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A winter occurrence of Harvest Mite Infestation

Christian COLLINOT
Clinique vétérinaire du ROC, 117, avenue du maréchal LECLERC, 86100 CHATELLERAULT

Past History

Moustic was a grey and white 3 year old castrated domestic cat. He spent his life as a town cat, without other animal companions, sometimes going out to the garden. From time to time, he accompanied his owners on holiday in the countryside, and took the opportunity to explore his new rural surrounds on these trips. He was fully vaccinated and wormed. Spot-ons were used only erratically as antiparasiticides, but were used this time as their usual veterinarian had warned them of an increased risk of flea infestation due to the unseasonable warmth (end of December, 2005).

Presenting signs

Since his arrival in the countryside for the end-of-year festivities, Moustic started scratching more and more, and developed an increasing number of skin lesions. He was taken to the veterinary clinic for this reason on 10 January 2006.

Clinical Examination

General Examination:

Other than the skin lesions, he was clinically normal, and in good general condition.

Dermatological Examination:

The lesions were very itchy.

Moustic presented with numerous erythematous lesions, each with a varying degree of alopecia, broken hairs, exudate and crusting. They were found on both the front and the back feet, particularly on the distal portions and between the toes, but also in the crook of the elbow.

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There were very crusty lesions on the ventrum, where grooming was particularly important.

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Some crusty lesions could be found on the head, particularly just in front of the base of the ears.

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There were minimal lesions on the back, apart from several crusts between the shoulder blades.

Differential diagnoses

This case presented as an erythematous, crusting, pruritic dermatitis. Allergic dermatoses, such as atopy, food and contact allergies, were considered, due to the irritation they cause. Parasitic agents were also considered, such as fleas, lice, Trombicula, and generalised Otodectes. Certain fungal infections, less adapted to the cat, such as T. mentagrophytes can also be pruritic. A behavioural disorder was also considered. Less likely causes, taking into account the age and general condition of the cat, might have been a viral infection (herpes, cowpox), pemphigus, or mycosis fungoides.

Complementary Examinations

The coat was carefully combed through, but no traces of fleas or flea dirt were found. Examination of the hairs confirmed the traumatic nature of the alopecia, with many broken hairs, but still keeping their normal structure. Microscopic examination of the crusts revealed dead mites or insects within them, too small to be Cheyletiella, and resembling the larvae of Trombicula, even if the time of year made this unlikely.


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Skin scrapings revealed living larvae of Trombicula autumnalis.

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Even if the time of year (early January 2006) was not the classic harvest mite season, this was a case of trombiculosis, which the author is qualifying as ‘winter’.

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