Killing ticks andinoculating people has failed, so researchers try immunizing mice viavaccine-laced food
· By Angus Chen on January 29, 2019
Kirby Stafford, Connecticut’s state entomologist, knows only one sure fire way to reduce tick populations enough to cut Lyme disease rates:killing deer. Otherwise, he says, “very little by itself really reduces ticknumbers enough.”
Bu tin some Connecticut neighborhoods Stafford has been testing a new strategy, one he hopes might show real promise after years of stymied efforts to drive new Lyme infections down: a vaccine for mice.
Roughly half of ticks carrying Borrelia burgdorferi,the bacteria that cause Lyme disease, pick it up by biting infected white-footed mice. That makes these fist-size fuzz balls the most important carriers of the bacteria and a prime target for a Lyme vaccine, Stafford says.In theory, vaccinating enough mice should lower the number of ticks that acquire Borrelia in the first place. And fewer infected ticks means fewer infected bites on humans.
The U.S. Centers for Disease Control and Prevention learns of roughly 30,000 cases of Lyme disease each year, but not every diagnosis gets reported to the CDC,and the actual number of new infections is likely over 40,000. That makes Lyme the most common disease transmitted by ticks, mosquitoes or fleas in the U.S. If untreated, it can go from rashes, swelling and joint pain to brain damage, weakened muscles and numbness that, in rare cases, can sometimes linger or recur for years.
Researchers began looking into wildlife vaccines for the disease shortly after problems developed with a human Lyme vaccine, says Maria Gomes-Solecki, an immunologist at the University of Tennessee and the creator of the mouse vaccine Stafford is testing in Connecticut. The human version, brand-named LYMErix, came onto the market in 1998 and was effective in adults after three doses. But it quickly became controversial as lawsuits emerged alleging it caused severe joint inflammation, along with other Lyme symptoms it was supposed to prevent.
Gomes-Soleckiclaims those allegations were never supported by statistical evidence but were“blown out of proportion” and stoked by anti-vaccine sentiment. “There are many reasons why vaccines are pulled from the market,” she says. “I don’t think these reasons were scientifically justified [in this case].” Still, the concerns halted sales enough that SmithKline Beecham (now GlaxoSmithKline) pulled the vaccine off the market four years after its introduction.
Gomes-Solecki and other immunologists began searching for new Lyme vaccines for humans, but she says nothing worked as well as the original.LYMErix is based on a protein called outer surface protein A (OspA), found onthe surface of Borrelia bacteria. The vaccine trains the immune system to recognize that protein and manufacture defenses against anything carrying it. And when a tick slurps up blood from a vaccinated individual, those defenses also destroy any Borrelia inside the tick—preventing it from infecting a new host.
Gomes-Solecki—who was a veterinarian before becoming an immunologist—says she found the science around Lyme disease fascinating, and emigrated from Portugal to the U.S. to study it. “With my background being veterinary medicine, I started thinking,‘If we can’t use [the vaccine] in humans, maybe we can target the animals that cause the illness,’” she says.
That hunch got its first real test in 2004 when a team of Yale University scientists (of which Gomes-Solecki was not a part) tested an OspAvaccine, designed for mice, on the rodents. It proved effective against Borrelia infection and in clearing the bacteria from ticks that bit an immunized mouse—but it was impractical. “Part of the problem with previous methods is they would capture wildlife and do injections,” says Joyce Sakamoto, a tick biologist at The Pennsylvania State University who is not involved with Gomes-Solecki’s research. “It’s incredibly laborious. Animals sometimes die in traps; that doesn’t help. Injections are very difficult.” In short, no one could ever vaccinate enough mice to make a dent in the Lyme epidemic using needles, Sakamoto says.
SoGomes-Solecki came up with something that could be broadcast into the environment like seeds: kibble that contains an oral vaccine but would be tastyto white-footed mice. “It’s our secret sauce, if you will,” says Mason Kauffman, a spokesperson with US BIOLOGIC, the company that Gomes-Solecki helped found to manufacture the mouse Lyme vaccine. The company designed the vaccine with layers “like a peanut M&M,” Kauffman says. In this case the“peanut” is a gray pet food pellet animal food–maker Purina Mills custom manufactured for the vaccine. “The ‘chocolate coating’ around the peanut is the vaccine, then the ‘candy coating’…is a coating that protects the vaccine from stomach acids,” Kauffman says. The vaccine enters the bloodstream through the animal’s intestines.
To read the entire article, go to https://www.scientificamerican.com/article/vaccinating-mice-may-finally-slow-lyme-disease/.