Canine Leishmaniasis

WHAT IS IT?

It’s a disease transmitted by a tiny very specific mosquito from the PHLEBOTOMOUS FAMILY. The name sand fly is sometimes heard in English but this is a misnomer, as there is far more risk of being bitten in 50km coastal strip of hinterland than actually on the beach or its immediate area. Most mosquitoes avoid seawater. The parasite, which is neither a bacteria nor a virus, infects the cells of the dog concerned with immunity and hence can play havoc with the dog’s natural defense mechanisms. Leishmaniasis is endemic in the Mediterranean Basin area. Whilst humans can and do contract this strain of the disease (NOT directly from infected dogs) a healthy adult’s resistance to it seems naturally high. Obviously the young, the very old, the sick (including those people on chemotherapy or with AIDS) are more susceptible, since their own immune system is underdevelopment or compromised.

HOW IS IT TRANSMITTED TO A DOG?

By the bite of a phlebotomous mosquito, which is infected by the leishmania organism and which is capable of transmitting the organism in an infective form. This process requires several days to occur, i.e. the biting of an infected dog does not allow the mosquito concerned to IMMEDIATELY pass that infection on to another dog in the vicinity. Neither can an infected dog directly infect another dog or human the presence of the intermediate host (i.e… the specified mosquito) is always needed for the cycle to occur. However, infected dogs DO add to the general risk factor in an endemic zone, being a ready source of the organism for the mosquito vector.

WHAT ARE THE SYMPTOMS OF INFECTION IN A DOG?

Many and varied – and frequently subtle! The incubation period itself can very from two months to years (commonly up to two years) but cases have been confirmed up to SEVEN years post initial infection. During this period the dog is symptom free and in fact many infected animals never DO become clinically diseased, being resistant to the organism presence in their body and holding its development in check. These animals can of course lose their resistance under the strain of another illness or injury in the future. Incubating and resistant animals may or may not show on standard serology testing, depending on the stage of infection they are in and the amount of antibodies the immune system is making at that time. These animals are clinically completely healthy.

Once symptoms of leishmaniasis DO start, they are often insidious, subtle and non-specific, just to make matters more complex still. We see skin lesions (often ulcers) that don’t seem to heal in a œnormal span of time, spectacle type alopecia round the eyes, recurrent lameness and/or fever, weight loss, lethargy, colitis (rarely) nosebleeds (occasionally). Not all, or even more than one symptom may occur in the same animal and many of these symptoms are seen in clinical practice for lots of other reasons! The dogs HISTORY is all-important. A dog with a history of living, or having lived, outdoors for a long spell of time (as such, this includes ex-stray or abandoned, kennelled or guard dogs) is high on the risk list for infection, and should be tested – preferably annually sick or not.

Classic cases walk through the clinic door of course to. These dogs often have severe and fairly specific skin lesions, long nails, swollen glands and some cases have liver and kidney problems too. Such dogs rarely look or feel well. Owners usually elect, with our guidance, to have the dog humanely euthanased once the disease is confirmed. Treatment is fairly toxic to the liver and kidney tissue and if these organs are already compromised the dog will just get sicker on medication.

The organism cannot be eliminated from the system in any of the above circumstances, but control of its effects is possible in many cases if the infection is caught early on. That’s to say, treatment can delay the development of symptoms, or prevent symptoms getting worse if they are mild, in some cases. Treatment also reduces the dog’s capability to infect a mosquito with active leishmania organisms and hence makes him less of a reservoir of potential infection and disease.

WHAT DOGS ARE AT RISK OF CONTRACTING THE DISEASE?

As we have said, those dogs who live outside day and night (or those who have done so in the past) for periods of time, particularly during the summer months (May – October) and particularly from dawn to dusk are at highest risk, DESPITE the use of special collars, ampoules etc. There is NO foolproof method of prevention and no vaccination to help us either as yet although hopefully this will not be too much further away from becoming a reality. The best advice is to avoid the outside lifestyle for the dog at high risk times. If this is not possible, have the dog screened annually (Autumn time is best), put mosquito netting up around the dogs kennel (shutting him in at dusk) and use a good quality insecticidal ampoule, spray and/ or collar.

MOST good quality modern insecticidal products have a degree of repellent effect. Use it AT LEAST as often as recommended by the manufacturer. Many products can be safely combined and even simple citronella collars and sprays can be a useful supplement to the above when the weather is hot and humid and the mosquitoes abound. Of course, dogs with pet lifestyles (i.e. sleeping indoors) should have regular inspectoral protection too, as much to control ticks and fleas, which can carry their own diseases and bring their own problems, as for leishmaniasis protection.

WHAT IS THE TREATMENT FOR LEICHMANIASIS?

This is a subject on its own! There are many different types of protocol – because none are perfect, none appear to eliminate the parasite and none are without potential side effects. The possibilities need to be considered for each case and your vet will explain the pros and cons to you. Some considerable value has been found in the use of an oral drug licensed for use in gout in man, but nobody really knows for certain exactly how it impedes the activity of the organism (many theories around). This can be combined with courses of specific injections in more severe cases, but as we’ve said, the irony is that these are the very dogs who may least tolerate side effects of medication if internal organs are involved.

DO THE MONTHLY ANTI-MOSQUITO TABLETS PREVENT LEISHMANIA INFECTION?

An emphatic NO! These tablets are NOT anti-mosquito anyway!! They are a PREVENTIVE medication for infection by the FILARIA bloodworm family, of which DIROFILARIA IMMITIS (the heartworm) is one. The disease is spread by completely different mosquito generally, although it’s fair to say that the same groups of animals are at high risk and that risk is highest at the same time of year as the leishmania peak occurs.

Finally remember, your dog’s lifestyle is a critical factor in helping to lower his risk of contact, there is no miracle product out there! Of course the myriad of wonderful insecticidal products now available are a valuable aid in the battle, but it’s no substitute for actually limiting the dogs EXPOSURE TIME to the culprit mosquito by one means or another

WRITTEN BY MARY ASHTON
EUROCENTRO CLINICA VETERINARIA
05/02/2004