Host-Parasite Relationship of Leishmania mexicana mexicana and Lutzomyia abonnenci (Diptera: Psychodidae)

Abstract

The life cycle of Leishmania mexicana mexicana in the gut of the sand fly, Lutzomyia abonnenci, was studied by light and electron microscopy. Development was suprapylarian with initial establishment of parasites in the bloodmeal (posterior midgut), and anterior migration of parasites to the cardia/stomodeal valve region beginning at 2.5 days post-infection. Flagellates were first observed in the esophagus at 3.5 days, in the posterior armature region of the pharynx at 5 days, and in the anterior pharynx at 7 days; but they were not detected in the cibarium or proboscis. Infection of the pylorus region of the hindgut and of the Malpighian tubules was also commonly observed. Three different morphological forms of L. m. mexicana developed in the gut: nectomonad promastigotes, short promastigotes, and paramastigotes. Nectomonads occurred primarily in the abdominal midgut after bloodmeal digestion, where they were oriented in longitudinal masses in the lumen, or interdigitated with epithelial microvilli via the flagellum. Short promastigotes found in the cardia/stomodeal valve region are described for the first time. These forms were smaller than nectomonads, showed an amplification of the kinetoplast, apposition of kinetoplast and nucleus, and were embedded in a gel-like matrix. To maintain position in the cardia, parasites commonly inserted the flagellum deep into microvilli or cytoplasm of the epithelium; adherence to the cuticular intima of the stomodeal valve was by flagellar modification and formation of hemidesmosome plaques. Paramastigotes occurred in the esophagus, were sometimes degenerated in appearance, and were attached via flagellar hemidesmosomes. Paramastigotes observed in the lumen of the pharynx were commonly degenerated and were not attached to the intima. L. m. mexicana was able to colonize the various gut habitats of Lu. abonnenci by a number of adaptations; this sand fly appears to be a suitable biological host for the parasite.

Malaria parasite chitinase and penetration of the mosquito peritrophic membrane.

“…(i) Parasites such as filaria invade before the formation of the peritrophic membrane (17). (ii) Parasites such as leishmania may persist in the remnants of the blood meal until the peritrophic membrane dissolves and then attach to epithelium (18). (iii) The parasite may penetrate the membrane after it is formed.…”

The life-cycle ofLeishmaniain the sandfly with special reference to the form infective to the vertebrate host

“…They defined nectomonads as long, slender, electron-dense unattached promastigotes and haptomonads as broad, electron-lucid promastigotes with modified fla gella capable of producing electron-dense plaques (hemidesmosomes) inside the sheath, associated with attachment to the cuticular intima of the stomodaeal valve. The same terms have been used for similar forms seen in other infec tions Lawyer et al, 1987;Walters et al, 1987Walters et al, , 1989a. The definitions of nectomonads and haptomonads were challenged by Walters et al (1989a) who preferred them simply to denote either free-swimming or attached promastigotes with no consideration of morpho logy.…”

“…With one exception, all accounts of the ultrastructure of leishmaniae in sandflies have shown attachment of pro mastigotes to the microvilli of the abdominal midgut by the insertion of the flagella of the parasites (Killick-Kendrick et al, 1974;Kaddu & Mutinga, 1981;Molyneux et al, 1986;Lawyer et al, 1987;Walters et al, 1987Walters et al, , 1989b. The excep tion is the only report, referred to above, on the ultra structure of a species of Viannia, L. panamensis, in the midgut of a sandfly by Walters et al (1989a) who sug gested that, because the parasites moved quickly from the hindgut to the anterior of the thoracic midgut, they perhaps had no « need to stabilize themselves in the midgut by association with the microvilli ».…”

Leishmania infections damage the feeding mechanism of the sandfly vector and implement parasite transmission by bite

“…3B). Similar detachment of the valve cuticle can be seen also in micrographs of other Leishmania-infected sandflies of the species Lutzomyiaflaviscutellata (29) and Lutzomyia abonneci (30). The underlying exposed epithelial cells showed various degrees ofdisruption, including loss ofcell membrane (Fig.…”