A laboratory model of canine leishmaniasis: the inoculation of dogs with Leishmania infantum promastigotes from midguts of experimentally infected phlebotomine sandflies.

Twenty-five dogs (beagles) were infected with Leishmania infantum by the intradermal inoculation of an estimated 5-8,000 metacyclic promastigotes harvested from the midguts of 320 experimentally infected P. perniciosus. Details are given of the methods of infecting the flies and harvesting the parasites. All dogs developed small, self-healing chancres at the sites of inoculation. Parasites were isolated from lymph nodes, bone marrow or spleen of 21 dogs, 12 of which developed signs of disease and raised IFAT litres to Leishmania. Nine of the 21 remained healthy over a five-year observation period. Six of the nine were shown to have a cell mediated immune response to Leishmania. No parasites were isolated from four of the 25 dogs, two of which had a demonstrable cell mediated immunity and another had low transitory IFAT titres. The fourth had chancres at the sites of inoculation. The results show that dogs can be readily infected with promastigotes from the midguts of sandflies. However, a high proportion develop a cell mediated immunity and show on signs of disease. It is suggested that serological surveys of dogs for canine leishmaniasis reveal neither the true prevalence of infection nor the intensity of transmission. The efficacy of controlling human visceral leishmaniasis caused by L. infantum by destroying seropositive dogs is questioned.