Interactions between Leishmania parasite and sandfly: a review

Leishmaniasis transmission cycles are maintained and sustained in nature by the complex crosstalk of the Leishmania parasite, sandfly vector, and the mammalian hosts (human, as well as zoonotic reservoirs). Regardless of the vast research on human host-parasite interaction, there persists a substantial knowledge gap on the parasite's development and modulation in the vector component. This review focuses on some of the intriguing aspects of the Leishmania-sandfly interface, beginning with the uptake of the intracellular amastigotes from an infected host to the development of the parasite within the sandfly's alimentary canal, followed by the transmission of infective metacyclic stages to another potential host. Upon ingestion of the parasite, the sandfly hosts an intricate repertoire of immune barriers, either to evade the parasite or to ensure its homeostatic coexistence with the vector gut microbiome. Sandfly salivary polypeptides and Leishmania exosomes are co-egested with the parasite inoculum during the infected vector bite. This has been attributed to the modulation of the parasite infection and subsequent clinical manifestation in the host. While human host-based studies strive to develop effective therapeutics, a greater understanding of the vector-parasite-microbiome and human host interactions could help us to identify the targets and to develop strategies for effectively preventing the transmission of leishmaniasis.

Development of antibodies to the iron-binding proteins transferrin and ferritin in dogs and mice infected with Leishmania parasites

Most microorganisms including Leishmania parasites compete with the innate immune defenses of the infected hosts to acquire iron, an essential nutrient necessary for their growth and replication. In mammals, iron is predominantly bound to protein carriers such as transferrin and ferritin and the strategies adopted by the infected host to restrict its uptake by pathogens are still not elucidated. We compared herein the development of anti-transferrin and anti-ferritin antibodies in hosts that differs by their susceptibility to Leishmania infection. Results showed that Leishmania infantum naturally-infected dogs which have developed canine leishmaniasis (CanL) demonstrated higher titers of IgG antibodies anti-leishmanial antigens and anti-iron binding proteins than those infected without clinical signs. In the experimental mouse model, C57BL/6 mice resisted L. major infection, developed lower titers of Leishmania-specific IgG antibodies than BALB/c susceptible mice but demonstrated also the production of anti-transferrin and anti-ferritin IgG antibodies. Overall, results are in favor that mechanisms, other than the polyclonal activation of B cells associated-hypergammaglobulinemia, a characteristic of susceptible animals, are likely involved and require a replicating parasite for the limitation of iron uptake.

Detection and differentiation of Leishmania parasites in asymptomatic canine by High-Resolution Melting analysis of microsatellite fragment in ITS gene

The high prevalence of Leishmania infection was reported in dogs as the main reservoir of CanL in many locations in the old world. Detection and firmly identification of Leishmania species in asymptomatic dogs by reliable method was considered and employed. Non-invasive and non-anesthetized blood sampling in asymptomatic dogs was conducted. Nested, conventional and real-time PCR with HRM technique was performed targeting ITS-rDNA gene. 88 asymptomatic dogs were sampled from three CanL endemic provinces of Iran in 2018-2019. 23 blood samples were Leishmania positive. L. major, L. tropica and L. infantum were accurately identified for the first time with HRM targeting ITS2-microsatellite. Three samples were mixed infections. CLC software TM predictions for microsatellite ITS-rDNA were 86.93 °C: L. major, 85.76 °C: L. tropica and 86.04 °C: L. infantum. Standard strains of Leishmania species were accurately separated with almost one to 2 °C deference (L. major: 86.61 °C, L. infantum: 85.41 °C, L. tropica: 84.82 °C). Each HRM curve represents one species in a sample for helping accurate identification of Leishmania species and even mixed infection when two curves are present. Detecting parasites at primary stages in asymptomatic cases is essential using Real-time HRM. As same as mammalian Leishmania in rodents which is present at early stages and non-pathogenesis, only L. major would exist and other Leishmania disappears. This can conclude also for L. major, L. infantum and L. tropica in dogs. The role of L. major existence in canine blood should be investigated more.

Genetically modified live attenuated vaccine: A potential strategy to combat visceral leishmaniasis

Visceral leishmaniasis (VL) is caused by a protozoan parasite Leishmania donovani mainly influencing the population of tropical and subtropical regions across the globe. The arsenal of drugs available is limited, and prolonged use of such drugs makes parasite to become resistant. Therefore, it is very imperative to develop a safe, cost-effective and inexpensive vaccine against VL. Although in recent years, many strategies have been pursued by researchers, so far only some of the vaccine candidates reached for clinical trial and more than half of them are still in pipeline. There is now a broad consent among Leishmania researchers that the perseverance of parasite is very essential for eliciting a protective immune response and may perhaps be attained by live attenuated parasite vaccination. For making a live attenuated parasite, it is very essential to ensure that the parasite is deficient of virulence and should further study genetically modified parasites to perceive the mechanism of pathogenesis. So it is believed that in the near future, a complete understanding of the Leishmania genome will explore clear strategies to discover a novel vaccine. This review describes the need for a genetically modified live attenuated vaccine against VL, and obstacles associated with its development.