Leishmaniasis: An Evolving Public Health Concern in Thailand

Abstract

Leishmaniasis is a parasitic disease caused by flagellated protozoa of the genus Leishmania. It is transmitted by infection from the bite of an infected sandfly. The 3 main clinical forms of the disease are cutaneous leishmaniasis (CL), visceral leishmaniasis (VL) and mucocutaneous leishmaniasis (MCL). Prior to 1996, all leishmaniasis cases were infected during the visit to the endemic areas. Thereafter, autochthonous leishmaniasis cases have been reported in Thailand. During 1996 to the present, at least 21 cases of autochthonous leishmaniasis have been confirmed in Thailand. Leishmania siamensis, a novel species of Leishmania, was suspected of being the causative pathogens in some of those cases, although the data supporting the existence of this new species is limited. Until recently, in-depth investigation using molecular characterization and isoenzyme analysis revealed that a suspected novel species consists of 2 different, but closely related strains: L. siamensis and L. martiniquensis. L. martiniquensis, a rare species firstly discovered on Martinique Island, is the cause of leishmaniasis in the majority of cases. Meanwhile, L. siamensis, a true novel species first and only reported from Thailand, was confirmed as the cause of leishmaniasis in two autochthonous cases. Two clinical forms (CL and VL) have been observed in both L. martiniquensis and L. siamensis infection. DNA of L. martiniquensis was found in black rats, suggesting their role as a natural reservoir. The presence of L. martiniquensis DNA in two sandfly species (Sergentomyia gemmea and Sergentomyia barraudi) that are commonly found in affected areas may also suggest their role as potential vectors. Here, we update the status of leishmaniasis in Thailand and its emergence as a potential public health concern.