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.