**4. Environmental variables**

#### **4.1. World variables**

It is a well-established fact that the maintenance of LV is related to the environmental variables favoring the presence of both the vectors and the vertebrate hosts at the same site [24], and it can occur also for LC.

It is known that the geographical distribution of leishmaniasis follows the distribution of sand fly niches, this fact is observed worldwide and in the regional analyses. However, the distri‐ bution of the sand flies is dependent on the environmental variables such as the temperature, the vegetation, and the humidity.

Indeed, the geographical variables are directly associated with the environmental variables in the biosphere and are inter-dependent. The geographical distribution of leishmaniasis generally occurs in the tropical and the equatorial regions, where warm and rainy weather prevails [10, 35, 36] favoring Phlebotomine reproduction [37, 38].

In fact, the analysis of the planet temperature map compared to the maps of reported cases of leishmaniasis (figures 4 and 5) demonstrates that these regions are parallel (figure 7).

In general, leishmaniasis is primarily present in the tropics, however, its incidence is increasing in other areas as well, and most likely this increase is associated with the global climate changes [25].

Geographical and Environmental Variables of Leishmaniasis Transmission http://dx.doi.org/10.5772/57546 117

**Figure 6.** World temperature map where darker colors indicate higher temperatures

the points where the eradication effort should be focused. Such approach would include the elimination of Phlebotomine along with the complete removal and killing of the natural reservoir hosts of *Leishmania* from the population. We shall not address these specific problems in this chapter, however, georeferencing studies using adequate maps such as Kernel maps (figure 5), utilizing the new technologies for geographical representation along with spatial analysis of databases [32] appear to be the principle strategies to combat leishmaniasis.

Leishmaniasis is a complex multi-systemic disease [33], and therefore, it requires multidisci‐ plinary team effort of public health agencies working together with the health professionals

Specifically as regards to the topic of this chapter, the monitoring of the reported cases from the data is an important tool on the geographical variables to control leishmaniasis since it may spread by the internal migration of the people to endemic areas and increasing its incidence

The analysis of the geographical region is the first step to monitor leishmaniasis, however, majority of causes for endemic outbreak are associated with the natural environment as well as man-made factors such as the human migration, the deforestation, the urbanization and the

It is a well-established fact that the maintenance of LV is related to the environmental variables favoring the presence of both the vectors and the vertebrate hosts at the same site [24], and it

It is known that the geographical distribution of leishmaniasis follows the distribution of sand fly niches, this fact is observed worldwide and in the regional analyses. However, the distri‐ bution of the sand flies is dependent on the environmental variables such as the temperature,

Indeed, the geographical variables are directly associated with the environmental variables in the biosphere and are inter-dependent. The geographical distribution of leishmaniasis generally occurs in the tropical and the equatorial regions, where warm and rainy weather

In fact, the analysis of the planet temperature map compared to the maps of reported cases of

In general, leishmaniasis is primarily present in the tropics, however, its incidence is increasing in other areas as well, and most likely this increase is associated with the global

leishmaniasis (figures 4 and 5) demonstrates that these regions are parallel (figure 7).

prevails [10, 35, 36] favoring Phlebotomine reproduction [37, 38].

due to elevated person-to-person transmission in the crowded living conditions [32].

and the scientists to generate the most positive results towards its eradication.

malnutrition [34].

**4.1. World variables**

can occur also for LC.

climate changes [25].

**4. Environmental variables**

116 Leishmaniasis - Trends in Epidemiology, Diagnosis and Treatment

the vegetation, and the humidity.

The world climate changes are implicated with physical consequences [21] as well as with the alterations of the vector niches and the reservoir species for the infectious diseases [21, 25].

According to Gonzalez *et al* [25], leishmaniasis is expanding to northern United States from Mexico and Texas, where it is considered autochthonous, primarily due to the increase in the niches of the sandflies associated with the reservoir hosts to *Leishmania*; however, other associated reasons could be dog importation [30] and the increase in human migration and/or travel in the recent years.

The movement of people occurs from countries where leishmaniasis is endemic to countries where climate is temperate. The people move from the temperate areas to the tropical and the equatorial climates, particularly for the holidays, sometimes they carry their dogs and other pets [30].

Climate is not the only factor associated with the vector niches, the vegetation also has some impact. In fact, in some regions, the climate indicates the existence of certain kind of vegetation, i.e., it is usual to think of the tropical forest in the tropical climate and the equatorial forest in the equatorial climate, however, it is possible to find desert, savanna, Cerrado (Brazilian savanna) and Atlantic forest in the same regions where the tropical and the equatorial climates prevail.

Phlebotomine prefers the forest areas, but, interestingly, it can also be found in open and urban areas [35].

In summary, the world environmental variables linked to Phlebotomine niche exist mainly in Latina America and some parts of Africa and Asia. The hot and the wet climates are associated with the forest and the woodlands areas; however, some species prefer open and the dry areas. In all these regions, it is possible to find some kind of host to *Leishmania*, nevertheless, the density of sand flies in some areas depends on the regional environmental variables.

#### **4.2. Regional variables**

In terms of the geographical and the regional variables, the main factor for the scattering leishmaniasis is the presence of Phlebotomine in the specific areas. In fact, since sandflies breed in soil or litter, they are dependent on the availability of water and the dampness. In addition, their small size enables them to live in various different microhabitats [36], however, an indepth analysis detailing the breeding sites of sand flies and their larval development remains scarce [15].

Nevertheless, the peri-urban areas are important risk factors for leishmaniasis transmission since they maintain the niches for Phlebotomine and natural reservoir hosts. Indeed, some studies have demonstrated the increase of known natural reservoir hosts including *Galus domesticus* [39] and the pigs [40] in such areas.

In relation to the local environment, the urban periphery is frequently inhabited by poor populations, they are forced to live far from downtown and these habitats grow as the people arrive there from the rural areas. This is a common case in the poor and developing countries. Such lesser-developed areas are comprised of the forests or the woodlands and become a favorable place to increase contact of sandflies with the people as well as domestic and wild reservoir hosts of leishmaniasis.

At the same time, this population has limited access to basic sanitation and sewage treatment, and therefore, it generates exclusionary urbanization [41].

In fact, the deforestation linked to unplanned urbanization seems to be the cause of peak incidence of leishmaniasis in some regions [32]. Urbanization parameters associated with the growing cities and the deforestation areas generate ecological changes [41] that could modify the forest flora; this in turn generates trunks of dead trees thereby increasing the amount of decomposed organic material as well as the microorganisms on the ground that positively affect Phlebotomine cycle [38, 42-45].

These findings justify that in the peri-urban areas there is increase in number of the infected people carrying leishmaniasis and other infectious diseases that are dependent on the vector transmission, the people in those areas get higher exposure to vectors and reservoir hosts.

The reservoir hosts to *Leishmania* are the rodents, the marsupials, the monkeys, wild canines [30], the domestic dogs, chickens, the cattle, the equine, the caprine, the bovine, the swine and the feline species [11-14, 30], they all inhabit the areas populated with the sand flies.

Indeed, the presence of the swine species in the peridomicile is an important risk of the contamination [40], and the contamination has also been found associated with the presence of chickens as wild predators that are potential wild reservoirs hosts of *Leishmania* and *feed* on them, thereby intensifying the parasite cycle to the human and the canine populations [39].

The life cycle of Leishmania is mainly associated with the ecological factors in the rural or the peridomicile areas that harbor the sand fly niches and the reservoir hosts with human habitation (figure 7).

**Figure 7.** Scheme showing the life cycle of sandflies, reservoir hosts and humans, based on [46].

The human knowledge about leishmaniasis is not complete; many factors are still unknown or only partially known. Nevertheless, the current knowledge on this disease is adequate to develop accurate eradication strategies for the government and the public to work together developing specific protections with control of Phlebotomine by using insecticides, by removing organic material in the peridomicile areas [47, 48] and exterminating the contami‐ nated reservoir hosts.
