The finding of this study goes in the same direction as the theoretical study of Costa et al. . These authors suggested, using mathematical models, possible impact on canine VL seroprevalence after the long-term continuous program, targeting both asymptomatic and symptomatic dogs, for lower and moderate transmission of HVL rate scenarios. However, it is worth mentioning that this study did not evaluated the impacts on LVH. In our study, areas are classified as having intense transmission, the intervention coverage was low and, even that, the finding suggested a decreasing effect on the occurrence of the disease in humans, after two years of canine serological coverage, jointly with the culling of asymptomatic and symptomatic positives dogs.
It is worth noting that, in the descriptive part of this study, the result was pointed out that Araçatuba has a peak in the incidence of LVH in 2007, followed by a valley in 2010. After this period, the incidence presented a stabilization. In Birigui, there were two peaks, one in 2006 (about 21 cases / 100 thousand inhabitants-year) and the other in 2011(about 16 cases / 100 thousand inhabitants-year), followed also by stabilization. According to data from the Notifiable Diseases Information System  this stabilization continues until 2019. Thus, the incidence of human VL remains below 8 cases / 100 thousand inhabitants per year for at least ten years in Araçatuba and, at least, six years in Birigui.
In Araçatuba and Birigui, due to its territorial characteristics and the intensity of HVL transmission, the visceral leishmaniasis control program (VLCP) recommends that census surveys be carried out to identify naturally infected dogs . It was, therefore, expected that the coverage of the canine serological survey would be 100%. However, it remained below 10% throughout the entire study period. The canine serological surveys only covered some of the sectors of these two municipalities, which was the reason these activities were not carried out as had been expected. This situation occurs in other municipalities elsewhere in the country and can be explained by public resistance to the VLCP, by structural difficulties from municipal administration  or by underfunding and lack of political support for the VLCP .
Results indicate that even in more populous municipalities, control measures targeting the canine reservoir in high priority areas may be effective at reducing human incidence. The effectiveness of the canine serological survey in reducing the risk for HVL, observed in this study (less than 40%), suggests that increasing the coverage of the serological survey, to the percentage recommended by the VLCP and may result in an even greater risk reduction. However, it is noteworthy that, as pointed out by other authors, given the operational challenges for the complete implementation of the control activities recommended in the VLCP, there are doubts about the feasibility of the suggested coverage levels[8, 29-31].
The coverage of positives dog culling, which is dependent on the canine serological survey, was high where the latter activity was performed. It is already known that when the infected dogs are eliminated the source of infection for the vector in that locality is reduced [32, 33]. Moreover, some studies suggest that canine culling has a lower cost compared to vector control [34, 35].
Some authors have found results similar to those of this study regarding the effectiveness of canine control. Costa et al. 
demonstrated that canine culling reduced the incidence of HVL by 80% when compared to areas that only received Insecticide spraying in Teresina, PI, Brazil. Nunes et al. , moreover,
revealed, in a two-year lag analysis, that the reduction in the incidence of HVL was statistically correlated with the increase in canine culling. Werneck et al.  showed that, as compared to insecticide spraying, only canine culling was effective in reducing the incidence of HVL, presenting an inverse relationship between these measures. Although those authors considered the positivity of the result to be biased due to the selective loss during follow-up, our results reinforce their findings.
Nevertheless, there is no consensus in the literature about the effectiveness of canine reservoir elimination. Dietze et al.  showed that canine culling did not result in a significant decrease in human incidence, pointing to the possibility of humans being reservoirs. Ashford et al., although they suggested that eliminating the majority of the positive dogs could reduce the human incidence, concluded that the attempt to remove them was insufficient to guarantee the elimination of the disease. Thus, they suggested that other reservoirs could be acting in the transmission, while also questioning the serological tests for the identification of the seropositive dogs. In addition, some authors point to problems related to canine cullings such as the lack of precision of the serological tests, the long delay between the identification and the canine culling, the refusal of the owners to cooperate and the replacement of the dogs that were culled[31, 38, 41, 42].
In addition to the technical issues, the most controversial aspect of canine reservoir elimination has been the ethical question considering the emotional involvement of both the owners and the subjects involved in the culling procedure [33-46]. However, it is noteworthy that HVL is a disease with high lethality if untreated, and it is in the process of geographical expansion [3, 47]. Thus, to stop canine reservoir control measures, it is first necessary that there is an efffective alternativepublic health programs.
Among these alternatives are the canine treatment, canine vaccination and the use of the insecticide-impregnated collar, available so far through the initiative of the owners. To date, there is canine treatment that was legally approved by the Ministries of Agriculture and Health in 2016, highlighting the fact that parasitological cure has not yet been proven. This treatment, in addition to being costly, requires the use of the insecticide-impregnated collar and repellent against the vector, as well as a follow-up of the canine patient by a veterinarian every 4 months, which makes it difficult to apply to the population in general [48, 49]. However, there are published recommendations of preserving the right to choose between responsible treatment and euthanasia for owners of infected dogs.
Dog vaccination, whose efficacy ranges from 58.1% to 80.8%, has been considered a good alternative , however, there is a lack of randomized studies that might demonstrate its efficacy for general use as a measure of VL prevention[42, 52]. In addition to the cost, one of the difficulties for large-scale dog vaccination is the need for three initial doses, with annual boosters, a strategy that is impractical for public health programs.
The use of insecticide-impregnated collars has been recommended as the most effective measure among those cited above [43, 53-55]. Silva et al.  demonstrated a reduction of 15% (p = 0.004) in Montes Claros, MG, Brazil, and 60% (p <0.001) in Fortaleza, CE, Brazil, in the vector population of captured. Kazimoto et al.  observed that there was a 53-59% reduction in the VL incidence in dogs resulting from the use of these collars. However, this measure requires continuous use in a large percentage of the canine population. Also, the collars must be changed every six months and replaced when lost. As a result, the authors warn of their high cost when used on a large scale[56, 58, 59].
One of the limitations of our study was the fact that insecticide spraying had zero or very low coverage in the municipalities studied, making it impossible to evaluate its effectiveness in reducing HVL incidence . This low coverage is indicative of the operational difficulties faced in the implementation, including the residents' refusal to apply insecticide in their homes, deficiencies in the quality control of the handling of the insecticide, a brief residual effect of the insecticide spraying and a lack of human and financial resources[7, 36, 60]. Another limitation is the fact that both dogs and humans move and there is no way to be sure that transmission of Leishmania occurred in the SUCEN sector where cases were assigned.
Another issue that must be considered is the lack of accuracy of available serological tests, especially for asymptomatic dogs. Grimaldi et al.  highlight the TRdPP®-Bio-Manguinhos presents high sensitivity (98%) for diagnosed dogs with symptoms, but low sensitivity to identify dogs without signs and symptoms (47%). Moreover, these authors discuss that the ELISA test, despite having reliable sensitivity (ranging from 93% to 100%) for symptomatic dogs, also presents less sensitivity for dogs without symptoms. It is noteworthy that, even using tests with low sensitivity for asymptomatic dogs, our results suggested an inverse relationship between HVL incidence and canine survey.
Moreover, we were unable to consider controlling the model for HIV/AIDS incidence during the study period. HIV/ AIDS coinfection is known associated with higher risk of VL human symptomatic infection and has important epidemiological and clinical implications. In endemic areas, it is common for cases of VL to be asymptomatic. However, HIV coinfection increases the risk of developing symptomatic VL by between 100 and 2320 times . Since it was not possible to adjust our models for the incidence of HIV / AIDS, it is not possible to state what effect this variable would have on the relationship between the incidence of HVL and the canine serological survey coverage, an issue that needs to be investigated in new studies.
Another limitation is the use of secondary data. Nevertheless, these data were indispensable and appropriate for the development of the study. It is worth noting that it is the health teams which make the decisions about the planning of the surveillance actions and control of VL in their respective municipalities based on this information. This information is essential for all involved in VL control efforts.
Strengths of the study include the consideration of the spatial and temporal dependence of the phenomenon studied and, consequently, more accurate estimates were obtained than in studies that did not take these dimensions into account. The proximity of Araçatuba to Birigui is also worth mentioning as it made it possible to evaluate the relationship between HVL and control measures more comprehensively and with greater study power, given the greater number of units of analysis.