Behavior in a mouse model of isolates of Leishmania donovani sensu lato cultured from the blood of patients with chronic cutaneous lesions

Cutaneous Manifestations of Human and Murine Leishmaniasis

The leishmaniases are diseases caused by pathogenic protozoan parasites of the genus Leishmania. Infections are initiated when a sand fly vector inoculates Leishmania parasites into the skin of a mammalian host. Leishmania causes a spectrum of inflammatory cutaneous disease manifestations. The type of cutaneous pathology is determined in part by the infecting Leishmania species, but also by a combination of inflammatory and anti-inflammatory host immune response factors resulting in different clinical outcomes. This review discusses the distinct cutaneous syndromes described in humans, and current knowledge of the inflammatory responses associated with divergent cutaneous pathologic responses to different Leishmania species. The contribution of key hematopoietic cells in experimental cutaneous leishmaniasis in mouse models are also reviewed and compared with those observed during human infection. We hypothesize that local skin events influence the ensuing adaptive immune response to Leishmania spp. infections, and that the balance between inflammatory and regulatory factors induced by infection are critical for determining cutaneous pathology and outcome of infection.

Intradermal infection model for pathogenesis and vaccine studies of murine visceral leishmaniasis

The levels of protection found in vaccine studies of murine visceral leishmaniasis are significantly lower than for cutaneous leishmaniasis; whether this is due to the high-challenge murine model employed and/or is a consequence of differences required in tissue-specific local immune responses is not understood. Consequently, an intradermal murine model of visceral leishmaniasis has been explored. Intradermal inoculation established a chronic infection in susceptible mice which was associated with a pattern of parasite clearance with time postinfection in the liver and skin; in contrast, parasite persistence and expansion was observed in lymphoid tissue (spleen and draining lymph node). The course of disease found appears to be similar to those reported for subclinical canine and human visceral leishmaniasis. Clearance of parasites from the skin was correlated with an inflammatory response and the infiltration and activation of CD4(+) and CD8(+) T cells. In contrast, in lymphoid tissue (lymph node or spleen), the production of Th1/Th2 cytokines (interleukin-4 [IL-4], IL-10, and gamma interferon) appeared to correlate with parasite burden and pathogenesis. In vaccination experiments employing the Leishmania infantum D-13 (p80) antigen, significantly higher levels of protection were found with the intradermal murine model (29 to 7,500-fold more than naive controls) than were found with a low-dose intravenous infection model (9 to 173-fold). Thus, this model should prove useful for further investigation of disease pathogenesis as well as vaccine studies of visceral leishmaniasis.

The epidemiology of leishmaniases in Lebanon

The prevalence of leishmaniasis in Lebanon was studied in 1993-97 for a Lebanese population sample of about 81,000 subjects (60% rural and 40% urban) constituting roughly 3.4% of the total population. The prevalence of cutaneous leishmaniasis was found to be 0.18% in the rural versus 0.41% in the urban areas. Visceral leishmaniasis was practically non-existent in both environments. In addition, skin tests were done and anti-Leishmania antibodies were sought in a sample of the population at risk in the rural area. Skin tests were positive in 2.5% of the tested subjects, and 1% of the normal population had elevated levels of anti-Leishmania antibodies. The difference between the prevalence of clinical disease and positive skin testing and/or antibodies may be due to the existence of past or present subclinical disease. An unexpected finding was that the prevalent dermotropic parasite in Lebanon belongs to the L. donovani complex. Further characterization of the isolates by molecular techniques and definition of the transmission cycle of this parasite may explain our epidemiological findings.