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Facing up to several fresh challenges

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01 February 2010, at 12:00am

RACHEL BALLANTYNE reports on a recent seminar where current issues on emerging diseases were discussed

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.