Differences in the association of dengue and leptospirosis incidences with respect to socio-sanitary vulnerability in the city of Santa Fe, Argentina

Abstract

The results indicate that the higher the degree of vulnerability or social and health exclusion, the higher the incidence of leptospirosis, while the opposite is true for dengue cases. The results also suggest that there are two sectors with a higher incidence of dengue, one located in the central-western area of the city and the other in the southwest, both urban sectors with greater social inclusion and health accessibility. On the other hand, leptospirosis has its highest incidence in peripheral neighborhoods of the city located in the islands and the river coast, with high vulnerability indexes. Likewise, a conglomerate of cases was observed in areas near the former Belgrano railroad tracks, where some settlements with high social and sanitary vulnerability indexes are also located.In contrast to this work, Vanlerberghe (29), based on studies carried out in Cali, Colombia, suggests that dengue incidences are higher in more unprotected sectors of the population. Based on a worldwide meta-analysis, Muligan et al. (11) suggest that the relationship between social marginalization or lack of protection variables and the incidence of dengue is under discussion. In the city of Santa Fe, dengue epidemics have been associated with the occurrence of imported cases (5), and these are generally people who have traveled to countries where dengue is endemic. Therefore, it is more likely that dengue epidemics are initiated in sectors of Santa Fe society with a certain purchasing power that allows for travel outside the country. The results of this study indicate that in Santa Fe we found a lower incidence of dengue in sectors with high socio-sanitary vulnerability indicators, coinciding, in this sense, with the studies of Muligan et al (11).In relation to leptospirosis, the results coincide with those found by different researchers (6, 18, 30, 31) who describe this disease as more likely to happen amongst marginalized sectors of society. Three of the variables analyzed showed this pattern. We observed an increase in the incidence of leptospirosis as socioeconomic conditions deteriorated, which was also reflected in the spatial analysis of the determinants of the disease in Greater Santa Fe (18). Peri-urban and suburban sectors present the greatest environmental and socioeconomic susceptibility for the occurrence of leptospirosis (18).Finally, we also found that the incidence increased with higher proportions of households whose heads of household did not complete primary education. In a study carried out in neighborhoods of the city of Santa Fe and nearby localities, we observed an influence of the educational level achieved by people in their ability to adopt practices to prevent the disease (32). We also found a higher incidence of leptospirosis the higher the degree of health vulnerability, which could be related to the fact that cases of leptospirosis with detectable or severe symptomatology usually occur. Although leptospirosis has been considered a neglected disease at international level (6), some countries have not developed public policies aimed at improving its prevention. Martins and Spink (8) consider that in Brazil leptospirosis is a doubly neglected disease, because the epidemiological surveillance system in that country does not have data that would allow an efficient characterization of the populations that are mainly affected, so that its impact and the profile of the people affected remain invisible. When comparing it with dengue, Martins and Spink (8) attribute the differences in the sectors of the population affected by these diseases to the characteristics of the vectors/reservoirs that transmit them. Although Aedes aegypti mosquitoes have an area of action of approximately 300 m, they can easily disperse throughout the territory. Moreover, females lay their eggs in containers with rigid walls, which are not necessarily exclusive to more unprotected areas (6). Leptospira transmission, on the other hand, involves their excretion in the host´s urine, persistence in the environment and entry into a new host. The main reservoir of leptospires are rats (Rattus sp.). These animals proliferate in urban environments with inadequate basic services, such as waste collection, closed storm drainage systems, and well-maintained green spaces. Thus, for example, rats are associated with micro-dumps, ditches, and unweeded areas. On the other hand, conditions that favor the persistence of the bacteria in damp soils are also often found in marginal neighborhoods with poorly maintained dirt roads and open canals (1). Thus, poorer living conditions increase the chances of contracting leptospirosis in an urban context (8). These could be the mechanisms that result in the increased incidence of leptospirosis that we observed in the city of Santa Fe as the socioeconomic stratum index increases toward less favorable conditions.It should be emphasized that the number of cases of these diseases may be underestimated due to underreporting in the National Health Surveillance System. This may be due to the fact that these diseases in some cases produce mild symptoms, for which some people do not seek health care. In other cases, these diseases may be under-diagnosed due to lack of access to adequate health care or deficiencies in the health system´s ability to diagnose these diseases.It is necessary to take into account that the location of the dengue data from the 2016 minor outbreak could not be accessed, and that the type of study applied does not allow us to conclude on individual associations and could fall into an ecological bias. The patterns found are general and the resulting associations allow guiding new studies that search for more specific variables and with greater explanatory power, with the aim of avoiding possible confounding biases In recent years, great emphasis has been placed on public policies aimed at controlling dengue fever, with variable results (33), while leptospirosis prevention campaigns are scarce. We consider that these results constitute an advance and a contribution to the analysis of how these diseases are distributed in the city of Santa Fe, with the aim of guiding the development of public policies that will make it possible to adequately address invisible diseases, such as leptospirosis.In general terms, this work coincides with the statement made by Dr. Mike Begon (pers. comm.) that leptospirosis is such a neglected disease that it did not even make it to the WHO list of neglected diseases (34). In the case of Santa Fe, leptospirosis is neglected, underdiagnosed and underestimated in relation to Dengue. It is also, coinciding with Martins and Spink (8), invisibilized. And this is related to the sectors it affects, unlike dengue.Inequity, marginality, low educational level and vulnerability based on the social structure are elements that promote the deterioration of health in cities (35). Health does not obey an exclusively individual order, but is a process that depends on how societies produce and reproduce themselves (36, 37). Public policies must be equitable and comprehensive, with a high degree of social relevance, and must not respond only to an ahistorical and decontextualized biological perspective (38). Public policies aimed at disease prevention should cover the totality of conditions without excluding any material, social, educational, cultural or economic context. This would make it possible to achieve an improvement in the overall quality of life, especially if participatory inclusion is promoted in the construction of a dignified community future. When public policies aimed at improving economic conditions or strengthening social protection are implemented, there are usually positive repercussions on the health of the population (39,40). It is essential to address the problems associated with zoonoses in a transdisciplinary manner, considering the "One Health" concept. There cannot be human health if there is no animal health, and both cannot exist if the environment is not healthy; if it is deteriorated, if it is not sustainable (41, 42). Applying the One Health concept to the case of leptospirosis and dengue, we can expect that a healthy environment that has good garbage and vacant land management and minimizes rainwater accumulation will present fewer opportunities for mosquitoes, rodents and leptospires to survive and reproduce. In turn, in a more diverse animal community, including rodent and mosquito predators, and with a low dominance of reservoir species, there will be less transmission of these pathogens. Finally, an empowered human population with basic needs met and with broad access to education and health care will have greater capacity for prevention, detection and treatment of these zoonoses. Therefore, taking into account all of the above, we consider that it is necessary to advance in unraveling the socio-environmental roots of the health problems generated by this system of accumulation and segregation (37) in order to move towards healthier relationships, with citizen protagonism, which shed light on the invisible diseases that affect invisible populations and subjects.