Trombiculiasis

The six-legged larvae of the genera Trombicula (chigger mite, harvest mite) cause a seasonal (in temperate or continental climates) and pruritic papular dermatosis both in dogs and cats.

Mites are often found on and around the pinna. The legs, interdigital areas, ventrum, and face are often involved, too. Pruritus is almost always present. Crusts, alopecia, and erosion are present on affected areas.

The diagnosis is usually easy because the larvae are visible to the naked eye (0.5 mm), have a bright orange to red color, and are tightly adherent to the skin, usually in clusters.

Treatment should aim at killing the mites present on the animal, relieving the pruritus, and preventing subsequent infestation. If infestation is localized, topical application of an otic ointment containing steroids and an insecticide is sufficient. Otherwise, an acaricidal spray should be associated with a 5- to 8-day course of oral prednisolone (1 mg/kg). If free roaming cannot be prevented, the prevention of reinfestation is difficult. An acaricidal spray with a strong repellent effect such as permethrin is an option for dogs but is toxic in cats. In one study on a small number of animals, fipronil spray applications seemed to achieve a more effective and last­ing result in dogs than in cats.⁶ Trombicula autumnalis adults are found in the outside environment. Compost areas should be enclosed so that the pet cannot access them. Treatment of other favorable areas (under trees, under the house, in bushes) with insecticides should be discouraged because of the toxicity to invertebrates (pollinating insects, honeybees) and children and the presence of residue on fruits or vegetables grown in the garden.