WITH growing numbers of pets
travelling abroad and with the ever
present threat of climate change
lurking, emerging and vector-borne
disease in dogs and cats within the
UK has become an increasingly hot
topic. But what does that actually
mean for practising vets and how
should we advise our clients
responsibly?
Merial Animal Health
recently organised an
evening CPD event,
with three eminent
speakers discussing the
current contentious
issues in the field of
emerging diseases. The
speakers included Dr
Jane Sykes, from the
University of California,
Davis; Susan Shaw and
Dr Eric Morgan, both
from the Bristol
veterinary school.
The speakers, all
experts in their fields,
delivered a wealth of
practical advice and tips
on dealing with diseases that
practitioners may not be used to
diagnosing and are sometimes still not
fully understood. This ranged from
discussion of risk factors for individual
dogs for Angiostrongylus vasorum infection,
to current treatment schedules for
imported vector-borne diseases such as
leishmaniasis and babesiosis.
Lyme disease
An international speaker in the truest
sense, Jane Sykes qualified from
Melbourne University in her native
Australia and has now spent many years
practising in the USA. The combination
has certainly given her a broad wealth of
experience to draw from and an
intriguing accent to engage delegates
with! Her subject was Lyme disease, Ixodes
and the dog.
Lyme disease was named after the
town of Lyme where its association
with tick bites was first recognised,
many years after the first reported case
in 1883 in Germany. A recent re-
emergence, most probably prompted by
changes in land use with people
adopting more rural living, now sees
Lyme disease as the most common tick-
borne disease in both the USA and the
UK – even George Bush has had Lyme
disease! It is now estimated to cost the
USA around $1 billion each year.
Borrelia burgdorferi sensu stricto is found commonly across the USA and is
strongly associated with arthritis in
humans; however, in Europe the strain
more commonly encountered is B.
burgdorferi sensu lato, which was first
identified in the UK in 20051. Lyme
disease is now endemic in many parts of
the UK and Ireland, such as the New
Forest and Thetford Forest. As a
zoonotic disease, dogs act as a sentinel of human infection.
The main vector in the UK is Ixodes
ricinus, commonly
known as the sheep
or castor bean tick. In
endemic areas, more
than half of adult
ticks may be infected.
Mice, squirrels,
hedgehogs and game
birds all act as
reservoir hosts.
It is important to
remember that ticks
need to be attached
for at least 24- 48
hours in order to transmit the Lyme
disease-causing organism, B. burgdorferi.
This leaves us an important window in which to remove or kill attached ticks to
prevent infection from occurring.
Signs of infection then take
approximately two to five months to
appear, and include fever, inappetence,
thrombocytopaenia and lameness, which
may initially be localised to the joint
nearest to the site of the tick bite. A
small percentage of dogs may develop
more severe complications, including
chronic treatment-resistant arthritis or
protein-losing nephropathy, which is
thought to be immune complex
associated.
However, whilst many dogs do not
show any signs of being infected, they
still provide a reservoir of infection for
ticks and hence other dogs.
In dogs, a diagnosis is made by
detection of antibodies via serology,
either using an ELISA test which is
available through IDEXX, or through
IFA testing (indirect
fluorescent
antibody). A positive
serology result,
however, does not
always mean the dog
has clinical Lyme
disease, only that it
has been exposed. In
addition, there are
several less
pathogenic or non-
pathogenic species of Borrelia circulating
in Europe, infection with which may
lead to positive test results using
serology. Thus, other possible causes of
clinical signs should also be considered
in dogs testing positive.
Bloodwork and urinalysis could be
offered in dogs testing positive that are
asymptomatic, but treatment with
antibiotics is not recommended if there
is no evidence of abnormalities such as
thrombocytopaenia or proteinuria. If a
dog is found to be positive for one tick-
borne disease, the possibility of co-
infection with other tick-borne
pathogens should be seriously
considered, and tick prevention should
be discussed with the owner.
Treatment of sick dogs with
doxycycline (Ronaxan, Merial) for four
weeks may resolve clinical signs;
however, complete elimination of the
spirochete may not occur. In the UK
prevention of the disease is very
dependent on the use of acaricides, as
well as minimising tick exposure and
speedy removal of visible ticks once
attached.
Imported diseases
Susan Shaw’s subject was Managing
imported exotic diseases in UK dogs 2009.
It is no surprise that with 670,000
animals, the majority being dogs, having
entered the UK under the pet travel
scheme (PETS) since the year 2000, the
veterinary profession is now regularly
diagnosing and treating vector-borne
imported diseases such as leishmaniasis,
babesiosis, ehrlichiosis and dirofilariasis.
A thorough travel history abroad
and within the UK should always be
obtained during the initial examination,
as it may give vital hints to which
pathogens should be given
consideration.
DEFRA has set up a voluntary
reporting scheme known as DACTARI
(dog and cat travel and risk information)
to carry out surveillance of exotic
disease in cats and dogs in Great Britain.
Susan Shaw was keen to stress, however,
that currently there are far fewer cases
reported on the DACTARI scheme
compared with those diagnosed at the
Bristol veterinary school (Table 1).
This implies that there is an under
reporting of cases to DACTARI and it is a real concern that government policy
regarding pet travel may be revised
based upon these apparently inaccurate
figures.
Leishmaniasis
Leishmaniasis is caused by a protozoan
carried by the sandfly, which is not
currently endemic in the UK. However,
there have been a few cases of
leishmaniasis dogs that have never
travelled abroad, but have been in close
contact with another infected dog. This
raises concerns as to whether this
disease could be directly transmitted
from dog to dog via other routes such
as biting.
The adoption of stray dogs from
Southern Europe is responsible for
many of the cases now being seen in
the UK. Often these dogs are at high
risk of infection, being in poor body
condition and obviously with no history
of use of sandfly preventives.
These dogs can even be imported
into the UK already on treatment for
leishmaniasis, their new owners being
unaware of the difficulty of obtaining
further medication in the UK, the long-
term nature of the treatment and the
potentially large cost.
Symptoms including skin lesions
(alopecia, scaling and ulceration) are
common, particularly involving the head
and pressure points. These occur in
combination with lymphadenopathy and
splenomegaly, weight loss, polyarthritis,
panophthalmitis and renal disease.
It is also important to remember
that the incubation period for this
disease can be months to years and leishmaniasis should be considered in
any dog that has travelled up to 7-10
years previously, especially to countries
surrounding the Mediterranean such as
Spain and Italy. It is usually most
commonly associated with animals that
have spent relatively prolonged periods
(weeks to months) in an endemic
country; however, a case has been
reported of acute disease in a dog that
spent just four days in Spain.
Diagnosis is most commonly made
by the demonstration of protozoal
organisms in tissue biopsy specimens
using both light and electron
microscopy. Serological tests are
available. PCR, particularly of bone
marrow, offers a sensitive and specific
diagnostic tool for this disease and can
also be useful in monitoring response to
treatment.
There are no licensed treatments
available in the UK, therefore treatment
usually involves the combination of
drugs requiring a special import licence
as shown below (Table 2). These
difficulties and potential associated high
costs should be seriously considered
before dogs from endemic areas are
adopted.
Tick-borne disease
With an increasing number of our
patients travelling abroad it is essential
to consider tick-borne diseases as a
potential diagnosis for relevant medical
cases. The possibility of co-infection
with more than one tick-borne disease
should also be considered.
- Babesiosis (piroplasmosis)
Babesiosis is caused by the protozoal
organisms Babesia canis and Babesia gibsoni
and is transmitted by ticks of several
species, some of which are found in the
UK. At present there has only been one
reported fatal case of babesiosis in the
UK – in an untravelled dog in 2005.
However, proposed changes to the
PETS derogation, eliminating the need
for tick treatment before entry into the
UK, could see this disease becoming
established.
Worryingly, there have also been
reports of transmission of Babesia gibsoni
by blood transfusions and dog bites in
other parts of the world such as
Australia. So vets should take extra care
not to be bitten when examining
imported dogs.
Dogs with babesiosis present with
signs associated with haemolytic
anaemia including high fever, lethargy,
weakness, red urine and, in severe cases,
collapse. Once jaundice is clinically
recognised there is a poor prognosis for
survival. Babesiosis should always be
considered in cases of haemolytic
anaemia, especially where there is a
history of travel.
Some dogs with partial immunity
may remain carriers for years, when
stress through surgery or other disease may induce a sudden onset of clinical
signs. This means that dogs could
develop clinical signs a year or more
after travelling to countries such as
France where the disease is endemic.
Diagnosis is by demonstration of
the protozoal organisms in blood,
lymph node, bone marrow or splenic
aspirates in combination with clinical
signs. Molecular (PCR) testing is
available from several commercial
laboratories and provides a reliable
diagnostic test.
There is no licensed product for the
treatment of dogs in the UK but a
cattle treatment, imidocarb, is available
through the cascade. This usually elicits
an excellent clinical response within 48
hours and a negative PCR test within 2-
4 weeks.
- Ehrlichiosis
Ehrlichiosis is caused by tick-transmitted
intracellular bacteria, the most common
and important of which in dogs is
Ehrlichia canis, transmitted by the tick
Rhipicephalus sanguineus. This tick is rare
in the UK but is well adapted to kennels
and indoor environments, so could
potentially establish if imported in
significant numbers.
German Shepherds are particularly
predisposed to serious disease and may
develop a fatal form of infection.
Transmission by blood transfusion also
occurs.
Clinical signs are predominantly
those of a bleeding disorder:
haematuria, epistaxis and retinal
haemorrhage. Thrombocytopaenia is
marked and platelet function is also
impaired. Reliable diagnosis can be
achieved with PCR testing on a
peripheral blood sample.
Doxycycline (Ronaxan, Merial) is the
treatment of choice and response in the
early stages of infection is reported to
be excellent.
Prevention of all tick-borne disease
through good tick control is most definitely better than cure.
Tick control can be
achieved not only through
timely application of
topical acaricides, but also
by regularly checking dogs
following possible
exposure and removing
any ticks found with a tick
hook. Clients travelling
with their pets should be
strongly encouraged to
take appropriate measures
to protect them from ticks
throughout the whole
duration of the trip, not
just to comply with the
PETS regulations when re-
entering the UK.
Angiostrongylosis
Angiostrongylosis – an emerging canine disease
in the UK was Eric Morgan’s subject.
When he asked whether many of us
had seen cases of A. vasorum,
approximately a third of the audience
responded “yes”. However, when he
asked if these cases had been
confirmed, the response was
significantly lower.
With increasing awareness of the
parasite thanks to the recent publicity
surrounding the disease now that
licensed treatments are available,
clinicians are now far more likely to
consider A.vasorum as a differential
diagnosis; however, they may not always
confirm their suspicions with laboratory
tests. Thus, we cannot be absolutely sure
that the apparent rise in cases is a true
reflection of the current epidemiology
of the parasite, or merely a reflection of
increased awareness.
It is thought that the organism is
endemic in most of the southern half
of the UK with a few sporadic cases of
infection further north. It is also
interesting to note that within endemic
areas, infection remains very patchy,
with some practices seeing lots of cases
and others nearby seeing none. Indeed,
it can even be that clients’ dogs from
certain parts of a neighbourhood are at
risk (perhaps all walking their dogs in
the same park), whereas those a few
streets away are not.
Slugs and snails are the intermediate
host for A. vasorum. To acquire an
infection the dog or fox must actively or
inadvertently eat a slug or snail. Eating
larvae in infected dog or fox faeces does
not pose a risk! After ingestion of the
slug or snail the larvae then migrate to
the right ventricle and pulmonary
arteries where they develop into adults.
The first stage larvae then penetrate
the alveoli, are coughed up, swallowed,
and passed out in the faeces. The exact
role of the fox in the spread of the
parasite is unknown, however the
presence of foxes in the dog’s
environment no doubt increases the risk
of infection.
