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Care of your dog - Mites
For centuries,
"mange" was a word used to describe almost all skin diseases
of dogs. A "mangy dog" was accepted as being a miserable,
run-down and scrawny animal.
Today, however, mange
is known to be a specific skin disease due to invasion of
the skin by tiny parasites called mites. There are two
common types of mites which cause mange: demodectic
and sarcoptic
mange. The two manges are quite different.
Demodectic
mange
This is
caused by the mite Demodex canis, and is the more
common form of mange. Most healthy dogs have this mite
present in small numbers as a normal inhabitant of their
skin and it causes no problems. Only when these mites
multiply and populate the skin in their thousands do they
cause trouble. Most dogs do not "catch" demodectic mange -
it develops from mites already present.
Demodectic mange can progress from a simple skin condition
to a severe problem if there is a failure of the dog's
immune system to prevent spreading. This may occur in a
debilitated dog or a dog suffering from another generalised
disease such as distemper or infectious
hepatitis.
At what age are
dogs affected?
The disease occurs typically in young dogs less than 12
months of age, however, exceptions do occur.
Signs and
diagnosis:
There are two distinct types of demodectic mange:
firstly there is a mild form localised to only a few sites,
usually around the head (especially the eyelids, corners of
the mouth and under the jaw) and forelegs. Patches of hair
loss are seen. There may be a slight itching, but often the
dog is not concerned. Usually only one to five patches are
present. The second type is a severe form, where hair loss
is widespread over the body, and is called "generalised"
demodectic mange. This form is a serious problem and may be
incurable in some dogs. When the resistance of the host dog
falls, demodex mites may breed to produce tens of thousands
of offspring. Frequently the skin becomes secondarily
infected with bacteria, and pustules (swollen pus-filled
pimples) develop. These may be itchy, causing further damage
when the dog scratches itself.
Diagnosis of demodectic mange is made by a vet taking skin
scrapings and observing large numbers of mites when the
sample is viewed under a microscope.
Treatment:
Mild cases mostly clear up by themselves in about a
month. For this reason, many different treatments have been
claimed to produce a cure, but preparations containing
benzyl benzoate, malathion, lindane and rotenone seem to be
most effective. Treatment of generalised mange must
be supervised by a vet, since these drugs are toxic. In
severe cases, treatment is prolonged and may be
unsuccessful. However, many dogs improve with age and the
problem may resolve once the dog is sexually
mature.
Distribution of
demodectic mange:
Sarcoptic mange
Scabies is a
mange caused by a mite called Sarcoptes scabei. This
mange is very different to demodectic mange.
Diagnosis and
distribution:
Dogs of any age may be infected. The areas most commonly
involved are the ears (especially the edges of the ears) and
the elbows, although any area of the body may be affected.
These areas become red and itchy. Hair usually falls out and
the skin becomes flaky and sometimes crusty. The dog
develops an intense itch and will rub and scratch vigorously
at the affected areas.
Who can catch
scabies?
Scabies is highly contagious to other dogs and may even
infect owners if they are in close contact with their
dog.
Treatment:
Treatment is always necessary. Scabies will not
get better by itself and the intense itching causes dogs to
mutilate their skin. Dips such as malathion, ronnel or lime
sulphur can be applied weekly until the skin clears up. This
may take a month or more. Ointments containing benzyl
benzoate, sulphur and other drugs which kill mites are
available from vets and some pharmacies. These can be used
if only small areas are affected. Spot-on preparations, such
as Revolution, can also be used.
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