College of Veterinary Medicine - Cornell University

Advancing Vaccines of Excellence

This year another outbreak of equine herpesvirus type-1 (EHV-1) swept through the United States in May, affecting 90 reported horses and killing 13. Cases of herpesvirus
Myeloencephalopathy (EHM), a neurological disease caused by EHV-1, have increased so sharply in number and mortality over the last five years that the USDA recently
classified EHM as an emerging infectious disease.

The virus can spread through air, nursing, and contact with infected animals, equipment, or hands. It remains in hosts for life, flaring up during times of stress or weak immunity to cause respiratory disease, abortion, and in the case of EHM, brain disease, paralysis, or death. Treatment, quarantines, lost training and competition time, and deaths pose enormous costs to equine industries worldwide.

“Vaccines induce strong antibody responses but only offer partial protection,” said Dr. Bettina Wagner, immunologist at the Animal Health Diagnostic Center at the College of Veterinary Medicine, where she leads the first team to study horses’ innate immune responses to EHV-1. “We need to understand how the virus interacts with the immune system in order to develop vaccines that effectively bolster horses’ abilities to build immunity.”

Wagner’s Zweig-funded research recently produced two papers published in the journal Veterinary Immunology and Immunopathology. They describe how EHV-1 keeps innate immune cells from producing crucial chemokines and cytokines, proteins that trigger and modulate the adaptive immune system to create specially-tailored T-cells designed to combat the virus and prevent severe clinical disease.

“Currently we are working to show that EHV-1’s ability to subdue innate immune responses prevents the host from developing enough adaptive T-cells to combat the virus,” said Wagner. “We are also exploring the factors that increase an infected horse’s susceptibility to neurological disease. We think that reduction of the body’s T-cell population plays a major role in causing EHM.”

Older horses seem to be more frequently affected with neurological signs and fatal outcome of disease than foals, and part of Wagner’s study explores how and why susceptibility to EHM increases with age. “If we can find out what immunological factors help protect younger horses from neurologic disease we can use this knowledge to develop vaccines to boost similar responses and offer increased protection,” said Wagner.

To fully understand how EHV-1 decreases protective immunity, Wagner also investigates which viral genes enable EHV-1 to manipulate immune systems. “We need to know how the virus interacts with the immune system and what genes drive those interactions,” said Wagner. “This will help us adapt new vaccines that can more effectively combat EHV-1.”

Herpesviruses affect nearly all vertebrate species, including all major livestock and companion animals. Human medicine has struggled to develop vaccines against the eight known herpesviruses that can infect people. Understanding how the horse immune system interacts with equine herpesvirus could help inform parallel herpesvirus research and vaccine development to protect people and other animals from these increasingly common infectious diseases.