**2.1. Incidence and prevalence**

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 affecting men working in the field [7].

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 (smear, isolation-culture and/or biopsy) and MST-positive response were recorded during 1987. In summary, an annual incidence rate of 0.5 per 1000 inhabitants was reported [9].

Asymptomatic infection is the term used to refer to those individuals living in endemic areas of LCL, exposed to sand fly bites, presenting a MST-positive response but without signs and symptoms of the disease. Based on the criteria given above, a study to determine the prevalence of asymptomatic infection was performed in four rural communities from Campeche. From January to December 1999, a total of 22/116 (18.9%) men of 15–45 years of age and working in the field showed a MST-positive response in the absence of signs and symptoms [10]. Asymptomatic infection by *Leishmania* is the most common outcome after parasite inoculation. It must be highlighted that studies of the biological, immunological and epidemiological significances of the asymptomatic infection have been neglected in Latin America. Therefore, this important challenge should be addressed.

In the state of Yucatan, cases of LCL were restricted to villages located in the South, near to the characterized endemic areas from Campeche and Quintana Roo. Recently, a new outbreak of LCL was reported in the municipality of Tinum, Yucatán. This village is located in the West of the state and no cases had been reported before. In 2015, 17 new cases were recorded by the health services of the Yucatan State in comparison with the only case reported in 2014. From those cases, 11 were from Tinum. This increased incidence is alarming and suggests possible changes in the epidemiological patterns of leishmaniasis in the Yucatan Peninsula that need to be studied [11].
