Emerging infectious fungal diseases of wildlife are increasingly common, with devastating consequences for biodiversity and ecosystem health. The development of effective management strategies for control of these diseases requires an understanding of whether the pathogen is novel or endemic. A novel pathogen invades new geographic regions and infects naïve hosts. Endemic pathogens naturally occur in the environment, but shifts in environmental conditions and/or host susceptibility heavily influence pathogenicity. There are stark differences in management strategies depending on the novel or endemic nature of a pathogen. Thus, making this determination is a key first step towards mitigating disease effects on host populations.
Fusarium keratoplasticum (Fk) and Fusarium falciforme (Ff), have been associated with mass mortalities in the nests of sea turtles. These are common species of filamentous fungi that are known opportunistic pathogens of humans. Sea turtle egg fusariosis (STEF) has been reported worldwide, but sampling has never been conducted at nesting sites in the United States. Florida has a high proportion of nesting sites in the US, but disease has never been reported as a major cause of hatchling mortality. Our objectives were to 1) quantify the Fusarium species diversity in Florida nesting sites; 2) determine if the presence of Fk and/or Ff is associated with nest mortality; and 3) examine the genetic diversity of Fk and Ff sea turtle isolates to determine whether they fit the novel or endemic pathogen hypothesis. We conducted selective sampling for Fusarium at three National Estuarine Research Reserves sites in Florida: Rookery Bay, Guana Tolomato Matanzas and Appalachicola. We isolated fungi from unhatched eggs, hatched eggshells and from sand inside and outside of 37 nests that were excavated for assessment of hatching success. We used an established three-locus multilocus sequence typing for identification of Fusarium isolates to the species-level, and to assess the genetic diversity of sea turtle nest isolates.
Results/Conclusions
We have identified 126 Fk and Ff isolates from two of three nesting sites. This makes up approximately 70% of the Fusarium species isolates from these sites. We have confirmed the presence of Fk in two of three sites, associated with unhatched eggs, hatched eggshells and sand inside nests, as well as Ff from sand outside of the nests at each of these sites. Identification of Fk and Ff at these sites, as well as the absence of disease-associated mortality, suggests an endemic origin of this pathogen.