Immunomodulation of Patients with Canine Visceral Leishmaniasis at Different Stages: A 12-Month Follow-Up Study Using LaSap

<b>Background/Objectives</b>: Canine visceral leishmaniasis (CVL) is one of the main neglected protozoan diseases in the world. Dogs play a fundamental role in the maintenance of <i>Leishmania infantum</i> in the Americas, and we have already encountered resistance problems with drugs currently used in these animals. <b>Methods</b>: In view of this, two new immunotherapeutic protocols were tested in 48 dogs, using <i>L. amazonensis</i> antigens plus saponin (LaSap) and only <i>L. amazonensis</i> antigens (La) as a control group. Dogs naturally infected with <i>L. infantum</i> were divided into four groups, according to clinical staging. A total of 24 dogs (stages 1 and 2) received a four-dose protocol, and another 24 dogs (stages 3 to 5) received six doses. All animals received a booster dose every three months until they were one year old. <b>Results</b>: Our results showed that dogs in the early stages of the disease respond better and are able to remain stable for longer, maintaining baseline laboratory biomarkers, in addition to having a lower parasite load. <b>Conclusions</b>: On the other hand, dogs in more advanced stages have a poor response, with stage 3 being a key point in clinical progression or regression.