TROMBICULID MITE INFESTATIONS
(Harvest Mite)
What is a harvest mite?
The harvest or grass mite (Trombicula autumnalis) is a mite the larval stage of which causes
considerable discomfort to cats and dogs during the late summer and autumn. The mite is seen in
suburban pockets. but is particularly abundant in chalky areas and gardens where soft fruit is grown.
The six legged larval stage is the only stage which attacks warm blooded animals. All other stages
live in the environment and are not parasitic. The larvae congregate on small clods of earth or on
vegetation. They are active during the day and particularly in dry sunny weather. When a warm
blooded animal comes into contact with the larvae they swarm onto it and attach onto skin
particularly in sparsely haired thin skinned areas. The larvae feed for 2 to 3 days and they drop off
onto the ground to complete the life cycle. The larval mite is orange and only just visible to the
naked eye - aggregations of mites can be seen as small orange patches, usually on the cat’s face.
What effect do harvest mites have on cats?
The six legged larval mite attaches to the skin of cats to feed. It fixes onto the skin by small hooked
fangs and then injects fluid into the skin which liquefies cells. The resulting liquefied food is
sucked back by the mite. The fluid injected by the mite is very irritant. Irritation causes the cat to
scratch, bite and lick which may result in extensive self-inflicted injury. The resulting skin lesions
vary from crusted spots to areas of hair loss to raw moist bleeding areas.
In cats mites are most commonly found on the ear flaps, on the sparsely haired area in front of the
ears and between the toes but they can be found almost anywhere on the body.
Individual cats vary greatly in their sensitivity to mites. Extreme sensitivity probably reflects the
development of an allergy to the mite or its products and affected cats will cause severe selfinflicted damage to themselves.
How are harvest mite infestations diagnosed?
Sudden onset of intense irritation in the Summer months would make one suspicious that harvest
mites might be involved although other ectoparasites and some forms of allergic skin disease can
cause similar symptoms.
Your vet can make the diagnosis by identifying the mite. Congregations of mites may be seen as
intensely orange spots on the skin. If fewer mites are present they may be seen on microscopic
examination of a superficial skin scraping.
Diagnosis can be difficult if cats are presented some time after the problem started as by then the cat
may have licked or scratched off all the mites.
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P O Box 438, PYMBLE NSW 2073 Australia
How can I get rid of harvest mites from my cat?
Your vet will give you appropriate treatment. Insecticides licensed for on-animal flea control will
effectively kill harvest mites provided that they reach the skin and not just the fur. This is more
readily achieved with a foam or pump-on liquid than with an aerosol spray or powder. The problem
is that unless the product has excellent residual action as soon as the cat returns to the infested
environment it will collect more mites. To avoid this the cat can be restricted to indoors during the
mite season. Fortunately there are now flea control products (e.g. ‘Frontline’) available with good
residual action which may be able to prevent or considerably reduce reinfestation. Such products
should be applied to the cat during the harvest mite season at the highest frequency suggested in the
instructions.
What can be done to stop my cat itching?
In most cases treatment for the mites will rapidly make the cat feel more comfortable. In cats which
are very sensitive to mites additional treatment with cortisone-type drugs and occasionally physical
restraints such as Elizabethan collars may be necessary to prevent further self-trauma.
Do harvest mites affect people?
People can be affected by harvest mites. These are not caught from cats or dogs but from infested
outdoor environments. People's ankles become affected by walking through infested vegetation but
more generalised lesions can follow sitting or lying in infested areas. A typical human skin reaction
consist of an intensely irritant rash. Specific treatment is usually unnecessary. Avoidance of
infested environments is the best way of preventing the problem.
Ark Veterinary Centre
A Lifelearn Product from:.
Arthur Webster & Associates Pty Ltd
P O Box 438, PYMBLE NSW 2073 Australia