HARVEST MITE INFESTATIONS
What is a harvest mite?
The harvest 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 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.
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 self-inflicted damage to themselves.
How are harvest mite infestations diagnosed?
Sudden onset of intense irritation in July or August 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 veterinarian 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.
How can I get rid of harvest mites from my cat?
Your veterinarian 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 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 (July to October) 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 anti-inflammatory therapy 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 generalized 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.
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