"Adult rabbits seem to be the most commonly affected by VHD, but it can also be seen in young rabbits older than eight weeks. There appears to be a wide range of morbidity (percentage of exposed rabbits that become infected). It can be as low as 30 percent or as high as 80 percent. Mortality among infected rabbits reaches 95 to 100 percent. The incubation period is 48 to 72 hours. The cause of VHD is under intense study by scientists in a number of countries. The agent is a virus that doesn't seem to have all the characteristics of any of the known virus classes. The route of entry into the host has not been completely determined, but the virus apparently can invade the respiratory tract or the digestive tract or can come in through scratches or abrasions in the skin. Experimentally, the virus has produced the disease when introduced orally, intramuscularly, or by intraperitoneal injection. The virus may also be transmitted by aerosols, direct contact, equipment used with meat or by-products, and possibly insects or rodents.

There appear to be three forms of the disease.

In the peracute form, all that is seen is a dead rabbit in the cage.

In the acute form of the disease, the rabbit shows depression, goes off feed, and has difficulty breathing. This rabbit dies in one or two days and exhibits incoordination, shaking, and evidence of pain prior to death. It may show blood-stained mucus nasal discharge. When the affected rabbit is first observed, the rectal temperature may be increased 2 degrees to 3 degrees Fahrenheit (normal rectal temperature 103 degrees F).

The third form of the disease seems to be much milder. The rabbit appears sick but then recovers and is immune to reinfection."