Diagnostic Challenges in the Era of Canine Leishmania infantum Vaccines

The diagnosis of canine leishmaniosis (CanL) is complex due to its variable clinical manifestations and laboratory findings. The availability of vaccines to prevent CanL has increased the complexity of diagnosis, as serological tests may not distinguish between naturally infected and vaccinated dogs. Current practices of prevaccination screening are not sufficiently sensitive to detect subclinically infected dogs, resulting in the vaccination of infected animals, which may lead to disease in vaccinated dogs that are also infectious to sand flies. This review evaluates the current techniques for diagnosing CanL, and focuses on new challenges raised by the increasing use of vaccines against this disease. Important gaps in knowledge regarding the diagnosis of CanL are underscored to highlight the need for novel diagnostic test development. Canine leishmaniosis (CanL) is an important zoonotic disease which is associated with the long history of companionship between dogs and humans. The recent introduction of commercial vaccines against CanL, and their wide use to prevent the disease, have created new challenges in the management of this infection. These challenges include finding diagnostic tests to reliably detect subclinical infection, in order to ensure that infected dogs are not vaccinated, and also to separate naturally infected dogs from vaccinated dogs. Serology for Leishmania infantum may be positive in both naturally infected and vaccinated dogs. Tests for cell-mediated immunity are currently not sufficient to distinguish natural infection from vaccination. Vaccinated infected dogs may still be infectious to phlebotomine sand flies, the insect vectors of Leishmania spp. Vaccinated seropositive dogs with suspected CanL should be tested for the presence of L. infantum parasites or leishmanial DNA.