Cause of rabbit disease outbreak confirmed

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Illustration: Two rabbits

Eight rabbits in a backyard rabbitry in Vanderburgh County, southwest Indiana, became acutely ill and succumbed to a deadly viral disease May 27. The animals were among a group of 11 black rabbits purchased May 24 at a Kentucky flea market and then introduced to the new owner's herd of about 200.

The Indiana Board of Animal Health and the Veterinary Services division of the Department of Agriculture's Animal and Plant Health Inspection Service initiated a joint foreign animal disease investigation June 3. An initial diagnosis of rabbit hemorrhagic disease was made at the Indiana Animal Disease Diagnostic Laboratory in Dubois. Four days later, the Plum Island Foreign Animal Disease Diagnostic Laboratory confirmed the diagnosis.

On June 8, 104 other rabbits on the premises were euthanatized. The outbreak appeared to be confined to those premises, except for two of the rabbits supplied to a local pet store that were found positive and euthanatized; one was already in an owner's home.

According to Dr. Sandra K.L. Norman, director of the Companion Animal Division, Indiana State Board of Animal Health, the agency has tested any connected rabbits and a few others that died suddenly, but none was found positive. She said authorities are fairly sure they have eliminated the main source of disease and exposure, although the seller of the infected rabbits in Kentucky has not been found.

In the United States, the only other reported outbreaks of rabbit hemorrhagic disease were in Iowa in 2000, and in Utah, Illinois (because of rabbit movement from Utah), and New York in 2001.

Highly contagious, RHD virus is passed in large amounts in the droppings of infected rabbits. The virus can also be spread by contact with rabbit products, rodents, and contaminated objects. Rabbits that recover can shed the virus for at least four weeks. The virus does not affect humans and is not known to be harmful to other animals.

Fever in infected rabbits may reach 40.5oC (105oF), but it often is not detected until the rabbits develop terminal clinical signs. Mortality ranges from 50 percent to 100 percent.

In a June 9 veterinary advisory, Dr. Norman told veterinarians that if they receive inquiries about sudden death in rabbits from their clients, they should assess the situation to determine whether the problem could be RHD, because high (outdoor) temperatures can also cause heat-related deaths. "The presence of clear or bloody, foamy discharge from body cavities is key to the differential," she wrote.

Rabbits of the genus Oryctolagus are susceptible to RHD virus. This genus includes most show, pet, and laboratory rabbits, but not wild rabbits in the United States.

No vaccine is legally available for use in this country.

The Rabbit Industry Council and ShowBunny co-sponsor the VHDInfo group for discussion of current events related to viral hemorrhagic disease and rabbit calicivirus disease, which are other terms for RHD.