Although the two diseases are different, they are closely related. Both are a type of hemorrhagic disease spread by small biting flies, known as midges, which reproduce in and around warm, stagnant water. This summer’s conditions likely created situations where midge populations “boomed” around limited water sources, leading to increased risk when deer gather at them.

Hemorrhagic disease outbreaks occur periodically in the Clearwater and Panhandle regions, often during hot, dry summers like 2025. In northern states and other regions where hemorrhagic disease is less common, deer have little to no immunity to the virus.

When outbreaks occur, they can be explosive and severe, causing high mortality in localized areas. The outbreaks tend to cycle, occurring every 3-5 years as herd immunity fluctuates, allowing deer populations to recover from hemorrhagic diseases quickly.