Lesions in generalised disease are multifocal patchy alopecia, with in some cases erythema, scaling, crusts, macules, lichenification and hyper-pigmentation (Figure 2) (Hnilica and Patterson, 2017).

Ceruminous otitis externa alone is also possible. Disease can occur in any age, breed or sex and is not contagious. It may be idiopathic or associated with an underlying immunosuppressive or metabolic disease such as feline immunodeficiency virus (FIV), feline leukaemia virus (FeLV), toxoplasmosis, systemic lupus erythematosus, hyperthyroidism (Figure 2), neoplasia or diabetes mellitus (Hnilica and Patterson, 2017).

FIGURE (2) In generalised D. cati, there may be scaling, erythema, crusting and lichenification. In this case, there was underlying hyperthyroidism
FIGURE (2) In generalised D. cati, there may be scaling, erythema, crusting and lichenification. In this case, there was underlying hyperthyroidism

© Anita Patel

FIGURE (3) The lesions seen in Figure 2 were resolved following thyroidectomy and topical treatment with fluralaner spot on
FIGURE (3) The lesions seen in Figure 2 were resolved following thyroidectomy and topical treatment with fluralaner spot on

© Anita Patel

Differential diagnosis

In the differential diagnosis, Hnilica and Patterson (2017) include:

  • Dermatophytosis
  • Cheyletiella
  • Otodectes cynotis
  • Other causes of otitis externa

Diagnosis

  • Skin scrapings. The mite is easier to find than D. gatoi
  • Tape strips
  • Histopathological examination. Mites may be seen in the stratum corneum or within hair follicles with an associated perifolliculitis and suppurative perivascular dermatitis. Negative findings are not conclusive to rule out of the diagnosis

Treatment

  • No specific licence exists for feline demodicosis treatment, therefore informed consent is required
  • Lime sulphur 2 percent dips should be applied weekly for four to eight weeks
  • Isoxazolines (fluralaner, sarolaner; as with D. gatoi)
  • Amitraz dips (0.0125 to 0.025 percent) applied to the whole body weekly to every two weeks (Hnilica and Patterson, 2017). Although reportedly effective, cats are sensitive to the use of amitraz and it is contraindicated in diabetic cats
  • Prognosis is variable depending on the underlying cause

Demodex gatoi

This is a short-bodied mite (Figure 4) found in the stratum corneum. Predisposed breeds are Burmese, Maine Coons, Bengals and multi-cat household cats. It is poorly responsive to routine flea treatments, with the exception of the isoxazolines (Matricoti and Maina, 2015).

FIGURE (4) Short-bodied Demodex gatoi
FIGURE (4) Short-bodied Demodex gatoi

© Anita Patel

Clinical signs

Signs include mild erythema and scaling, which is often generalised. Pruritus is commonly seen and likely due to hypersensitivity to the mite. Signs may be severe and poorly responsive to anti-inflammatory doses of glucocorticoids. Self-induced inflammatory lesions and symmetrical alopecia (Figure 5) may also be seen. Be aware that unlike D. cati, D. gatoi is contagious.

Differential diagnosis

In the differential diagnosis, Hnilica and Patterson (2017) include:

  • Dermatophytosis
  • Hypersensitivity (Cheyletiella, Otodectes, fleas, food, atopy)
  • Psychogenic alopecia
FIGURE (5) Symmetrical ventral alopecia and self-inflicted lick lesions can be seen on the medial thigh due to D. gatoi
FIGURE (5) Symmetrical ventral alopecia and self-inflicted lick lesions can be seen on the medial thigh due to D. gatoi

© Anita Patel

Diagnosis

  • Due to excessive licking, the mite may be difficult to find. If there is more than one cat in the household, consider sampling all cats because the mite is easier to find in non-pruritic carrier cats
  • Skin scrapings (multiple)
  • Tape strips
  • Faecal flotation
  • Trial therapy is often required

Treatment

  • All in-contact cats need treatment
  • Fluralaner spot on can be used for cats
  • Selamectin and sarolaner spot on (Walker, 2018)
  • 2 percent lime sulphur dips. Clinical improvement is often seen within three to four weeks, with a total treatment time of six to eight weeks suggested (Hnilica and Patterson, 2017)
  • Prognosis is good

Unnamed Demodex mite

This mite is found in the hair follicles and, in some cases, concurrently with D. cati. It is a distinct species (Ferriera et al, 2015). It has a blunted abdomen and is associated with immunosuppression. The clinical signs and treatment options are similar to those described above for D. cati.

References
Author Year Title
Ferreira, D., Sastre, N., Ravera, I., Altet, L., Francino, O., Bardagí, M. and Ferrer, L. 2015 Identification of a third feline Demodex species through partial sequencing of the 16S rDNA and frequency of Demodex species in 74 cats using a PCR assay. Veterinary Dermatology, 26, 239-e53.
Hnilica, A. K. and Patterson, A. P. 2017 Small Animal Dermatology: A Color Atlas and Therapeutic Guide, 4th ed. Elsevier, St Louis.
Matricota, I. and Maina, E. 2015 The use of oral fluralaner for the treatment of feline generalised demodicosis. Journal of Small Animal Practice, 58, 476-479.
Walker, C. 2018 Treatment of Demodex gatoi mange in two sibling Bengal cats in the UK with a combination of selamectin and sarolaner (Stronghold Plus) a case report. British Veterinary Dermatology Study Group meeting, 77-79.

David Grant, MBE, BVetMed, CertSAD, FRCVS, graduated from the RVC in 1968 and received his FRCVS in 1978. David was hospital director at RSPCA Harmsworth for 25 years and now writes and lectures internationally, mainly in dermatology.

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