**3. Ecology of the endemic area**

The Yucatan Peninsula is a discrete biotic province of approximately 143,500 km2 . The region is a broad, flat shelf of marine limestone of geologically recent formation (Paleocene to Recent). The peninsula includes the states of Yucatan, Campeche, Quintana Roo and a portion of Tabasco east of the Rio Usumacinta and north of the Sierra del Norte de Chiapas. The peninsula is surrounded on three sides by water and bounded on the south by highlands that isolate this region from the rest of Central America. An interesting observation is that because of its geographic isolation, the Yucatan Peninsula is an area of mammalian endemism with fauna that differs markedly from the rest of Mexico. The climate is subtropical with a relative humidity of 80%, an unpredictable rainy season (annual rainfall over 1401 mm) mostly during the summer, and an average temperature of 27 ± 5°C [16].

#### **3.1. Parasites**

Epidemiological studies and molecular characterization of the New World leishmaniases have revealed that the genus *Leishmania* Ross, 1903 (Protozoa: Trypanosomatidae) is by far much more complex than originally thought. The genus is comprised of 30 species infecting a wide variety of mammalian hosts (wild or domestic) and vectors. Each of the New World species of *Leishmania* has unique ecological and geographical distributions [17]. From an epidemiological point of view and disease‐control stand‐point, to know whether an organism, causing the disease in a given area, is of the same species as that found in suspected mammalian reservoirs and insect vectors, is very important [18].

Based on both the clinical and epidemiological features of the disease, as well as on the biological characteristics of the parasite in laboratory animals [19–21], *L. (L.) mexicana* Biagi, 1953 emend. Garnham, 1962, was considered the main agent of LCL in the Yucatan Peninsula. Nevertheless, its characterization at the genus and sub-genus level was not done in those studies.

Therefore, from January 1990 to July 1992, 153 patients with LCL determined by both clinical diagnosis and parasite visualization (smear, biopsy and/or isolation-culture) were studied. All of them were infected in the state of Campeche. Parasite isolation by needle aspirates taken from the edge of the lesions was positive in 49%. Isolates were characterized by isoenzyme markers (glucose phosphate isomerase, mannose phospate isomerase, nucleoside hydrolase, phosphoglucomutase, 6-phosphogluconate dehydrogenase and glucose-6-phosphate dehydrogenase). Seventy (93.3%) were identified as *L. (L.) mexicana* Biagi, 1953 emend. Garham, 1962 and 5 (6.7%) as *Leishmania (Viannia) braziliensis* Viannia 1911 emend. Matta, 1916 [22].

Later on, a study to identify *Leishmania* parasites isolated from humans and wild rodents from the state of Campeche, using IFA with Mabs was carried out. The main purpose was to determine if the parasites of both types of hosts were of the same biotype. All the isolates obtained from wild rodents reacted with monoclonal antibodies M7 and M8 and were thus identified as *L. (L.) mexicana*. No differences in reactivity patterns were found among the different strains of *L. (L.) mexicana* from humans and wild rodents [22].

Finally, to assure that *L. (L.) mexicana* is the main agent causing LCL in the state of Campeche, a study leading to the identification by PCR of *L. (L.) mexicana* in the potential vectors *Lutzomyia olmeca* and *Lutzomyia cruciata* was performed [23].
