Trombiculidiasis

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Trombicula autumnalis
Phylum Arthropoda
Class Arachnida
Order Trombidiformes
Family Trombiculidae
Genus Trombicula
Species T.autumnalis

Caused by: Trombicula autumnalis also known as: Harvest mite — Neotrombicula autumnalis — Chiggers

Introduction

Trombicula mite bites Tim Vickers 2008, wikimedia commons

Trombicula autumnalis are surface mites found worldwide. It will attack and parasitise any animal including humans, causing parasitic skin infestation (trombiculidiasis). Only the larval stage is parasitic however, and adult mites are found living in the soil.

Identification

The mites are bright orange in colour and hairy. They have six legs and no spiracles. They breathe through their cuticle.

Lifecycle

The lifecycle of Trombicula autumnalis mites lasts around 50 to 70 days. The nymphal and adult stages are free-living in the soil. 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.

Pathogenesis

The larvae insert their mouthparts into the host's skin and inject cytolytic enzymes. They then feed on partly digested host tissue causing irritation and potentially a hypersensitivity reaction. The Mites are mainly found on the head, ears and flanks of pets and can be found on the face and limbs of grazing animals, depending upon the host height.

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 ('hot-spot') during the season.


Trombiculidiasis Learning Resources
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Trombicula autumnalis publications


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





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