Science
For decades, the government has been carrying out an ambitious plan to mass vaccinate the wild animals by airplane.
The story of America’s rabid raccoons begins in Florida. Rabies was once rarely found in raccoons, but in the ’50s, an outbreak began spreading from the Sunshine State. It diffused first to neighboring states and then made a great leap north into the mid-Atlantic, possibly via the shipment of over 3,500 Florida raccoons to hunting preserves in Virginia. From there, rabid raccoons ambled their way as far north as Canada and as far west as Ohio. The East Coast became “one solid belt of raccoon rabies,” says Charles Rupprecht, the former chief of the CDC’s rabies program.
In the early days of the outbreak, officials quickly realized that mass killings of raccoons would not be popular with the public. Residents on one Florida island with a rabies outbreak were so attached to their raccoons that a restaurant owner was feeding them 400 pounds of dog food a month.
For the past 30 years, the U.S. government has embarked on a far more unusual and elaborate campaign: mass immunization of raccoons. Every summer and fall, the USDA, in collaboration with local agencies, drops millions of packets of oral rabies vaccines over the U.S. by air and by hand. The vaccines come in two flavors: fish meal and vanilla. When a hungry raccoon bites into the packet, the liquid vaccine coats its mouth, immunizing it against the rabies virus. We’re now trying to save raccoons from the rabies outbreak we once unwittingly helped unleash. As far as management strategies for dangerous wildlife go, mass immunization is a pretty gentle one.
A similar vaccine campaign has already eliminated strains of rabies from coyotes and foxes in the Southwest. It has also slowly pushed back the northern front of rabid raccoons from Canada into Maine. The immediate objective is to prevent rabies from spreading any farther north or west, but eventually, says Richard Chipman, the national rabies-management coordinator at USDA, “our goal is to push back rabies to the ocean. We want raccoons rabies-free by 2063.”
This mass immunization effort in raccoons is ultimately a roundabout way of protecting humans. Rabid animals notoriously like to bite—the virus hijacks the central nervous system and makes animals unusually aggressive. So when rabies takes hold in a raccoon population, the virus tends to spread to other animals: feral cats, foxes, unvaccinated dogs, even humans. And rabies is virtually always fatal in humans, unless we get a timely dose of antibodies plus the vaccine, which together are known as rabies postexposure prophylaxis. When the outbreak reached New Jersey in 1989, the need for rabies postexposure prophylaxis “started going through the roof,” Rupprecht says. (The treatment costs thousands of dollars per person.) Eliminating rabies in raccoons wouldn’t eliminate rabies in the U.S. entirely, as bats are another important reservoir, but “it’s getting the biggest bang for the buck,” Chipman says. Human rabies exposures are 600 percent higher in areas where both raccoon and bat rabies circulate, compared with areas where there is only bat rabies.
Two types of vaccines are now used in raccoons. The first was jointly developed by the Wistar Institute in Pennsylvania and the French biotech company Transgene in the 1980s; scientists inserted a gene for a rabies protein into another live virus called vaccinia. This vaccine worked well in lab animals, but then came the problem of how to actually inoculate raccoons in the wild. Rupprecht, who was at Wistar at the time, remembers batting around ideas to grow the virus in eggs or put it inside Slim Jims or sausages. The breakthrough came when people trying to prevent raccoons from breaking in and eating their fish baits called the scientists for help. Rupprecht and his team weren’t in the raccoon-deterring business, but they were in the raccoon-attracting business—so they thought, Why not fish? They tried encasing vaccines in fish-meal-bait polymer, which worked brilliantly. The manufacturer now also makes plastic packets of the vaccine coated in fish oil and fish meal. “We typically sort of equate it to a small ketchup packet,” says Jordona Kirby, rabies field coordinator at the USDA.
The second vaccine is also made of the same rabies gene inserted into a different virus called adenovirus. This vaccine is loaded into a blister pack, which is in turn coated in edible vanilla wax. Technically, it’s still experimental; the USDA team has been field-testing it since 2011 and expects FDA approval soon. Their preliminary results, Chipman says, suggest that it stimulates much higher antibody levels in raccoons than the older vaccine does.
Distributing the vaccine is a three-pronged process. Small airplanes equipped with a conveyer belt—“a little bait treadmill,” Kirby says—drop the vaccines over large, empty rural expanses. Helicopters that can fly lower drop them over suburbs. Dense urban areas are the hardest to reach: The team actually walks around setting up bait stations or J-shaped tubes filled with the fish-meal polymer cubes. The idea is to make sure that raccoons, specifically, try to eat these; they can reach into the pipes with their dexterous hands, whereas possums, skunks, and feral cats cannot. The program is aiming to vaccinate at least 60 percent of raccoons in an area to stop the spread.
The team—and those who come after—still have a lot of work ahead in eliminating rabies in raccoons by 2063. “I’ll be, in fact, 103 then, but I hope to still be standing and smiling and cheering these guys on,” Chipman told me over the phone from West Virginia, where he had just finished supervising the distribution of rabies vaccines. In October, he’ll be out in the field again for the second leg of the campaign, this time starting in Virginia and going south until the ocean.
Sarah Zhang is a staff writer at The Atlantic.
