VL is a pathology considered endemic in the American continent. 97% of the cases reported in 2020 happened in Brazil, and the other cases were reported in Argentina, Bolivia, Colombia, Paraguay, Venezuela, and Uruguay [9]. In Brazil, the region with the highest VL incidence is the Northeast, with about 61% (1767) of incidence in comparison with another region in Brazil as shown in figure1.
In 2016 the incidence in the Northeast was 53% (1490) and 49% (1824) in 2017, in the following years, 2018 and 2019 incidence were 57% (1735;1241 respectively), also year 2020 the incidence was 59% (959) of cases in Northeast. The highest incidence per 100.000 inhabitants was in 2017 which there was in the northeast 3.2/with 1000.000 inhabitants, the North region 4.3/100.000 inhabitants, the Midwest region reported 1.1 cases per hundred thousand, the Southeast 1/100.000 inhabitants, and the South region with 0.1 /100.000 inhabitants.
There was a fall in cases notified in 2020. Cases per hundred thousand in the Northeast were 1.7, North reported 1.6 cases per hundred thousand, Midwest there were 0.5/100.000 inhabitants and Southeast 0.3/100.000 inhabitants. In the region south no cases were reported in 2020 [2]. The Northern and Northeastern regions presented the highest levels of income per 100.000 inhabitants, as the regions present an ascending and uncontrolled urban development accompanied by precarious housing and sanity conditions. These parts of the country, suffer from a lack of effective preventive measures. In addition, climate, and regional vegetation further the population growth of Lutzomyia, as well as more mosquitoes in these regions than in others, thus the most intense infection occurs in these regions. In some cases, the variations in the environment provide niches to the sandflies in a region with lower humidity, lower rainfall, and higher temperature as is the climate present in Brazilian North [14].
Figure 1 shows the case evolution of the LV notification according to the macro-region of Brazil. Brazilian Northeast is a leader in the notification, second is Sullenest followed by North and Midwest. South region has the lowest incidence. In 2017 and 2018 the Northeast shows that there was a high notification, and it has a drop in cases in 2020, which can be related to underreporting due to the overload in heath sectors caused by the Covid-19 pandemic. Lack of priority is common in neglected diseases and can be led to the reduction of epidemiological control measures and notifications, which poses a risk to public health, as the disease is spreading without the necessary care to control it [2].
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Data indicated in Figure 2 show the evolution of the VL incidence coefficient per 100.000 inhabitants in the state of Pernambuco located in the Brazilian Northeast, between the years 2015 and 2020. The VL incidence in Pernambuco in 2015 was 1.3 per 100.000 inhabitants higher than in 2016 when there was 0.8 per 100.000 inhabitants. In the year 2017, the incidence was 1 per 100.000 inhabitants. Also, in 2018 there were 1.2 per 100.000 inhabitants, while in 2019 were 1.1 per 100.000 inhabitants and in 2020 were 0.7 per 100.000 inhabitants [4].
Pernambuco has a notification index of 175, 118, 185, 200, 181, and 113 respectively for each year. In 2016 there was a reduction of 32% in cases in relation to 2015 and the three subsequent years. There was a significant increase, in the year of 2017 there was an increase of 56.8% concerning the year 2016, and in 2018 there was an increase of 8,1% in relation to the previous year. In 2019 there was a decrease of 9,5% in relation to the year 2018. And in 2020 there was the smallest number of cases, a decrease of 37.6%. [2].
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Figure 3 represents data on notifications of VL between 2015 and 2020 divided by Pernambuco macro-regions. It was observed that River São Francisco Valley and Araripe macro-region in 2015 had the highest rate compared to other regions. The same profile of LV case incidence in this region was observed in 2016 and 2017. River São Francisco Valley and Araripe macro-region is a region with outstanding agriculture and livestock, which is in the city of Petrolina, the largest fruit production center of the state. Thus, the environment propitiates a favorable ambient for mosquito reproduction and propagation, increasing the rate of infected dogs, humans, and other wild animals [19]. That may be the reason, the disease spreads quickly through the River São Francisco Valley and Araripe macro-region [2].
An increase of case notifications in the Metropolitan macro-region in 2018 may be observed in Figure 3, showing an advance of the disease in an urban area. In 2019 occurred an outbreak of the disease in the Metropolitan Region, which was reduced in 2020. One of the reasons why this region has elevated values is because of high population density, due to sanitation problems, and the history of regular floods also other problems [2]. As it is shown in the study made by Buarque et al. (2021) the VL there are more cases in the Agreste macro-region and River São Francisco Valley and Araripe macro-region, but it was observed that because of growing urbanization in the Metropolitan macro-region the VL is increasing [17].
Agreste macro-Region presented the lowest rate of VL-infected people between 2015 to 2016, showing an increase in the following two years and a reduction in 2019 and 2020, as can see in figure 3. The Sertão macro-region presented a similar profile of LV confirmed cases as compared with Agreste macro-Region.
The cases of the LV for the Sertão macro-region showed a relatively controlled oscillation because this region is marked by drought, sparse vegetation, and an area where livestock predominates. The Sertão macro-region does not present a favorable environment for mosquitoes to infect a greater number of the host than other regions of the state because of the dry weather, high thermal amplitude, and little vegetation which reduces the moist places propitious to mosquitos breeding [2][18].
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From 2017 to 2019 there was a reduction in cases in the River São Francisco Valley and Araripe Macro Region and an increase in the Metropolitan Macro Region, proving that the immigration of the population from rural to urban endemic areas favors the expansion of the disease throughout the state.
The mortality average of VL in the state of Pernambuco between 2015 and 2020 was 8.1%. The co-infection of the LV with HIV revealed an increase during the years (Figure 4). 2020 showed the highest percentage of incidence of co-infection, about 11.5 % of patients with Leishmaniasis and HIV at the same time [2]. As shown in Figure 4, the mortality of co-infected patients has been rising since 2017, a worrying fact and there must be greater control to avoid co-infected patients, and by that the mortality can be reduced [3]. An interaction occurs between HIV and leishmania in the host cellular that aggravates the clinical development and increases the lethality rate three times higher than an infection only with VL [16] The coinfection worsens the patient’s clinical condition, and it is a serious health challenge to public health [14].
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To obtain an LV epidemiological profile, table 1 summarizes the distribution of the variables investigated according to the case notification per year. Regarding sex, it was observed higher prevalence of men LV infected. The data reveals an average of 67.2% of male incidence between the years 2015 to 2020. The susceptibility of males has been observed in other studies and it is supposed that higher levels of testosterone are associated with the increase of VL in males [14]. But as it is demonstrated by Buarque et al. (2021) the cause of prevalence in males is unknown and the prevalence could be related to greater traffic of males in the region where the vector is. Another factor is that males do not take care of health and hygiene and do not go to doctor’s appointments frequently [17].
As can be shown in Table 1, according to age, it was observed high LV incidence cases in children under 10 years old and adults with age between 20 and 59. The higher incidence in children can be explained by the factor that they have more contact with dogs, which increases the probability of an infected dog passing the disease to a child and their immune system is not mature which favors a lot of neglected diseases [17]. As shown in the study by Lima et al. (2018) in children, VL has been associated with malnutrition and poverty and as a method of intervention it is for supplementation of micronutrients then these measures will lead to a healthier childhood, and this could lead to protection against opportunistic pathogens [14], improve the immunity system also can be used in adulthood against various opportunists’ pathologies.
Regarding the LV method of diagnostic laboratory, the method is the first choice to confirm the infection. The clinical analysis is especially important in an endemic region once the correct diagnostic provides more chance of cure if they follow the suitable treatment. The index of patients that abandoned the treatments is extremely low, there were two patients in 2016 and one in 2020. The percentage of patients that dies due to VL is about 12,5% on average between the years 2015 to 2020.
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Figure 5 shows the percentage of incidence of VL in the schooling profile of VL-infected patients in the state of Pernambuco between 2015 and 2020. According to information from DATASUS, every year there is a higher omission about schooling an average of 40.3% of the total reported cases. In all years, it was observed an increase in the number of the case of patients with early childhood education, followed by elementary, high school, illiterate, and bachelor education. Because of the lack of information, this proportion may not report the reality concerning the education of sick people. This profile can be explained by the fact VL mainly affects people with little education, where an illiterate is eight times more likely to be infected by VL. It is worth mentioning that there is a high incidence in children under 5 years old who are not yet literate. Due to the incidence of omission, the present study is not conclusive to evaluate the real profile of the diseased [15].
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Currently, in Brazil is adopted the strategy of the National Visceral Leishmaniasis Surveillance and Control Program (PNVCLV) that citing euthanasia as a measure to control the pathology in canine reservoirs, as the main standard to prevent the transmission of the disease to a human. Despite being used, this measure must follow the current law and it presents many challenges such as lack of resources and infrastructure, and ethical and emotional issues, which raises the question of how effective this practice is. Alternative methods are sought to avoid canine infection such as vaccination and the use of collars with deltamethrin. These measures should be studied and implemented, mainly in regions with a high incidence as prophylactic measures to prevent the spread of the disease and consequently, control the disease [7]. The spread of the disease is caused by the changes in the agrarian structure of Brazil, mosquito adaptation, malnutrition, and lack of basic sanitation are considered factors that favor urbanization and geographic expansion of VL. In Pernambuco, this factor is quite remarkable due to the socioeconomic situation of the state [15].
The COVID-19 pandemic affected surveillance and control actions across Brazil in actions such as field searches to identify mosquito outbreaks and early diagnosis in dogs and humans, and detailed analysis of endemic cities, among other actions. Until 2019 the disease was endemic with a higher incidence even if there is a strategy to control neglected diseases, the state does not have a significant reduction in cases, which proves that it must increase the vector control measures, identification, and treatment of patients and preventive measures. After the COVID-19 pandemic, the number fell, which can be related to underreporting. Therefore, plans must be made to contain the disease, especially in endemic regions, with treatment for humans, the use of collars in dogs, and vaccines as a preventive method [3].