Understanding Transmission of Leishmaniasis in Foxhounds

02/27/2012

Leishmaniasis is a parasitic disease that can affect both dogs and humans – with serious outcomes. Weight loss, depression, bloody noses, and enlargements of the liver and spleen can all be signs of this infection in both species. However, whereas human leishmaniasis is relatively responsive to early treatment, the same can not be said of canine infections. With zoonotic visceral leishmaniasis (ZVL), the type of leishmaniasis seen in dogs, relapses are the rule rather than the exception, and it can be fatal.

FoxhoundZVL is usually thought of as a tropical disease, spread by sand flies found in the hot climates where the disease is endemic, but the growing number of infected Foxhounds seen in North America seems to defy that explanation. Sand flies are certainly found in some regions of the United States, but they’re not common, and after ZVL killed four Foxhounds in NY in 2000, doctors began to look for an alternate explanation for the high prevalence of leishmaniasis in the breed.

Thanks to research funded in part by the AKC Canine Health Foundation, there is now a better explanation of why so many Foxhounds are infected with ZVL – even those who have never traveled to an area where the disease is naturally found. A group of scientists from Iowa State University and the University of Iowa investigated whether it might be possible for a female Foxhound infected with leishmaniasis to spread the infection to her puppies – bypassing the need for a sand fly vector. That type of mother to child transmission, which scientists call vertical transmission, could explain why ZVL is a growing problem in each new generation of dogs, even for pups kept safely away from geographic danger zones.

What the scientists found was that 10 out of the infected dog’s 12 puppies showed signs of infection with the leishmaniasis parasite. Furthermore, right after birth, six of eight tested puppies showed infection in multiple organ systems – suggesting that the infection had taken place during pregnancy, not simply that the puppies were exposed to the parasite during birth. Interestingly, when the remaining four puppies were tested three months later, far fewer of them had signs of infection in multiple organ systems. That suggests that the puppies’ immune systems may have been able to bring the infection under control – at least for a time – which could perhaps give the parasite more opportunities to spread.

This research could turn out to be incredibly important in the quest to control the problem of ZVL in American dogs. If further studies continue to show that vertical transmission of leishmaniasis is an effective way for the parasite to spread, then removing infected animals from the breeding pool could potentially do a lot to limit the problem of leishmaniasis in geographic areas where it would not normally be found – and where infection by sand flies does not seem to pose a major risk. Insecticides alone haven’t proven to be enough. Maybe we finally understand why.

This work was funded by AKC Canine Health Foundation grant 1220-A.

Scientific Publication:

Boggiatto PM, Gibson-Corley KN, Metz K, Gallup JM, Hostetter JM, et al. 2011 Transplacental Transmission of Leishmania infantum as a Means for Continued Disease Incidence in North America. PLoS Negl Trop Dis 5(4): e1019. doi:10.1371/journal.pntd.0001019

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