According to a ProMED report on April 28th, equine influenza subtype H3N8 is responsible for ongoing mortality in mustangs corralled in Colorado. More tham 100 horses died in April according to the Bureau of Land Management. Horses were transferred from Rio Blanco County in Colorado near the Utah state line in late fall 2021 following wildfires and were part of a population of 2,500 wild mustangs rounded up from rangelands.
Equine influenza caused by H3N8 is a common cause of respiratory disease in equines and is endemic to the continents of Europe, Asia and the Americas. Stressed horses are obviously more susceptible to infection with both viral and secondary bacterial pathogens and this would be especially the case with wild horses confined in pens in close proximity, facilitating infection by inhalation of aerosol droplets and fighting..