The first part of this miniseries reviewed Echinococcus multilocularis and tick-borne pathogens, including Babesia canis. In this second article, the focus is on Dirofilaria species and Leishmania, both of which present an increasing concern and need for control and advice.
There are numerous fly-borne nematodes to which the travelling pet may be exposed. One of the most widespread and pathogenic of these is the heartworm Dirofilaria immitis. Another notable example is the skin worm Dirofilaria repens.
D. immitis (heartworm)
D. immitis is a filarial heartworm primarily of canids but which can also infect ferrets and cats. It is endemic throughout southern and parts of eastern Europe and is a significant cause of heart disease and bronchitis in infected pets. Transmission occurs through feeding by infected mosquitoes.
Coughing, tachypnoea, dyspnoea and exercise intolerance are the most common clinical signs seen in infected dogs. Acute clinical signs are associated with thromboembolism, subsequent pulmonary hypertension and caval syndrome. Worm death can also lead to thromboembolism and anaphylaxis. Chronic signs tend to be respiratory in nature and include coughing, dyspnoea, anorexia, vomiting and, rarely, chylothorax. Chronic respiratory signs tend to be more common in cats.
Climate change, however, has allowed spread of the parasite northwards, raising the possibility that if this trend continues, endemic foci could establish in the south of England
Although the mosquito vector is endemic in most European countries, including the UK, a colder climate in northern Europe has prevented heartworm from becoming endemic. This is because the adult mosquito does not live long enough in colder climates for the heartworm to complete its lifecycle. Climate change, however, has allowed spread of the parasite northwards, raising the possibility that if this trend continues, endemic foci could establish in the south of England.
Control and prevention of entry into the UK
Prophylaxis is desirable in travelling pets to reduce the risk of adult infection establishing. Monthly administration of a licensed macrocyclic lactone (milbemycin, moxidectin, selamectin and also eprinomectin in cats) is highly effective as a preventative treatment and should be continued until the return to the UK. The use of a licensed fly repellent in dogs will also act as an advantageous second line of defence but should not be relied on alone. A variety of products are licensed for heartworm prevention with the option of combined flea, lungworm or tick treatment. Spot-on and tablet formulations are both available, so client preference should also be considered to maximise compliance.
D. repens is a parasitic nematode of dogs and, less commonly, cats. It is closely related to the heartworm D. immitis. While D.immitis resides in the heart, however, D. repens is a parasite of subcutaneous tissue. Infection can lead to skin and ocular disease and the parasite has zoonotic potential if people are exposed to the bites of infected mosquitoes.
The mosquito vectors for D. repens are already endemic in the UK and D. repens has less stringent temperature requirements than D. immitis, meaning that it is more likely to establish. Transmission occurs in a similar manner to D. immitis but with adult worms (Figure 1) living in skin nodules and subcutaneous tissues rather than the cardiovascular system. Infection can be subclinical or lead to dermatitis and skin nodules. Less commonly, adult worms migrate to the eyes of the host where they may be visible and cause ocular complications.
Vigilance for relevant clinical signs is vital so treatment can be initiated before UK mosquito populations are exposed to infection. Licensed moxidectin/imidacloprid spot-on formulations are available for treatment and also prevention. They should be considered for cats and dogs travelling to northern Europe where D. immitis prevention is not required but D. repens exposure is a possibility.
Leishmaniosis is caused by intracellular protozoan parasites of the genus Leishmania, with Leishmania infantum being the predominant species in cats and dogs. It has zoonotic potential and is a significant zoonosis in endemic countries where the sand fly vector is present. Transmission occurs primarily through bites from infected phlebotomine sand flies, limiting the distribution of the parasite; however, transmission can also occur via blood transfusion and congenital and venereal transmission, as well as possibly dog bites.
[Leishmania] has zoonotic potential and is a significant zoonosis in endemic countries where the sand fly vector is present
This is a concern, as increasing numbers of cases are being seen in the UK in imported and travelled pets. Rapid diagnosis of infection is important as identification of subclinical carriers and rapid recognition of relevant clinical signs will allow prevention of these secondary modes of transmission in addition to monitoring and treatment of infected pets.
Canine leishmaniosis is chronic in nature with a variety of presentations and periods of remission. Signs are due to immune-complex deposition in various organs and include alopecia, hyperkeratosis, dermal ulcers, polyarthritis, ocular inclusion bodies, uveitis, hepatopathy, glomerulonephritis and neurological signs associated with spinal and CNS granulomas. Periocular alopecia is a classic sign and easily mistaken for atopy. Subclinical carrier states are common with incubation periods of months or years and relapses in chronically infected patients. An association between leishmaniosis and feline leukaemia virus (FeLV)/feline immunodeficiency virus (FIV) has been recognised in cats.
Control and prevention of entry into the UK
Disease prevention is essential for dogs travelling to endemic countries. Sand flies feed at night with the greatest activity at dawn and dusk so avoiding outdoor activity at these times helps to prevent exposure. Sand flies are also poor flyers so if camping outdoors, breezy high locations are desirable.
Some exposure to bites is likely, however, even if these precautions are taken, and so the use of insecticides with “knockdown” capabilities to prevent flies from biting is required. Pyrethroids are the drug class of choice for fly knockdown and licensed spot-on and collar preparations are available for dogs in the UK. Although it is not licensed for sand fly repellence, the Seresto collar is likely to have some efficacy and is the only useful option for cats. Treatment should be applied one week before travel as pyrethroids take time to reach full distribution and activity. No fly repellent is 100 percent effective and so vaccination to reduce disease should also be considered in dogs spending long periods of time in endemic countries.
The increased movement of pets, fluid vectors and parasite distributions in Europe make protecting UK pets and owners from exotic diseases increasingly challenging. Veterinary professionals are on the front line of UK biosecurity and must be prepared to give accurate travel advice to clients. In doing so, pet and human health will benefit and the entry of novel parasites into the UK can be delayed or avoided.
Although parasite protection when travelling abroad may seem complex, endectocides give the opportunity for treatments to be combined
The need for animal health certificates means that clients must engage with vets before travelling abroad. This is the perfect time to remind owners of the animal and public health disease risks associated with travel. Although parasite protection when travelling abroad may seem complex, endectocides give the opportunity for treatments to be combined. Fly repellence, if required for Leishmania protection, will also protect against ticks. If tick/Leishmania prevention is used in combination with a macrocyclic lactone and praziquantel for tapeworm, then all major groups of parasites will be protected against.