Leishmaniasis is defined as a cutaneous, mucocutaneous, or visceral anthropozoonotic disease, resulting from the inoculation of protozoa belonging to the genus Leishmania.

The World Health Organization classifies leishmaniasis as one of the most important neglected tropical diseases. It is considered endemic in at least 97 countries, with 1 000 000 cases reported in the last 5 years.¹

Regarding “old world” cutaneous leishmaniasis (OWCL), the disease has classically been seen most often in children. In contrast, “new world” leishmaniasis of the skin typically affects adult patients who live in rural areas, usually doing agricultural work. Over time, however, an increased number of pediatric cases have been reported in Latin America, which would be considered the “new world.” Affected countries include Brazil, Colombia, Argentina, and Venezuela, where the number of cases in children ranges from 6% to 35% of all patients with leishmaniasis.²,³ The important population at risk in developed countries include adventurous tourists, migratory workforce, and military personnel. They are exposed to the disease when visiting or inhabiting endemic areas around the world. The vectors for leishmaniasis are sandflies, either Phlebotomus (in old world disease) or Lutzomyia (for new world leishmaniasis). Other humans, dogs, and rodents represent the main reservoirs for the microorganisms in nature.

More than 20 species of Leishmania may cause disease in humans. Each one is associated with a particular clinical presentation (Table 18-1). Sandflies acquire the microorganisms when they bite infected animals or people. The flies then transmit flagellated promastigotes from their proboscises, by biting other hosts. Once inside macrophages, dermal dendrocytes, or Langerhans cells, the promastigotes lose their flagella and become amastigotes. In that form, they multiply and infect neighboring cells and live in the cytoplasm. If a Th1 response is activated, the production of IL-2 and interferon-γ can eradicate the organisms. However, if the response is inadequate or is instead the Th2 form—with the production of IL-4, IL-5, and IL-10—the disease process continues and becomes chronic.⁴

Children have been always an important population affected by OWCL, either in wet, rural, areas where Leishmania major is the dominant pathogen or in dry, urban regions in which Leishmania tropica is preponderant. Although the classical form of new world cutaneous leishmaniasis (NWCL) was associated with young males working in rural areas, an increasing number of children have recently been affected. They may live in rural locales that are affected by deforestation or in crowded periurban areas.

The usual presentation of cutaneous leishmaniasis (CL) is in its ulcerated form, beginning either as a papule or as a nodule (Figures 18-1 and 18-2). The lesional ulcer is shallow with elevated borders, and it is either covered by a crust or open with a red, granulomatous bottom. OWCL tends to resolve spontaneously in a matter of months, although Leishmania aethiopica may be associated with a more protracted course. In NWCL, cases caused by Leishmania mexicana often
remit spontaneously as well, but those caused by Leishmania braziliensis are usually chronic. They carry a risk for evolution to mucocutaneous leishmaniasis. Lesions are solitary or few in number; common locations include exposed areas of the face, upper extremities, hands, ears, and legs.

CL may be clinically polymorphic, rather than being represented by a single ulcer. Other variants include impetigo-like, lupoid, plaque-like (Figure 18-3), sporotrichoid, agminate, zosteriform, verruciform, or pustular, imitating acute folliculitis or a furuncle. Multiple papular lesions in several sites typify the disseminated form of CL. A particular variant seen in the pediatric population is leishmaniasis recidiva cutis (Figure 18-4); in such cases, a few papular lesions manifest as recurrent disease around a scar caused by a previous, ulcerated lesion. They may subsequently become annular and tend to be chronic.⁵,⁶,⁷

Mucocutaneous lesions are associated with infections by L. braziliensis or L. aethiopica. The ulcers in this condition usually begin in the nasal septum and progress to involve
the perinasal skin, nasopharynx, or larynx. Children can also have labial and oral involvement. Mucocutaneous lesions usually follow cutaneous disease by months to a few years.

Diffuse CL is the anergic form of leishmaniasis, very similar pathophysiologically to the lepromatous form of leprosy. It is caused in Central and South America by Leishmania amazonensis, and in Africa by L. aethiopica. The clinical presentation features multiple papules, nodules, and plaques located in any skin area, but they are usually situated on the face and extremities. A response to treatment may be seen initially, but it is usually followed by persistent recurrences and then unremitting lesions.⁸

The skin biopsy is one of the most useful tools for the diagnosis of CL. Appropriate samples are either punch or incisional biopsies from the edge of an ulcer or the center of a solid lesion, and they should include the deep dermis.

Pathologic findings are similar in OWCL and NWCL. The most common observation is a diffuse inflammatory affecting both the papillary and reticular dermis. In some instances, the pattern is more focal and band-like, or perivascular and interstitial throughout the corium. Less commonly, one can see well-formed granulomas of the tuberculous type, which are sometimes necrotizing. They are surrounded by a diffuse lymphoplasmacytic and histiocytic infiltrate. Overt granulomas tend to be observed most often in chronic lesions, such as those of recidivans cutis and lupoid forms of CL.

The usual components of the inflammatory infiltrate include lymphocytes, plasma cells, and histiocytes with clear cytoplasm, as well as isolated giant cells. The epidermis may be normal in appearance, hyperplastic, or ulcerated. The papillary dermis usually contains a histiocytic infiltrate, but it may be completely spared, with a Grenz zone. Because of the abundance of plasma cells, Russell bodies are not uncommon. Other occasional constituents of the infiltrate include neutrophils and eosinophils.