Forum: geographic spread and urbanization of visceral leishmaniasis in Brazil. Postscript: new challenges in the epidemiology of Leishmania chagasi infection.

Visceral leishmaniasis is a disease that reemerged in various locations in Brazil in the 1980s and spread to new areas, including the Southeast and Central-West of the country. Previously, visceral leishmaniasis was a disease that occurred in rural areas of the Northeast, mainly affecting children 1. However, most cases of visceral leishmaniasis now come from periurban areas of cities in Northeast, Central-West, and Southeast Brazil 2,3,4. The articles in this Forum 5,6,7,8 discuss key aspects related to the urbanization of visceral leishmaniasis in Brazil, including new approaches to deal with the disease and conditioning factors for the vector’s capacity to transmit Leishmania. The complexity of vector and reservoir control is identified as a factor that hinders the management of visceral leishmaniasis in the country. The Forum proposes a new discussion and reassessment of current intervention measures. The latter focus on culling dogs infected with Leishmania and residual-action pesticide spraying, but these measures are normally implemented after human cases of visceral leishmaniasis have already been identified, often long after the occurrence of Leishmania infection, due mainly to its long incubation period 9,10. Still, as commented in the article by Maia-Elkhoury et al. 5, the regularity of these intervention measures can have an impact with a reduction of up to 39% in Leishmania infection in humans, according to studies by the Brazilian Ministry of Health. The peri-urbanization of visceral leishmaniasis in Belo Horizonte, presented by Oliveira et al. 6 as an example of this process in Brazil, was similar to that observed in the Northeast, with subsequent spread to other cities in the Southeast and Central-West. It is worrisome that these endemic areas have a high population density, thus placing the population at increased risk of infection. Dogs have traditionally been considered the principal reservoirs of Leishmania chagasi in periurban areas 11. Canine visceral leishmaniasis generally precedes human disease in these new areas 4. This was demonstrated in the visceral leishmaniasis epidemic in Araçatuba, São Paulo State 12,13. Studies in the State of Rio Grande do Norte show a 32.6% Leishmania infection rate in dogs in an endemic area on the outskirts of the State capital Natal, with a 30% six-month seroconversion rate in these animals. Asymptomatic Leishmania infection in humans is also high, with 24.6% of individuals presenting anti-Leishmania antibodies and 38.6% of these showing a positive delayed hypersensitivity skin test to Leishmania antigens 14. The high asymptomatic Leishmania infection rate in humans, as observed in Rio Grande do Norte, shows that visceral leishmaniasis is only the lesser component in the process, and that asymptomatic infection is more frequent. The role of asymptomatic Leishmania infection in humans and canines has still not been fully