**Abstract**

Leishmaniasis is a vector-borne tropical/subtropical disease caused by an intracellular parasite transmitted to humans by sand fly bite. It is endemic in Asia, Africa, the Americas, and the Mediterranean region. Worldwide reports include 1.5–2 million new cases each year, more than 300 million at risk of acquiring the disease, and 70,000 deaths per year. Clinical features depend on the *Leishmania* species and immune response of the host, varying from localized cutaneous disease to visceral form with potentially fatal outcome; however, the common presentation is either cutaneous, mucocutaneous, or visceral leishmaniasis. Many therapeutic agents are being used in *Leishmania* treatment, but the only effective treatment is achieved with current pentavalent antimonials. WHO considers Leishmaniasis as one of the "Neglected Tropical Diseases" that continues to be prevalent despite international, national, and local efforts towards its control and elimination over the last decade. This chapter reviews the global perspective of Leishmaniasis with increasing recognition of emerging "Atypical forms" and new surge of disease across the world mainly due to increasing conflicts in endemic areas leading to forced migration among other causes. All these challenges related to environment, disease, and vector pose major implications on WHO's leishmaniasis control and elimination plan.

**Keywords:** *Leishmania*, sand fly, vector, parasite, protozoa, phlebotomine

#### **1. Introduction**

Leishmaniasis is a vector-borne disease caused by an obligate intracellular protozoa of genus *Leishmania* and is transmitted by the bite of a female phlebotomine sand fly (**Figure 1**). It is a poverty-related disease with an estimated 0.7–1 million new cases reported per year from approximately 100 endemic countries. It is reported from all continents except Australia and Antarctica.

The disease is primarily zoonotic with exception of *L. donovani* and *L. tropica*, although some evidence exists that animal reservoir exists for these species too. There are about 53 species of *Leishmania* described with more than 20 species pathogenic to humans and each distinct species causing different clinical manifestations ranging from self-resolving cutaneous ulcers to disfiguring mucocutaneous lesions to life-threatening systemic visceral disease [1–3]. The outcome depends on multiple factors including parasite characteristics, vector itself, and host factors in a particular patient's immune status. The World Health Organization (WHO) considers leishmaniasis as not only one of the neglected tropical diseases but also a

#### **Figure 1.**

*This photograph depicts a right lateral view of a* Phlebotomus papatasi *sand fly which had landed atop the skin surface of a human volunteer. This specimen had just completed its ingestion of its blood meal, which is visible through its distended transparent abdomen. Sand flies like this* P. papatasi *are responsible for the spread of the vector-borne, parasitic disease, leishmaniasis (courtesy of Centers for Disease Control and Prevention/ prof. Frank Hadley Collins and James Gathany) (https://phil.cdc.gov/Details.aspx?pid=10276).*

public health problem that requires elimination by developing effective therapeutic regimens and prevention/control plans.
