About 500,000 Americans got the unpleasant surprise of a new Lyme disease diagnosis this summer, according to insurance claims data, a number that could drop if scientists succeed in developing a vaccine for the tick-borne disease.
Previous vaccines were discontinued in the 1990s due to low consumer demand, but things are much different now: Lyme disease cases are skyrocketing, and doctors and the public are becoming more aware that for some patients, the infection can become chronically debilitating.
While long-haul Lyme disease was once controversial, with some doctors claiming antibiotics could cure all patients, the spread of long-haul COVID has warned skeptics that lingering symptoms are real. About 10% to 20% of confirmed Lyme cases are not curable with antibiotics. This should spur interest in new vaccines, such as those being developed by Pfizer and the French company Valneva.
But even if this new vaccine is successful, it won’t be the final answer to the Lyme disease problem. Several labs are working on other prevention strategies, such as a vaccine that would kill ticks before they can transmit disease, thereby preventing some of the more dangerous tick-borne diseases. And the new preventative measures shouldn’t slow efforts to unravel the mystery of persistent Lyme disease, which can cause joint pain, fatigue, memory loss and other symptoms.
Linden Hu, a professor of immunology at Tufts University who specializes in Lyme disease, explains why developing a Lyme disease vaccine is so difficult: The bacterium that causes it, Borrelia burgdorferi, is a shape-shifting bacterium. When it infects ticks, it’s covered in a protein called OspA (outer surface protein A). Once inside the human body, OspA stops functioning and the bacterium expresses other proteins, including ones that can mutate to evade the immune system.
As a result, people do not develop natural immunity to Lyme disease and can become infected multiple times.
Both the old and new vaccines get around this problem by encouraging the immune system to produce a continuous supply of antibodies against OspA. When ticks ingest blood containing the antibodies, the antibodies kill Borrelia burgdorferi before the bacteria can be transferred from the tick to you.
But for it to work, you need a lot of antibodies. The 1990s vaccine was a fairly large effort, requiring a series of three shots over a six-month period, followed by a yearly booster shot. The new vaccine is nearly identical to the previous one, so will likely require a similar number of shots. It works in exactly the same way, with a slight tweak at the molecular level. It’s missing the part that was suspected of causing arthritis in a few people, but the data shows that vaccinated people didn’t have more arthritis than controls.
Another effort is led by Mark Klempner, a professor of medicine at the University of Massachusetts Chan Medical School. One of the developers of the vaccine in the 1990s, Klempner is now focusing on antibody treatments that would protect people almost immediately and remain effective for up to six months. Because they don’t stimulate the immune system, they don’t cause the side effects that come with vaccines, and patients could get the treatment when they need it—maybe just before a camping trip or, for people who live in areas where Lyme disease is prevalent, in the spring before peak tick season.
Even better would be a drug or vaccine that kills ticks before they can transmit Lyme disease or other pathogens. (Ticks also transmit many other dangerous diseases, including babesiosis, ehrlichiosis, Rocky Mountain spotted fever, and alpha-gal syndrome.) Tufts’ Hu is pursuing this approach in collaboration with Tarsus Pharmaceuticals, by repurposing a tick-killing drug for dogs to prevent disease in humans. Others are considering vaccines that induce immunity to proteins in tick saliva, with the same goal of killing ticks before they can transmit disease.
Others think more aggressive tactics should be considered. Hu said it would theoretically be possible to eradicate Borrelia by giving antibiotics to wild mice. (Mice are the bacteria’s ultimate host, and ticks pick up the bacteria by feeding on them.) Studies have shown that bait laced with the antibiotic doxycycline can kill 90 percent of Borrelia bacteria in mice and ticks, Hu said. Because of the risk of antibiotic-resistant bacteria proliferating, researchers are turning to very specific antibiotics that target just Borrelia.
Many other unanswered questions may hold the key to a better solution: Scientists still don’t know what causes the chronic condition — perhaps an autoimmune disease caused by an unfortunate combination of the person’s genes and those of a particular strain of bacteria.
It’s still not entirely clear why cases have risen so dramatically—warming temperatures are part of the story, but not the only one. Northeastern University biologist Konstantin Takacs is looking for answers in the behavior of bacteria in a variety of animals, including ticks that have been around since the time of the dinosaurs and wild mice that have reached a sort of immune truce with coronaviruses, much like some bats have.
He also said he doesn’t understand why the disease is so prevalent in some areas and not others — it may have to do with the distribution of housing development, farms and forests.
The new vaccine will be a good first step, but it’s not the end of the story.
Copy story link
Source link