Canine visceral leishmaniasis (CVL) remains a significant disease worldwide. In Brazil, its treatment is performed using miltefosine, which has demonstrated promising outcomes in dogs. This study represents the first attempt to treat and monitor dogs with CVL in natural conditions over the course of one year. The dogs were divided into two groups: G1 received miltefosine and allopurinol for 28 days, while G2 received miltefosine for 28 days, followed by allopurinol for one year. The follow-up involved clinical, hematological, and biochemical evaluations, as well as the detection of Leishmania DNA in skin and bone marrow samples. By the end of the follow-up, dogs in G2 exhibited improved staging compared to their initial conditions, whereas those in G1 showed worsened staging. Leishmania DNA in skin and bone marrow decreased between 6 and 12 months after treatment. Our observations indicate that the treatment using miltefosine reduces the detection of the parasite in the skin and bone marrow for up to one year following its administration. The continuous use of allopurinol contributes to control of the disease in dogs. These findings provide valuable insights into the response of dogs treated in natural conditions, offering essential information for veterinarians and public health authorities.

Canine visceral leishmaniasis (CVL) is a zoonotic disease caused by Leishmania infantum and transmitted by sand flies, with domestic dogs serving as the main urban reservoir of the parasite. In Brazil, treatment of infected dogs has been authorized more recently than in other countries, resulting in limited knowledge regarding clinical response to therapy, persistence of infectivity, and the role of treated dogs in transmission dynamics in endemic areas. In this study, domiciled dogs naturally infected with L. infantum were treated with miltefosine (Milteforan®, Virbac, Carros, France) in combination with allopurinol, followed for 12 months, and assessed for their ability to infect sand flies through xenodiagnosis performed one year after treatment initiation. Clinical features, laboratory abnormalities, and cutaneous parasite load were evaluated for their association with infectiousness to sand flies, aiming to identify accessible indicators of transmission potential applicable to routine veterinary practice. At 12 months, 53% (10/19) of dogs remained infectious to Lutzomyia longipalpis. Antibody titers ≥ 1:160 and more advanced clinical stages were significantly associated with infectivity to L. longipalpis. These findings indicate that quantitative serology and clinical staging, according to the Brasileish - Study Group (2018) guidelines, may serve as practical tools for veterinarians to assess the infective potential of dogs under follow-up after CVL treatment.