Introduction
Leptospirosis is a zoonotic disease of widespread distribution and increasingly global importance caused by pathogenic bacteria of the genus Leptospira (Cerqueira and Picardeau, 2009). It can affect virtually any mammalian species, which may harbor the pathogen in their renal tubules and shed the bacteria via urine, contributing greatly to the spread of leptospires into the environment (Faine et al., 1999).
Humans living in urban communities with poor sanitation are highly susceptible to infection, and although rodents are considered the main source of infection in such conditions (Felzemburgh et al., 2014), wildlife and domestic animals have been increasingly attributed to human cases of leptospirosis, particularly in rural areas and underdeveloped tropical regions (Barragan et al., 2016; Biscornet et al., 2017; Zarantonelli et al., 2018).The annual global incidence of the disease in humans is estimated at 1.03 million, leading to nearly 60,000 deaths every year (Costa et al., 2015). Still, leptospirosis is typically difficult to distinguish from other acute febrile illnesses, and the real global incidence tends to be much higher.
Leptospirosis has been extensively reported in insular environments across the world (Victoriano et al., 2009; Petrakovsky et al., 2014; Dietrich et al., 2018; Guernier et al., 2018; Pratt and Rajeev, 2018). Small tropical islands generally have the highest morbidity and mortality, thus characterizing the disease as a major health issue in these locations (Costa et al., 2015). For example, in the Seychelles, leptospirosis was identified as the major health threat for human populations (Biscornet et al., 2017). Similarly, other locations such as Mayotte island (Desvars et al., 2013), Sri Lanka (Warnasekara et al., 2019) and French West Indies (Cassadou et al., 2016) have also reported numerous cases of human leptospirosis. In addition, travel-related leptospirosis is highly associated with tourist activities in tropical regions, and the majority of tourists with confirmed leptospirosis have been originally infected in tropical islands (Bandara et al., 2014; De Vries et al., 2018).
Despite low genetic biodiversity is usually expected in restricted territories, leptospiral diversity in islands can be largely influenced by environmental factors such as geography, soil, climate, biotic interactions and anthropogenic activities (Desvars et al., 2013). Indeed, a surprisingly high diversity of leptospiral strains and different animal reservoirs have been described in the Caribbean islands (Valverde et al., 2013), South West Indian Ocean islands (Guernier et al., 2016; Dietrich et al., 2018), and Pacific islands (Guernier et al., 2018), thus indicating complex interactions between invasive species, native fauna and highly diversified environmental conditions. The evolutionary drivers of such diversity are poorly understood, however it is assumed that different leptospires can be introduced onto insular environments along with domestic and synanthropic species, such as rodents, cattle, goats, sheep, pigs, poultry, domestic dogs and cats (Russell et al., 2018). Such range of invasive mammals may boost the introduction of a highly variable number of leptospiral strains, which may adapt rapidly to new environments and available wildlife hosts (Desvars et al., 2013).
Brazil currently stands as the country with most reported cases of human leptospirosis in Latin America (Schneider et al., 2017), with an average of 3,890 cases annually. Despite the major burden of the disease, the disease in Brazilian islands has been overlooked and leptospiral biodiversity circulating among insular fauna is unknown.
Fernando de Noronha is an inhabited oceanic archipelago composed of 21 islands and islets located approximately 354 km offshore from the Brazilian Northeast coast. The main island has nearly 3,000 habitants and a total area of 18.6 km2. The island is regarded as a World Natural Heritage site by UNESCO, and the concurrent tourist population is roughly twice the resident population, making Fernando de Noronha one of the most sought-after destinations in Brazil. Invasive livestock has been introduced in the island since 1731 including goats, poultry, cattle, and horses, which are currently bred in backyard conditions by local farmers (Russell et al., 2018). Dogs and cats were also introduced, and predatory behavior of feral cats currently poses as a major threat for the local fauna (Dias et al., 2017). Synanthropic rodents (Rattus rattus, Rattus norvegicus , and Mus musculus ) were first introduced by Portuguese and French colonizers, and the density of black rats is now estimated at 3,700 individuals/km2 in the main island (Russell et al., 2018).
Although previous cases of human leptospirosis have been reported in Fernando de Noronha by the local authorities, only one study have accessed leptospiral infection in the island (De Morais et al., 2018). Leptospirosis in Fernando de Noronha may result from an intense interaction with animal reservoirs and defining their role on the transmission dynamics is pivotal to prevent infection of local habitants and tourists. This study proposes the first large-scale investigation ofLeptospira infection in synanthropic, domestic and wild animals from Fernando de Noronha, Brazil, and describes the molecular and serological characterization of the first leptospiral strain isolated on the island.