Leishmania donovani

Abstract: The group of diseases known as the leishmaniases are caused by obligate intracellular protozoa of the genus Leishmania ([39][1]). Natural transmission of leishmania is carried out by a certain species of sandfly of the genus Phlebotomus (Old World) or Lutzomyia (New World). These are present in

Abstract: From the early 1900s, visceral leishmaniasis (VL; kala-azar) has been among the most important health problems in Sudan, particularly in the main endemic area in the eastern and central regions. Several major epidemics have occurred, the most recent--in Western Upper Nile province in southern Sudan, detected in 1988--claiming over 100,000 lives. The disease spread to other areas that were previously not known to be endemic for VL. A major upsurge in the number of cases was noted in the endemic area. These events triggered renewed interest in the disease. Epidemiological and entomological studies confirmed Phlebotomus orientalis as the vector in several parts of the country, typically associated with Acacia seyal and Balanites aegyptiaca vegetation. Infection rates with Leishmania were high, but subject to seasonal variation, as were the numbers of sand flies. Parasites isolated from humans and sand flies belonged to three zymodemes (MON-18, MON-30 and MON-82), which all belong to the L. donovani sensu lato cluster. Transmission dynamics have not been elucidated fully; heavy transmission in relatively scarcely populated areas such as Dinder national park suggested zoonotic transmission whereas the large numbers of patients with post kala-azar dermal leishmaniasis (PKDL) in heavily affected villages may indicate a human reservoir and anthroponotic transmission. Clinical presentation in adults and in children did not differ significantly, except that children were more anaemic. Fever, weight loss, hepato-splenomegaly and lymphadenopathy were the most common findings. PKDL was much more common than expected (56% of patients with VL developed PKDL), but other post-VL manifestations were also found affecting the eyes (uveitis, conjunctivitis, blepharitis), nasal and/or oral mucosa. Evaluation of diagnostic methods showed that parasitological diagnosis should still be the mainstay in diagnosis, with sensitivities for lymph node, bone marrow and spleen aspirates of 58%, 70% and 96%, respectively. Simple, cheap serological tests are needed. The direct agglutination test (DAT) had a sensitivity of 72%, specificity of 94%, positive predictive value of 78% and negative predictive value of 92%. As with other serological tests, the DAT cannot distinguish between active disease, subclinical infection or past infection. The introduction of freeze-dried antigen and control sera greatly improved the practicality and accuracy of the DAT in the field. An enzyme-linked immunosorbent assay using recombinant K39 antigen had higher sensitivity than DAT (93%). The polymerase chain reaction using peripheral blood gave a sensitivity of 70-93% and was more sensitive than microscopy of lymph node or bone marrow aspirates in patients with suspected VL. The leishmanin skin test (LST) was typically negative during active VL and converted to positive in c. 80% of patients 6 months after treatment. Immunological studies showed that both Th1 and Th2 cell responses could be demonstrated in lymph nodes from VL patients as evidenced by the presence of messenger ribonucleic acid for interleukin (IL)-10, interferon gamma and IL-2. Treatment of peripheral blood mononuclear cells from VL patients with IL-12 was found to drive the immune response toward a Th1 type response with the production of interferon gamma, indicating a potential therapeutic role for IL-12. VL responded well to treatment with sodium stibogluconate, which is still the first line drug at a dose of 20 mg/kg intravenously or intramuscularly per day for 15-30 d. Side effects and resistance were rare. Liposomal amphotericin B was effective, with few side effects. Control measures have not been implemented. Based on observations that VL does not occur in individuals who have a positive LST, probably because of previous cutaneous leishmaniasis, a vaccine containing heat-killed L. major promastigotes is currently undergoing a phase III trial.

Abstract: We have found that an important Th2 cytokine, IL-10, is produced by tissues from patients acutely infected with Leishmania donovani. In all individuals tested, IL-10 mRNA production was increased in lymph nodes taken during acute disease over that observed in postacute samples. In contrast, both pre- and posttreatment lymph nodes had readily detected mRNA for IFN-gamma and IL-2. A down-regulating effect of IL-10 on leishmania-induced proliferative responses was demonstrated when Hu rIL-10 was added to cultures of PBMC from clinically cured individuals. PBMC from individuals with acute visceral leishmaniasis responded to stimulation with leishmania lysate by producing IL-10 mRNA. Simultaneously cultured PBMC collected from the same patients after successful chemotherapy produced no detectable IL-10 mRNA after leishmania antigen stimulation. Neutralizing anti-IL-10 mAb added to PBMC from patients with acute visceral leishmaniasis markedly increased the proliferative response to leishmania lysate. Finally, we observed mRNA for IL-10 and IFN-gamma concurrently in a lesion from a patient with post-kala-azar dermal leishmaniasis (PKDL). These results indicate the production of IL-10 during L. donovani infection, and suggest a role for this cytokine in the regulation of immune responsiveness during visceral leishmaniasis.

Abstract: To determine the relative contributions of respiratory burst–derived reactive oxygen intermediates (ROI) versus reactive nitrogen intermediates (RNI) to macrophage-mediated intracellular host defense, mice genetically deficient in these mechanisms were challenged with Leishmania donovani, a protozoan that selectively parasitizes visceral tissue macrophages. During the early stage of liver infection at wk 2, both respiratory burst–deficient gp91phox−/− (X-linked chronic granulomatous disease [X-CGD]) mice and inducible nitric oxide synthase (iNOS) knockout (KO) mice displayed comparably increased susceptibility. Thereafter, infection was unrestrained in mice lacking iNOS but was fully controlled in X-CGD mice. Mononuclear cell influx into infected liver foci in X-CGD and iNOS KO mice was also overtly impaired at wk 2. However, granuloma assembly in parasitized tissue eventually developed in both hosts but with divergent effects: mature granulomas were functionally active (leishmanicidal) in X-CGD mice but inert in iNOS-deficient animals. These results suggest that (a) ROI and RNI probably act together in the early stage of intracellular infection to regulate both tissue recruitment of mononuclear inflammatory cells and the initial extent of microbial replication, (b) RNI alone are necessary and sufficient for eventual control of visceral infection, and (c) although mature granulomas have traditionally been associated with control of such infections, these structures fail to limit intracellular parasite replication in the absence of iNOS.

Abstract: We report the cloning of a Leishmania chagasi antigen gene and an evaluation of leishmaniasis patient antibody responses to the recombinant protein, rK39. rK39 contains a 39-amino acid repeat that is part of a 230-kDa protein predominant in L. chagasi tissue amastigotes. Sequence analyses showed this protein, LcKin, to be related to the kinesin superfamily of motor proteins. Southern blot analyses demonstrated LcKin-related sequences in seven species of Leishmania, with conservation of the repeat between L. chagasi and Leishmania donovani. Serological evaluation revealed that 98% (56 of 57) of Brazilian and 100% (52 of 52) of Sudanese visceral leishmaniasis patients have high antibody levels to the rK39 repeat. Detectable anti-K39 antibody was virtually absent in cutaneous and mucosal leishmaniasis patients and in individuals infected with Trypanosoma cruzi. The data show that rK39 may replace crude parasite antigens as a basis for serological diagnosis of visceral leishmaniasis.