**1. Introduction**

Leishmaniases are a group of diseases caused by at least 20 species of parasites of the genus *Leishmania* that are transmitted to humans and other mammals by the bite of *Lutzomyia* species (in America) and *Phlebotomus* species (in the Old World). Reservoirs of these parasites include domestic and wild animals and, sometimes, humans; therefore, Leishmaniasis transmission

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

may be zoonotic (from animals to humans) or anthroponotic (from one human to another). In humans, *Leishmania* infections cause a spectrum of illness that depends on the parasite species involved, inoculum size, and host immune response [1, 2], affecting skin, mucous tissues, or organs of the mononuclear phagocyte system and producing clinical symptoms of cutaneous leishmaniasis (CL), mucosal leishmaniasis (ML), and visceral leishmaniasis (VL), respectively.

*Leishmania* spp. infections are acquired when an infected vector bites a mammal to consume its blood. In turn, the vector is infected when it feeds upon the blood of an infected reservoir species and ingests the transmitting parasites (as amastigotes). Transmission cycles of leishmaniasis have been found to have a focal distribution in specific geographic areas. These sites are called the natural foci of infection. The foci of infection are the places where the key elements necessary for transmission are present: vectors and reservoirs. The limits of infection foci are generally determined by the spatial distribution and relative density of the vector species. Hence, conducting entomological surveys and determining the behavior of vectors are important to clarify the epidemiological risk of infection. In turn, the presence of these elements, and especially of vectors, is conditioned by abiotic ecological factors such as climate, humidity, altitude, temperature, and vegetation [3, 4].

The study of the foci of Leishmaniasis transmission is complex due to the following factors: (1) the diversity of phlebotomine species; (2) the variety of *Leishmania* species; (3) the incrimination of a phlebotomine species requires that the vector meet certain criteria, including exhibiting anthropophilic behavior, being infected with the same species of *Leishmania* isolated from humans infected during the outbreak, and demonstrating geographical distribution consistent with the distribution of reported human cases; (4) the variety of methods required to incriminate potential mammalian reservoirs in an area, which involve capturing and analyzing many samples, isolating and identifying the species of *Leishmania* and determining the parasite prevalence and transmissibility; and (5) the challenge of diagnosing human cases with the clinical form of leishmaniasis, *Leishmania* species causing the disease, and locations in dwellings where transmission occurred [5, 6].

On the other hand, to facilitate the design and implementation of specific control measures, recognition of the transmission mode within a focus and determination of the eco-epidemiological risk of infection are required. Factors that must be determined include the following: (1) the geographical area associated with greatest risk of transmission, or "macrofocus"; (2) the population group at increased risk of becoming infected and developing the disease; (3) the time of year during which increased activity of phlebotomine species in the intradomicile environment occurs (nictemeral behavior); and (4) the place within the dwelling where contact between vectors and the population group at highest risk of infection, or "microfoci," are located [2]. Therefore, understanding the transmission of *Leishmania* infection, identifying the foci of transmission, and designing strategies and control measures requires a combination of different disciplines such as the health sciences, epidemiology, social sciences, entomology, cellular and molecular biology, and ecology, giving rise to eco-epidemiology. In addition to the inclusion of transmission (i.e., the vector), parasite, and reservoir dynamics as objects of eco-epidemiological study, this methodology also includes the study of associated ecological factors and human behaviors that affect the transmission of the disease.

As such, application of the eco-epidemiological methodology allows for determination of the following parameters: (1) identification of the species of *Leishmania* and phlebotomine in a given region, both overall and specifically those that serve as vectors, and determination of the role of domestic or wild reservoirs; (2) definition of the macrofocus (i.e., the geographical areas where the vector is present), its limits, and the environmental characteristics that allow the vector to develop, including ecological markers such as temperature, vegetation type, soil, altitude, and other aspects that characterize the macrofocus; (3) identification of both times during which there is a greater risk of infection (i.e., the times of night during which increased vector insect activity occurs) and locations in which vectors have a higher rate of natural infection with *Leishmania* and more contact with a population at risk using vector bionomics and behavior; (4) definition of the microfocus, which, as previously stated, is the location in a dwelling where contact between the human population and the infected vector occurs, that is, if this location is inside the home (intradomicile), around homes (peridomicile) or outside the home (extradomicile); (5) accurate determination of the population group most affected by the disease or at increased risk of infection, for example, if this population comprises men, children, or people who perform some activity (such as loggers, workers in mines, or some special type of farming or hunting) or if entire families are affected by the disease; and (6) identification of medical systems used by the community, i.e., how the population conceives the disease and its cause, from whom they seek treatment, and how the disease is treated. The identification of these parameters allows for the generation of elaborate risk maps and design of rational, economical, and effective prevention and control measures [7].
