The ACARUS Laboratory

Managing imported exotic diseases in UK dogs: 2011

Susan E. Shaw  & Séverine Tasker
UK veterinary practitioners are now regularly dealing with travelled dogs with leishmaniosis and other vector-borne imported diseases as well as advising on risk and prevention protocols for owners that travel with their animals. Cases of Babesia canis, Brucella canis, trypanasomiasis, Leishmania Ancylostoma braziliese have now been diagnosed in UK in travelled non-quarantined dogs.

Diseases transmitted by sand flies

Leishmaniosis: Leishmaniosis is caused by the protozoan parasite Leishmania infantum, and in the Old World is transmitted by sand flies of the Phlebotomus species. Dogs are the major reservoir for this infection. This infection causes disease in humans, particularly in immunosuppressed adults and children. It is extremely common in countries surrounding the Mediterranean and in South America. In endemic areas of Spain, Italy and the Balearic Islands, the infection prevalence in dogs may approach 90%. Most recently it has spread across the USA and Canada, particularly in the fox hound breed, despite the fact that there are no competent sand fly vectors in these areas. Both direct dog-to-dog transmission and vertical transmission have been suggested, and spread through contaminated blood products has occurred in the USA. Sand fly species which are not recognised as traditional vectors could become adapted to transmitting the disease. This disease is chronic and may have an incubation period of months to years. 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, glomerulopathy, polyarthritis, panophthalmitis and epistaxis. Other signs of immune-mediated disease are seen. Excessive non-protective antibody production may result in hyperviscosity syndrome. Diagnosis can be made by the demonstration of protozoal organisms in tissue biopsy specimens, serology and PCR. Information on the treatment of canine leishmaniosis

Diseases transmitted by ticks

Babesiosis (piroplasmosis):Babesiosis is caused by the protozoan parasites Babesia canis and Babesia gibsoni as well as other new species that have recently been characterised. They are transmitted by ticks of several species and are tropic for red blood cells. Canine babesiosis has a global distribution commonly affecting domestic dogs in Africa, Europe and Asia. Young to middle-aged dogs may be more predisposed, although any dog which does not have immunity is predisposed. Although ticks are the major means of transmission, there have been reports of transmission of Babesia gibsoni by blood transfusions and biting. Dogs with babesiosis show signs related to haemolytic anaemia including high fever, lethargy, weakness, red urine and collapse in severe cases. Later, severe anaemia, jaundice and multiple organ failure can occur. It appears that dogs with some immunity may remain carriers for years, and stress or other diseases may induce sudden onset of clinical signs of weakness and collapse. Diagnosis is made by demonstration of protozoal organisms in blood, lymph node, bone marrow or splenic aspirates in combination with compatible clinical signs. Serological tests are not routinely available but PCR testing is now available to all practitioners.
 
Treatment depends on the species of Babesia (Table 1). No product is licensed for use in dogs in the UK. Most commonly, imidocarb dipropionate is used although the small babesia species such as B. gibsoni require more complex therapy such as the anti-malarial ataquavone in combination with azithromycin. Treatment for shock and anaemia may be required in severe cases. There is no vaccination for dogs available in the UK (one is available in France for B. canis) but the disease is prevented by aggressive tick control (Table 4). The common babesia species affecting dogs do not cause disease in humans.

Table 1. Treatment of Babesiosis

*Drugs are not licensed for this purpose in the UK   

Ehrlichiosis: :Ehrlichiosis is caused by tick-transmitted intracellular bacteria that invade monocytes and macrophages (Ehrlichia canis) and in some cases, platelets (Anaplasma, previously Ehrlichia platys. The most common and important species affecting dogs is E. canis. It is transmitted by the tick Rhipicephalus sanguineus, which is well adapted to kennels, houses and cars. It has been reported from the USA, Europe and Africa. German Shepherds are predisposed to serious disease and may develop a fatal form of infection. Transmission by blood transfusion also occurs. Clinical signs include intermittent fever, lymphadenopathy, bleeding (petechiation, haematuria, epistaxis, retinal haemorrhage), weight loss, severe eye disease, other signs of immune-mediated disease and bone marrow hypoplasia subsequent with cytopenias. Thrombocytopenia is marked and platelet function is also impaired. Excessive antibody production leads to high protein levels and may result in hyperviscosity syndrome. Diagnosis is made by demonstration of organisms in white blood cells, or by specific PCR on a peripheral blood sample or splenic aspirate. Serological testing is available but cross-reactions may occur with other ehrlichial organisms and two samples one month apart are required to confirm active infection. Doxycycline is the treatment of choice for ehrlichiosis and response in the early stages of infection is reported to be excellent. Antibiotic therapy should be administered for a minimum period of 28 days (Table 2). There is no vaccination but the disease may be prevented by aggressive tick control (Table 4).  Ehrlichia canis does not cause disease in humans but some of the less common ehrlichial species found in the US are zoonotic.

Table 2. Treatment of Ehrlichiosis

Diseases transmitted by mosquitoes

Imported heartworm disease (Cardiopulmonary dirofilariasis):

Heartworm disease is caused by the nematode, Dirofilaria immitis that is transmitted by mosquitoes of many species. Cardiopulmonary dirofilariasis is common in southern Europe, USA, Canada, Australia and south-eastern and eastern Asia including Japan. In Europe, it is prevalent in Portugal, Spain, southern France, Italy, Greece and other peri-Mediterranean countries. The dog is the primary host for Dirofilaria immitis although other canids, cats, sea lions, ferrets and occasionally humans may be infected. The microscopic larval parasites are transmitted by mosquitoes into the skin and from there they migrate slowly through the body to the right pulmonary artery. Here they may reach adult size (up to 30 cms). The onset of disease is usually slow (months to years) unless the dogs have been exposed to a large number of infected mosquitoes at the same time. Clinical signs include exercise intolerance, coughing, weight loss, and occasionally death. Diagnosis is by demonstrating worms in the pulmonary artery using ultrasound, characteristic heart and lung changes on radiography and use of serological testing. Treatment of heartworm infection in dogs is complex and potentially dangerous (Table 3). As they are killed, the worms are washed into the pulmonary vasculature where they cause thromboembolism. It is now known that Dirofilaria harbour ehrlichial bacteria (Wolbachia) with which they are synergistic. A 30 day course of doxycycline is recommended prior to treating with adulticides to kill the Wolbachia. This may disable the adult worms but also decrease the severity of thromboembolism thought to be exacerbated by Wolbachia. There is also work from Italy to suggest that ivermectin given at the preventative dose (6 mg/kg) once every 15 days for 6 months given with the doxycycline for the first 30 days is macrofilaricidal and up to 60% of dogs are heartworm negative at 6 months. However, there are still pulmonary changes indicative of thromboembolism in heavy infestations or in hypersensitive dogs and direct efficacy and safety comparisons with melarsomine are yet to be performed.
 
This is believed to disable the worm and no drugs are licensed in the UK for treatment of heartworm and they must be imported. Corticosteroids and supportive oxygen in severe cases, combined with cage rest are advocated. Heartworm can be easily prevented using selemectin or milbemycin which are available and licensed in the UK. In addition, synthetic pyrethroids have repellent activity and can be used as part of a mosquito control programme (Table 4).  Heartworm can cause pulmonary or subcutaneous nodules which can be confused with neoplasia in areas of high prevalence but most infections are asymptomatic.

Table 3. Treatment of imported heartworm

*ivermectin not licensed for this use in dogs

Dirofilaria repens: subcutaneous canine dirofilariasis: an emerging problem

This mosquito-transmitted filarial parasite is being increasingly reported and the prevalence of canine infection in endemic areas of southern Europe (Italy, Spain, Greece, France, Balkans, Russia) is increasing. It is now established in Germany and is likely to be spread through travelling infected dogs which are reservoirs of infection.  Infection is also reported in wild canid species, wild and domesticated cats, and other carnivores. Like D. immitis it may infect humans, and although most infections are asymptomatic, reports of clinical disease are increasing. Dogs are the principal reservoir of infection and the parasite can be transmitted by several species of mosquito. Co-infection of mosquitoes with both D. immitis and d. repens have been reported.  The biological life cycle is similar to D. immitis except that the adult worms primarily reside in subcutaneous tissues. The clinical significance of infection varies but nodular skin lesions and abscesses are often reported. Aberrant migration of adults can also occur particularly into the ocular tissues. The adult parasite and microfilariae contain Wolbachia symbiont bacteria and as in cardiopulmonary dirofilariasis, host inflammatory and immunological reactions to the bacterial proteins can result in exacerbations of disease. In humans, both nodular skin, subconjunctival and other ocular lesions are being increasingly reported. Tentative diagnosis is by detection of microfilaraemia in absence of D. immitis positive antigen testing and/or demonstration of adult parasites in biopsies from nodular lesions. Adult worms may be macroscopically identified in subconjunctiva of dogs with eye lesions. PCR testing is available in some research centres but commercial testing is not available at this time. Differentiation between the filarial parasites of dogs will become increasingly important in areas where their distribution overlaps. Chemotherapeutic regimes for D. repens are as for D. immitus as well as surgical removal of the adults from subcutaneous lesions. To date there is no specific recommendations for prevention of infection in dogs although this may change particularly as the number of zoonotic infections is expanding.

Vector Control

Table 4.  Products available for control of vector-transmitted diseases in dogs (2009) 

** Use an effective residual acaricide and apply several days before leaving and then monthly thereafter.  Dogs should be closely examined every day and ticks removed with a specifically designed tick removing hook, using gloves. Remember that larval and nymphal ticks are extremely small. Recommendations must also take into consideration the current (due to change 01.01.12) PETS regulation to apply an acaricide 24-48hrs before return to the UK. Unfortunately, there are several anecdotal reports of live ticks still being found on dogs after travelling.