Brazil faces challenges in canine visceral leishmaniasis control

Visceral leishmaniasis is considered a globally neglected disease, and in Brazil its expansion and urbanisation led to the creation of the Visceral Leishmaniasis Surveillance and Control Program, which recommends identifying human and canine cases, vector control and prevention. Three recent Brazilian studies, read together, show what happens when those recommendations meet municipal routine.

A study published in 2024 in the Revista Brasileira de Parasitologia Veterinária investigated the epidemiological situation in municipalities of Mato Grosso and the execution of programme activities between 2019 and 2021. Human case data came from the Notifiable Diseases Information System (SINAN), and the entomological and canine surveys from the State Health Department. In the period, 30 human cases were recorded, distributed across 16 municipalities. Vectors were identified in half of the municipalities where entomological investigations took place, with Lutzomyia longipalpis predominant. A total of 15,585 dogs underwent serological testing, and 18.91% were seropositive for Leishmania infantum. Only three municipalities, however, conducted consecutive canine surveys. The authors conclude that, although the disease is widely distributed in the state, few municipalities carry out the programme's actions, confirming the disease's neglected status.

Which dogs are most at risk? A study published in 2022 in Research in Veterinary Science gathered data from four endemic cities in different regions, Fortaleza, Brasília, Palmas and Bauru, and used parasitological tests, such as skin lesion culture and histological or immunohistochemical skin analysis, to define infection, avoiding some of the problems of serological surveys. Canine positivity was 9.8% overall, with wide variation: Bauru 18.7%, Brasília 8.4%, Fortaleza 7.9% and Palmas 4%. In logistic regression adjusted for city, males were twice as likely to be infected; dogs living outdoors 1.5 times; and dogs in households rearing chickens 40% less likely. An interaction indicated that the protective association of being purebred was stronger among dogs older than seven years. The authors propose using these factors to identify higher-risk groups of animals and target control interventions.

Collars impregnated with 4% deltamethrin are used in endemic areas to reduce transmission from dogs, but continuous exposure to the insecticide may select resistant sand flies. A study published in November 2024 in Parasites & Vectors exposed six field populations of Lu. longipalpis, collected in areas where the collars had been used, to CDC bottle bioassays at diagnostic doses of 21.9 and 30 μg per bottle and to dose-response experiments. At the 21.9 μg dose, three populations were susceptible; two, from Ceará and Minas Gerais, had mortality of 94.9% and 95.7%, indicating possible resistance; and one, from Ceará, was classified as resistant, with 87.1% mortality. Resistance intensity was low, with resistance ratios between 2.27 and 0.54 at the dose that kills half the insects. The authors conclude that most populations remain susceptible, but that the resistant Ceará population calls for understanding resistance mechanisms where collars are widely used.

For the veterinarian in an endemic area, the three papers offer three concrete tasks: demand and record the municipality's canine surveys, advise owners on modifiable risk factors such as keeping the dog in a protected environment at night, and monitor collar effectiveness locally, since vector susceptibility is not uniform across the country. This summary does not replace the official guidelines of Brazil's Ministry of Health for diagnosis and management.