**4. Discussion**

American visceral leishmaniasis is a disease that has been showing significant geographic expansion in Brazil. Decades ago, it was mainly present in the states of the Northeast and North regions. Currently, it has gained importance spreading into the Southeast and Midwest regions, and recently in the South region [3, 39].

*Lutzomyia (L.) longipalpis* is present in most of the states of Brazil, except in Santa Catarina, Acre, and Amazonas, demonstrating the high adaptability to different types of vegetation, climate, habitats, and feeding sources [3, 9, 11, 40]. The state of Tocantins lacks entomological studies with records of *L. (L.) longipalpis* in 16% of its municipalities [29–37], while there are reported humans cases in 89% of the municipalities [24]. These facts show the need for further entomological studies, given the wide distribution of the disease in the state. The assumption of the presence of *L. (L.) longipalpis* in municipalities with AVL records does introduce some minor uncertainty in the analyses. The vector could be absent from an AVL focus if another sand fly species acts locally as a competent vector. So far, the only species that gathers enough evidence in the literature that plays an important role in the transmission of *L. (L.) infantum chagasi* is *L. cruzi* [13–15], and its distribution is restricted to Mid-West Brazil, in municipalities as far as 600 km from Tocantins State. Its presence in Tocantins is unlikely, then. The presence of *L. (L.) longipalpis* was assumed only in municipalities where the information was missing, so given the wide distribution of *L. longipalpis* in Brazil [12] and, more specifically, in Tocantins State [29–37], the chances of its capture in a new sand fly survey are high.

It is noteworthy that the 13 municipalities that have no record of human cases can be classified as vulnerable areas to AVL, because they border other municipalities that have records of human cases. Such municipalities deserve special attention, because according to the guidelines of the Manual of Surveillance and Control of AVL, conducting entomological survey is recommended in order to verify the presence or absence of the vector, and to check its spread in the city, in order to classify the vulnerable municipality as receptive (with the presence of vector) or unreceptive [3].

The application of remote sensing products and techniques in epidemiological studies began in the 1970s [41], and in conjunction with the use of GIS, it has facilitated the integration of environmental parameters and health data to develop models that can be used for understanding the AVL epidemiology [42]. The analysis of the stratification of the municipalities showed that Araguaína, Paraíso do Tocantins, Porto Nacional, and Palmas retained the intense transmission through the years, while 50% of the municipalities had expansion of the transmission of AVL, demonstrating its importance as a public health issue in the state.

The municipalities that had higher increase of deforestation were Aragominas, Araguatins, Lagoa da Confusão, Araguaína, Ceará, Xambioá, Santa Fé do Araguaia, Pequizeiro, and Piraquê. Araguaína was the municipality that showed the most deforested area in

As it was with the incidence of AVL and land use, deforested areas were positively correlated

Deforested areas and stratification of AVL were positively correlated in the last years, from

American visceral leishmaniasis is a disease that has been showing significant geographic expansion in Brazil. Decades ago, it was mainly present in the states of the Northeast and North regions. Currently, it has gained importance spreading into the Southeast and Midwest

*Lutzomyia (L.) longipalpis* is present in most of the states of Brazil, except in Santa Catarina, Acre, and Amazonas, demonstrating the high adaptability to different types of vegetation, climate, habitats, and feeding sources [3, 9, 11, 40]. The state of Tocantins lacks entomological studies with records of *L. (L.) longipalpis* in 16% of its municipalities [29–37], while there are reported humans cases in 89% of the municipalities [24]. These facts show the need for further entomological studies, given the wide distribution of the disease in the state. The assumption of the presence of *L. (L.) longipalpis* in municipalities with AVL records does introduce some minor uncertainty in the analyses. The vector could be absent from an AVL focus if another sand fly species acts locally as a competent vector. So far, the only species that gathers enough evidence in the literature that plays an important role in the transmission of *L. (L.) infantum chagasi* is *L. cruzi* [13–15], and its distribution is restricted to Mid-West Brazil, in municipalities as far as 600 km from Tocantins State. Its presence in Tocantins is unlikely, then. The presence of *L. (L.) longipalpis* was assumed only in municipalities where the information was missing, so given the wide distribution of *L. longipalpis* in Brazil [12] and, more specifically, in Tocantins State [29–37], the chances of its capture in a new sand fly survey are high.

It is noteworthy that the 13 municipalities that have no record of human cases can be classified as vulnerable areas to AVL, because they border other municipalities that have records of human cases. Such municipalities deserve special attention, because according to the guidelines of the Manual of Surveillance and Control of AVL, conducting entomological survey is recommended in order to verify the presence or absence of the vector, and to check its spread in the city, in order to classify the vulnerable municipality as receptive (with the presence of

The application of remote sensing products and techniques in epidemiological studies began in the 1970s [41], and in conjunction with the use of GIS, it has facilitated the integration of environmental parameters and health data to develop models that can be used

with human cases of AVL from 2007 to 2014 (**Table 2**).

regions, and recently in the South region [3, 39].

the state.

2009 to 2014 (**Table 3**).

104 The Epidemiology and Ecology of Leishmaniasis

vector) or unreceptive [3].

**4. Discussion**

Some studies used GIS as an important analysis tool of the distribution of leishmaniasis vectors. In Belo Horizonte, an area that has one of the highest rates of human and canine AVL of Brazil, it was possible to correlate peridomestic environmental features and the vectors. *Lutzomyia (L.) longipalpis* showed higher abundance in areas of animal sheds with poor hygiene conditions, which favor the development of sand flies. In contrast, the proximity of areas with vegetation exerted little influence on the incidence of AVL, corroborating its urban profile [43].

In studies in Maranhão State, *L. (L.) longipalpis* was the most abundant sand fly species found in the Cerrado biome; in Bahia State, specimens were captured in areas of Caatinga and Atlantic Forest, demonstrating its adaptation to different environments [44–46].

Considering the assumption of *L. (L.) longipalpis* being present in municipalities where there are autochthonous records of human cases of AVL in Tocantins, the vector occurs in all classes of land use, being adapted to all environments including disturbed areas, corroborating studies that discuss its adaptation to changing environments [9, 34, 40, 47, 48]. A positive correlation was observed between the presence of *L. (L.) longipalpis* and areas of secondary vegetation [49] and ombrophilous forest in Tocantins, indicating that the vector is adapted to different environments, especially in areas recovering from human interventions or from natural causes.

In the analysis of the cumulative incidence of AVL and classes of land use, there was a negative correlation with agricultural areas, which can be explained by the increasing use of chemicals in plantations that reduce the number of insects [50–53], including sand flies [54, 55], and consequently reduce the number of human cases.

In the state of Mato Grosso, *L. (L.) longipalpis* occurs in the Cerrado biome, in forests and transition zones, which were suggested by some authors as potential breeding sites for this sand fly [56]. *Lutzomyia (L.) longipalpis* is also present in areas of different climatic conditions, such as semiarid areas (in the Caatinga biome), and wetter areas, with high adaptability to different habitats and environmental conditions [57–59]. Considering that the state of Tocantins covers two distinct biomes, Cerrado and Amazon, the occurrence of *L. (L.) longipalpis* in both biomes confirms its generalist behavior, being associated with diverse habitats [14].

Environmental changes, such as deforestation, impact the distribution of tropical diseases [60–63], potentially affecting the spatial distribution of the vectors of leishmaniasis [64]. The state of Tocantins presented constant increase of deforestation, especially in northern and western regions, areas with occurrence of human cases of AVL. In this scenario, Araguaína (municipality with the highest deforested area from 2001 to 2014) has become a priority for the Ministry of Health, for surveillance and control of AVL. In recent years, Araguaína has been producing high records of AVL. From 2007 to 2014, it was the second Brazilian municipality with the highest production of AVL, while in the years 2007 and 2008 it had the highest number of human cases in Brazil [24].

It is known that AVL transmission remains active in areas with environmental changes, such as deforestation [65]. Thus, it is argued that continuous deforestation processes increase the number of people exposed to infection, creating conditions for the emergence of epidemic outbreaks [10, 16, 48], because it alters the natural conditions and habitats of some species of mammals, hosts of *leishmania*, that become closer to areas inhabited by the human population. This fact enables sand fly vectors with feeding plasticity, such as *L. (L.) longipalpis*, to transmit the parasite to humans [9, 10, 66, 67].

Studies conducted in Mato Grosso do Sul (area that has experienced a loss of native vegetation), demonstrated the presence of *L. (L.) longipalpis* in regions with little vegetation and low humidity, suggesting that the species would be adapted to different environmental conditions, and that it has been associated with human dwellings (captured inside houses) [68]. This study showed positive correlation between deforested areas and human cases, as well as with the incidence of AVL, from 2007, showing that deforested areas have higher incidence rates for AVL, and that deforestation would maintain transmission.

In the state of Tocantins, *L. (L.) longipalpis* was present in all classes of land use, and its dispersion into new areas clearly demonstrates that it is a species adapted to impacted environments, such as large areas of deforestation. In recent years, 57 municipalities, equivalent to 47% of the total, were originally classified as municipalities without transmission of AVL, and they are currently classified as sporadic transmission. According to the Manual of Surveillance and Control of Visceral Leishmaniasis [3], in municipalities with sporadic transmission, the actions related to the vector are limited to the knowledge of the species and dispersion of the sand fly population, besides the canine survey. Such evidence suggests that the actions of surveillance and control, in Tocantins, are not planned in a satisfactory manner, i.e., without considering the loss of large areas of vegetation and as a result people live in risk areas, becoming exposed to the infection of AVL.

The current aims of the CPVL [3] highlight silent municipalities (those with no human or canine cases), suggesting that they must be incorporated into surveillance and control actions of AVL, in order to avoid or minimize the spread of the disease into new areas. For example, in Tocantins, the analysis of stratification in the state has shown that nearly half of the municipalities have gained transmission of AVL through the years. The results presented here show that in the last 12 years, the cities of Araguaína, Paraíso do Tocantins, Porto Nacional, and Palmas remained as intense transmission areas, which demonstrates the continued production of new human cases. The positive correlation between deforested areas and stratification since 2009 clearly shows the influence of growing deforestation on the disease in the state. These observations, coupled with the fact that there was an increase in transmission in 50% of municipalities, possibly due to changes in the environment, demonstrates the real need for an evaluation of the control and surveillance actions being carried out, and that in the future the AVL can surprise health managers with a high number of human cases.

with the highest production of AVL, while in the years 2007 and 2008 it had the highest num-

It is known that AVL transmission remains active in areas with environmental changes, such as deforestation [65]. Thus, it is argued that continuous deforestation processes increase the number of people exposed to infection, creating conditions for the emergence of epidemic outbreaks [10, 16, 48], because it alters the natural conditions and habitats of some species of mammals, hosts of *leishmania*, that become closer to areas inhabited by the human population. This fact enables sand fly vectors with feeding plasticity, such as *L. (L.) longipalpis*, to transmit

Studies conducted in Mato Grosso do Sul (area that has experienced a loss of native vegetation), demonstrated the presence of *L. (L.) longipalpis* in regions with little vegetation and low humidity, suggesting that the species would be adapted to different environmental conditions, and that it has been associated with human dwellings (captured inside houses) [68]. This study showed positive correlation between deforested areas and human cases, as well as with the incidence of AVL, from 2007, showing that deforested areas have higher incidence

In the state of Tocantins, *L. (L.) longipalpis* was present in all classes of land use, and its dispersion into new areas clearly demonstrates that it is a species adapted to impacted environments, such as large areas of deforestation. In recent years, 57 municipalities, equivalent to 47% of the total, were originally classified as municipalities without transmission of AVL, and they are currently classified as sporadic transmission. According to the Manual of Surveillance and Control of Visceral Leishmaniasis [3], in municipalities with sporadic transmission, the actions related to the vector are limited to the knowledge of the species and dispersion of the sand fly population, besides the canine survey. Such evidence suggests that the actions of surveillance and control, in Tocantins, are not planned in a satisfactory manner, i.e., without considering the loss of large areas of vegetation and as a result people live in risk

The current aims of the CPVL [3] highlight silent municipalities (those with no human or canine cases), suggesting that they must be incorporated into surveillance and control actions of AVL, in order to avoid or minimize the spread of the disease into new areas. For example, in Tocantins, the analysis of stratification in the state has shown that nearly half of the municipalities have gained transmission of AVL through the years. The results presented here show that in the last 12 years, the cities of Araguaína, Paraíso do Tocantins, Porto Nacional, and Palmas remained as intense transmission areas, which demonstrates the continued production of new human cases. The positive correlation between deforested areas and stratification since 2009 clearly shows the influence of growing deforestation on the disease in the state. These observations, coupled with the fact that there was an increase in transmission in 50% of municipalities, possibly due to changes in the environment, demonstrates the real need for an evaluation of the control and surveillance actions being carried

rates for AVL, and that deforestation would maintain transmission.

areas, becoming exposed to the infection of AVL.

ber of human cases in Brazil [24].

106 The Epidemiology and Ecology of Leishmaniasis

the parasite to humans [9, 10, 66, 67].

In a recent study conducted in the city of Porto Nacional (TO), *L. (L.) longipalpis* was more abundant in urban areas compared to rural areas, confirming its adaptation to these environments. In addition, its anthropophilic behavior and feeding plasticity might have contributed to the installation of the AVL transmission cycle in urban areas and to its maintenance in rural areas [34].

The correlation analysis of the incidence of AVL with the classes of land use showed distinct correlations over the years, demonstrating again that the vector of AVL, *L. (L.) longipalpis* is adapted to different types of vegetation. The positive correlation with urban areas shows that human cases are present in the urbanized environment, and that *L. (L.) longipalpis* was near the urban areas of the state of Tocantins municipalities, corroborating studies that indicate its adaptation to this modified environment [3, 9, 69, 70].

In the urban area of Campo Grande (MS), correlation was found between the abundance of *L. (L.) longipalpis*, percentage of vegetation cover, and the average vegetation index. However, there was no significant association between the diversity of habitats and abundance of the vector; the authors suggest that large trees can offer better microenvironmental conditions favoring the reproduction of the sand fly [71].

Urbanization changes the microclimate in cities and nearby locations, creating heat islands that result in warmer average temperatures when compared to less disturbed areas [72, 73]. Temperature changes might increase vectorial capacity and reshape epidemic curves that determine the receptivity of areas for the pathogen [73].

A study conducted in northeast Brazil showed no significant correlation of *L. (L.) longipalpis* with the average monthly temperature, relative humidity, or precipitation, demonstrating its adaptation to different climatic conditions [74]. In Barra do Garças (MT), a priority municipality to the Ministry of Health, it was found that *L. (L.) longipalpis* was the most abundant sand fly species with abundance peaks occurring during the rainy season, and correlation with relative humidity in urban areas [75].

The diversity of environments where AVL should be considered as determinant factors in the maintenance of the disease added to the biological, geographical, and social factors [12, 48]. This evidence is related with epidemiological data from last decades, which reveals the suburbanization and urbanization of the disease, with outbreaks in major cities and capitals [3].

Most of Tocantins State (88% of its area) is covered by the Cerrado biome, which had 49% of its forest cover cleared due to anthropogenic environmental interventions in the period 2002– 2011. The state of Tocantins lost 0.45% of the biome between 2010 and 2011. It is noteworthy that the Cerrado is the second Brazilian biome that suffered the most changes with human occupation, following the Atlantic Forest [49].
