Modeling by scientists suggests that the virus behind equine infectious anemia could be cleared from horses through repeated vaccination with antibodies.
Equine infectious anemia virus (EIAV) primarily infects horses. It shares many characteristics with HIV in humans, including its viral structure, genome, life cycle, and transmission via blood.
The virus establishes a persistent infection and is transmitted between horses by biting flies. There is no current vaccine or treatment, and infected horses enter a lifelong carrier state if they survive the acute phase of the infection.
The disease is found widely throughout the world, with many jurisdictions requiring euthanasia of infected horses.
Researchers Elissa Schwartz, Christian Costris-Vas and Stacey Smith described the infection as a substantial concern for equine health worldwide, being one of only 11 equid infections requiring reporting to the World Organization for Animal Health.
Recent outbreaks have been reported in North America, South America, Asia and throughout Europe.
Genetically diverse strains of the virus have been found. Infection typically consists of three stages: An acute stage characterised by high fever and a low platelet count; a chronic stage with spiking viral loads, recurring fevers and weight loss; and a symptom-free phase with a decreased viral load and an absence of apparent clinical signs.
“One of the reasons these viruses are difficult to control is because mutation allows them to escape from therapies and immune responses,” the trio said. “We need to better understand how antibodies can control EIAV infection when the virus mutates.”
The study team, writing in the journal Viruses, said research has shown that protection against the virus can be achieved in horses with severe combined immunodeficiency (SCID) through three infusions of processed plasma from long-term immunocompetent horses infected by the virus.
They noted that vaccination of horses by infusion of plasma-containing EIAV-specific antibodies is not a treatment under development. Indeed, the plasma infusion work in SCID horses was undertaken to gain insights into vaccine development for HIV infection in humans.
The potential for antibody infusions to control EIAV holds great promise for the potential elimination of other lentiviruses, such as HIV, they said. However, the usefulness of this approach is limited by the potential for mutant escape.
The study team applied mathematical modeling, taking into account ongoing mutation and the relationship between growth and antibody control, to determine whether multiple infusions had the potential to eliminate the virus in horses altogether.
The work showed that seven infusions of an antibody vaccine, provided they are properly timed, are sufficient to eradicate both the wild-type and the mutant strains of the virus in a horse.
“This suggests a route forward for viral control not only of EIAV but for other virus infections in which escape by neutralisation-resistant mutants is a concern,” they said.
Schwartz is with Washington State University; Costris-Vas and Stacey Smith are with the University of Ottawa.
Schwartz, E.J.; Costris-Vas, C.; Smith?, S.R. Modelling Mutation in Equine Infectious Anemia Virus Infection Suggests a Path to Viral Clearance with Repeated Vaccination. Viruses 2021, 13, 2450. https://doi.org/10.3390/v1312245