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INTRODUCTION

Leishmaniasis refers to a constellation of clinical syndromes caused by protozoa belonging to the genus Leishmania. Autocthonous acquisition of these diseases by humans occurs in more than 90 countries of the world, located in all continents except Antarctica.1 The distribution of these diseases is determined largely by the distribution of the different species of Leishmania. Remarkably and despite their highly similar genomes, the different species display quite unique biological characteristics leading to differences in localization, predilection for dissemination, and pathogenicity for human and other vertebrate hosts. The incidence of cutaneous leishmaniasis (CL), the most common form of disease, ranges from 0.7 to 1.2 million new cases per year. Visceral leishmaniasis (VL), the second most common form, has been estimated up to 400,000 cases annually but recently may have dropped below 100,000 per year.2 However, these estimates may be highly inaccurate. As an illustration, the actual incidence of VL in 14 villages in an endemic area of Bihar, India (population 26,444) according to a household survey was 8.13-fold higher than records of reporting agencies in the same 3-year period of time.3

Leishmaniasis has afflicted humans for centuries, documented in pre-Incan pottery from Ecuador and Peru showing cutaneous and mucosal lesions on pottery.4 The etiologic protozoan was discovered nearly simultaneously and published in sequential months of the 1903 British Medical Journal by Sir William Boog Leishman, a British military physician, and Charles Donovan, an Irish medical officer in the Indian Medical Service, who observed the parasites microscopically in samples from fatal cases of patients with febrile illnesses, in the Indian cities of Dum Dum near Calcutta (hence the name, Dum Dum fever) and Madras, respectively.4,5

There are more than 20 defined species of Leishmania found to cause human disease, a number that expands and contracts as the taxonomic lines are redefined. Most cases of leishmaniasis are vector-borne and transmitted through the bite of a Phlebotomine sand fly, with notable exceptions now being discovered (see Transmission below). Considering the discoveries of new Leishmania species, new clinical forms of leishmaniasis, expanded knowledge of the spectrum of reservoirs and vectors/modes of transmission, and newly appreciated magnitude of human asymptomatic infections, the factors underlying the maintenance and expansion of leishmaniasis in human populations must be reassessed. In addition, due to imperfect diagnostic and therapeutic measures, the control of leishmaniasis at an individual and a community-wide level, remains elusive. In this chapter, we attempt to define the uncertainties and point out areas in which there are critical needs for more complete knowledge of the spectrum of leishmaniasis.2

LIFE CYCLE AND TAXONOMY

The different Leishmania species share similar life cycles and transmission characteristics (Fig. 134-1). It has been taught that most mammalian leishmaniasis, and all vector-initiated leishmaniasis is initiated by the bite of a phlebotomine sand fly vector belonging to the Lutzomyia spp. in the ...

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