Protozoan parasites Leishmania donovani (family: Trypanosomatidae) cause fatal visceral leishmaniasis (VL) and the infection relapses in apparently cured population as post kala-azar dermal leishmaniasis (PKDL) in the Indian subcontinent. In recent years co-infection of another Trypanosomatid parasite Leptomonas with L. donovani during VL/PKDL in this region has become prominent. The observation of clinically lesser-known insect parasite, Leptomonas in leishmaniasis is intriguing to researchers. The presence of Leishmania look alike Leptomonas in the cultures of clinical isolates of Leishmania has been worrisome to those, who prefer to work with pure Leishmania cultures for drug and vaccine development or immune response studies. The exact implications of such a co-habitation, which might lead to a delay in the diagnostics of VL and elevate mortality, need a thorough investigation. Also whether Leptomonas is involved in leishmaniasis manifestation needs to be ascertained. Thus we are currently witnessing a new paradigm of a parasitic co-infection in VL/PKDL cases in India and this review outlines various opportunities for further research in understanding such emerging co-infection.

Zoonotic visceral leishmaniasis (ZVL) caused by Leishmania infantum is an important disease of humans and dogs. Here we review aspects of the transmission and control of ZVL. Whilst there is clear evidence that ZVL is maintained by sandfly transmission, transmission may also occur by non-sandfly routes, such as congenital and sexual transmission. Dogs are the only confirmed primary reservoir of infection. Meta-analysis of dog studies confirms that infectiousness is higher in symptomatic infection; infectiousness is also higher in European than South American studies. A high prevalence of infection has been reported from an increasing number of domestic and wild mammals; updated host ranges are provided. The crab-eating fox Cerdocyon thous, opossums Didelphis spp., domestic cat Felis cattus, black rat Rattus rattus and humans can infect sandflies, but confirmation of these hosts as primary or secondary reservoirs requires further xenodiagnosis studies at the population level. Thus the putative sylvatic reservoir(s) of ZVL remains unknown. Review of intervention studies examining the effectiveness of current control methods highlights the lack of randomized controlled trials of both dog culling and residual insecticide spraying. Topical insecticides (deltamethrin-impregnated collars and pour-ons) have been shown to provide a high level of individual protection to treated dogs, but further community-level studies are needed.

In humid forests tree buttresses and tree trunks are used as diurnal resting sites by phlebotomine sandflies (Diptera: Psychodidae). When several species are present on the same buttress, the sandfly species are spatially segregated resulting in a pattern of vertical stratification on the buttress within 100 cm of ground level. A change in the distribution of one species induces a change in the distribution of an adjacent species. This is demonstrated under both natural and experimental conditions. Observations of sandflies at dawn and dusk have revealed that the buttress is used as a swarming site; this behaviour provides our favoured explanation for the patterns of vertical stratification on tree buttresses.

Development and forward migration of Leishmania parasites in the sandfly gut is accompanied by morphological transformation to highly motile, non-dividing ‘metacyclic’ forms. Previous studies in vitro have demonstrated that this metacyclogenesis is associated with developmentally regulated changes in expression of two major surface glycoconjugates of Leishmania, the lipophosphoglycan (LPG) and the glycoprotein protease GP63. Studies presented here are the first to examine in situ the changes in expression of these two important surface molecules which occur during amastigote-initiated development of L. major in its natural vector Phlebotomus papatasi. Immunocytochemical analysis using a GP63-specific monoclonal (3.8). and others recognizing metacyclic-specific (3F12) and common (WIC79.3) epitopes of LPG on logarithmic and metacyclic promastigotes, demonstrates: (1) clear expression of LPG and GP63 from 2 and 7 days post-bloodfeeding, respectively; (2) developmental modification of the LPG molecule as parasites undergo forward migration and morphological changes associated with metacyclogenesis; and (3) striking deposition of large amounts of parasite-free excreted LPG on/in the epithelial cells of the gut wall.

Transmission of leishmaniasis is effected by a specific developmental stage, the metacyclic promastigote. The precursors of metacyclic promastigotes were a distinct subpopulation of parasites, identified for the first time as a new stage in the life-cycle and named leptomonad promastigotes. Microdissection of infected sandflies into 4 midgut regions and foregut allowed precursor-product relationships to be established for amastigote-procyclic promastigote, procyclic-nectomonad promastigote, nectomonad-leptomonad promastigote and leptomonad-metacyclic promastigote developmental switches. Metacyclic promastigotes occurred mainly in the thoracic midgut and cardia, coincident with the accumulation of a promastigote secretory gel (PSG) plug in these anterior regions. The gel-like plug was isolated from flies with mature infections and found to contain predominantly leptomonad promastigotes. The PSG plug also contained the majority (75%) of the total metacyclic promastigote population in the sandflies, which were concentrated at the anterior pole. The PSG plug was found to be the main site of metacyclogenesis, and acted as a reservoir of leptomonad promastigotes from which metacyclic forms differentiated and migrated forward to promote the infective potential of the fly. The PSG plug occluded and distorted the midgut, forcing the stomodeal valve open and affecting the feeding success of the sandflies, such that they experienced difficulty in taking a full meal. Collectively, these data support the role of the PSG in the transmission of leishmaniasis, by conditioning the midgut environment for metacyclogenesis and altering the feeding ability of infected sandflies.

Saliva inoculated by sandfly females during feeding stimulated production of high levels of anti-saliva antibodies. To determine whether 3 species of the genus Phlebotomus have species-specific salivary antigens we performed dot-blots and immunoblots using sera from mice, hamsters and rabbits repeatedly bitten by sandflies. Important differences were found in the antigen components of the salivary gland lysates (SGL) of Phlebotomus papatasi, P. perniciosus and P. halepensis. In total 4–9 species-specific antigens were detected in each species by immunoblotting. Cross-reactivity was not detected between P. papatasi and the other species tested; in the SGL of P. papatasi sera from animals bitten by this species recognized 5–7 major antigens while sera from animals bitten by other species did not react. A weak cross-reaction was observed between P. perniciosus and P. halepensis; in SGL from P. perniciosus, the sera from rabbits and hamsters bitten by this species recognized about 8 intense bands while sera from animals bitten by P. halepensis reacted weakly with up to 4 saliva polypeptides.

Feeding performances of 3509 male and 4838 female sandflies, Sergentomyia ingrami, fed on 46 native or indigenous and exotic or introduced species belonging to 21 families of plants found in Kenya were examined. The results indicated more feeding on certain families than on others. The most used families were Musaceae, Araceae and Compositae, while the least was Alliaceae. A liking for certain species was also detected in families with more than one species investigated. Generally, the most used species were Bidens pilosa (Compositae) and Lycopersicon esculentum (Solanaceae). Interaction between the sex of the sandflies and the tested plants was minimal, suggesting that in most cases males and females had similar species likings. Sergentomyia ingrami fed more on two of the exotic species investigated.

The ability of a Kenyan sandfly species, Sergentomyia ingrami, to feed on various species of native or indigenous and exotic or introduced plants of Kenya was investigated using the Anthrone test. Some flies contained more sugar than others when they were tested after exposure to the plants.

Studies on the vertical distribution of phlebotomine sandflies were carried out at Marigat (Kenya) at determined heights above ground level in both wooded and open fields. Traps set up at different heights from 0–11 m (in wooded area) and 0–9 m (in open field), showed a clear vertical zonation of sandflies as large numbers were collected between 0–7 m in the first site and 0–4 m in the second ones. Among the nine sandfly species collected, Sergentomyia bedfordi Newstead and S. antennatus Newstead were the only species recorded at a height of 11 m above the ground and the commonest sandflies at all studied heights. Overall, more sandflies were collected from the wooded area than the open field. The relationships between the sandfly relative abundance and their heights of flight above the ground showed significant negative correlation coefficients.

Investigations of the phlebotomine sandflies fauna in a visceral leishmaniasis focus of Aba Roba in Ethiopia were carried out. This resulted in finding Phlebotomus celiae for the first time in the country. Previously, this species was incriminated as a vector of visceral leishmaniasis in Kitui, Kenya where the disease is endemic. It is possible that P. celiae has a wide distribution covering areas of similar ecological niches as those of its first description.

Adults of various phlebotomine sandfly species were obtained from leishmaniases endemic foci in Kenya using several trapping methods. Ten species were successfully reared from egg to adult in the laboratory; and large colonies of Sergentomyia schwetzi, S. bedfordi, S. ingrami, S. antennatus, S. adleri, S. garnhami, Phlebotomus duboscqi and P. martini established. Generally, the development of Phlebotomus spp. from egg to adult took longer (54.7–57.2 days) than Sergentomyia spp. whose developmental time with the exception of S. garnhami, varied between 36.5–42.3 days.

The paper reviews advances in our understanding of the vectorial capacity and vector–parasite relationship in Kenyan sandflies since the early 1900s (when sandflies were first reported in Kenya). Of the 38 species of sandflies known to occur in Kenya to date, three (Phlebotomus pedifer, P. martini and P. duboscqi) can naturally carry biochemically and serologically confirmed Leishmania (aethiopica, donovani and major, respectively) and 12 (Phlebotomus rhodhaini, Sergentomyia garnhami, S. squamipleuris, S. africanus, S. kirki, S. ingrami, S. antennatus, S. bedfordi, S. schwetzi, S. affinis, S. graingeri and S. clydei) carry various flagellates of biochemically or serologically unknown character.

Current research on naturally infected wild-caught sandflies indicates that L. aethiopica promastigotes have close association with structures resembling a peritrophic membrane and invade P. pedifer gut cells. Promastigotes invade the malpighian tubules of S. garnhami and S. antennatus.

Studies on laboratory-reared sandflies show that P. martini is susceptible to L. donovani amastigotes and that cultured promastigotes of L. donovani can survive in the guts of S. schwetzi, S. ingrami and S. adleri.

Experimental infection of sandflies with Leishmania is discussed and priorities for laboratory work set.

Sandflies caught from termitaria at Tseikuru (Kitui District) and Masinga (Machakos District) were dissected and examined for the presence of Leishmania. Leishmanial parasites were found in the guts of 12 out of 112 Sergentomyia garnhami from Tseikuru and in 2 out of 48 S. antennatus from Masinga. Five of the 12 S. garnhami and 1 of the 2 S. antennatus had leishmanial parasites in the malpighian tubules. Electron microscopic investigations revealed that in the malpighian tubules of S. garnhami the parasites were either free in the lumen or in close contact with the basement membrane.

Non-setting adhesives available were assessed for catching insects of medical and veterinary importance. Physical, chemical and handling properties are described. The results of tests are given using the most suitable adhesives against Glossina spp. (tsetse), Aedes aegypti (mosquito), Lutzomyia longipalpis (sandfly), triatomid bugs and cockroaches. Details are given of a formulation suitable for the capture of most insects in a variety of climatic conditions. The manufacturer's addresses are given to prevent difficulties in ordering and obtaining these products.