Rabbit calicivirus infection confirmed in Iowa rabbitry

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A rabbitry in Crawford County, Iowa was found to have rabbit calicivirus infection, also known as viral hemorrhagic disease. The premises are quarantined, and the disease appears to be contained.

USDA-APHIS Veterinary Services and the Iowa Department of Agriculture and Land Stewardship are working together to address the situation. The owner lost 25 of 27 rabbits. Veterinary Services assisted the state of Iowa in depopulating the remaining two rabbits and in cleaning and disinfecting the premises. The agency also is communicating its findings to all states and to the rabbit industry to encourage them to report to Veterinary Services or the state veterinarian each rabbit death in which the cause is unknown and the clinical history is consistent with that of rabbit calicivirus infection. Veterinary Services will investigate reports of suspected rabbit calicivirus infection as part of the foreign animal disease surveillance program and will continue to evaluate suspected cases at the USDA-APHIS Foreign Animal Disease Diagnostic Laboratory at the Plum Island Animal Disease Center, Greenport, Long Island, NY.

The first infected rabbit identified had been allowed to roam near the house, and it died March 9, 2000. Rabbits housed in hutches began dying March 16.

Rabbit calicivirus infection is a highly infectious viral disease of the European rabbit (Oryctolagus cuniculus), the species from which all US domestic and commercial rabbits are derived. Wild rabbits that are native to North America (eg, cottontail rabbits and jackrabbits) are not susceptible to rabbit calicivirus infection and do not develop clinical signs of the disease, nor are humans or other mammals affected.

The virus can be transmitted by direct contact with infected rabbits or indirectly by contact with objects contaminated with the virus. It damages the liver, intestines, and lymphatic tissues and causes terminal blood clots. Few clinical signs are observed, and the rabbits die within six to 24 hours of the onset of a fever. Rabbits that recover may become carriers of the virus and may shed the virus for at least four weeks.

The source of the Iowa infection has not been determined. There have been no introductions of rabbits onto the premises in the past two years, and the rabbitry is in a rural location. August 1999 was the last time rabbits left the farm and returned. In January 2000, six rabbits, all healthy and more than two months old, were sold. There are no known premises with rabbits in the near vicinity. Veterinary Services and the Iowa Department of Agriculture and Land Stewardship are continuing to investigate.

A private practitioner sent samples from the first rabbit to the Iowa State University Veterinary Diagnostic Laboratory on March 22. Rabbit calicivirus infection or toxic hepatopathy was suspected on the basis of the animal's clinical history and microscopic lesions in the liver. On March 24, a second rabbit was found to have similar lesions. The state and federal officials were notified March 27, and a foreign animal disease investigation began immediately. Epidemiologic information was collected, and samples were sent to the USDA's Foreign Animal Disease Diagnostic Laboratory. The laboratory suspected rabbit calicivirus infection on the basis of results of a hemagglutination inhibition test and electron microscopy. The laboratory forwarded samples to a laboratory in Spain for confirmation. The laboratory confirmed the diagnosis by polymerase chain reaction assay and western blot. Samples were identified by a laboratory in Italy as being rabbit calicivirus subtype a, which is similar to the type found in Europe and dissimilar to the type found in Australia and New Zealand.

Rabbit calicivirus infection was first reported in 1984 in the People's Republic of China. The first report of the disease in the Western Hemisphere was in Mexico City in 1988. Mexico is the only country that has been successful in eradicating the disease.

For additional information, contact USDA-APHIS, Veterinary Services, Emergency Programs staff at (301) 734-8073, (800) 940-6524, or emocatusda [dot] gov (emoc[at]usda[dot]gov). A question-and-answer sheet and fact sheet are posted at www.aphis.usda.gov/vs/ep/index.html.