Introduction
In the last two decades there has been an unprecedented and worldwide
emergence of fungal pathogens threatening animal and plant biodiversity
(Fisher et al. 2012). Recently, there has been increasing concern over
the emerging fungal pathogen Fusarium in endangered sea turtles,
which causes hatching failure in eggs of sea turtles worldwide
(Smyth et al., 2019).
So far, reports of the pathogenesis and distribution of this pathogen
has been limited to sea turtles, and it is unknown whether this pathogen
also poses a threat to freshwater and terrestrial turtle species, of
which there are 356 known species
(Rhodin et al.,
2017).
First reports of sea turtle eggs colonized by fungi were done by
Wynecken et al. (1988), who described hatching failure of diseased eggs
within natural and artificial nests. Since then, several studies have
reported the presence of fungi (Phillott & Parmenter, 2001) and
bacteria (Craven et al., 2007) in unhatched eggs and female cloaca,
indicating that turtle eggs are not laid sterile and have a commensal
surface microbiome. Fungi from the genus Fusarium were identified
as pathogenic to sea turtle eggs
(Sarmiento-Ramírez et
al., 2010), and in 2012 Fusarium solani was recognized as a new
fungal emerging infectious disease (EID) that may be contributing to
population declines in sea turtles
(Fisher et al.,
2012). Infections caused by ~60 species belonging to
the Fusarium solani species complex (FSSC) have been reported in
sea turtles around the globe
(Brofft Bailey et
al., 2018; Candan, 2018;
Sarmiento-Ramírez et
al., 2014).Fusarium has been isolated from both diseased and asymptomatic
sea turtle eggs, and infection may be vertically transmitted from the
mother cloaca or horizontally transmitted from the environment
(Sarmiento-Ramírez et
al., 2014). Given the large number of Fusarium species and their
global range, it is possible that this fungal disease is not limited to
sea environments and may also be spreading to freshwater environments.
Indeed, Fusarium is thought to thrive in water and damp
environments (Smyth et
al., 2019), and therefore fresh-water turtle species may also be at
risk, yet there has been to date little surveillance of non-oceanic
turtle species.
In this study, we screened 680 eggs from artificial nests of an
endangered freshwater turtle species (P. unifilis ) that inhabits
the Amazon and Orinoco basin in South America for visual symptoms of
fusariosis and assessed hatchability. We tested 68 eggs by PCR forFusarium infection and sequenced eight of those amplicons on an
Illumina platform to screen for members of FSSC.