Fighting Lyme Disease With a Vaccine — for Mice
WHY YOU SHOULD CARE
Because a mouse trap baited with vaccine-laced pellets could be key to fighting Lyme disease.
Kathleen O’Rourke was the ultimate supermom. A mother of two in Los Altos, Calif., she volunteered at several schools, served as a staff member for her church and played league tennis — until 2004, when her world started to unravel.
Her hands and feet tingled, and she constantly felt like she was walking through a fog. She needed 16 hours of sleep just to get through the day. “It was like being in a sheer-sided pit and trying to climb out with your fingertips,” she said. But her doctor dismissed it as postpartum depression.
The CDC recommends using fine-tipped tweezers to grasp the tick as close to the skin as possible and pull upward with steady, even pressure. Don’t twist or jerk the tick. After removing the tick, clean the bite area and your hands with rubbing alcohol, an iodine scrub, or soap and water.
One afternoon, her fourth-grade son, Louis, started screaming that a tick had latched onto his stomach. O’Rourke immediately pulled it out. Soon afterward, Louis had trouble breathing, and his feet felt so heavy he had to crawl to the bathroom. But his pediatrician couldn’t figure out what was wrong. After O’Rourke ran an Internet search on the symptoms, she suspected right away that he had Lyme disease. A specialist confirmed her hunch and prescribed Louis an intensive course of antibiotics. His symptoms cleared eight months later. Now that she knew the symptoms, O’Rourke was tested and was diagnosed with Lyme disease herself. It took four years of antibiotic treatment until she could return to her normal, busy life, including co-founding the Bay Area Lyme Foundation.
Mice can eat the vaccine-laced pellets and return to their environment, making them less likely to infect the ticks that bite them.
But what if there were a way to prevent Lyme disease altogether? University of Tennessee researchers have developed an oral vaccine that could protect humans from Lyme disease — when the vaccine is given to mice.
Each year, an estimated 300,000 people in the U.S. are diagnosed with Lyme disease, an illness caused by the bacteria Borrelia burgdorferi. Mice can carry the organism and transmit it to baby ticks that feast on their blood. When those ticks mature, they can infect new mice — or other animals, including humans. A bite from an infected tick can trigger symptoms ranging from joint aches and fever to numbness and confusion.
When it’s spotted early, Lyme disease usually responds to an intensive antibiotic regimen, but it’s tricky to diagnose. Many symptoms resemble those of the flu, rheumatoid arthritis and other diseases. What’s more, ticks also carry bacteria that cause diseases other than Lyme.
In a few years, homeowners might be able to place vaccine-laced food pellets in “drive-through” mouse traps with openings at both ends, so mice can eat the bait and return to their habitat, essentially becoming walking, squeaking tick vaccinators.
Redirecting the research
In 1998, GlaxoSmithKline developed a Lyme disease vaccine for humans, which exposed their immune systems to a harmless amount of a protein on B. burgdorferi’s surface called OspA. As a result, the immune system recognized the bacteria as foreign and released antibodies that attacked them when they reappeared. But the vaccine was pulled off shelves in 2002 after it caused severe side effects.
I could see this sold in little boxes in your local Home Depot.
— Maria Gomes-Solecki, molecular biologist, University of Tennessee
Instead of abandoning hope, University of Tennessee molecular biologist Maria Gomes-Solecki decided to apply the vaccine to another B. burgdorferi carrier: mice. Ticks that sucked the blood of vaccinated mice would also ingest antibodies the mice had produced, which would kill any bacteria the ticks carried, preventing them from transmitting the disease.
Gomes-Solecki’s team developed an oral vaccine that could be mixed into an oatmeal-based pellet. Since the tick’s life cycle lasts two years, they set a testing period of five years. “Only after we deployed the vaccine for 4 to 5 years would we see a drastic effect in the number of infected ticks,” she said.
Each afternoon, the researchers baited traps with vaccine pellets in four plots, each about the size of two football fields, in a wooded area in Dutchess County, New York. At the same time, they set traps baited with placebo pellets — which contained no vaccine — in three similar plots nearby. The next morning, they collected the trapped mice and measured OspA antibody levels in their blood. They also collected ticks from each plot and tested them for the presence of B. burgdorferi DNA.
…a whopping 76% drop in the number of infected ticks.
Blood samples from mice captured from the vaccine-treated plots showed high levels of anti-OspA antibodies, indicating that they had been immunized. But had the mice passed their immunity to ticks?
The number of infected ticks in the treated plots fell steadily over time. When the project hit the five-year mark, Gomes-Solecki held her breath. “It was going to either make it or break it,” she said.
The vaccinated plots showed a whopping 76 percent drop in the number of infected ticks, while plots receiving placebo pellets saw no decline. “I was ecstatic,” Gomes-Solecki said.
Since then, Gomes-Solecki has co-founded a company, U.S. Biologic, to market her vaccine, which is awaiting USDA approval. She expects it to hit the market in a few years.
Although she can envision aerial crop dusters dispersing vaccinated pellets in remote areas, she also thinks that homeowners can use them to bait traps, just like she did in her study. “I could see this sold in little boxes in your local Home Depot,” she said.
Gomes-Solecki tested the presence of anti-OspA antibodies in mice only. But the traps also captured chipmunks and squirrels, suggesting that the vaccine should target other animals that also carry B. burgdorferi.
But the study has its skeptics. Tom Mather, director of the University of Rhode Island Tick Resource Center, notes that the study was performed under highly controlled conditions in a single habitat and wonders whether the findings will hold up in the real world, which is much more variable. And other animals, such as chipmunks, might still play a role in transmission. “I would just be cautionary,” he said.
He adds that the findings are “modest,” comparable to those of tick repellents that homeowners can spray around their yards — except a vaccine would take five years to work, while repellents have an immediate effect.
”Lyme disease is like a thief,” O’Rourke said. “It takes people away.” Like catching any crafty thief, fighting Lyme disease will require a more integrated approach that also involves developing better diagnostics, for example. Let’s hope it doesn’t outsmart scientists’ latest booby trap.