Treated dogs with visceral leishmaniasis remain infectious to sand flies: Clinical staging and serology as practical proxies of transmission risk.

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.