Two rabbits

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Rabbit hemorrhagic disease virus (RHD or RHDV) is a highly contagious calicivirus that often causes sudden death in domestic and wild rabbits. It was first seen in China in 1984 but may have originated in Europe. The virus has been found in 40 countries. RHDV2, a new strain, was first seen in Europe in 2010 and is now seen more often than the first strain.

RHD does not pose a threat to humans or other animals, but in the U.S., it is reportable at the state and federal level, and to the World Health Animal Organization.

Infection with RHDV causes lesions throughout internal organs and tissues, particularly the liver, lungs and heart that result in bleeding. The blood has difficulty clotting, which contributes to the bleeding because clotting stops bleeding. Bleeding may be internal only or you may see it. Mortality rates ranging from 5 to 70% have been reported for RHDV2. The rabbit may develop a fever and then die within 36 hours. Death usually occurs either from liver failure or hemorrhage. At death, they may have a blood-stained, frothy nasal discharge.

The time from infection to first signs may be as long as 9 days. Infected animals may appear dull and be reluctant to eat; have congested membranes around the eyes; show signs of nervousness, incoordination or excitement; seizures; and/or make paddling movements. They may have trouble breathing.

Rabbits can contract the virus through contact with infected rabbits or with other animals or materials — such as food, water, bedding and vehicles — that have been in contact with infected animals. According to the U.S. Department of Agriculture, just a tiny amount, possibly even just a few virus particles, is enough to cause infection. The virus is highly stable and can remain active for months in varied temperatures and over distances, enabling it to be spread by biting insects.

In the U.S., it began as a disease of domestic rabbits. The first verified cases of RHDV2 in wild rabbits in the U.S. was when five desert cottontails and one black-tailed jackrabbit in New Mexico tested positive in April 2020. Later, deaths were noted in Arizona, Texas, and New Mexico. The deceased rabbits were lying out in the open, suggesting that they had died quickly. RHDV is endemic in Australia and New Zealand, where it was introduced illegally to control the wild rabbit population, as well as in Cuba, parts of Asia, Africa and much of Europe. Outbreaks also have occurred in domestic rabbits in the Middle East.

Subtypes

There are several strains of RHDV. The calicivirus is seen in three forms.

Peracute

Without having appeared ill at all, infected rabbits are found dead, often with a bloody discharge from their nose or genitourinary tract (the organs that produce and excrete urine plus the reproductive ones). Sometimes the rabbit's mouth and stomach are full of material that is supposed to be in the digestive tract. Because rabbits have such a rapid digestive system, the appearance of this material in their mouths means the disease moves rapidly.

Acute Form

Over a 12-hour period, rabbits become lethargic and depressed and are not interested in eating. A low-grade fever begins, and discharge is seen from the eyes and nose. Oftentimes neurologic signs can be seen, including incoordination, mental dullness, lameness in a back leg, tremors, paddling, seizures, and back spasms. Oftentimes they will be found lying down. They get sick quickly, have trouble breathing, and their heart beats too quickly. Because they are not getting enough oxygen, their mucous membranes, such as gums, can turn blue.

When they are near death, blood comes from openings in the body, notably the nose and urinary/fecal outlet. Death in the acute form often occurs within 24-72 hours from onset, at least in studies.

The "subacute to chronic" form is similar to the acute one but is less severe and death is possible within one to two weeks after infection.

Asymptomatic Form

The classic RHDV strain causes an infection without any symptoms in kits younger than 8 weeks of age. Despite a few bloody noses, these kits thrive even with the infection. They end up having life-long immunity to the particular strain they had, but not to any others.

Transmission

According to the U.S. Department of Agriculture, a very low dose, possibly as little as a few viral particles, is enough to cause infection. The virus is highly stable, especially in organic materials, and can remain viable for months in varied temperatures and over distances, enabling it to be spread by biting insects.

Infected rabbits have to be isolated from all other rabbits. They cannot transmit it to animals other than rabbits, so you and your non-rabbit pets are safe. RHD can get in through the mouth, eyes, eyelids, or nose. Bodily fluids and feces of an infected rabbit are thought to contain the virus. The virus can be transmitted from a dead rabbit, and even the fur may be infectious.

The rabbits who survive can shed the virus for at least a month afterwards and has been seen in seemingly healthy rabbits 15 weeks later. Be sure to talk to your veterinarian about when your recovered rabbit can join the others in your home.

Diagnosis

RT-PCR tests are often used for diagnosis. Tests to detect viral antigens are available.

Treatment

Treatment is limited to supportive care, such as IV fluids and medications to treat specific symptoms.

Prevention

There are vaccines being developed. In the U.S., Medgene Labs has received emergency use authorization for their experimental RHDV2 vaccine from the USDA Center for Veterinary Biologics (CVB). The best prevention is not sharing equipment with other rabbit owners and regularly disinfecting all your rabbit equipment, such as waterers, feeders, and toys. You can inactivate the virus with 4-10% sodium hydroxide or 1-2% formalin.