Spreading disease by air is much easier than containing it by any method
LANGLEY, Washington––About sixty feral Belgian hares, long beloved village pets in Langley, Washington, may be the latest casualties of deliberate releases of the rabbit hemorrhagic disease RHD-1 in Australia and New Zealand, 8,000 and 7,500 miles across the Pacific Ocean, respectively.
The bunny hop diagonally across the Pacific, if that is what happened, took several years and a mutation of the RHD-1 calicivirus into a milder form, RHD-2.
RHD-2 may have reached nearby Vancouver Island, British Columbia, Canada, only days to months after RHD-1 releases in Australia, beginning in 2017, and New Zealand, beginning about a year later.
Despite routine precautions, RHD in either form could easily have hitchhiked from either Australia or New Zealand with insects or insect larvae unknowingly transported by passengers, luggage, or cargo on any of dozens of 20-to 21-hour direct flights per day from Down Under airports to the Vancouver International Airport.
Insects themselves could have completed the journey to Langley.
“Barnyard scrambles” introduced Belgian hares
Langley is a tourism-oriented town of just over 1,000 residents located along the Saratoga Passage, an inland arm of Puget Sound. Twenty minutes south of ANIMALS 24-7, Langley stands within sight of British Columbia from high points on clear days.
Langley has hosted the Island County Fair since 1912.
For about 40 years, from 1960 to 2000, the Island County Fair featured a “barnyard scramble,” in which rabbits, poultry, lambs, piglets, and young goats were released to be chased by children. The children were allowed to keep whatever animals they caught and did not kill in the effort. Some of the animals, however, escaped––especially the Belgian hares, who found a haven in surrounding fields, yards, and woods.
Fifteen years after the “barnyard scramble” ended, several irate local gardeners urged the Langley town council to exterminate the allegedly invasive feral hare colony.
But almost the whole rest of the community petitioned to save the hares. Veterinarian Dave Parent reassured Langley residents that the Belgian hares carry no menacing diseases. Falconer Steve Layman, whose rescued and rehabilitated birds had been proposed as hare executioners, said nature would level the Belgian hare population if and when it taxed the carrying capacity of the habitat, and recommended leaving the hares alone.
Where did RHD come from?
The Langley view of feral hares––who do not mingle with or visibly compete with abundant native varying hares––could scarcely contrast more with the official perspectives of Australia and New Zealand. Both nations have been trying to exterminate introduced rabbit populations since 1860, just six years after rabbits imported from Britain were first released as prey for hounds in 1854.
Those rabbits do not appear to have brought any deadly diseases with them.
“The origins of RHD are not completely understood,” agree the Program for Monitoring Emerging Diseases (ProMED) moderators, whose daily readership includes more than 80,000 zoonotic disease and public health experts worldwide.
“The causative virus may have emerged from avirulent caliciviruses circulating
asymptomatically in European rabbits,” the ProMED team believes.
“The first known outbreak occurred in the Jiangsu Province of China in 1984, apparently spread from within a group of commercially-bred Angora rabbits imported from Germany.”
RHD hit China hard, then spread worldwide
Rabbit hemorrhagic disease (RHD) found in China a “naïve host population,” meaning rabbits whose ancestors had not previously been exposed to the caliciviruses in question, and therefore had not developed or passed along any immunity.
“Within nine months,” according to ProMED, “this disease had killed 14 million domesticated rabbits in China.”
As the new form of rabbit hemorrhagic disease mutated and spread, “By the late 1990s, outbreaks had been reported from 40 countries, and RHD had become endemic in a number of areas throughout the world. Naturally occurring RHD outbreaks were reported in geographically distant regions, such as Cuba, Uruguay, and Reunion Island.
“Other regions, including the Americas, have experienced periodic outbreaks in domesticated rabbits,” ProMED explains.
Native North American rabbits appear to be immune
“However,” adds ProMED, “the species of wild rabbits found in North America,” most commonly varying hares, “are not susceptible to these RHD viruses, which facilitates eradication” of the viruses from North American habitats after feral and domestic European and Asian rabbit varieties die out.
As RHD-1, the first diagnosed form of RHD, kills from 70% to 90% of rabbits of European and Asian ancestry who are exposed to it, but does not spread to wild rabbits, North American outbreaks tend to be self-limiting.
Outbreaks discovered in Quebec, Ohio, and Pennsylvania are believed to have been eliminated through the combination of vaccination, quarantine, and limited ability to infect new populations.
But a mutated RHD virus, RHD-2, may prove to be more problematic. RHD-2 appears to emerge more-or-less spontaneously in the wake of RHD-1 outbreaks, including those resulting from deliberate releases. Once established, RHD-2 also spreads independently.
“RHD-2 emerged in Europe in 2010 and has spread widely among domesticated and wild rabbits there,” the ProMED information summary continues. “This virus has also been found in Australia. RHD-2 affects animals vaccinated against older RHD viruses, as well as unvaccinated rabbits. Whether RHD-2 could affect any wild North American lagomorphs [members of the rabbit/hare family) is not yet known.
“RHD [in either variant] is readily spread,” ProMED warns, including via “contaminated food, bedding, and water. Insects can transmit this virus long distances. Flies are very efficient mechanical vectors; the infectious virus can persist in flies for up to nine days, and only a few virions [the infectious component of a virus] are needed to infect a rabbit by the conjunctival route,” meaning through eye fluids.
RHD-2 is harder to identify
Either form of RHD kills rabbits, according to ProMED, through inducing “primary liver necrosis and a massive disseminated intravascular coagulopathy in all organs and tissues. The most severe lesions are in the liver, trachea and lungs.”
RHD-2 tends to be more difficult to contain and eradicate, ProMED explains, because “Rabbits infected with the RHD-2 virus typically do not show the symptoms that are common with RHD-1 infection, so it is far more difficult to diagnose from simple observations.”
Also, “Deaths from RHD-2 occur later and over a longer period of time than [deaths from] RHD-1: typically this is 3-9 days following infection.”
This allows each infected rabbit––and rabbit parasites––more opportunity to infect others.
“In mainland Europe,” ProMED adds, “RHD-2 is now very common, particularly in France.”
Australia & New Zealand spread rather than contain the disease
Usually veterinary health agencies make every effort to contain diseases deadly to commercially raised species as rapidly as possible, with the full cooperation of farmers.
Australia and New Zealand, however, were and are exceptions.
Sheep ranchers had already virtually exterminated all native carnivores big enough to kill a rabbit by the time rabbits were introduced in 1854. Thylacenes, or “Tasmanian tigers,” were already scarce, though not extinct until 1936 when the last known specimen died at the Beaumaris Zoo.
Burrowing native marsupials who had been the chief prey of the native carnivores were also in decline, many of them already extinct, leaving behind thousands of miles of already-dug tunnels and warrens suitable for rabbit reproduction.
Soon ranchers fretted that rabbits might be out-eating their sheep. Rabbits also made easy scapegoats for economic hard times, especially after World War II, when the introduction of synthetic fibers and declining demand for mutton brought an abrupt contraction of the sheep industry worldwide.
One disease failed, so Aussies & kiwis try another
Both Australia and New Zealand introduced the flea-borne disease myxomatosis in 1950, killing an estimated 99.9% of their rabbit populations with repeated releases before the offspring of resistant survivors recaptured the habitat.
The governments of Australia and New Zealand welcomed the discovery of RHD as a potential replacement for myxomatosis in ongoing biological warfare against rabbits.
But before a weaponized strain of RHD was ready for deployment, it escaped from a quarantined Australian government testing site on Wardang Island in September 1995, killing rabbits across four Australian states.
That caused sheep farmers in both Australia and New Zealand to become so eager to deploy RHD that instead of awaiting the official release of the weaponized version, they made their own RHD-infected baits from the remains of dead rabbits found where it had already hit.
The result was widespread introduction of a weaker form of the RHD virus, which in effect immunized the rabbits who were not killed.
Released millions of infected fleas
Racing to stay ahead of the farmers, against much scientific and humane advice, Australian agriculture and wildlife authorities in mid-October 1996 released millions of RHD-carrying Spanish rabbit fleas at 280 sites.
The released strain, RHD-1, initially killed up to 90% of the rabbits in the targeted areas, but within two years proved ineffective as a population control agent.
Studies done in Tasmania, Victoria, and New South Wales, Australia, and on the South Island of New Zealand, discovered that within one year of RHD-1 deployment, the surviving rabbit populations doubled. After two years, they tripled.
Meanwhile, hungry feral carnivores, such as cats and foxes, who formerly fed on young rabbits, preyed more heavily upon native birds and marsupials.
Raptors also suffered. Studies released in October 1998 by the Australian Raptor Society, Birds Australia, and the state government of South Australia implicated the RHD-1 releases in declines of brown falcons and wedge-tailed eagles. In lieu of hunting rabbits, wedge-tailed eagles in particular took to scavenging roadkill. Many were road-killed themselves.
Frankensteins return to the lab
Instead of recognizing that rabbits had come to occupy a valuable place in the Australian and New Zealand food chains, the Down Under Dr. Frankensteins returned to their laboratories to tinker further, while politicians blatantly misrepresented the longterm results of the previous experiments.
A Korean variant of RHD-1 called K-5 was in 2017 released at 418 sites around Australia where rabbits had reportedly developed immunity to the original form of RHD-1.
Immunity to RHD-1 may have emerged because––as the Weekly Times, billing itself as “The voice of the Australian country since 1869,” reported in February 2016––RHD-2 was already “spreading across southeastern Australia.”
Releases of K-5 at 100 sites in the Otago region of southeastern New Zealand began in April 2018.
By December 2018, reported the Otago Daily Times, RHD-2 was discovered in Central Otago, having already emerged around the Bay of Plenty in the far north of the North Island of New Zealand, and near Marlborough, at the northern end of the South Island.
“This is a concern”
“This is a concern,” the Otago Daily Times said, “as it could create immunity to K-5,” and as it “cannot be eradicated or contained now that it has been confirmed in wild rabbits on both the North and South Islands.”
Australia rather than New Zealand would appear to be the most likely source of the RHD-2 outbreaks on Vancouver Island, first discovered in February 2018, before the K-5 releases in New Zealand began.
RHD-2 hit 10 feral rabbit colonies on Vancouver Island in 2018, obliging the Richmond Animal Protection Society to euthanize 66 rabbits by order of the British Columbia Ministry of Agriculture.
That did not suppress RHD-2, which re-emerged around Parksville, B.C. in April 2019.
While Parksville is about 200 miles from Orcas Island, Washington, it is only about 100 miles by one of the busiest highways in British Columbia from Victoria, the provincial capital, which is only 10 miles from Orcas Island––not far for a bug to be blown.
RHD-2 spread follows the ferries
RHD-2 was discovered on Orcas Island, according to the Washington State Department of Agriculture, on July 9, 2019, and was confirmed to be present by the USDA Animal & Plant Health Inspection Service nine days later.
Following the Washington State Ferry routes, RHD-2 spread during the summer to Lopez and San Juan islands. RHD-2 was identified on Whidbey Island on November 7, 2019.
Feral rabbits are believed to be at immediate risk in both Langley and Fort Casey, five miles and less than one mile, respectively, from ferry landings, though not on routes directly linked to previous outbreak locations.