Studies on the ultrastructure, virus-like particles and infectivity of Leishmania hertigi.

Five strains of Leishmania hertigi hertigi isolated in Panama and three strains of L. hertigi deanei isolated in Brazil were studied. Ultrastructural examination of promastigotes grown in culture showed virus-like particles (VLPs), 55--60 nm diameter, in the cytoplasm of all strains. The VLPs were normally either organized in paracrystalline clusters or associated with induced tubules. In some cases the VLPs were associated with dense vesicular bodies. Mitochondria with which the VLPs were associated had enlarged elongate or circular cristae. Elongate 'microbodies' containing rod-like structures were observed in promastigotes grown in culture. Poor infections of promastigotes developed in the midguts of 10% of laboratory-bred Lu. longipalpis following experimental feeding on cultures of L. h. hertigi. VLPs were seen in a promastigote in the midgut of a sandfly five days after feeding. Laboratory mammals proved poor hosts for L. hertigi. Cryptic infections in the visceral organs of immunosuppressed hamsters and immunodeficient 'nude' mice were detectable only by culture. Infections of DS cell and mouse peritoneal macrophage cultures showed amastigotes with a high ribosomal density and deep invaginations of the pellicular layer. VLPs were rarely seen in these amastigotes.