Canine visceral leishmaniasis in Teresina, Brazil: Relationship between clinical features and infectivity for sand flies.

Leishmania chagasi is an intracellular parasite transmitted by the bite of the phlebotomine sand fly Lutzomyia longipalpis, which is the most important of American visceral leishmaniasis. In the gut of the vector, amastigoste forms of the parasite transform into metacyclic promastigotes, from there to the foregut, where they could be transmitted in the next blood meal. Xenodiagnosis is an important tool for the detection of Leishmania, especially when associated to molecular techniques, both being useful for the monitoring and evaluation of dog infectivity in endemic areas. In this study, direct search of Leishmania from material obtained through xenodiagnosis performed in dogs captured in Teresina (Piauí State, Brazil) identified that the predominant forms of the parasite were the procyclic and metacyclic forms located in the hindgut, detected between the 5th and 6th day after the blood meal. Using polymerase chain reaction (PCR), we revealed that dogs with different clinical status were able to infect phlebotomines, the rates of sand fly infection being higher for symptomatic dogs (13%) as compared to asymptomatic ones (3.5%). The direct search was able to demonstrate infection only in phlebotomines in which the blood meal was performed on symptomatic dogs, with a rate of infection of 1.6%. The results underline the importance of using PCR and xenodiagnosis for the detection of Leishmania sp. And for the evaluation of infectivity of dogs in endemic areas, especially those that are asymptomatic.