Skin irritation from immature Ixodes ticks on dogs and cats in Sydney

Abstract

Infestations of larval and nymphal Ixodes spp. were identified in 16 dogs and 16 cats from several small animal clinics in Sydney. Cases occurred in late summer or autumn, peaking in February, and were seasonally recurrent in some individuals. Clinical signs of infestation included a papular dermatitis and irritation or pruritus that ranged from severe to mild or absent. The distribution of tick attachment tended to be cranial and ventral, with the face, legs, axillae and ventrum the most commonly affected sites. The estimated number of ticks in each infestation varied from less than 10 to more than 100. Basic morphological examination of ticks collected from affected animals was performed by attending veterinarians using light microscopy, and larvae and nymphs belonging to the Ixodes genus were identified. Ticks collected from 17 animals and submitted to the Department of Medical Entomology, Westmead Hospital were putatively identified as I. trichosuri (57%) and I. holocyclus (25%) larvae. Histopathological samples of attachment sites collected from three dogs and one cat were characterised by ticks attached in well-demarcated invaginations of the skin ('tick craters') associated with variable epidermal and/or dermal necrosis, focal eosinophilic intraspinous pustules, mild to marked eosinophilic and neutrophilic, superficial to deep, dermal perivascular to interstitial inflammation, and moderate to marked superficial dermal oedema and red cell extravasation. A range of topical acaricidal preparations, including fipronil and synthetic pyrethroids, were used for treatment.