I’ve written a fair bit about leishmaniasis in dogs lately, mainly in the context of potential risks from imported dogs. This parasitic infection is a concern because it can be serious and hard to treat, and also affects humans. Dogs are the main reservoir of Leishmania infantum, and it’s an important cause of disease in people in some regions.
The cases of leishmaniasis that we’re seeing in Canada (a relatively large and increasing number) have been associated with the dubious practice of importing dogs from endemic regions (e.g. Greece, Israel, Spain). One of the counter-arguments that comes up sometimes is “we don’t have any vectors of the parasite in Canada” (i.e. insects that can spread L. infantum from one animal to another, or from animal to person). However, the statement really should be “we don’t have any known vectors of teh parasite in Canada”. We can’t say with any certainty that none of the many insect types that are found here could transmit the parasite.
Further, while insects are the main concern as the natural vector and means of spreading the parasite widely (and, most concerning, into the wild canid populations that are abundant in Canada), they’re not the only concern. As a bloodborne infection, Leishmania has many other potential routes of transmission between dogs and from dogs to people.
A Finnish study in the journal Acta Veterinaria Scandinavica (Karkamo et al 2014) illustrates some of these concerns. The study describes autochthonous (non-imported) leishmaniasis in dogs that had never left Finland or received a blood transfusion.
The short story:
- A male dog (dog A) was sent to Spain for 6 months in 2009 as part of a breeding exchange. When he got back to Finland, he was diagnosed with leishmaniasis. He was ultimately euthanized.
- Dog B was a Spanish dog that was in Finland as part of the exchange. He tested positive for Leishmania antibodies some time after his return to Spain. He had limited contact with the other dogs, but bred dog C in 2009.
- In June 2010, dog A accidentally (well, accidentally from the breeder’s standpoint… I’m sure it was intentional in his mind) mated with dog D, but pregnancy either didn’t occur or was aborted.
- In August 2011, dog A got into a fight with another male (dog E).
- In 2012, dog E "accidentally" bred dog D (daughter of dog C).
- In the spring of 2013, that male (dog E) got into a fight with a different female (dog C).
- Dogs A, D and E were euthanized because of severe leishmaniosis that did not respond to treatment.
(If your head is spinning, there’s an easier-to-interpret figure in the paper.)
The assumption is that:
- Dog A was infected in Spain and brought the parasite back to Finland.
- Dog C was infected by breeding or fighting.
- Dog D either got infected from its mother, mating with dog A or E, or fighting with dog E.
- Dog E was infected by bites.
The authors’ conclusions also apply to non-Nordic regions:
It is likely that exotic diseases will be identified at increasing rates in Nordic countries in the future. Climate change may allow new insects to spread and survive in the Nordic countries and these insects may carry and spread new pathogens. Travelling of dogs has become more and more commonplace, which increases their risk of contracting and spreading diseases. The risk of spreading of the new vector-borne diseases within the Nordic countries has until now been considered low. Our findings show that this risk is not negligible and that leishmaniosis can spread in non-endemic areas without known vectors. In order to control this kind of risk, imported and breeding dogs should be tested for leishmaniosis before they leave their country of origin or before returning back home.
This case series only demonstrated risk to dogs, but the human aspect can’t be dismissed. We don’t know the true risks to humans from non-insect sources such as needlesticks, bites or contact with infected blood (e.g. contact of blood from an infected dog with an open sore). The risk is probably low but can’t be discounted. Stopping importation of infected dogs, and testing dogs coming from endemic areas would be a logical step to reduce the risks to dogs and people in non-endemic regions (although I won’t hold my breath).