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.

Tsetse movement in wind fields: possible epidemiological and entomological implications for trypanosomiasis and its control

This paper presents evidence that tsetse flies (Glossina) can be dispersed by wind. This dispersal in West Africa is suggested to be along a south-west north-east axis. The implications of wind dispersal of Glossina for chemical and genetic control operations is discussed. Field experiments necessary to test this hypothesis are recommended. A study of human trypanosomiasis foci in West Africa has revealed that foci are orientated in roughly parallel lines in a south-west north-east direction. This directionally was significant when compared with 7 other compass points. It is proposed that foci could be populated by infected flies dispersed from the south west, where denser populations exist, on the prevailing winds in the late dry/early rainy season. The significance of these ideas in relation to the epidemiology of Trypanosoma brucei rhodesiense in Ethiopia and T. evansi are discussed.

Trypanosoma (megatrypanum) melophagium in the sheep ked, Melophagus ovinus. A scanning electron microscope (SEM) study of the parasites and the insect gut wall surfaces

A description of the different stages of Trypanosoma (M.) melophagium in different regions of the gut of the sheep ked (Melophagus ovinus) as observed by the SEM is presented. The extensive pile carpet or palisade colonization of the midgut and pylorus is described. The method of attachment and the relationship of the parasites to the microvilli in the midgut and the cuticle of the pylorus and ileum observed by other methods are confirmed. The micro-structure of the surfaces themselves in the regions of the gut to which parasites attach are described. The use of the technique for the study of other similar systems is discussed.

Leishmania in phlebotomid sandflies. IV. The transmission of Leishmania mexicana amazonensis to hamsters by the bite of experimentally infected Lutzomyia longipalpis

Leishmania mexicana amazonensis was cyclically transmitted in the laboratory from hamster to hamster by single bites of experimentally infected Lutzomyia longipalpis . The sandflies were denied suitable conditions for oviposition and were induced to take a second, infecting, meal while still gravid. In three transmissions, cutaneous lesions developed rapidly on two hamsters, whereas that on the third remained small for 8 months, almost disappeared, and then grew to the usual large size. In some infected flies, parasites migrated to the pharynx and buccal cavity but then died and disintegrated; in others, healthy parasites were attached to the cuticular intima of the oesophagus and pharynx by hemidesmosomes. The common failure of leishmaniae to become established in the foregut of many experimentally infected sandflies may be because parasites die after migration and not because they fail to migrate. One cause of the death may be a lack of plant juices, a food of sandflies in nature. At the second potentially infecting feed, sandflies usually probed many times and took either no blood or only a small meal. It is suggested that parasites in the foregut block the pores of cibarial sensilla which probably control engorgement; such an interference would be an advantage in the evolution of Leishmania .

Leishmania in phlebotomid sandflies. III. The ultrastructure of Leishmania mexicana amazonensis in the midgut and pharynx of Lutzomyia longipalpis

The fine structure of the promastigotes of Leishmania mexicana amazonensis in the midgut, cardia, oesophageal valve and pharynx of the sandfly Lutzomyia longipalpis is described. Differences were found between the nectomonad and the haptomonad promastigotes. There were fewer subpellicular microtubules in the nectomonads than in the fatter haptomonads; the mitochondrion of nectomonads was a single straight longitudinal ramus while that of haptomonads had a tortuous shape; the kinetoplast and nucleus lay closer together in the haptomonads which also had fewer free ribosomes and lipid containing bodies than the nectomonads; the nucleus was spherical in haptomonads but elongate in nectomonads. The reservoir region in the nectomonads was notably voluminous and the surface was modified for pinocytotic uptake of material through coated vesicles, and also for exocytosis. In both haptomonads and nectomonads, a contractile vacuole was present adjacent to the reservoir; flagellar-parasite desmosomes formed a collar anchoring the flagellum as it emerged from the reservoir; four reservoir-associated microtubules ran parallel to the flagellar reservoir; the basal body, axoneme and paraxial rod were similar in structure to those of other trypanosomatids. Apparently intracellular promastigotes were found in the midgut cells. Preliminary studies of pharyngeal forms showed that they were attached by hemidesmosomes to the cuticular pharynx. These forms were not typical promastigotes but had an opisthomastigote-like configuration with the reservoir running past the nucleus. Differences in the ultrastructure of Leishmania in the sandfly and in culture are discussed, and it is concluded that cultural forms should not be considered identical to those in the vector.

Observations on a trypanosomatid flagellate in a flea, Peromyscopsylla silvatica spectabilis

The method of attachment of a trypanosomatid parasite to the cuticular epithelium of the hindgut of a flea Peromyscopsylla silvatica spectabilis by a desmosome-like structure is described; the flagella are modified and have enlarged intraflagellar areas which occupy the whole surface area of the gut, including clefts and folds of the epithelium. Unusual features of the parasite itself include a very much reduced flagellar pocket and pellicular microtubules which are made up of doublets and triplets. The problems of differentiation and characterisation of monogenetic insect flagellates are discussed in the light of these findings.

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

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.

Trypanosoma bouffardi of West African Ploceidae (Aves)

Trypanosoma bouffardi Leger & Blanchard, 1911, is described from naturally infected Lagonosticta s. senegala, Estrilda b. bengalus, Vidua chalybeata, Estrilda t. troglodytes and Amadina f. fasciata, all of which are new host records for Nigeria; Vidua chalybeata is a new host record for trypanosomes.

There was no significant morphological difference between populations of this trypanosome in the various natural and experimental vertebrate hosts.

T. bouffardi was transmissible to nine species of Ploceidae belonging to the three subfamilies Estrilinae, Ploceinae and Viduinae; but not to Pycnonotus barbatus, chickens or pigeons.

The parasitaemia produced by infections of T. bouffardi reached 4·1 × 105 parasites/mm3 of blood.

Reproduction of the trypanosomes was synchronous and discontinuous and occurred in the blood by unequal binary fission of trypomastigotes. Occasionally longitudinal equal binary fission of trypomastigotes also took place. There was no concentration of dividing forms in the tissues.

T. bouffardi did not grow on NNN medium although it has been grown for a short time on the medium described by Yesufu (1970).