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Hewison's
Corner
Ticks
and tick-bourne diseases |
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In my last article I introduced members to the Pet Travel Scheme,
this article concentrates not only on tick-bourne diseases in the
UK but also what may potentially be imported from overseas.
Ticks are arthropods (of the
class Arachnids - as are spiders).
There are two main species
native to the UK the Sheep Tick (Ixodes ricinus) and the Marsh Tick
(or ornate cow tick) (Dermacentor reticulates). Another tick, the
Brown Dog Tick (Rhipicephalus sanguineus) is of importance as it
may carry a human disease called Mediterranean Spotted Fever if
dogs pick it up on their travels via the PETS scheme – this
is one of the reasons why all travelling pets must be treated with
effective tick-control before re-entering the UK.
Where and when do ticks live?
Ticks like warmth and humidity. We find them in grassland, scrub
and shrubs where they lie in wait for a passing host. In the UK
they are most active between March and November.
Ticks and disease
For a tick to transmit disease
it must first feed on an infected host – they suck their blood
with penetrating mouthparts. When full the tick falls off the host
to the ground where it will develop to the next stage in its life-cycle,
it will then infest another animal by feeding on it. A tick has
a slow life cycle, sometimes taking four years to complete from
egg to adult, the host gradually increasing in size. The larvae
may feed on hedgehogs and rodents, the nymphs on rabbits and the
adults on sheep, deer, our dogs and us humans.
1. Lyme disease (Borreliosis) in dogs and people
This is caused by bacteria that are carried by ticks. The signs
of this disease signs are intermittent lameness, swollen joints,
lethargy and fever. These symptoms can become severe and can even
cause death. It is most important for all owners to be aware that
ticks can transmit this disease to dogs and people in this country
and the matter of using effective tick control cannot be taken lightly.
2. Ehrlichiosis in dogs and people
Although not common in the UK it is often seen in southern Europe,
Africa, and the USA. It is caused by a Rickettsial bacterium which
affects certain blood cells and may cause dogs to suffer from a
fever, anorexia, weight loss, stiffness and prolonged bleeding.
It can be passed to humans if we are bitten by an infected tick.
3. Babesiosis
Babesia is a protozoan parasite carried by Dermacentor and Rhipicephalus
ticks. The Dermacentor ticks have been found on cattle in the south
of England and the Rhipicephalus has been identified in dogs in
quarantine kennels. Babesiosis is serious, causing a loss of appetite,
fever, anaemia, fatigue and discolouration of urine. It is potentially
fatal if left untreated and can also affect humans. Fortunately,
however, it does not normally occur in the UK and is more common
in southern Europe, Africa and Asia.
Preventing these diseases
Avoidance – removal of long
grasses and trimming of shrubs in the garden limits the likelihood
of exposure. Try to keep your dog away from tick breeding grounds
such as tall grass or brush especially during the warmer, months
of the year. Remember, they will be most likely found in areas where
there are more sheep and deer. Of course summer is the peak season
for gundog working tests and these are exactly the sort of areas
where we send our flat coats into for the most challenging retrieves!
Repellents and pesticides
– in my experience these vary greatly in their efficacy –
the most effective preparations are only available through your
vet who will give you the best advice on what should be used for
your circumstances. There are long lasting, waterproof spot on preparations
and chemical-impregnated collars that can be used.
Physical removal –
I strongly recommend the use of a tick hook. These are cheap, simple
to use and the most effective means of removing the entire body
of the tick (including its mouthparts). Please remember not to touch
the body of the tick yourself – always use a tissue. There
are reports of people gaining exposure to disease through contact
of their skin to the body of the tick.
When we visited Northumberland
this summer we spent our evenings at the B&B going through our
dogs with a fine tooth comb and tick-hook. It is surprising how
many you find – despite using the chemical preventatives.
Other parasites
I have chosen to discuss ticks in
this article; sadly there is not enough space for me to include
detail on the other main disease risks (Leishmaniasis and Dirofilariasis)
identified from travelling overseas. These diseases are transmitted
by sand-flies and mosquitoes - it is very important to be aware
of these if you visit the Mediterranean regions of Europe with your
dog.
Speak to your vet about if before you leave.
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Gastric dilatation and volvulus.
Gastric dilatation and volvulus (GDV) or ‘bloat’
is not a disease specific to flat-coats but it much discussed
amongst flat-coat owners as it is more common in large breed dogs
and it is a true veterinary emergency. If left untreated a dog
with bloat can rapidly die through associated shock. For this
reason it is important that we all learn the signs to look out
for so we might improve our dog’s chances of surviving it
should it occur.
I will also discuss why we think the
condition arises and how we may try to prevent it.
Anatomy of
the stomach
The stomach is part of the long tubular pathway
through which the dog’s food passes. It is an expandable,
muscle-lined sack containing glands in its walls that produce
acid and digestive juices. Food enters the stomach in the oesophagus
and exits through the duodenum to pass on to the small intestines.
What happens when a dog bloats?
The stomach can dilate as a result of the dog
literally swallowing air (‘aerophagia’). If the stomach
twists it pinches the point where the oesophagus enters –
this means air and food that is in the stomach becomes trapped
and the dog can neither belch nor vomit up its contents. A pinch
effect at the exit of the stomach also prevents air passing into
the intestines.
Signs to look out for.
Call your vet immediately if your dog is displaying
the following signs: non-productive retching, salivation, abdominal
distension (particularly where a hollow, drum-like sound can be
made with a tap of a finger), weakness and collapse.Treatment.
If a twist hasn’t happened then a dog with bloat may occasionally
be treated without surgery. Once the dog has been given treatment
for shock the vet may be able to pass a stomach tube with the
dog conscious allowing air to escape through the tube. Most cases,
however, require emergency surgery to decompress the stomach and
correct the twist. Once corrected, the stomach may be permanently
sutured to the side of the body to prevent a further twist (this
is called a gastropexy).
Dangers.
When the stomach dilates it squeezes the blood
vessels in the walls reducing their ability to supply blood to
the muscular wall. The stomach is closely associated with the
spleen, and a twist of the stomach may also interfere with the
supply of blood to the spleen. Delays in treatment for bloat causes
the stomach and spleen to be at great risk of necrosis and many
dogs will have to have their spleen removed – some may also
require a portion of stomach to be removed.
Once the circulation is re-established there is further risk to
the dog of shock, leading to concern over damage to other body
organs, most especially the heart.
Prevention.
There have been lots of ideas about why
a dog’s stomach bloats, in my experience I can remember
only one case where I know for certain what the cause was. It
involved an Italian Spinone that had eaten some loft insulation
(to this day I do not understand why!) the insulation had blocked
the entrance to the stomach preventing the dog from belching gases
from the food it was busily digesting.
Other more detailed studies have suggested
that the incidence of the condition is higher in older dogs, in
fast-eating dogs, in dogs only fed once a day and in dogs fed
from a raised food bowl. We always try to avoid walking or working
our dogs just before or just after a meal.
Bearing in mind that I am writing this article
for owners of one breed in particular I am pleased to tell you
that it has been reported that bloat is notably less common in
happier dogs.
Keep those Tails Wagging!
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Glaucoma
in flat-coated retrievers.
Glaucoma is a condition where the pressure
of fluid in the eye increases above normal. The increased pressure
squashes the structures around the outside of the eyeball against
its bony socket and results in pain and damage. The damage to
the fine blood circulation to the optic nerve head and the damage
to the retinal cells can lead to permanent impairment of vision
or blindness.
The sad thing is that it is a proven
hereditary condition in flat-coated retrievers. This means that
anyone who is interested in breeding needs to be aware of the
condition, how a veterinary ophthalmologist tests dogs for glaucoma
and what the test results mean.
Anatomy of the eye
The fluid (aqueous) that gives the eye
its shape is produced by the ciliary processes which are located
around the rim of the dog’s lens. The fluid passes in front
of the lens and through the centre of the coloured iris (i.e.
through the pupil). As the fluid is continually being produced
it needs to be continually removed to prevent a pressure increase.
This drainage is crucial to prevent the development of glaucoma
and it occurs in a small angle between the iris and the cornea.
The flow of
aqueous through the eye. Image taken from the BSAVA Manual of
Small Animal Ophthalmology, 2nd Edn., BSAVA, 2006.
Goniodysgenesis / Closed-angle glaucoma
Goniodysgenesis is the commonest cause
of primary glaucoma in flat-coated retrievers. It is a developmental
abnormality of the pectinate ligament in both eyes. This ligament
sits across the drainage angle. Pectinate means ‘looks like
a comb’ and this is how a normal ligament appears when highly
magnified. A dog with goniodysgenesis looses this classic appearance
and the comb looks more like a sheet of tissue with only a few
drainage holes in it. The condition may also cause the drainage
angle to be narrower than normal. This results in a slower drainage
and an increase in fluid pressure.
Treatment
There are various medical treatments
used to control glaucoma but these are often not enough to control
the increased pressure in a dog with goniodysgenesis. These often
require specialised surgical treatments and none of these are
ideal either. All these dogs require prompt attention. If your
dog is affected by a sudden onset painful eye, with a milky cornea
and red conjunctiva please make sure you take it to the vet urgently.
Testing
The drainage angle cannot be seen without
the right equipment so ophthalmologists use a technique called
gonioscopy to view the ligament in the drainage angle. A goniolens
is placed on the cornea (a bit like placing a contact lens) and
a magnifying scope is used to view the angle. The vet will use
topical anaesthetic on the eye first and although the dog may
fidget the procedure is quick and is not painful.
The test usually only needs to be performed once in a dog’s
life (from four to six months old).
Please note that the gonioscopy is not
a part of the routine BVA/KC eye scheme that check for other hereditary
eye diseases, it is these tests that need frequent re-evaluation
to be accurate.
Results and breeding
The result of a test will be either ‘affected’
or ‘not affected’. This is of note because the dog
may be affected to a varying degree – it is up to the scoring
vet to use criteria to decide how narrow the drainage angle is
before that dog is deemed to be affected and there is an appeals
procedure should any doubt arise regarding a dog’s test
result.
The degree to which a dog is affected
by goniodysgenesis influences their likelihood of suffering from
painful glaucoma in that eye. A dog may only be partly affected
– and so be less likely to suffer from an increase in pressure
and blindness. It is wise to know the criteria of your dog’s
eyes for the individual dog’s sake
An affected dog may not show clinical
signs until they are five or six years old and by this time they
may already have been used for breeding so it is very important
to use the results of testing when selecting healthy breeding
animals.
It is wise to mate an unaffected dog to another non affected dog.
It may be appropriate to mate a slightly affected dog to an unaffected
if all other aspects of the dogs’ health are sound and they
are of good ‘breed type’. But, for the sake of the
breed NEVER mate an affected to an affected dog.
The disease has high heritability – this means that the
disease has a highly genetic basis, which in turn means that if
affected dogs are not bred from then the disease should be relatively
easy to eradicate. Diseases with lower heritability and therefore
less genetic basis are more difficult to eradicate by selective
breeding.
Current figures suggest that approximately
one in a hundred flat-coated retrievers may be affected by goniodysgenesis.
From information collected by the Flat-coated Retriever Society’s
Health Committee it is evident that we can none of us be confident
that our breeding line is not affected.
Contact your own vet for details of your nearest testing ophthalmologist.
Have your dog tested before you breed. |
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