The first report of Rabbit Hemorrhagic Disease (RHD) type 2 in the United States was detected in one of five pet rabbits in Medina County, Ohio this fall. The first announcement of RHD2 was made on September 21, 2018, by Dr. John Clifford, Official Delegate, Chief Trade Advisor, Animal and Plant Health Inspection Service, United States Department of Agriculture to the World Organization of Animal Health (OIE). Formalin-fixed tissue examined by a private pathology laboratory had microscopic changes of severe widespread hepatic necrosis that were consistent with RHD infection. The office of the State Veterinarian was notified of the pathology report, and an investigation identified frozen liver tissue retained by the submitting veterinarian. This tissue was forwarded to the Foreign Animal Disease Diagnostic Laboratory (FADDL) at Plum Island (New York) and was found on 9/20/2018 to be positive for nucleic acid of RHD2 virus and not for that of RHD type 1 virus.
As a follow up, ODA field staff and the ADDL worked closely with Division of Wildlife staff to harvest and test several cottontail rabbits from the area. None of the harvested rabbits had gross or microscopic lesions of RHD infection, however tissues from those rabbits were submitted to FADDL for testing. None of the six wild cottontails were found to have RHD2 nucleic acid or antigen in liver tissue, The last surviving pet rabbit at the index case premise was also negative for evidence of RHD infection. It is unknown how this virus gained entry to the barn where the affected pet rabbits were kept. Investigations of more than a dozen other rabbits from around Ohio that died acutely have not detected any additional cases of this highly infectious and contagious calicivirus. The virus may be transmitted orally by secretions and excretions including oral, nasal and pharyngeal secretions, urine and feces; transmission by insects is considered significant in the transmission among wild rabbits. The incubation period may be as short as 1-3 days, with death usually occurring within 12-36 hours after onset of a fever.
Rabbit owners are encouraged to use the highest levels of biosecurity possible to avoid entry of this virus (and other pathogens) into their rabbitries. No vaccine against RHD is currently available in the USA. Veterinarians are encouraged to contact the ODA (614-728-6220) to report outbreaks of acute deaths in rabbits with high mortality rates while additional information is learned about the status of RHD virus in Ohio.
Dr. Jeff Hayes, MS, DVM, ADDL Pathology Section Head