Leishmania in phlebotomid sandflies I. Modifications of the flagellum associated with attachment to the mid-gut and oesophageal valve of the sandfly

Abstract

The modes of attachment of promastigotes of Leishmania mexicana amazonensis in the gut of experimentally infected sandflies (Lutzomyia longipalpis) were examined with the electron microscope. During the second and third days after an infective blood meal, parasites multiplied inside the meal, which was encased in a peritrophic membrane in the posterior mid-gut; some nectomonads at the periphery of the meal became embedded in the membrane, which prevented contact between the parasites and the microvilli of the wall of the gut. As the digested blood meal passed into the hind-gut on the second or third day, some of the cells of the wall of the mid-gut were shed into the lumen, and the microvilli were then reduced in height and occupied a smaller area of the epithelial surface. On the fourth and fifth days, as the microvilli lengthened and increased in surface area, the parasites became attached to the microvilli of the posterior mid-gut by inserting their flagella between them; no junctional complexes were observed between the flagella of nectomonads and microvilli. The flagella of some unattached parasites became greatly swollen and membranous whorls began to form in the flagellar sheath. In the cardia, the promastigotes transformed from slender nectomonads to fat haptomonads. The latter forms were tightly, packed against one another and against the microvilli of the cardia, but were not attached to this part of the gut. However, in the oesophageal valve where the lining of the alimentary canal changed into cuticle, many haptomonads formed hemidesmosomes within their flagellar sheaths and became attached to the cuticular lining of the valve and the posterior part of the oesophagus. These modes of attachment are compared with those of other trypanosomatids, and their possible importance in the establishment of infections in the anterior station of sandflies and transmission by bite is discussed.