Dermotropic Leishmania donovani in Sri Lanka: visceralizing potential in clinical and preclinical studies.

The visceralizing potential of apparently dermotropic Leishmania donovani in Sri Lanka (L. donovani-SL) was investigated through long-term follow-up of cutaneous leishmaniasis (CL) patients and in vivo and in vitro experimental infection models. CL patients (n = 250) treated effectively with intra-lesional antimony therapy were followed-up six monthly for 4 years. There was no clinical evidence of visceralization of infection (VL) during this period. Infection of BALB/c mice with L. donovani-SL (test) through intra-dermal route led to the development of cutaneous lesions at the site of inoculation with no signs of systemic dissemination, in contrast to the observations made in animals similarly infected with a visceralizing strain of L. donovani-1S (control). Cytokine (IL-10, IFN-γ) release patterns of splenocytes and lymph node cell cultures derived from mice primed with experimental infections (with either test or control parasites) revealed significantly high IFN-γ response associated with test mice with CL, while prominent IL-10 levels were observed in association with control mice with VL. Furthermore, diminished infection efficiency, intracellular growth and survival of L. donovani-SL parasites compared with L. donovani-1S were evident through in vitro macrophage infection experiments. These studies confirm, for the first time, the essential dermotropic nature of L. donovani-SL suggesting natural attenuation of virulence of local parasite strains.

CHARACTERISTICS OF PHLEBOTOMINE SANDFLIES IN SELECTED AREAS OF SRI LANKA.

Cutaneous leishmaniasis (CL) is an endemic disease in Sri Lanka. Studies on vector aspects, although important for better understanding of disease transmission dynamics, are still limited. The present study describes the species distribution and behavioral patterns of sandflies within selected disease-prevalent zones in the country. Adult sandflies were collected from several field sites over a two-year duration in Sri Lanka using cattle-baited net traps, CDC light traps and manual methods. Species identification was performed using standard keys. Leishmania donovani and source of blood meal in blood-fed female sandflies DNA were identified using PCR-based methods. Aggregation period of adult sandflies during overnight collections was also noted. The collected sandflies were identified as Phlebotomus argentipes glaucus (previously known as morphospecies A) and a non-vector species, Sergentomyia zeylanica. Presence of L. donovani DNA was found in 2/634 female sandflies. The parasite ITS1 region of SSU rDNA had 99% sequence similarity with L. donovani from Bangladesh and India. The peak aggregation period of sandflies within cattle-traps was between 8:00 PM to 11:00 PM, indicating that vector control strategies could be conducted during this time period. As Sergentomyia zeylanica is likely to be merely a biting nuisance and showed more of an anthropophilic behavior, whereas the probable vector of CL in Sri Lanka (P. argentipes glaucus) demonstrated zoophilic behavior, has implications for the planning of future vector control strategies.