Leishmaniasis – not caused by a mosquito bite

This very common disease in the Algarve and much of Portugal is transmitted by the bite of the sand fly (not a mosquito), is not usually curable, and can be fatal. The bite injects the Leishmania parasite into the dog, similar to a mosquito and malaria. It can take months to years to develop the disease following infection. It is not generally contagious, but if an infected dog fights a non-infected dog, transmission via blood can occur. It is believed that 65% of dogs in the Mediterranean basin have been infected by the time they are 3 years old. Rarely, cats can be infected too. The cats more likely to catch it are those with immune system diseases like FIV or FELV (cat leukaemia). It is also a zoonosis – people (usually the immunocompromised) can catch it from a sand fly bite. The frequency of human infection varies from country to country, being a large problem in malnourished, poverty-stricken or war-torn places. Signs of the disease in dogs include scaly thick grey skin, inflammation of the eyes, long gnarly claws, bone marrow problems, nose bleeds, and organ failure.

The photos show some of the lesions typically found on the ears early in the course of the disease, and the inflammation the can occur on the surface (and inside) of the eye.

Diagnosis can be complicated. It usually involves blood tests and possibly lymph node/ conjunctiva/ bone marrow biopsy.

Treatment varies depending on temperament of the dog and also financial considerations.

Treatment involves medications to suppress the parasite, drugs to (where indicated) make the eyes comfortable and/or support kidney function, and multiple blood tests to check progress.

The medications are typically injections twice daily for a month or liquid in the food for a month. There are also tablets (allopurinol) that are taken daily for the long term. The injections tend to have a lower relapse rate that the liquid, but some dogs find they sting and can create lumps.

Some dogs never relapse, effectively living a normal life. Others relapse repeatedly or have disease that progresses irrespective of what we do; these have a worse long-term prognosis.

Prevention – There are various things we can do to reduce the chance of your dog catching leishmaniasis. Understanding the behaviour of the sand fly is very important – we can modify the lifestyle of the dog to reduce the chance of being exposed.

  1. Sand flies are most active between dusk and dawn. They sleep during the day. Keeping your dog indoors from dusk reduces the risk.
  2. Sand flies are only active if the temperature is more than 9 degrees; there is a lower rate of transmission in winter, but the risk is not zero – the winter of 2018-19 was quite mild.
  3. They are weak fliers – they struggle to make it upstairs (renowned UK parasitologist and vet Ian Wright describes them as being like Daleks). Thus, having the dog sleep upstairs is recommended.

Some, but by no means all, flea and tick collars repel sand flies. One of the most sophisticated brands (Seresto) prevents 75% of the bites – better than the competition. It lasts about 7 months.

Several spot-on pipettes (for dogs) on the market also repel the pesky fly – but read the small print carefully – some (like Vectra 3D) protect for a month, others only 2 weeks.

In the last few years, at least 2 vaccines against leishmaniasis have come onto the market, both of which claim approximately 75% efficacy. They do not prevent infections; rather they prevent the infection becoming full-blown disease. The closest analogy would be to an AIDS vaccine – HIV is still contracted, but does not develop.

Given that the disease does have such a bearing on global human health, the quest for a cure is ongoing. One day, there will be one, which also works for dogs. Until then, the best we can do is try to prevent it in the first place.

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