Trombiculidiasis

Also known as: Harvest mite — Chiggers

Introduction

Neotrombicula autumnalis is a non-burrowing mite that it found worldwide. It will attack and parasitise any animal including humans, hence it is zoonotic. Only the larval stage is parasitic however, and adult mites are found living in the soil. The mite is bright orange in colour and hairy. Eggs are laid in soil and once hatched, larvae climb up vegetation in search of a host to attach to. As the name suggests, numbers are greatest in 'harvest' time, late summer, in temperate climates and all year round in the tropics.

The mite is a surface mite and forms tunnels in epidermis by injecting saliva, then eating digested tissue fluid. This causes irritation and can lead to a hypersensitivity reaction should the animal be bitten again. In small animals the mites are generally found around the head, ears and neck, whereas in large animals mites are found on the face and limbs.

Clinical Signs

The animal will show signs of intense pruritus and orange to red coloured larvae may be visible on the skin. There will be a erythematous, papular rash and also crusting and scaling.

Diagnosis

Clinical signs and the time of year is indicative of the parasite. On physical examination, it is likely the parasite will be seen. Skin scraping, coat brushing or a tape strip may reveal the presence of the mite. Microscopically, the skin will appear hyperplastic with superficial perivascular dermatitis and the presence of eosinophils and mast cells.

Treatment and Control

Treat infected animals with a licensed acaracide. Control is almost impossible, if animal has a known hypersensitivty reaction then try to avoid affected areas during the season.

References

Brown, C.M, Bertone, J.J. (2002) The 5-Minute Veterinary Consult- Equine, Lippincott, Williams & Wilkins

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition) Elsevier Science

Foster, A, and Foll, C. (2003) BSAVA small animal dermatology (second edition) British Small Animal Veterinary Association

Fox, M and Jacobs, D. (2007) Parasitology Study Guide Part 1: Ectoparasites Royal Veterinary College