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 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. From 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, However, the data supporting the existence of this new species is limited. Until recently,
in-depth investigation using molecular characterization and isoenzyme analysis revealed that this 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 firstly 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. The 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.