Calicivirus Nightmare: The Terrifying World of Death

Calicivirus history

According to PubMed Central, Calicivirus was first noticed in Jiangsu Province in China in 1984. It was found in a group of Angora rabbits that had been transported from Germany. In less than a year it had killed over 140 million domestic rabbits and spread over 50,000 km_² across China.

Korea then started reporting outbreaks which were connected to fur importation from China.

By 1986, Italy first reported the virus, where it then quickly spread across Europe. Outbreaks in Spain, particularly along the Iberian Peninsula, where rabbits originated, were reported in 1988 and Portugal in 1989. This caused severe reduction in all wild lagomorph populations, obliterating the remaining rabbits who survived the myxomatosis outbreak years before.

Domestic rabbit populations in North Africa were wiped out.

South America started reporting outbreaks in 1988 because they imported products from China. Mexico was the only country to successfully eradicate RHD from their country in 1992. People suggest that it was because all wild rabbit populations were were gone, other say it was because they contained all outbreaks and controlled it effectively.

North America reported their first outbreak in 2000 and has had frequent outbreaks since then.

The virus continued to spread, and outbreaks were reported in Cuba, Uraguai and other South American countries.

Now, RHDV outbreaks occur in almost all countries, but is considered to be an epidemic in Europe, Asia, parts of Africa, Australia and New Zealand.

Calicivirus in Australia

The rabbit meat and fur industries had significant economic losses due to RHD as it did not discriminate between wild and domestic rabbits. In Australia and New Zealand, rabbit are considered a pest ❝and a major threat to the endemic wildlife flora and fauna❞ (PubMed Central). RHDV was considered to be an effective control for rabbits.

In 1991, Australian CSIRO scientists tested the effectiveness of the RHDV in laboratories. They specifically tested the v351 strain, which was isolated in Czechoslovakia in 1987, and was imported into Australia in 1991. It was confirmed to be lethal to wild European rabbits at the Australian Animal Health Laboratory. A field trial was then conducted in 1995 on Wardang Island in the Spencer Gulf, South Australia.

Calicivirus accidental release

An accidental release of Calicivirus occurred in late 1995. According to the Port Lincoln Times, Thu 19, October 1995 article called Virus hits mainland: ❝Three years of testing of the virus at CSIRO Australian Animal Heath Laboratory, have shown RCD is safe for all animals except rabbits. The virus was transferred into quarantine pens on Wardang Island in March 1995. The Australian and New Zealand Rabbit Calicivirus Disease Program is a consortium comprising all Australian and New Zealand Governments, Australian Nature Conservation Agency, CSIRO, Meat Research Corporation, International Wool Secretariat, the CRC for Vertebrate Biocontrol and the National Farmers Federation❞ suggested that the virus was going to benefit the economy.

However, ❝[t]he virus escaped from Wardang Island where scientists were researching its ability to biologically control rabbits ❞ where locals found two rabbits within 6 days that showed signs of the virus. Then the article continues with ❝[t]here have been no further cases of RCD on Wardang Island where rabbit control measures have been highly effective❞ which meant they thought the disease died out.

However, it didn’t, and covered their tracks by saying ❝[a] PISA coordination centre has been set up at Port Victoria❞ which simply meant Primary Industries South Australia (PISA) were implementing and agreeing on contingency plans, and nothing was actually done to stop the virus from spreading across the mainland. PISA simply wanted to ❝grow primary industries and drive regional development❞ (a quote from PIRSA’s About Us page) and eradicate rabbits, not taking into account how it was transmitted to the mainland and the measures they needed to take to control it before it got out of hand.

Although they did say that ❝Vaccines are being prepared to protect domestic rabbits.❞

Of course a stack of stupid newspaper articles appeared in various papers:

Apparently, it escaped the strict quarantine measures and was suspected to be transported by insects or air currents to the mainland… or journalists…

This sparked the widespread release, and in less than two years it became an endemic pathogen across southern Australia.

The initial spread was estimated to be about 50km a week and killed up to 95% of rabbits in its wake. Unlike Myxomatosis, where it needed damp and riverine areas to spread, RHD loved the dry, arid areas, which seemed to be perfect for the Australian environment.

The New Zealand government decided not to release the pathogen. However, the Czech strain of the virus was illegally obtained and released by farmers.

Calicivirus was approved

In 1996, RHDV was officially approved for release to control rabbit populations in Australia. It is a biocontrol agent. It was very successful in reducing populations; however, it did not reduce population in some areas cool/wet regions of Australia, these rabbits had special antibodies that reacted differently to the virus and didn’t kill them. At that point in time it was only used as in injection with live rabbits. In 2006 the use was extended to allow it to be added to carrots or oat bait, then in 2015 a new lyophilised (freeze dried) formulation was registered for both injection and bait use.

This lead to the theories that other caliciviruses were circulating in these rabbit populations, which formed some protection to them. This is when they manipulated the RHDV to be RHDV1A, it was specially designed to target the rabbits with antibodies. Studies concluded that the antibodies can be used as a protection against RHDV, and so they called it RCV-A1, and use it in the vaccinations to protect pet rabbits against RHDV1 and its sub-types.

What is Calicivirus (RHDV)?

Early on, scientists found it hard to classify RHDV because it is non-cultivable (cannot be reproduced on a petrie dish). It was suspected to be a parvo-like virus (among others), but was finally assessed to be from the Caliciviridae family. Because Calicivirus (also known as Rabbit Haemorrhagic Disease Virus (RHDV)) is a naturally occurring RNA based virus, they struggled to figure out where it belonged and later decided that it was related to Lagovirus.

Calicivirus infect many different animals, including humans, and it causes a variety of diseases like gastroenteritis, respiratory infections, haemorrhagic disease, vesicular lesions and reproductive failure.

Even though scientists have seen cross-transmission between animal species, they have not been able to replicate it in laboratories, and have chosen to say that Calicivirus doesn’t cross-transmit.

How is Calicivirus transmitted?

Science suggests that the main transmission of any Calicivirus is through:

• direct contact with affected rabbits
• fomites – bodily fluids, faeces, urine
• transmission via handling, clothing and equipment
• mosquitoes, flies, birds, predators, scavengers, humans
• the air, inhalation, dust
• direct contact with infected live or dead rabbits

Use a parvovirus cleaning protocol after suspicious cases.

Virus is shed in urine, feces, and respiratory secretions. Transmission is via direct contact, contact with carcasses or fur from affected rabbits, or fomites such as water, feed, utensils, clothing, or cages. Flies and other insects may also serve as vectors, and the virus can be found in feces from predators that have eaten infected rabbits.

Exposure to the environment can occur through baits and injections, and laboratory studies have shown that mammals and birds play a role in the transmission of RHDV. Example, soil exposed to droppings (rabbit or another animal), can be contaminated with the RHDV virus particles.

RHDV1&/2 can live for 90 days on hay and fabric

About Strains

In Australia, there are 2 different types of calicivirus. RHDV1 and RHDV2.

However, there are many sub-types.

1. RHDV1 (Chinese strain) released 1995
   1. RHDV1 K5 (Korean strain) released in 2017aa. RHDV 08Q712 (K5 Korean strain) Incheon (pending approval)
   2. RHDV1 v351 (Czech strain) released in 1996
   3. RHDV1a (Sydney strain) released 2014
2. RHDV2 strain (“RHDV2 strain was not released in Australia by any government department and it is not known how the virus entered the country.” APVMA, AVA)

The RHDV1 and RHDV2 strain are completely different viruses.

How does RHDV affect rabbits?

It causes liver damage and results in liver necrosis and/or internal haemorrhages.

Rabbits will have a high temperature (>40°C), anorexia and lethargy, jaundice may be observed in the eyes and ears.

RHDV1

The government released RHDV1 in 1996 to control wild rabbits. Over time, its effectiveness has been decreasing. To boost the strain’s effectiveness, they released RHDV1a in March 2017, which now occurs naturally.

It is categorised into “classical” (RHDV1) and “A” (RHDV1A).

It is made to affect European rabbits (Oryctolagus cuniculus).

RHDV2

It is not known how RHDV2 was released in Australia and it is now the dominant strain.

The virus was made to affect European rabbits (Oryctolagus cuniculus), Sardinian cape hare (Lepus capensis mediterraneus) and Italian hare (Lepus corsicanus).

According to Arizona Department if Agriculture RHDV2 is less deadly than RHDV1 or RHDV1a, which is not correct.

EBHSV

Australia does not have EBHSV

European Brown Hare Syndrome Virus (EBHSV) affects European brown hare (Lepus europaeus), Mountain hare (Lepus timidus) and Italian hare (Lepus corsicanus).

The RHDV vaccines are not effective against EBHSV.

RCV-A1

Rabbit calicivirus (RCV) is a non-leathal and temporary protection against RHDV infection.

This is a nonpathogenic virus.

Incheon a.k.a RHDV 08Q712

The NSW Department of Primary Industries (NSW DPI) has submitted an application seeking approval of a new biological constituent (RHDV 08Q712 Incheon) which is a highly concentrated version of the RHDV K5, as it contains more than 30,000 units per part than the RHDV K5 virus. As this new strain is freeze dried (lyophilised), it must be reconstituted in distilled water prior to use. At this point in time (2023), it’s placement in the poisons schedule is not recommended – which means it is too dangerous, and could be a hazard to humans.

This new Incheon strain can infect and mutate humans. It can also cause “host switching”, which is where it can jump between different animals (rabbit to human to horse etc). The Australian Pesticides and Veterinary Medicines Authority (APVMA) suggest that “host switching” is unlikely, but it is possible.

The Incheon strain can also has the potential to cause ecotoxicity and can have a direct impact on non-target plants and animals.

Vaccinations

For RHDV1, 1A and RHDV1-K5, a 12 monthly vaccination is recommended.

Vaccination should be administered to healthy animals. Young animals are more likely to show post-vaccination lethargy and inappetence.

Reactions to the vaccine can occur if it is not performed with a new needle, or if the vaccine is given intradermally.

Filavac an inactivated bivalent vaccine, and is licensed for use in Australia.

According to the manufacturer:

Filavac will protect against the RHDV2 Australian strain.

Bunnies need a single vaccination at 10 weeks of age, and they are immune to RHDV1&2 after 7 days. It lasts 12 months. Bunnies will need a booster every 12 months.

If your rabbit has had Cylap, you must wait a minimum of 6 months before giving then the Filavac vaccine.

If there is an outbreak of RHDV2 in your area, and you are concerned, contact your vet as they may be able to dose the rabbit sooner.

Side effects are fever, lethargy, and a lump at the injection site.

Biosecurity practices

• Keep a closed rabbitry
• Exclude wild and feral rabbits and predators from rabbitry
• Wash hands between handling rabbits in different pens or cages
• Clean and disinfect* equipment, tools, footwear, feed and water containers, cages, etc.
• Control flies and biting insects
• Remove brush, grass, weeds, trash, and debris from rabbitry
• Protect feed from contamination by flies, birds, rodents, etc.
• Do not feed grass or other forage that could be contaminated with the virus
• Do not use forage, branches, etc. for bedding
• House rabbits indoors if possible
• Do not share equipment with others who raise rabbits
• Remove and bury or dispose of dead rabbits promptly
• Submit carcasses for examination and sampling promptly
• Contact a veterinarian promptly if sick or dead rabbits are observed
• Do not transport rabbits into or out of RHD quarantine areas
• Quarantine new rabbits or those returning from shows for one month

Infected Rabbits

Clinical signs of RHDV2 can be seen 3-5 days before death.

• pyrexia
• seizures
• hypoglycaemia
• anemia
• significant increases in liver and kidney enzymes
• death

If you suspect your rabbit has died of RHDV, you can get a free test kit from the CSIRO by emailing your postal address to scientist Dr Robyn Hall: robyn.hall@csiro.au

RHDV is highly infectious. It has a 40%-100% morbidity (40%-100%) rate and a 100% mortality rate.

The number of rabbits affected during outbreaks peaks in 2 to 3 days and the disease course may last only 7 to 13 days. The incubation period is 1 to 3 days.

RHDV can live in carcasses for up to 3 months, and a few weeks in dried excretions/secretions.

Rabbits who survive the infection can shed the virus for up to 30 days, or as long as 105 days. Surviving rabbits can have immunity to that strain for an unknown amount of time.

Parvovirus cleaning protocol

It is recommended to use phenol classed products or 10% bleach.

1 part bleach in 30 parts water.

Use on all hard surfaces, tiles, concrete, paving, bottoms of shoes. Anything that can be washed in bleach should be.

Leave bleach on for 10-15 minutes.

Then clean thoroughly with soap and water and apply the disinfectant for the recommended contact time. Rinse well and let dry before allowing animal contact.

What does it do?

This information is taken directly from ScienceDriect

❝ RHDV replicates in the liver, resulting in severe hepatic necrosis and death from disseminated intravascular coagulation. In peracute disease, rabbits become febrile, lethargic, and collapse and die within 12 to 36 hours of infection; they may be found dead with no premonitory signs. With acute disease, affected rabbits are febrile and show signs of depression, lethargy, anorexia, constipation, or diarrhea. Some may show neurologic signs such as ataxia, opisthotonos, excitement, or seizures. At the end stage of the disease, tachypnea, cyanosis, and a blood-tinged foamy nasal discharge are often seen. In some rabbits, the course of the disease is slower, with the animals exhibiting jaundice, depression, anorexia, and fever, eventually dying within 1 to 2 weeks. ❞

Explain it to me

The family Caliciviridae has four genera:

1. Vesivirus – swine virus, feline calicivirus (FCV)
2. Lagovirus – RHDV1 and RHDV2, only affects rabbit and hares
3. Norovirus – primarily human variants of the viruses
4. Sapovirus – prototypes of the Vesivirus and Lagovirus

The Calici part of the name comes from the cup-shaped surface depressions. These depressions are called calix which is another word for cup.

The virus particles (virions) are 40.5nm in diameter with 32 calix shaped structures, and it comprises of 90 arch-like capsomers.

Calicivirus’ (especially human variants) cannot be grown in cultures. A single structural protein makes up the antigen for all of the viruses.

Do the math

It is estimated that wild rabbits have caused approximately $206 million in losses a year to the agricultural industry. Yet, they say that in 2019, they have recouped $6 billion dollars due to RHDV.

According to the Environment Protection and Biodiversity Conservation Act 1999 (DotE 2015), rabbits are a threat to 300 threatened species:

• 15 birds
• 20 mammals
• 6 reptiles
• 1 invertebrate
• 1 fish
• 1 amphibian
• 260 plant species

Official Information Links

Australian Pesticides and Veterinary Medicines Authority – APVMA

Australian Veterinary Association – AVA