The origins and potential cross-species transmission of paramyxoviruses and other RNA viruses between native snakes and invasive Burmese pythons in the Florida Everglades

TL;DR

A new ferlavirus outbreak in wild snakes in Florida is reported, and novel viruses are found in invasive pythons, raising concerns about cross-species transmission.

Contribution

The first documented ferlavirus outbreak in free-ranging snakes and discovery of novel RNA viruses in invasive Burmese pythons.

Findings

A reptilian ferlavirus related to anaconda paramyxoviruses caused a disease outbreak in wild eastern mudsnakes.

A novel hepacivirus with a putative third protease was discovered in Burmese pythons.

The first terrestrial alphavirus in the U.S. in over 50 years was identified in invasive pythons.

Abstract

During November–December 2020, a disease outbreak involving eastern mudsnakes (Farancia abacura abacura) was documented in the Greater Everglades Ecosystem, Florida, USA. Moribund snakes were observed writhing on riverbanks with concomitant frothy oral discharge. Pathological examination revealed necrotizing enteritis and pulmonary edema, and a reptilian ferlavirus phylogenetically related to anaconda paramyxoviruses was isolated. While ferlaviruses are well-described pathogens of snakes in zoological and private collections worldwide, this represented the first outbreak of ferlaviruses recorded in free-ranging snakes. To biologically characterize this virus, we performed in vitro analyses including host range, relative infectivity, and temperature-dependent fitness assays. As one outstanding question in paramyxovirus biology is the functional role of the U protein, which is unique to ferlaviruses, we investigated its spatiotemporal expression in infected cells, demonstrating its localization to viral inclusion bodies. Additionally, we sampled Burmese pythons (Python molurus bivittatus), an invasive constrictor species, in and around the outbreak site in the Everglades for reptilian ferlaviruses, resulting in the discovery of the first terrestrial alphavirus detected in the United States in over 50 years and a novel hepacivirus that putatively contains a third protease which is evolutionarily conserved among lower vertebrate hepaciviruses and may have arisen by duplication of the NS2-3 protease. Although the impact of Burmese pythons on the Everglades ecosystem via the predation of native species has garnered much attention, little is known regarding the diversity of viral pathogens they harbor and the potential risks they may pose to native wildlife and other animal hosts through viral cross-species transmission.

Although the evolution, molecular biology, and pathogenesis of numerous disease-causing animal paramyxoviruses have been examined extensively, studies on reptilian ferlaviruses—which have been responsible for large-scale mortality events in snakes in managed settings for decades—have lagged significantly. Herein, we document the first recognized ferlavirus disease outbreak in free-ranging snakes and provide new insights on the ferlavirus-specific U protein and reptilian host range that make these viruses unique among the paramyxoviruses. In searching for the potential source of ferlaviruses in nature, we discovered other novel RNA viruses in Burmese pythons, an invasive constrictor species introduced into the Everglades. In addition to extending the known diversity of reptilian viruses, these findings provide new fundamental insights into mammalian virus evolution and highlight the potential dangers of the cross-species transmission of such viruses into native snakes and other wildlife.

Figures