Wildlife officials recently announced outbreaks of Rabbit Hemorrhagic Disease Virus Type 2 (RHDV2) ravaging Texas, New Mexico, Colorado, Arizona and California. The U.S. Department of Agriculture (USDA) deems RHDV2 as seriously contagious and nearly always fatal amongst domestic and wild rabbit species and their close relatives, hares and pikas. RHDV2 is not zoonotic, so it won’t infect livestock, pets or humans, asserts the California Department of Fish & Wildlife (CDFW). Still, Texas Parks & Wildlife (TPW) advise against pets consuming rabbit carcasses.
Rabbit Hemorrhagic Disease Virus (RHDV) is the viral agent causing rabbit hemorrhagic disease (RHD). Science Direct says RHDV belongs in the calicivirus family, which infects many animals including pigs, cattle, cats and even humans. Norovirus, for example, is a human calicivirus. But humans seem unaffected by RHDV.
There are two worrisome strains of RHDV — RHDV1 and RHDV2. House Rabbit Society, Veterinary Practice, as well as both the Vaccine and Veterinary Research journals document RHDV1 as first emerging in China back in 1984, when, in just one year, 140 million rabbits were decimated. China claims that the outbreak started in Angora rabbits imported from Europe. Eventually, RHDV1 spread to over 40 countries and hit the U.S. in 2000. Given its estimated 95% mortality rate, Australia and New Zealand notoriously introduced RHDV1 into their wild rabbit populations as pest biocontrol.
RHDV1 mutated, begetting RHDV2, which was first identified in 2010 when domesticated rabbits in France showed clinical signs of RHD despite being already vaccinated against RHDV1. By September 2018, RHDV2 reached the U.S., manifesting among domestic rabbits in a rural Ohio farm, documents the Veterinary Information Network (VIN) News Service.
The USDA considers both RHDV1 and RHDV2 invasive pathogens, as they are not native to North America. A joint paper put forth by the Center for Food Security & Public Health, Institute for International Cooperation in Animal Biologics, Iowa State University, the World Organization for Animal Health (OIE) and the USDA revealed RHD can be difficult to eradicate. Not only can the virus strains survive over seven months on rabbit carcasses, but they also withstand temperatures below freezing and above 120 degrees Fahrenheit.
House Rabbit Society cites several differences between RHDV1 and RHDV2. Incubation is two to 10 days for RHDV1, but three to nine days for RHDV2. Rabbits with RHDV2 can be asymptomatic yet spread the virus for up to two months. There is no known cure for either strain. While a vaccine exists for RHDV1, there are currently no USDA-licensed vaccines for RHDV2. That RHDV2 can “potentially surviv[e] more than 3 months without a host” has prompted some U.S. veterinarians to import RHDV2 vaccines despite a convoluted process.
The USDA and VIN News Service warn RHD is highly contagious, spreading easily by direct contact with rabbit excretions and secretions — saliva, sweat and biowaste. Sharing food, water, bedding, fomites and vehicles spreads RHD. Other vectors are infected rabbit meat, pelts, even insects.
Besides farmers and pet owners, biologists and conservationists are worried about this virus. As declining rabbit populations have repercussions in habitat food chains, RHDV2 could cause severe consequences down the line.
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