**2.2. Clinical picture**

in countries from the United States to Argentina, except in Uruguay and Chile. ACL is an important health problem affecting the poorer population and is thus one of the most neglected diseases. Depending mainly on the *Leishmania* species and the host immune response, the spectrum of clinical forms includes localized cutaneous leishmaniasis (LCL), disseminated and diffuse cutaneous leishmaniasis (DCL) and mucocutaneous leishmaniasis (MCL). The former is the most commonly occurring disease with approximately 0.7–1.2 million new cases every

In south-eastern Mexico, the Yucatan Peninsula is an important endemic area of LCL, locally known as the "chiclero´s (gum collectors) ulcer". The LCL was first described by Seidelin in 1912, who classified the agent as morphologically indistinguishable from *Leishmania tropica* [3]. Since then, the humid forest of the Yucatan Peninsula has been documented as an endemic

The purpose of this chapter is to review the most relevant studies performed in the last 30 years in the Laboratory of Immunology of the Autonomous University of Yucatan. This research has covered the characterization of the "chiclero´s ulcer", its diagnosis and treatment, and the identification of risk factors as well as the *Leishmania* vectors and reservoir species that are

Leishmaniasis control is usually hampered by ignorance of the true incidence/prevalence of infection, thus underestimating human suffering and disability caused by the disease. After parasites are inoculated by a sand fly, the infection outcomes might be either an asymptomatic infection or a clinically manifested infection. Most studies done in Latin America with reference to ACL have been focused on incidence/prevalence of the disease (clinical infection). In the first approach and after diagnostic tools were implemented, a total of 63 cases of LCL were recorded in the state of Campeche between 1982 and 1987. The most common clinical presentation was a chronic ulcerated lesion (with an evolution time longer than 10 years), located predominantly on the ear (39%). Single lesions were found in 49/63 (78%) cases

Based on these data, a program for the study and surveillance of LCL in collaboration with health services from the state of Campeche was established. First of all, a study to determine the incidence of LCL was carried out in seven rural health communities of the state of Campeche from January to December, 1987. Montenegro skin test (MST) was carried out on a sample batch of 449 persons randomly selected from men aged 15–45 years. Risk factors including age (15–45 years old), sex (male) and exposure (working in the field) had been identified previously [8]. MST-positive response ranged from 24 to 90% among the communities studied. These wide-range results could reflect differences in endemicity of LCL in the state of Campeche. A total of 56 new LCL cases with both a positive parasitological diagnosis

important to be known in order to develop control strategies.

**2. Epidemiology of LCL in southern Mexico**

year [1, 2].

focus of LCL [4–6].

138 The Epidemiology and Ecology of Leishmaniasis

**2.1. Incidence and prevalence**

affecting men working in the field [7].

The clinical picture of LCL in the Yucatan Peninsula was characterized through a study performed between January 1990 and December 1995 [12]. A total of 683 patients with cutaneous lesions suggestive of LCL were examined. Parasite demonstration by smear, biopsy and/or isolation-culture was positive in 445 cases (65.1%). From these samples, *Leishmania (Leishmania) mexicana* was successfully isolated, cultured and identified by either isoenzyme characterization and/or monoclonal antibodies in 136/445 cases (30.5%). The LCL clinical picture was limited to these 136 cases in which *L. (L.) mexicana* was identified. Males (94.1%) between 10 and 40 years of age (85.3%) were mainly affected. The most common lesions were single (84.5%), rounded (52.6%), ulcerated (72.5%) and located on the ear (39.9%). A total of 72.8% cases detected were classified as acute with less than 3 months of evolution. Since in those years an active surveillance program for LCL was implemented in the state of Campeche most cases were acute. In summary, the clinical picture of LCL caused by *L. (L.) mexicana* is characterized by a commonly single, rounded, painless ulcerated lesion, without lymphangitis and/or adenopathy; with the absence of mucosal involvement, and when located on the ear (the most common location) tends to become chronic if left untreated, causing the destruction of the pinna and disfiguration.

The importance of the active surveillance program was highlighted by the observation of changes in the clinical form with time. The manifestation of LCL has evolved, during the last years, from the typical single, rounded, small and ulcerated lesion worldwide recognized as "benign" (**Figure 1A**–**C**), to nodular lesions with an increased diameter as well as the appearance of multiple lesions (**Figure 1D**–**F**). Those findings are suggestive of changes in pathogenicity of the parasite that need to be studied.

**Figure 1.** Clinical spectrum of the LCL in southeastern Mexico. (**A)** Acute ulcerated lesion on ear; (**B)** typical small, rounded, ulcerated lesion in forearm; (**C)** chronic lesion on ear; **(D and E)** nodular infiltrated lesions; (**F)** multiple ulcerated lesions in forearm.
