Helleborus net necrosis virus (HeNNV) also known as Hellebore black death is an RNA virus that can cause serious disease in Hellebore plants by stunting or deforming the plant as it grows. The disease marks the leaves of the hellebores with black streaks, often following the veins of the leaf, and creating ring patterns. It can also mark the sepals and flowers with black spots or streaks, but it will not always do so. When symptoms are severe new leaves will have limited growth before dying off. The most seriously affected in the UK is "Helleborus orientalis", but all hellebores are susceptible to the disease. The most effective method of treatment against black death is to dig up and destroy all infected plants immediately. Many viruses are not transmitted through seeds, so it is possible to raise new disease resistant plants this way.