Around here, infection in dogs caused by Leishmania infantum typically comes up in the context of imported dogs, particularly those from countries around the Mediterranean (e.g. Greece, Israel, Spain). This parasite is usually transmitted between a variety of mammalian species, including dogs and humans, by certain species of sandflies. We’re quite lucky here in Ontario because the kinds of sandflies that transmit Leishmania don’t live here (yet), and we have yet to identify any local insect vectors that can do the same job. There is still some risk of transmission from an infected dog to others, but it’s much more limited (e.g. direct handling of infected tissues by veterinary staff). The other really concerning aspect of this disease is that it is very hard to completely clear the infection – so while acute episodes can often be treated, infected dogs are prone to recurrent bouts of illness throughout their lives, and remain a potential reservoir of infection for others (including people), even when infection is subclinical.
Despite the blood-borne parasite’s typical reliance on its favorite insect vectors, there have been instances of transmission within groups of dogs, possibly from breeding or fighting or other very close contact. One outbreak in foxhounds in the early 2000s affected dogs in 18 states in the eastern US and even spilled over into dogs in Ontario and Nova Scotia, but fortunately there was no evidence found of infection in people in contact with the dogs. Another report described a rather convoluted web of contacts between five dogs in Finland, two of which were infected with Leishmania while abroad, and resulting in infection of the other three.
Most recently, a case of leishmaniasis was described in a young Boxer dog born in California that had never been overseas (de Almeida et al. 2020). There are a few notables from the case report:
- The dog was 1.3 years old when it first presented, and while it had never been overseas, its dam had been imported from Spain, where canine leishmaniasis is endemic. (The dam reportedly died of an “unknown cause” the following year.)
- It took a year and a half to finally determine that the dog’s illness was being caused by Leishmania (in part, no doubt, because it wasn’t on the radar for a dog that had never been to a high-risk area).
- Despite multiple courses of antibiotics and other treatments, the dog’s condition gradually deteriorated and it eventually developed neurological signs as well. It was euthanized just over a year later, a little less than three years after it initially presented.
The authors concluded that the dog was likely infected through vertical transmission from its dam, since California is not currently considered an endemic region for this disease. There are now several studies that have examined the ability for various species of sandflies that are found in certain states to transmit this parasite, which makes it all the more important to avoid creating a canine reservoir in the US through increased scrutiny and testing of imported dogs (and in this case their puppies as well).