# Zoological transmission of encephalomyocarditis virus in the United States: Virus evolution, host ecology, and capsid antigenicity derived from an outbreak

## TL;DR

This study investigates how encephalomyocarditis virus spreads in zoos in the U.S., focusing on its evolution, host animals, and vaccine responses.

## Contribution

The study provides the first comprehensive analysis of EMCV transmission, host ecology, and antigenic variation in North America.

## Key findings

- Invasive and native rodents are linked to EMCV outbreaks and zoo animal transmissions.
- Long-term antibody responses in elephants following autogenous vaccination were characterized.
- A reverse genetics system was used to assess cross-protection against diverse EMCV strains.

## Abstract

Encephalomyocarditis virus (EMCV) is a rodent-borne picornavirus that has repeatedly caused severe outbreaks resulting in the deaths of zoo mammals – most notably elephants – for decades. However, within North America, little is known regarding the diversity of EMCV that exists in nature, the reservoir or amplifying hosts important for maintaining the virus, and the epidemiology of zoo-associated outbreaks. This lack of knowledge of the EMCV strains that circulate in North America has impeded a more thorough understanding of how genetic and antigenic variation may affect pathogenicity or potentially vaccine-induced protection from disease. Herein, following a zoological outbreak of EMCV in Florida, we conducted the most comprehensive comparative phylogenomic analysis of virus isolates from fatal zoo animal cases and local rodent species to date, identifying both non-native, invasive rodents and native mice and rat species as potentially important in precipitating and/or maintaining outbreaks, with multiple transmissions to zoo animals. After development of an autogenous vaccine, we investigated the duration and magnitude of neutralizing antibody responses in elephants monthly for multiple years, providing a unique fine-scale, long-term profile of responses to vaccination. To better understand how antigenic variation may affect vaccine-induced protection, we constructed a reverse genetics system to determine the level of cross-protection afforded by autogenous vaccination against capsids derived from various divergent EMCV strains and serotypes. These results provide new advancements in understanding EMCV transmission and antigenicity in North America, which can be used as a foundation to ultimately enable zoos to better protect animals from this important pathogen.

Much has been learned about the molecular biology and pathogenesis of encephalomyocarditis virus (EMCV) over the last several decades, as it has been used as an important model system on many fronts, including deducing mechanisms of myocardial pathogenesis and viral-induced diabetes, antiviral immunity, polyprotein processing, as well as a prototype for protein expression via an internal ribosome entry site (IRES), ribosomal skipping, and ribosomal frameshifting. Despite this wealth of information, very little is known about the ecology and evolution of the virus in nature, in particular in the United States. To zoological institutions, EMCV is a major concern, as it can cause devastating outbreaks resulting in fatal myocarditis and/or encephalitis in numerous wildlife species. Herein, we investigated an outbreak that was precipitated by the death of an African elephant, in hopes to begin to shed light on the transmission dynamics and genetic and antigenic diversity of EMCV that exists in North America.