#16,721
Earlier this week in China: NHC Confirms Human Avian H3N8 Infection In Henan Province we saw the first confirmed human infection with avian H3N8, but this influenza subtype can also be found in Canines (CIV) and Equines (EIV).
There are subtle, genetic differences between the AIV, CIV, and EIV versions of this subtype, and each pretty much stays in its own lane, infecting only birds, dogs, or horses. But all three lineages continue to evolve, and that increases their potential to jump species.
Originally, Canine H3N8 evolved directly from Equine H3N8, when it abruptly mutated enough to adapt to a canine host, and rapidly began to spread among greyhounds at a Florida race track in 2004 (see EID Journal article Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida).
While equine H3N8 isn't considered to be a zoonotic disease, it has jumped species (to dogs in 2004), and has been shown experimentally capable of infecting both pigs (see J.Virol.: Experimental Infectivity Of H3N8 In Swine) and cats (see Equine influenza A(H3N8) virus infection in cats).
In 2019, an EID Journal Historical Review of Equine H3N8 warned:
Volume 25, Number 6—June 2019
Historical Review
Equine Influenza Virus—A Neglected, Reemergent Disease Threat
Alexandra Sack, Ann Cullinane, Ulziimaa Daramragchaa, Maitsetseg Chuluunbaatar, Battsetseg Gonchigoo, and Gregory C. Gray
.C. Gray)
Abstract
Equine influenza virus (EIV) is a common, highly contagious equid respiratory disease. Historically, EIV outbreaks have caused high levels of equine illness and economic damage. Outbreaks have occurred worldwide in the past decade. The risk for EIV infection is not limited to equids; dogs, cats, and humans are susceptible.
This is a topic we also looked at in 2018, in Equine H3N8: Looking At A long-shot In The Pandemic Sweepstakes and before that, in 2014's Study: Dogs As Potential `Mixing Vessels’ For Influenza.
So, while the risks of human infection are believed to be very low - when we see outbreaks of H3N8 - we tend to pay attention.
Earlier this week the Bureau of Land Management (BLM) announced the deaths of scores of wild horses at a facility in Colorado (see FluTrackers thread CO: Mystery illness kills 95 horses at a federal cañon city holding facility, facility on quarantine).
Overnight, the BLM announced a viral (Equine H3N8 influenza) cause has been identified.
A VIRUS HAS BEEN IDENTIFIED AS THE PRINCIPAL CAUSE OF THE OUTBREAK AND MORTALITY AT BLM’S WILD HORSE AND BURRO FACILITY
CAÑON CITY, Colo. – An equine influenza virus that is not uncommon among both wild and domestic horses has been identified as the likely cause of the respiratory disease outbreak and associated mortality that is occurring at the BLM’s Wild Horse and Burro Corrals located on the Colorado Department of Corrections (CDOC) East Canon Complex in Canon City, CO. Positive polymerase chain reaction (PCR) laboratory test results from two leading veterinary diagnostic laboratories in the United States identified the virus in nasal swabs and lung tissue from several horses.
This strain of equine influenza (subtype H3N8) is not related to the current outbreak of highly pathogenic avian influenza (subtype H5N1) that is currently impacting wild birds and poultry across the United States.
The PCR testing has also identified two equine herpes viruses (EHV-2 and EHV-5) but these commonly occur in normal, healthy horses, and it is unclear to what extent these may also be contributing to the severity of the clinical signs observed in the more severely affected group of horses at the facility.
More typical mild clinical signs of influenza are also being observed in approximately 10-20 percent of the other 2,184 horses at the facility that are not from West Douglas. No mortality has occurred in the larger groups of horses. The West Douglas horses were gathered in an emergency operation in 2021 following a wildfire that impacted their habitat. As of today, April 28, 95 horses have died at the facility since April 23.
“The Bureau of Land Management will review operations at the Canon City facility to prevent future outbreaks like this from occurring,” said BLM Colorado Acting Associate State Director Ben Gruber. “This tragic outcome was influenced by a population of horses that may have been particularly vulnerable given their time in the West Douglas area and their exposure to last year’s wildfire that prompted their emergency gather.”
“This unfortunate event is being taken very seriously by the Department of Corrections and the BLM,” said CDOC Executive Director Dean Williams. “We are working in coordination to mitigate the spread of the virus and identify and prevent any potential risk which could lead to future similar events.”
BLM continues to work with the attending veterinarians on scene as well as the diagnostic laboratories, veterinarians and epidemiologists from the US Department of Agriculture and the Colorado State Veterinarian’s Office to investigate and mitigate the factors that may be contributing to the most severe cases and prevent further spread of the disease. The facility remains under a voluntary quarantine with no horses allowed to leave the premises at this time and for the foreseeable future until it has been determined that the animals are again healthy and pose no risk to the domestic equine population in the community.
The veterinarian report and additional information can be found online at https://www.blm.gov/programs/wild-horse-and-burro/herd-management/herd-management-areas/colorado
-BLM-
- Equine influenza virus (EIV) strains are undergoing significant antigenic drift (evolutionary changes or mutations that lead to new virus strains the immune system doesn’t recognize), and this antigenic drift is the most probable cause for the increased incidence of influenza vaccine failure in the U.S.;3
- Ongoing sequencing of real-world influenza isolates infecting U.S. horses demonstrates significant antigenic differences in field isolates and isolates contained within most vaccine strains, thus inhibiting their ability to offer adequate protection against current circulating strains of equine influenza;
In 2016, in Epizootics, Host Ranges, and Conventional Wisdom we looked at the history of equine epizootics - including the panzootic of 1872 - and at a study (see A Review of Evidence that Equine Influenza Viruses Are Zoonotic) that argued that human EIV infections occasionally occur.
