Leishmania infantum—you might think it's just another parasite studied and then forgotten in veterinary school. But revisiting this intracellular
parasite of dogs and humans may be a good idea.
Endemic to the Mediterranean region, including portions of Europe, Asia, and Africa and some areas of South America, the parasite
has recently been on the rise in North America. A patient with a suspicious travel history is not the only one to be concerned
about. In endemic areas, the disease caused by Leishmania infantum infection, known as visceral leishmaniasis, is predominantly transmitted by the sand fly. However, in North America, the infection appears to be passed to puppies during
gestation, birth, or nursing. Direct contact with infected blood has also been shown to be a means of transmission.
While sand flies are found in regions of North America where Leishmania species has been documented, no vector-borne transmission has been seen to date. However, dogs are the main reservoir for
this disease-causing parasite, and it may only be a matter of time before vector transmission is recognized. Given its zoonotic
potential, watching this emerging parasite is warranted. A recent Veterinary Clinics of North America article provided an overview of this expanding threat, including the results of ongoing investigations.
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The foxhound is the breed most affected in North America. This may be because of a genetic predisposition. Additionally, proximity
to wooded areas puts these dogs in close contact with sand flies and climates similar to those in endemic areas. Infected
sand flies have not been reported in the United States, but they should be considered an able vector. The distribution of
this protozoan parasite has been steadily spreading to include many states, ranging from New Jersey to Kansas.
Between 2000 and 2003, the Centers for Disease Control and Prevention looked at serum samples from more than 12,000 foxhounds
as well as other dogs and wild canids. Results indicated an 8.9% seroprevalence of Leishmania species in foxhounds but not in other randomly selected dogs or wild canids. In an ongoing study, the researchers are finding
9.8% of the dogs are now seropositive in participating foxhound kennels. They are also finding that among high-risk kennels,
13.5% of dogs are seropositive and have clinical disease; 44.8% of dogs in these high-risk kennels have positive results on
qualitative polymerase chain reaction assays. In endemic countries, a higher percentage of positive results are seen in breeds
from southern Europe including Spinones and Neapolitan mastiffs. The origin of the infection found in the North American foxhounds
studied by the CDC has been linked to infected hounds from southern France that were imported to Great Britain before arriving
in the United States.