Epizootic Hemorrhagic Disease (EHD)

Epizootic Hemorrhagic Disease (EHD) is a viral illness spread by biting Culicoides midges (often called “no-see-ums”) that primarily affects white-tailed deer but can also infect other wild ruminants and, occasionally, cattle. EHD is not a human health risk. 

EHD has circulated in the southern United State for decades and has become more common in northern states as climate patterns shift and midge populations expand. Culicoides midges breed in moist soil and muddy areas. They can travel short distances on their own but may be carried long distances by wind. The virus cannot spread directly between animals or from animals to humans. 

EHD in Deer 

White‑tailed deer are highly susceptible to EHD, especially in regions where the virus is newly introduced. People may notice deer that have died suddenly, often near water, or deer that appear weak, tired, or unusually slow to move. 

Outbreaks often occur in late summer and early fall, when midge activity peaks. EHD activity usually drops off after the first hard frost, when the biting midges that spread the virus die. For more information see the ODFW website. 

EHD in Cattle 

Most cattle show mild or no illness, although some may develop clinical signs such as fever, oral lesions, eye or nose discharge, lameness, a drop in milk production, or respiratory discomfort. Deaths can occur in infected cattle, but most recover in 3-30 days. Some cattle may remain lame or unthrifty for a prolonged period. 

Infected pregnant cattle may experience reproductive impacts, including early embryonic loss, decreased fertility, or, less commonly, abortion and neurological defects in calves, sometimes referred to as “dummy calves.” 

EHD Prevention 

There is no specific treatment or prevention for EHD. Livestock management focuses on supportive care and reducing exposure to biting midges during late summer and fall. 

Vector‑control strategies, insect‑repellent applications, and careful observation of susceptible animals (e.g., white-tailed and mule deer) to remove livestock from affected areas can help reduce disease impact. While cattle generally recover, reproductive losses and temporary declines in performance make prevention and surveillance important for herd health. 

Outbreak Information and Updates 

In late February 2026, veterinarians and cattle producers in Northeast Oregon reported an unusual increase in late‑term abortions and the birth of dummy calves. Diagnostic testing identified EHD virus in fetal tissue from multiple cases. 

• Reports are primarily from Northeast Oregon. 
• Most affected herds have reported grazing in Wallowa or Baker counties during the late summer or early fall of 2025.
• ODFW confirmed EHD in white-tailed and mule deer mortalities in Wallowa and Baker counties during fall 2025.
  

EHD Cases in Oregon