Echinococcus granulosus is a zoonotic cestode parasite that is responsible for cystic Echinococcosis (CE), one of the designated “neglected tropical diseases” by the World Health Organization [1]. The parasite cycles between intermediate ungulate hosts and canid definitive hosts as hydatid cysts in various organs and adult worms in the small intestines, respectively. Humans become incidentally infected with the disease following ingestion of infected eggs shed in the feces of definitive canid hosts. The resulting pulmonary and hepatic cysts, termed hydatid cyst disease, are difficult to diagnose and treat in animals and humans, cause substantial economic loss, and can be fatal as cysts compress host tissues or rupture within the host [2].
There are currently 10 recognized genotypes (G1-G10) of E. granulosus and are grouped into two major clades. Echinococcus granulosus sensu stricto, the “pastoral biotype,” refers to strains G1-3, while strains G6-8 and G10 are within the E. granulosus sensu lato clade, referred to as E. canadensis, or the “sylvatic biotype” [3, 4]. The sylvatic biotype historically has been considered less pathogenic to humans, but severe human cases in recent decades have shifted this paradigm and illuminated E. granulosus sylvatic biotype as a notable public health threat [5].
In 2000, the Tennessee Wildlife Resources Agency (TWRA) implemented a re-establishment plan for elk (Cervus canadensis) into the Sundquist Wildlife Management and Royal Blue Wildlife Management Area (WMA) public lands in Campbell, Scott, Morgan, Claiborne, and Anderson Counties of Tennessee (TWRA 2000). Royal Blue WMA has since been absorbed into the North Cumberland Wildlife Management Area (NCWMA). Additionally, in 2001, the National Parks Service reintroduced elk into the Cataloochee Valley area of the Great Smoky Mountains National Park (GSMNP). In both locations, elk had been extirpated since the mid-1800s. From 2000 to 2008, a total of 201 elk were released into the NCWMA, and from 2001 to 2002, 52 elk were released into the GSMNP [6–8]. A 2016 TWRA survey documented 349 elk within NCWMA, suggesting that the reintroduction was successful to date, and populations have remained steady in subsequent years [8]. In both locations, re-introduced elk were originally sourced from Elk Island National Park (EINP) in Alberta, Canada due to the park’s history of disease testing animals and having the Manitoban subspecies (C. c. manitobensis), which is considered the closest genetic stock to the extinct eastern elk (C. c. canadensis). A portion of the imported elk came from Land Between the Lakes (LBL) National Recreation Area, Kentucky; however, all LBL elk were originally sourced from EINP. Prior to translocation, elk were screened for major pathogens, including brucellosis, bovine tuberculosis, Johne’s disease, anaplasmosis, vesicular stomatitis, bluetongue, epizootic hemorrhagic disease, infectious bovine rhinotracheitis/bovine viral diarrhea, and several strains of leptospirosis [7]. No similar testing was available for E. granulosus. E. granulosus is not currently considered endemic in GSMNP or NCWMA, but since the reintroduction of elk, the E. granulosus strain G10 (sylvatic biotype) has been diagnosed in one elk at necropsy. Moreover, an E. granulosus infection has been suspected in several other elk [9]. No previous reports of echinococcosis in wildlife in this region exist, although they are well documented in wildlife in Canada [10, 11].
With the reintroduction of elk into the NCWMA and GSMNP ecosystems, a pathway for the maturation and spread of Echinococcus was newly recreated. It is an emerging concern that the transmission of Echinococcus from the translocated animals into wild or domestic canine populations and other sympatric cervids has occurred, thereby establishing a sustainable transmission cycle and reservoir for the disease. This creates a public health risk, as the GSMNP hosted 11.4 million recreational visitors in 2018 (https://irma.nps.gov/Stats/Reports/Park). Similarly, NCWMA is a multi-purpose public land that hosts large numbers of visitors and issues 15 elk harvest permits annually (https://tn.gov/twra/hunting/big-game/elk.html). Due to the high tourist load in these recreational areas and the presence of wild canids (coyotes, foxes) and free-roaming domestic dogs, both of which can serve as definitive hosts, there is increased opportunity for wildlife and domestic animal contact, as well as zoonotic transmission [12].
This study describes E. granulosus lesions and molecular characterization from necropsied elk from NCWMA and GSMNP, as well as investigates parasite transmission in the NCWMA by examining coyote intestinal samples for eggs or protoscoleces. The establishment of a baseline prevalence and ecology data of this pathogen will help fill a critical void in the current awareness of the parasite. Due to the zoonotic potential of this pathogen, this information is vital to informing wildlife management policy, clinical medical and veterinary medical practice, and public health efforts [13].